D-Jetronic Tuning

[Adriel Rowley]

Georg and Ray Greenwood have been a great resource, and I thank them for it! Georg's are mostly in the F.I. sticky, so the posts do not need to be brought to one place, plus, everyone should read it in its entirety. Then, please come to this thread.

Trouble is, Ray's gems are hidden in various places, including Shop Talk Forums (Searched over 20 pages to try and find anything, thus why this has not come out yesterday, in response to the M.P.S. thread.) So I thought I would try and bring them all together. With them gathered, and more advice, the D-Jetronic can be tuned for a specific engine, stock to hot. With a custom tuning, one can gain performance and gasoline mileage.

The parameter that this will be for tuning with stock harness, with a rebuilt harness, using two cantilever plugs (L-Jetronic and later), and/or rebuilding an engine for D-Jetronic, but with performance parts. The latter is to try and help the folks who are rebuilding engines, and desire more performance than stock, but still want to use D-Jetronic.

Similar thread on Shop Talk Forums, but is too specific for over all tunig. http://www.shoptalkforums.com/viewtopic.php?t=98817&highlight=

Electric Supply/High Voltage System

[raygreenwood]

Lots of D-jet info on STF. I think I am pushing 10,000 posts over there...probably half about D-jet or fuel injection (stock types) in general.

A couple of thinsg about D-jet. Bear in mind that I love this system. But....built in logic wise, its a very "stupid" system. By that I mean...it only knows what it receives from the sensor net. That net includes the harness. It also does not really have "logic" liek a modern system. It has very limited response choices to what it receives for information.

So...with this in mind, you must make sure that the things that D-jet does not have a sensor for...must either remain as the factory left them (because the brain is set up for that)...or if you modify them....insure that what they read is as stable as possible.

I just started an experiment last week..that may make harness building much much easier for a lot of people. In general...for injectors, ambient air temp sensor and the three wire plug on the trigger points.....its not too hard to find L-jet plugs that fit fabulous. That takes care of those....but plugs for the MPS, ECU and TPS are very hard to find...and are actually verging on impossible.....for to find plugs that can fit dual cantilever L-jet terminals.
That being said....I did locate...some micro-miniature ring type terminals that take a screw that is....about .040" in diameter. I am testing the ability to.....get this.....drill nice clean holes in the TPS terminals, the MPS and the ECU terminal strips. Then....attache the ring terminals with matching machine screws, nuts and lockwashers....and them seal with circuit board varnish. This accomplishes what the L-jet terminals would do...which is a connection that cannot loosen or vibrate loose....but even tighter.
Since you will be building a new harness anyway......its very easy to find an intermediate L-jet style plug to put between main harness and TPS, main harness MPS and main harness and ECU. These would be 0-resistance connections with either nickle tin plate.
You could leave the intermediate ECU plug back behind the fire wall. It would not be visible. This could even be retrofitted to an otherwise good stock harness.

I have not used points in about a decade. Adding a pertronix or equivalent...is a HUGE performance and system stability item.
Adding a hotter ignition across teh board....a 40KV coil for instance...or a jacobs system...is HUGE. All of teh VW's are sporting a basic improved 1930's ignition. The fuel injection models with higher compression and lean burn aresriously under-ignited.

Be careful with ratio rockers. The fuel injection system...especially D-jet...does not respond that well to extra lift. It can screw up the vacuum signature. It does respond to a little bit of lift...but responds better to a little more duration.
You should when building a D-jet engine...spend all the time required on setting up PERFECT valve geometry. Its critical for D-jet
Also.....valve adjustment is critical. Set them cold...check them hot...repeatedly. You will fid...that no two valves expand the same. I readjust mine hot......to get rid of teh slight variances....and it makes a world of difference.

The D-jet system has no sensor for fuel pressure. Its fuel stability is not great. When you get a GOOD gauge.....that is accurate to 1/2 psi full scale.....you will find this out. When you correct that problem....a whole world of tuning and throttle response opens up. Its that critical and is not expensive to fix.

The trigger point resistance, connections and repeatability are critical.

Adjusting the timing properly is critical. Poorly adjusted ignition timing...changes the injection timing point...because...teh triggers are slaved to the distributor.

A really interesting and enlightening experiment: Take a trigger set and slot the screw holes. Install them. Start it up...and slide the triggers around.
Watch the fuel pressure gauge....it goes MAD! This is because injetion timing variations....cause the engine to run ...odd...or even bad. This changes the vacuum signature radically.....that changes the movements inside of the MPS....that changes the pulsewidth of the injectors....which causes huge quick drains to the fuel pressure. It can swing several psi each directio just idling...and gets worse when you rev it. It rpoves injection timing is critical...and that the stock fuel pump cant supply the volume...at pressure...to correct for it. Get a feeder pump.

You can get around the limitations of the sensor net...somewhat...by lying to the ECU. Ballast the ambient air and CHT with resistors when necessary.

There is a lot you can do with this system.

One huge thing is to improve the exhaust. The stock exhaust is very limiting and traps heat.

I don't know if Web cam makes an imroved fuel injection cam like they do for the type 4....but if they do...its a HUGE improvement.

D-jet CAN take other than stock cams with better than stock lift and duration ...but some rules apply. The valve overlap and lobe center must be preserved as much as possible...and more importantly....the intake valve timing must be preserved as closely as possible. This is the critical thing that D-jet is centered around....intake valve timing. Take your time on these things and this system can really run well....much much better than the factory left us with.

One last thing. I found with type 3's as well as type 4's that running with loose decks and lower than stock compression changes the tunability and vacuum signature. With the relatively consistent cooling of type 3's....and better fuel delivery than carbs....it appreciates good compression with D-jet and even better than stock compression. Don't get crazy with it....but 8.0:1 should be no problem. This and a tight deck will also reduce the maximum timing necessary......and cause cooler head temps.

The cold start system works great...when you need it. I have found that when its really cold ...below freezing...if all is adjusted really well with baeline fuel mixture....the cold start system helps. It can put too much fuel in. To change this....you can add a ssmall regulator....or use a brass plug in the nipple of the cold start injector and drill the hole out very small....so the volume is greatly reduced. In this way you can tune what it delivers. At all other times.....say not so cold.....if the thermotime switch is operating properly....the inejctor does not come on so its not a problem. Ray

[Tram]

Nope, I'm not a big fan of swapping out parts for parts from other makes/ models and screwing with its' head, unless you're making changes like going with a 1776. And, if you do, all that info belongs in the "PERFORMANCE" forum, IMHO.

I've driven bone- stock T3s for 35 years, complete with their factory defective harnesses and connectors, complete with their factory underpowered generators, and complete with their factory inefficient injectors, yaada yaada, yaada, etc. Stupid? My tuchus.

I'm a believer in running, maintaining, diagnosing, and fixing our cars. I'm not a believer in re- inventing the wheel. Maintaining the wheel that the good Lord, Herr v. Nordhoff, and Bobby Bosch have provided me is good enough for me!

That's my story, and I'm stickin' to it!
_________________
Немає виправдання для війни! Я з Україною.

[Adriel Rowley]

[Tram]

[Adriel Rowley]

[Adriel Rowley]

[Bobnotch]

[Adriel Rowley]

[raygreenwood]

There is nothing really wrong with D-jet from the factory. But bear in mind that this is the first major production mark of electronic fuel injection. It had a very short run in total number of vehicles...if not total number of years. All books and manual from teh era...including dealer manuals...and including the Bosch fuel injection manual usually state that there is little in theway of user servicable parts. This is mostly due to the fact that the average Joe in 1968 could not source orf afford the level of basic test equipment I can get from even the crudest electronic supplu these days.....much less understand all the necessary concepts in those easrly days.

In short...this means that there was very limited overall development of the D-jet system during its production run. There were very few indpendent mechanics experimenting either with expanded tuning technics or aftermarket funtionality of the system...ie...racing etc.
The system was superceded before it really started to get "played" with.

If you can find a brand new NOS harness...built...use it. But....again and this is not an opinion developed by me....it was tested anddeveloped by the manufacturer of the harness components themselves. The D-jet connector system was superceded because it had a high rate of faults...due to the design of the component end connctors.
With parts being harder to get every day....I find no usefulness in going through the trouble to build a world class harness...just to use parts that were proven to be less than satisfactory ...by the factory....and replaced.

I'm all about keeping my 412 original. You look under the hood...and it looks like factory...almost. But its about funtionality. I want to drive my cars...not look at them under glass.

Its a fact of life that most of the type 3's and 4's in the Pacific nothwest ran quite a bit longer than those in my area. They ought to...it is drastically cooler there. I live in Virginia right now....but just moved from Dallas Texas.
A bone stock D-jet car...impeccably tuned...lives half the life of one with the mods I have made. They run far too hot....with bone stock specs.... for climates that have 30 days per summer of well over 100F and distances between cities averaging 4 hours at 75 mph.

I can do high speed cruising in hot weather much better with a type 4 engine than a type 3.....but still it lives a shorter life in stock trim. Parts for type 3 engines are cake to find. Try finding a set of original domed pistons or good heads for a type 4. I don't care to have to rebuild a $4,000 engine every 5 years for the sake of painstaking originality.

Its the same level as saying I must have the original rear drum brakes when I could have bolt on discs.....or I must run the same make of skinny, high sidewall 1974 michelins...for the sake of being original.
You won't survive in Dallas traffic without usable accleration on par with at least a modern 4 cylinder (which I get)....and you will end up stuck to someones bumper or in the ditch without marginally improved brakes and tires. You can make a daily driver or you can keep an original toy.

At some point in time....every one of you will need to replace the injection harness. You can update and even "improve" while keeping your car operable.....or strive for total originality and stay stuck with a basic Mod "1" level of 1966 tuning development. I'm not selling anythng...so its your choice. I suggest you do some research. Because if you don't believe what I am relaying to you (not telling you....simply transfering information I have learned).....you have NOT done your research...and are simply hanging onto what you know for sentimentality.

Question....6-7 years from now....when your neighers kid finally busts out your quarter window with a baseball....and old glass is non-existent...and new glass is nonexistent....what are you going to do? Defiantly drive it around with no glass....or bite the bullet and slap in a piece of plexaglass....or spend the money to have it custom made....or adapt something better.Whoooooa!....none o' thats original! See the point?

So....when someone offers you a new made piece of glass...are you going to complain that because its tinted it aint original? Won't get very far with that.

You want to drive long miles reliably in D-jet in the kinds of climate half this country has.....there are things you really should improve that were left undeveloped by the factory.

Off to the performance forum for what is simply enhanced tuning? Hardly...in my opinion. Ray

[Adriel Rowley]

[KTPhil]

Hmmm, SoCal gets more than 30 days over 100 yet there are a lot of original VWs living a healthy life on SoCal roads, including those I have driven for 35 years. I don't see tham as problematic in hot climates (other than from the lack of A/C in the cars I have driven! )

[Tram]

[Adriel Rowley]

[Tram]

[Adriel Rowley]

[raygreenwood]

Bobnotch......the failure in GM's connectors is one of the most widely known and highly hidden issues with GM. They have had HUGE recalls of various fuel injection related components. But the recall of a component actually masked the issue that harnesses got replaced at the dealerships. GM's components are actually excellent.
In mid 80's through the mid 90's most especially...recalls for "cannot duplicate" issues went through the roof.

Ford has some of the same issues with their non-tensioned pin type terminals from the 80's (molex style...which are crap for fuel injection)....and single cantilever type connectors. What they did as a stop gap was buy dual cantilevers under licnese from AMP...while they developed their own variants of the Dual cantilever terminal.

GM locked themselves out of this process for the most oart because they waited too long and stayed with the "we don't use that terminal because it was not invented here" state of mind.

That means that AMP, Bosch and Ford hold over 40,000 patents on EFI terminals. About 30,000 by AMP alone. There are just not too many connectors GM can invent that will not violate existing patents. They are still using largely single cantilever and molex style terminals. There are an even dozen style of connector in a 10 (80 to 90) year period for GM. None of which are up to date compared to what Europena, Japanese and even Ford use.

That being said...sure.....there are a great many...probably the majority....of any car brand that seem to run well and for long oeriods of time.

It does not depend on one thing all the time. For one...GM's weather pack plug bodies and seals are superb. Some of the best. The terminals themselves are not.

I have had first hand problems with connectors on GM vehicles that were under 30K miles. Pontiacs with their V-6's from 85 to 90 had numerious recalls.

There were a handfull of problems that also exacerbated the terminal issue. The improer tying down and immobilizing of harnesses...and ignition wires...under the hood causes excessive vibrational wear not only to terminals but to insulation of harness.

It also must be mentioned that the system that GM used for diagnostics in the 80's and 90's was so poor (the C.A.M.M.S. system/machine)....that it was WRITTEN policy at most dealers to keep a box of known good sensors on hand to plug and play for diagnostics because teh camms system could not localize faults that had variances under 5-10 milivolts. Unlike most other common EFI systems like Bosch and the Japanese cars......you could not simply take a digital VOM and verify what GM ODB-1 and earlier systems had wrong with them ...to backstop the camms machine...because the way GM sensors were designed, the millivolt level voltage from a simple volt meter could destroy certain sensors.

The list of cannot duplicate faults on GM vehicles is vast...compared to most other manufacturers. This is also why when GM took a controlling financial interest in Saab....the electrical system quality of the engine became so abysmal...that Sabbs after 1991....are generally not worked on by private Saab mechanics because of the harness failure and warrantability issues. Unduplicatable EFI faults are mostly tracked to either variable temperature sensor faults....and harness...most of the time. Ray

[Adriel Rowley]

[raygreenwood]

Ok....I also realize I am being cryptic about what I have done with D-jet. Some of this is for these reasons:
(1) I have about 5,000 post (i'm estimating)...on STF....that go into much greater detail. But I'm not trying to drag people from one forum to another. Not trying to be rude is what I'm trying to be.
The atmosphere is different here in Samba...I like them both for different reasons. I understand that publicizing other forums gets sticky sometimes.
(2) There were a great many of these mods that I...surmised, speculated on dreamed about etc.....long long ago before I actually had enough tools and knowledge to explore them. More importantly that was before I had enough spare parts that were not actually involved in my daily driving or someones else's...to experiment on.
Once I got past the stage where my daily driver was not my only car...maybe 1995.....I went full tilt into testing and experimentation to prove a great deal of these things to myself.

In short...if I get too descriptive...but not detailed enough...it could very easily push some people here into starting modifications they are not really up to yet...therby potentially destroying parts they cannot replace.
Yes....if you are not careful and do not know teh exact specifics and ranges of the mods you are going to do...you can destroy parts...or engines.
I'm careful as to what level of information I impart....before I get down to dissertations and exact measurements. I have nothing to sell...and I am not going to withhold anything from anyone who needs or wants information I have. That is counter productive to my goal of keeping as many type 3 and 4 cars on the road as possible.

(3) People say.... "a picture is worth a thousand words". I am a photographer. I work within the printing industry....and I am here to tell you I think that statement is oversold and under-explained.

A great many technical pictures seem to impart a HUGE amount of information. But unless you have an exact knowledge of teh system being shown.....and x-ray vision....you can't see some of the things that you may be missing that may be crucial.

I actually believe....more precisely.....that a picture based "tutorial"..with two dimensional technical schematics.....with included explainations in plain english...is worth a thousand words.

Before I delve into these things....I want to make sure that everyone has the interest and the attention span....because I CAN bore the crap out of you... . And...some of these subjects are not subjects you can get bored with...because you miss details...and break parts.

As an example.....I would say there is no series of .....say..... 3 pictures and a diagram that one could make .....that will explain to anyone except possibly.....TRAM, Brand Anders ....and a few others who have spent many years inside of MPS's...with numerous disections......exactly how to adjust...let alone modify them. I am not saying that anyone is NOT capable of doing this. Just that youcannot get in a hurry and make assumptions about these things.

I ahve lots of pictures done over the years of what I have worked on. Many of them are not digital. I am just starting to scan them in.

I can start dropping in some pictures as I go along. In the next month or so...I am going to hopefully cast another new harness for my 412. I have some mods I want to add.
Yes.....the harnesses I make for my cars have a cast jacket around the wires. I use 400F castable silicone in a table top mold I made two years ago. I broke that mold in storage while waiting to get my goods moved to Virginia so have had to make another. The wires...without termianl ends are instered into the table mold and centered in the bores with silicone rubber bands.
The bores in the polyester table mold were made by heating cheap styrene rods the correct diameter of what is needed for the right amount of wires to go to each place on the engine...and draping them over the sheet metal and engine until they cooled. Take each peice of plastic off and measure the length needed...while conforming to engine surfaces.......to reach where it needs to go.
Then......straighten/flatten the rods by heating lightly....make clean joints between teh rods to indicate where each tube section joins teh main harness with "sculpy modeling plastic. Then lift the whole apperatus up...and suspend it about 1/4" off a 1/4 sheet of acrylic. Around this you cast 1/8" thick layers of polyester until you are exactly at half the cross section of all of the rods that make up your dummy harness. Insert register pins.
Let it dry....spray on powered urethane mold release. Cast the top half to about 3/4" thick. Let it dry, pull the mold apart, pull out the dummy rods. Clean with soap and water, apply mold release. Spend about 3 hours inserting and centering the wires. Apply a bead of RTV around mold...apply top half. Connect vacum pump to one end and pre-worked 1 quart tank of high temp pourable silicone.
It takes roughly 3 minutes to vacuum the silicone into the mold. Let it dry for 24 hours. Demold....crimp on terminal ends. The boots are cast in.

Lot of work...but a bulletproof harness. When I get t o recasting a harness soon...I will make video and photos. Ray

[Bobnotch]

Ray, I always read your posts, because they're so insightful, and full of hidden tidbits of info. Yes, you can get a little long winded , but it's because you're trying to make a point, or get the needed info out in a way that the reader understands. Some of us here aren't engineers, so we need it dumbed down a little to understand (plain simple talk), as the info can get pretty complicated. But we're glad you're willing to share it with us, at least I know I am.
_________________
Bob 65 Notch S with Sunroof
71 Notch ...aka Krunchy; build pics here;
http://www.thesamba.com/vw/forum/viewtopic.php?t=249390 -been busy working
64 T-34 Ghia...aka Wolfie, under construction... http://www.thesamba.com/vw/forum/viewtopic.php?t=412120