D-jet TVS adjustment and TB and TVS modifications

[raygreenwood]

D-jet TVS adjustment and TB and TVS modifications

NOTE: this is for the late model four and five wire TVS…ONLY!

So since someone asked I am going to do a more complete “how to” for adjusting the D-jet TVS. I will also get into by next week….corrective mods for the one slight defect that I found in some late date makes of Bosch TVS.

This defect is that some of the TVS made in the mid to late 80’s (maybe even 1990’s) had a peculiarity to either the molding of the floating fork or the spacing of the on/off poles in the switch that cause a LARGE hesitation when taking off the line or on gear shift throttle transitions…that cannot be tuned out.

Also to be included probably in about a week since I already have the pictures done…will be a “how to” for swapping the 2.0L L-jet TB onto the 1.7/1.8 D-jet plenum.
This is a nice modification and has several benefits including better breathing for an uprated 1.7L (meaning one with better cam, larger valves and better exhaust). It makes for better throttle response and has a more reliable closing spring system.

PLEASE READ THROUGH THIS WHOLE TEXT FIRST ESPECIALLY THE PART ABOUT ADJUSTING AND THE SECTION TITLED “THE OBJECT OF THE TVS OPERATION” SO YOU UNDERSTAND WHAT IS ACTUALLY GOING ON. Adjusting is really simple...but its about inspection and READJUSTING to account for wear in your particular TVS for best function

First item: Cleaning the TVS

First…do not be afraid of this thing. Just be careful. Since on the 1.7L and 1.8L you need to remove the TB to adjust….you might as well do it all while you are at it.

One of the problems with age in these TVS’s is that the tin plating on the spring loaded contacts from the plug body oxidize and transfer that oxide to the brass circuit board which causes intermittent connectivity.

1. Only use contact cleaner or MEK or you can use Berrymans B12 Chemtool. You want to AVOID using anything with isopropyl alcohol or Isopropanol. The nylon parts of the switch fork can be damaged/attacked by Isopropyl alcohol.

DO NOT use Gumout carb cleaner. It has Isopropyl alcohol in it.

2. Get a fine point sharpie pen. The cap is perfect for removing the forked center hub.

3. Get a plastic safe synthetic instrument oil to lube the center hub after you clean it. If nothing else…a drop or two of the lightest synthetic motor oil you can find. DO NOT use 3-in-1 household oil. It can have issues with plastics. If you want to buy something specific…buy these:

LaBelle Lubricants…..plastic safe hobby oil (think model trains and RC race cars)…superb. They have a whole range of lubricants. Any good hobby shop has them for cheaper.
https://www.amazon.com/Labelle-Industries-Plastic-Compatible-Motor/dp/B001W8XD44

Or

Superlube synthetic PTFE oil is also superb and very light and you can buy this oiler pen at Home Depot

http://www.homedepot.com/p/Super-Lube-7ml-Precisio...lsrc=aw.ds

I originally bought this to use on my TVS and it works perfect.

4. DO NOT lube any of the circuit board inside of the TVS. It will gather dust and create an oil and dust slurry that will wear out your TVS in no time.

Let’s start:

Why do I need to clean and lube this thing so carefully?

Because of how its manufactured, the grit that gets in and mixes with the lubricant over time is the primary reason these units wear out.

This is how the plate and hub are assembled. The wavy spring washer puts pressure between the flat washers and the nylon fork.
The steel swaged tube in the middle keeps it all centered and under tension. As the lube dries out, gets pushed away…or gets gritty over time…it begins to wear out the bore in the nylon fork causing it to move sloppy and it gets excessive rotating slack…more than the 2° designed into the system.

It’s the grit/dust that causes the biggest wear problem. So you want to clean it very well to get all of the old oil out…and then lubricate it well in just the right spots.

If it was oiled from the factory…why do I need to worry about what kind of oil I am using?

I have no idea what the factory used to lube these with. It was either a very light grease similar to lubriplate or a medium to light oil. I have NOS ones in the box and it’s still hard to tell.

But….I can tell you that the fact that many oils attack nylon and make it brittle is precisely why I find a lot of these well used units that have a chip snapped out of the “D” shaped hole in the nylon shaft bushing under the brass tension snap ring at the top (making them permanently broken)….that it was the original oil that after numerous years along with heat and moisture absorption that caused the nylon to become as brittle as dust and break easily. So….you might as well re-lubricate this part with an oil known to be good to plastic.


1. Disassembly for cleaning:

First take the cap from a fine point Sharpie and push out the center hub from the back side of the mounting plate. This is the perfect size to compress the center bushing and push it out the top.

Now it looks like this. Clean everything very well with circuit cleaner spray…and work the hub back and forth carefully to get all of the grease/oil/ out from between the washer and spring washer stack up. Blow dry with compressed air.

You now need to remove the plug assembly…wait…what?....why?

This is an NOS TVS. See the nice shiny circuit board connector prongs on the right side that are coming from the wiring harness plug? They are bright and shiny because they are “TIN” plated.

See the ugly black oxidization on these connector prongs? That is oxidized TIN. It transfers that oxide to the surface of the board under the contacts and is one of the primary reasons for poor connections.

You need either a pair of long nose Vise grip pliers or a pair of channel lock pliers.

NOTE: we are NOT going to clamp down hard enough on the plug to make any marks.
That is NOT the object here. We want adjustable pliers so we can set the gap precisely so we do not clamp down on the soft plastic. We just need the leverage. In a pinch.....I have even done this with my hands or with a crescent wrench.

The pliers are not actually touching the plastic here. There is about 0.030” of gap on each side of thge plug between plug and plier jaws.

Make sure the center hub is rotated to about mid stroke so that the long tail of the center hub is NOT over the spring contact strip

Simply hold the plate tightly and rotate the pliers from the 3:00 position to the 12:00 position…and POP…the plug comes right off.

By the way….this is how they can make the same exact part…using the same circuit board number inside….and have either a four pin straight plug, a five pin straight plug, or a four pin or five pin angled plug like type 3 and some other cars use. The plug pops right of and its why it has SPRING LOADED board contact pins.

This is what you will find. That is TIN oxide that has transferred to the brass contact pad.

Now you can do all of your cleaning.

This what it looks like before and after cleaning

Reassembly of the plug to plate:

Place the plug at an angle with one end of the forks wedged in the slot/groove. Tap lightly with a screwdriver handle…sideways at the green arrow shown above to wedge the prong firmly in the slot on the plug. Push down on the high end of the plug until the other prong….and the prongs are beveled slightly ….just is poised at the edge of the other end of the slot.

It should look like this:

Without adjusting your pliers…meaning leaving them in the same setting you had when you removed the plug….open the jaws and squeeze the plug and plate between the green arrows. And…POP!..the plug is back on!

Here is a little more explanation:

Notice the curved tips of the tangs of the plate that hold the plug on. This is why you push the plug in at an angle to get that curved tip at the highest point in one side of the groove....then rotate the plug downwrad/inwrd to "scoop" under that horn or tip.

You can see from this photo how the curved "horns" of the prongs just protrude around the edges of the top of the plug to grasp the plug tight.

Cleaning the wiper arm contacts:

Why do we need to do this?

One would think that just spraying with contact cleaner would clean the small ball contacts on the ends of the wiper arm….but it may not. You will notice from these photographs that the ball contact on the end of the wiper arms is actually made from a small droplet of solder.

Why would they use solder instead of just putting a dimple in the end of the wiper arm like they did on the plug contacts?

Because….the circuit board surface is made of BRASS. While its harder than copper its still a soft metal.

The ball tip on the wiper arm is made of solder because it’s SOFTER than the brass circuit pattern it wipes across and produces less wear. It’s probably a mixture of lead, indium and bismuth. With time/age it can oxidize on the surface and create a less accurate connection. Also the solder is so soft that it can get small grit embedded in its surface which also speeds wear to the brass circuit.

For the most part the wear line you see in the brass circuit is from oil and dust that has clustered around the end of the solder ball on the wiper arm. So…we will clean it.

What this is…is a strip of polyester medical bandage material soaked in circuit cleaner…slipped under the wiper contact arm and dragged through about 3-4 times. I’m using very light finger pressure on the contact tip to hold it against the cloth. You can use even a knee bandage or band-aid for this type of cloth….something like a “telfa pad” material or similar. Something with a fine weave that does not leave fibers behind.

See the residue it left behind? Also notice the detail of the contact. You can clearly see that it is a solder ball placed on a hole in the end of the copper arm.


Adjusting the TVS:

First….what IS the object here?

From the books…and both of these books describe the METHOD of adjusting... correctly…but do not describe the actual position that wiper arm must be in with regard to the circuit board…after adjustment.

There is also some totally incorrect and ALMOST irrelevant information in these texts.

So you may in fact do the adjusting PROCEDURE correctly…but still not have the wiper arm in the best position on the circuit board. This can be caused by wear in the floating contact or from stickiness of the floating fork or from some previous owner tinkering with the hard stop of the wiper arm.

Errors from the Brown Bentley type 3 manual:

There are SEVERAL problems with the method that the Bentley manual describes:
1. it’s not accurate….with regard to final position of the wiper arms inside. They are not even having you remove the cap and look inside.

2. You will do more accurate adjusting by NOT turning on the ignition and simply using a volt meter with the cap off of the TVS so you can observe what is happening and see any errors from wear.

3. Notice the text highlighted in red above ….this is totally incorrect and shows a lack of knowledge on the part of the writer of how the system works. This is what has confused so many people with regard to adjusting the late TVS (four and five wire).

Why?.....because there is not ONE part inside of the late model TVS that can or will make a clicking sound. The faint click(s) you will hear…when adjusting the TVS with this method with the ignition on….is FROM THE FUEL INJECTORS under the control of the injection circuit attached to wire #9.

When you move the TVS plate…it places load/friction on the hub shaft and moves the forked switch hub inside…changing the forked switch from the “off” pole to the on pole….while simultaneously causing the wiper arm to slide onto one of the contact strips on the circuit…causing an injection.

4. And this is THE MOST important ERROR….

Notice the red highlighted text…..you should NEVER be able to open the throttle ANY amount without immediately getting an injection event within the first 2° of throttle movement. This is what causes stumbling and bucking off the line.

You must NEVER have throttle OPEN movement to admit significant air….. without added enrichment.

This is the adjusting procedure from the Henry Elfrinks D-Jet manual which is superb…but makes the same cryptic mistakes. They are speaking of the late model TVS (411/412/914 and C and E series type 3)….but are describing and showed pictures of….the two wire B-series TVS from B series type 3.

You will also notice that they say nothing of turning on the ignition…right? In the early two wire TVS…you can in fact hear a click from inside of the TVS when the wiper arm comes out of the parked position when you open the throttle…and you do not need to turn on the ignition.

What are we adjusting and why?

First let’s identify some parts of the TVS:

The object of the TVS operation: is for the all of the wiper contact arms (only one of which is for enrichment…the others are for wide open throttle signal or for EGR signal or fuel shut off for costing/overrun depending on model) ….to be in the CORRECT parked position on the circuit board when the throttle is closed and the “forked switch” is making contact with the “off” pole.

What is the correct position? The correct position is that the solder ball contact on the wiper arm must either be on the first pad of the # 20 circuit trace when the forked copper switch rotates enough to make contact with the “on” pole….so that injection can happen immediately on at least one pair of injectors…..OR….when parked and off….the solder ball on the wiper arm must be in that first gap space between contact strip #9 and #20….so that within that short 2° of movement it takes from the forked copper switch to move from “off” to “on” position….the solder ball has made contact with strip #9…again so immediate injection of at least one of the pair of injectors can happen in very short order.

Because of the way the forked copper switch and forked nylon hub/yoke that surrounds it operate…the operation window is really 1°-3° of movement of the forked nylon hub or yoke to push/move the forked copper switch before the TVS switches from off to on.

It is just the only way they could affordably make a switch accurate enough to positively be either off or on and not float between off or on (which can happen with age or manufacturing issues and causes horrible bucking at part throttle cruise

An illustration of where the wiper arm contacts should be when “parked” with throttle closed:

What each part of the circuit is:

In detail….The red bar shows where the main enrichment wiper arm SOLDER ball shout sit when throttle is closed….on pad/strip #20.
You can see the wear mark stop point from when it was new. It is far enough back from the edge before going into the bare brown circuit board area between strips 20 and 9 that within the 2° allowable movement….it will actually turn on and cause injection BEFORE it goes into the dead area between contact strips.

The blue bar shows the parked position of the overrun or idle shut of contact. The wiper arm on that track MUST be parked on #17 when throttle is closed to signal that you are “neither accelerating nor decelerating” You are at idle.

IMPORTANT: If the whole switch assembly is advance enough that the idle wiper arm is in the gap between contact pad #17 and trace # 22/47…..and...IF... the throttle makes small movements within 2°-3° but you are not actually opening the throttle plate further on purpose (usually caused by poorly adjusted throttle cable)…..the system does not KNOW it’s supposed to be at idle. It’s neither at idle nor enrichment so you get a dead spot.

The green arrow: Points to the less than ideal….but perfectly functional…adjustment location that the factory shop manual typically puts your solder ball on the wiper arm in contact with….when the standard adjustment method from the manuals is used and there is wear or slop or the stop tang has been adjusted.

This is FINE….IF…..the wiper ball contact is actually in the dead space between # 20 and #9 and is VERY close to the edge (within 2° but not more) from the edge of contact strip #9.
In this case you want the wiper ball to make contact with #9…within 2° of movement BEFORE the forked copper switch makes contact with the “on” pole….so that there is no hesitation before injection….AND…..in this slightly advanced position….the parking wiper MUST still be on the parking pad for circuit trace #17……….and looking at the difference in gap between #20 and #9…compared to the gap between #17 and #22/47….this is very hard to do.

This is why the ideal adjustment position shown by the red and blue bars is better.

This is why opening the TVS cap to see where the solder ball contact and wiper arms actually end up after adjustment is critical.

Adjustment how to:

1. Connections:

You CAN use a spare D-jet plug with wires…but it is better to pull the female connectors and wires out so you can clean them and tighten them for a snug fit. You only need 3 wires for this.

Your main connections in green are # 20 for the black probe from your VOM and # 12/47 for the red probe (it really doesn’t matter which color you connect to which).

If your switch has wear or has had adjustment to the metal hub stop tang…..and the solder ball on your wiper arm is in the gap between strips #20 and #9….you will use the connections shown in yellow #9 and 12/47.
Set your VOM to CONTINUITY preferably with an audible beep. If you do not have a beep you need to set the VOM up where you can see the readout in a hands off fashion as you will need both of your hands.

NOTE: before starting…inspect your throttle body and make sure that it closes all the way and the plate is centered in the bore. If it has a big crack of light at one edge….loosen the screws that hold the throttle plate to the shaft and re-center the plate and tighten the screws. Make sure the throttle plate moves freely.

With the VOM connected properly and with the audible beep or visible needle ready….use your thumb on one hand to keep the throttle plate firmly closed through the whole process. Have the TVS screws barely snug so you have to use light force to move the TVS plate. There should be no discernable up or down movement possible for the TVS plate.

While holding the throttle firmly closed…rotate the TVS plate counterclockwise (green arrow) until it stops moving. Do not force it any farther. There should be no beep or needle movement from the VOM. Remember to observe the parking position of the wiper arm (red circle).

What you are looking for:

Notice how the contact on the end of the wiper arm is DEFINITELY just on the edge of contact strip #20.

A close up detail

AND….

The forked copper switch should be against the shorter “off” pole that is on the side closest to the steel stop tab.

NOW…rotate the TVS plate CLOCKWISE…..until you hear A CONSTANT beep or needle movement. Lock the plate with one screw for the moment.
Now….inspect the solder ball contact position on the wiper arm and the forked copper switch position.

If the VOM is beeping the forked copper switch should be like this picture…making contact with the “on” pole. And…

If it a very new switch or NOS….the wiper arm solder ball will be in this position…advanced slightly but still in contact with #20 contact strip.

This may look TOO subtle so let us compare: Notice how the contact is still on #20 but is very close to moving off?

NOW…lock the TVS plate…and rotate the throttle plate full open and then back to closed position.


This is what the factory manual forgets to do: Now…while holding the throttle plate closed…re-test with the VOM and recheck the position of the wiper arm contact and forked switch.

If all is well at this point.…you have an “ideal” condition, very fresh TVS with little or no wear. Lock the TVS screws and install in the vehicle.

However in about 50% of TVS because of wear and drag in the hub and fork system….yours will NOT be ideal. This is where the 2° added movement adjustment comes in.

In most cases your wiper arm contacts fall in these two positions. The right hand wiper arm is usually not as far out of adjustment because it is making a smaller radius arc.

In this case, switch your VOM probe to pin #9….and close the TVS all the way again (counter clockwise)…perform the adjustment as before…but keep turning the plate until the VOM beeps….signaling that the wiper arm has made contact with the next in line wiper strip (#9).


Final Check: now while still holding the throttle plate closed and the TVS screws locked…unplug the VOM probe from #9 and plug it into #17. The VOM should beep signifying that the parking/idle wiper is still in contact with #17 when the throttle is fully closed.

Ray

[Lars S]

Ray,

/Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold

[KTPhil]

I'll have to study this and figure out how to implement it most easily (least amount of disassembly). Replacing my broken distributor dramatically improved the low rpm and off-the-line smoothness, but I'd still be interested in tuning the TVS more precisely to get the very best throttle response. Thanks for all the work detailing the steps with photos.

[raygreenwood]

[raygreenwood]

Part 2...supplements....and some modifications!



So some of this information is just for clarification and historical that may make the main body of this document a little less confusing.

Bear in mind….the first part was ONLY about how to adjust and what you are looking for when the switch is being adjusted and when it IS adjusted.

NOTE: I can already hear the wheels turning in some D-jet heads….and will no doubt see comments coming about the “fact” that so many have NEVER done any adjustment other than what the books say….and never had any troubles.

To these comments I offer these thoughts:

• For as many people who claim the “book” adjustment is just fine…I can find an EQUAL number of owners (and not just in the VW forums…Mercedes, BMW, Porsche, Volvo etc.) who find that adjusting seems to have no effect or never seems to be exactly right or they can never get rid of all of what seems to be a TVS related hesitation or “bucking/shuddering” effect.

• To be fair to that last point, in many cases they may have just as many other incorrect EFI system functions (ignition timing, main fuel mixture, throttle cable slack, fuel pressure, wiring issues, vacuum leaks etc.)….that can be causing the hesitation and in that case they should not even be adjusting the TVS…YET.

• The factory adjustment listed in the books is for the most part correct. The problem is that it does not take into account age/wear/damage or owner related tweaking of parts that can prevent proper position of the wiper arms (bending of the stop tang or the fork switch itself).

The book offers no physical inspection data. Only data on how to judge a TVS based upon what the Bosch injection tester says. I got to see firsthand that many years ago…many shops threw away perfectly serviceable parts that only needed minor adjustment or cleaning to account for wear.

And….as I have shown…there is a critical position that the wipers need to be in to operate especially in the later models that employ the fuel shut off and the 1280 rpm idle/shut-off speed cycle in the ECU.

• Far too many owners…who swear their cars purr like a kitten….when I happen on a chance to drive or work on their cars…...I have to nicely inform them that their car DOES NOT in fact “purr like a kitten”…and that when tuned more tightly and especially when the engine was factory new with new parts, these cars ran MUCH better than most do now and were in fact VERY smooth.

Too many owners get used to the little discrepancies and justify this as…”well…it runs great for a 40+ year old car and I’m happy”. That’s fine….but in many cases you can do better if you want or need to.

• With some more diligent inspection and cleaning you can double the life of your TVS. That in itself is good reason to get into this. These parts do not grow on trees.

• The last problems with TVS adjustment have to do with a couple of actual parts discrepancies I have found in NOS parts and with the need to tune tighter on EVERY injection related part if you have made modifications to the engine to make it perform at a higher level (Larger valves, changes to intake or TB, Camshaft, compression, exhaust, ignition etc.).

When you make modifications to the system…the engine becomes more sensitive to inputs and it changes the way it needs to be tuned and the TVS CAN be a part of that work and have very good effect.


Further clarification points that may help:

What the TVS REALLY is for the most part is the equivalent of the accelerator pump in a carburetor. Its main function is that it supplies instant IMPULSE enrichment to add to the inlet air…ONLY…when the throttle is moving toward open.

In the middle years of type 3 and the late years of type 4 with D-jet you have several methods of “impulse” enrichment:

1. The copper full load diaphragm in the MPS which supplies a subtle amount of enrichment when starting off from a stop for just a split second when you FIRST crack the throttle. This helps to cover any hesitation during that 2° movement gap of the TVS and is why so many owners get away with sloppy adjustment.
This diaphragm also supplies “some” enrichment when at WOT and there is very little vacuum and is why it is called the full load stop

2. The TVS supplies injector impulses outside of and in addition to, the regular timed impulses from the trigger points…and…supplies those impulses alternating between injector pairs about every 4.4° of throttle opening rotation from 2° from full closed to wide open throttle position.

So the TVS enrichment is very evenly applied and is VERY important to prevent hesitation.

3. Some TVS on some system models also supplies a signal that notes “wide open throttle” and can signal the ECU to change injector pulse width to enrich based on that fact. This is done from the ground track on the circuit which is the inner wiper arm.

Some better drawings from the Henry Elfrinks Volkswagen fuel injection Manual. I am including them because they are excellent drawings and it may help for clarity.

This is a pretty good book. I have the thinner cheaper one from this link. The thicker one above is also excellent and worth the money.
https://www.amazon.com/s/ref=nb_sb_noss?url=search...cal+manual

The drawing on the left is the very earliest two wire TVS. We are not dealing with those models here. There are effectively three TYPES of D-jet TVS (but numerous models).
The one on the left is simply to signal throttle closed and throttle open. It has no injector impulse strip.

The second one…I have an example of one that is identical to the left hand TVS with the same very early switch type and a simple contact strip to give injector impulse. From memory it is either three or four wire and I am not sure it even came from a VW. We are not dealing with that one either.

The drawing on the right above...is a simplified but very clear example of the most common four and five wire types for 41/412/914 and many type 3, we are dealing with in this “how-to”. In this drawing it is in the throttle closed/idle position.

This sketch shows when at idle with throttle closed, which circuit is activated. It is only the #17 that is connected right now. The forked switch makes contact with the “pole” on the rotating hub that is connected to the inner wiper track which is #17 in the plug.

You will note that the inner wiper track is also connected to #17 at this point…but its contact to the outer wiper arm contact strips is currently BROKEN by the RED switch bar to the left.

The contact # 14…shows on this diagram to be also connected to that inner wiper track….and on some TVS…it is. On others with FULL LOAD/WOT enrichment…it is not connected to #17 UNTIL the throttle is fully opened as can be seen in this picture.

This is what happens when you apply your foot to the throttle…the throttle plate starts to open…the force (yellow arrow) goes the other direction and connects # 9 and #20 with the inner wiper track #17…which is a ground to the system. It disconnects the loop between #17 and #14 which was signaling fuel shut off and/or throttle closed.

The reason why these “authoritative” sketches in the books have confused so many people when they look carefully to figure out how the TVS works…. is that they are not careful with their circuit lines….and not careful to detail ALL models of TVS.

In the first drawing (with no colored lines) It looks like in the basic picture is that when you come off the throttle…it breaks all contact to #17 (the inner wiper track) and you are at a loss to figure out where…during throttle open stroke….the inner wiper track is getting its connection to # 17.

It’s getting it right here inside of the yellow circle. In this model of TVS…#17 is connected all the time to the inner wiper track.

HOWEVER…..that is a very basic four wire sketch. In reality…if you remember….our four and five wire TVS’s with all kinds of mods like WOT enrichment, EGR on/off function, and fuel shut off on deceleration….use #17 and #14 for different functions (sometimes not at all).

In the circuit board picture above, # 9 and #20 are still “impulse” contact strips….but # 17 is not used for the inner wiper arm ground loop for 9 and 20. This is done by #12/47…which also supplies the same ground contact to # 2/14…which is a wide open throttle signal as can be seen by the gap in its trace.

# 17 in this case is ONLY being used for throttle closed idle fuel shutoff. So if throttle is completely shut above 1280 rpm…the ECU shuts off fuel completely.
If throttle is shut completely below 1280 rpm…the ECU pays attention to the signal from #17 and allows idle mixture injection level to keep the engine running.


Other items: Defects and modifications.

Not to show off….just to let you know partly where I got some of the next information on the defect I am going to describe.

This is the bulk of my TVS collection. About half are NOS. One of the NOS TVS in this picture had a defect that made it inoperable. I have found about 10 of these over the years. From what I can tell and measure, it is because of a molding defect in the nylon forked hub.

The problem is that the distance center to center on the “ON/Off” poles….is too wide. This means that at idle…the forked switch in the picture above will correctly be in contact with the “off” pole as seen in the picture above.

But….when you open the throttle….the forked switch will never be able to make contact with the right hand “ON” pole. So…..you get no enrichment. That effect will cause lean misfires, popping, shuddering and once you reach highway speed and try to hold a steady speed….it shuts off injection and you go into instant deceleration.

If this effect sounds familiar to some of you…you may have gotten one of these parts!

The reason why only a few would be this way is because of the way plastic parts are injection molded. Usually a mold will have numerous “mold positions” of the same part.
They usually mold several parts at once. At any given time…one or more “positions” in the mold may either be worn out or might be cooler or hotter (most injection molds over a certain size are water heated/cooled to keep the plastic temperature uniform).

The wear to the mold position or the poor heating fluid can cause one out of many parts to be oversized, undersized or distorted.

I have measured many TVS pole diameters and distances over the years since I found the first of these. For an example of what is wrong I measured all of them in the picture above that I had on hand.

You can see the natural variation in spacing that is also part of the reason why just an arbitrary 2° as outlined by the “books”….is not always perfect. The contact poles or pins are actually pretty damn uniform over 30 years…but the nylon part molding is a little less so.

The notes below are IMPORTANT:

The entry in red was the defective part. I kept it because…..

The two entries in blue had a rather narrow fork gap between the poles. It made them touchy to adjust…but made them VERY noticeably responsive. Very smooth throttle transition!
I learned something here that was worth replicating when possible…and if I could narrow the gap on the defective part…I could not only repair it…I could IMPROVE IT!

So…this how I repaired and improved it. I crimped a ferrule cut from an electrical connector onto the “OFF” pole and filed it to size before installation.

In this picture you can see that this switch has not been adjusted yet. You can see the gap between the forked switch and the “OFF” pole…which is good but narrower than normal (see below).

And…you can tell it is not adjusted as you can see that the hub is firmly against the metal stop tang.

In this picture you can see that the gap between forked switch and “Off” pole is very slightly smaller….tighter…closer…than normal….and the hub is now spaced off of the steel stop tang.

This is a comparison shot between the repaired/improved defective TVS both unadjusted and adjusted and with a shot of what the normal gap looks like on a TVS switch fork.

This repair/modification can make the TVS MUCH more responsive!.

This is what the repaired/modified switch contact position is like when its adjusted properly.
Note the contact ball tip position just on the edge of the #20 contact strip. It still has enough contact travel that when the forked switch closes the gap it has of less than .010”…it will still be on contact strip #20 giving almost instantaneous enrichment impulse.


The throttle body modification:

This is a really excellent modification! I do not know if it will help a bone stock 1.7L…but it should certainly help a 1,8L that is bone stock with either D-jet or L-jet.

It helps a lot on a 1.7L that has larger than stock valves and light porting, with a web #73 cam and higher compression.

This is a TB from a bus 2.0L engine. This particular one has a boss for EGR but it has not been machined. Another really good part of this TB is that it has throttle shaft seals top and bottom, has the positive return spring unit which is superb for adjusting the TVS and keeps the TB very positively closed with even spring tension.

Most importantly…it has a larger diameter!

NOTE: yes…that is a throttle kicker from an automatic car. I was experimenting with using it with a 004 four speed. It has some benefits…but the jury is still out.

The larger 2.0 TB is 44.9mm and the 1.7/1.8 TB is 42.3mm

I ran this for about 40k miles. Really excellent mod. I will be machining the outer opening bell down shorter to better fit the intake boot. You need to make sure you find a bus TB that has the TVS boss.

Not all of them had them and there are numerous part number variations but the part # listed 022 130 067A has all of the TVS boss, filled in EGR boss, screw holes for TVS and has enough correct vacuum lines installed and bosses for others than can be drilled.

These TB also had an o-ringed idle adjusting screw. Yes…it also had a port hole drilled in the throttle plate from the factory. It was just easier to put a screw in the port hole, swage the back and install it than to try to find another plate.

I used a muffler and tail pipe expander tool to cleanly enlarge the hole. It took five minutes. It is actually much cleaner than it looks here. The stock 1.7/1,8 plenum is on the left.

Ray

[MontrealAircooledNut]

This is an amazing tutorial!! Thanks Ray for this incredible write up which , no doubt, will help many.
_________________
Notchback 1965
Fastback 1970
Beetle 1971
Squareback 1973
412 wagon 1974

[raygreenwood]

A correction:


The 1.7L TB part number I listed is INCORRECT!

It should be:
022 133 062
022 133 062 A
022 133 062 B

I will have to look for the 2.0L TB and 1.8L tb to find out exact numbers. My apologies.

The TB #'s are part # 9 in the parts list below

The numbers at the right end of the line pertain to this models list

It tells you whether they are sedan auto or manual or Variant auto or manual

Ray

[sallittjob]

Hey Ray,

I'm trying to diagnose a lack of WOT enrichment on my 73 412.

I pulled the throttle body and adjusted the TVS as you've outlined here (thank you for the excellent post!) and it is perfect to your images and test procedure.

I have a wideband on the car and a fuel pressure gauge. The car was set to 31 PSI or so when I got it. I backed it down to 28psi yesterday and went for a drive. I also adjusted the ECU idle CO pot to get my idle AFR to 13.5:1.

I'm really happy with the AFR map across the entire map except for WOT. When I pin the gas to the floor in 3rd gear (auto), it goes to about 11.5:1 and then leans out to 14:1 or so sustained. I want to get it closer to 12.5-13:1 at WOT.

I feel like the ECU isn't adding enrichment for WOT. So if that is the case, my throttle cable isn't opening the throttle body all the way (haven't checked) or the WOT signal from the TVS isn't going off. I have the throttle cable set so there is no slack in it with the TB closed and the auto kicker pulled back fully. I've confirmed that the idle signal is working correctly.

I was thinking of just bumping the fuel pressure up to 30psi and then retesting to see where WOT ended up. But I don't think it will get me to where I want and that will just increase fueling across the entire range which seems counter productive.

Any ideas or tips on how to check that the TVS WOT signal is properly triggering?

Thanks!
_________________
57' Beetle Deluxe
1192cc SP

71' Super Beetle
1968cc DP

73' 412 Sedan
1679cc FI

75' Westy
1800cc FI

[raygreenwood]

[daves1800]

I have to start by saying that I'm extremely happy that I found the Samba and this thread earlier this year. Then I will be very honest in saying that I don't own a DJet VW or Porsche. However I do own a few TVS or as they are in my marque's nomenclature TPS, but precisely the same D-Jet accelerator pump functionality. This thread let me disassemble a TVS/TPS and share part of what I found. Others did more still.

https://volvo1800pictures.com/document/TPS/TPS-Volvo_72_73_Operation.gif

The Volvo cars do not utilize the WOT enrichment mentioned here and thus the animation does not include that function.

However, that is a fine example of collaboration to produce a result. I've learned a heck of a lot this year on DJet, following some Mercedes-Benz forum threads Then it struck me, how about an all-marques discussion group, so I started one: https://groups.io/g/djetdevelopment
Yes, I know all about Dr. DJet's site, but I'm locked out as are my M-B friends.

Cheers,
Dave F. '73 Volvo 1800ES, '72 Volvo 142E

[raygreenwood]