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  View original topic: I Need Help with L-Jet / AFC Fuel Injection Topic Goto page 1, 2, 3 ... 31, 32, 33  Next
borninabus Tue Sep 27, 2011 7:09 am

it's long overdue, folks.

poor guys over in the T3 forum are having to answer LJet questions because we don't have a topic.

while i'm no FI expert, i am fairly competent and confident working on the system.
there are a few of you out there that know this system in & out (you know who you are) and should frequent this topic to help the uninitiated out.

i suspect i'll be in here answering AND asking.

the only "special" tools you will need are a volt/ohm meter (multimeter), a simple test light & a 50 or 100psi fuel pressure gauge.
you should also know that the T1 & T2 AFC systems are essentially the same.
but the T3 & early T4 (like in a T4 car) are not the same system. they use DJet; MPC FI.

those who seek help should start here:

first, YOU MUST RULE OUT ANY AND ALL OTHER POSSIBLE PROBLEMS
such as: vacuum leaks, fuel supply, ignition, electrical, compression, valve adjustment...etc...etc...etc...
just like a carburetor you must make sure every thing else is as it should be; or else you are just chasing your tail.
GOT IT?

Then, and only then may you proceed:

VW AFC Troubleshooting Guide
In this guide you will find a step-by-step problem solving process designed for the VW technician with a working knowledge of the system.
I have this book and it is dirty :wink:

If you don't know what a potentiometer is you should start here:

AFC Training & Troubleshooting; AKA: LJet Explained.
Here you will find hard numbers such as an ohm curve for resistance @ temp for TS2; descriptions of each individual part and how the system works together as a whole.

Print these out and put them in the 3 ring binder that contains your Idiot Guide, your Official Service Manual published by Robert Bentley Publications, your laminated color wiring diagram for your year bus & your Ratwell pages of interest.

What?
You don't have a 3 ring binder like this?
Get one!

Other threads:
AFM adjustment

Randy in Maine Tue Sep 27, 2011 10:09 am

and a fuel pressure gauge.

Ol'Beetle Tue Sep 27, 2011 2:40 pm

Bosch's take on this subject here.

busdaddy Tue Sep 27, 2011 3:34 pm

And of course Ratwell's photos of all the parts because you can't try to fix it if you don't know what it is: http://www.ratwell.com/dotmac/Sites/Parts/PhotoAlbum62.html

babysnakes Tue Sep 27, 2011 4:50 pm

Thanks to OL'Beetle I need a 5 ring binder. :lol: Really this thread is needed. I am a noob to L-Jet much less any other FI. I will be referring to this sticky.Thanks borninabus.

ccpalmer Sat Oct 01, 2011 5:54 am

All I know is the only issues I ever had with FI in a Bus was leaky vacuum tubing and elbows.

lostorbit Sat Oct 01, 2011 6:17 am

Send your old fuel injectors off to be rebuilt for about a quarter of the price of new injectors. Use WitchHunter or Cruzin Performance. I personally used Cruzin, sent off five old injectors (an extra in case one couldn't be serviced). They come back as good as new. Rebuilt internals, sandblasted, painted, new seals, hoses, and nozzles. Pick up old injectors at shows and swap meets whenever you come across them.



Comparison of the old and new:


borninabus Sun Oct 02, 2011 9:29 am

lostorbit wrote: Send your old fuel injectors off to be rebuilt...
thanks for pointing this out.
i won't even begin to troubleshoot a "poor running" problem without having this done.
these injectors have all had 35 years of dirty gas run through them. and to top it off they probably sat unused for 5 or 10 years.

i must confess i usually just get new ones. and of course new seals are in order upon installation.

thanks everyone for adding to this topic.
maybe we'll get a question one of these days...

Amskeptic Mon Oct 03, 2011 7:49 am

Here's a theoretical comparison of D-Jet versus L-Jet.

D-Jet was introduced first. It uses manifold pressure to determine how much fuel the engine requires.

Pressure, as you know, goes both ways. We are all sitting around in 14psi atmospheric pressure... if you walk into a room with 0 pressure, you explode. Step out of your deep sea explorer, you implode. When we talk about "vacuum", we are merely talking about pressure-that-is-less than atmosphere.

The D-Jet fuel injection reduces fuel quantity at less pressure , and increases it at greater pressure. Because this is all occurring at less-than-atmospheric pressure, we all here translate the above by saying D-Jet provides less fuel quantity at high vacuum, and more at low vacuum. At idle, the engine is pulling against a closed throttle plate and has high vacuum, so very little fuel is allowed. You punch the gas, the engine is now able to gulp in additional air, the manifold vacuum drops (i.e. the true pressure increases) and D-Jet increases fuel quantity. The manifold pressure sensor is unfortunately a somewhat delicate device. Like our thermostats, it uses pleated bellows that react to changes in manifold pressure as measured against atmospheric pressure. A leaky manifold pressure sensor can wreak havoc with your mind.
The great thing about this system, is any vacuum leaks make the D-Jet think that you are accelerating. It is a fail-safe of sorts. Vacuum hose splits will will soot up the tailpipe over time while you wonder why your fuel mileage is so horrible. The not so great thing about this system is that it was not precise enough to get the emissions down, and any transient error, like a vacuum leak, would cause a rich-fail.

L-Jet is more precise. It does not rely on pressure. It relies strictly on the wind speed in the intake tract. Low speed air, less fuel. High speed air, more fuel. The air flow meter has a spring-loaded weather vane attached to a potentiometer that's it. Simple. Pretty precise too, being on the atmosphere side of the intake allows instantaneous reaction.
Problem with this system is that any intake leaks that sneak into the engine without the L-Jet being aware of it, causes a lean condition. This can be dangerous to an air-cooled engine with hot exhaust valves.

After working on both systems for several years, I have found that most problems are simpler than our fertile imaginations scare up. It is critical to stay calm and focused and make a plan of inquiry that you stick to. If you wander around in despair replacing parts willy-nilly, you can get lost. The most common problems are stupid simple fixes:
Loose or damaged vacuum hoses
Loose or damaged electrical plugs/spades
Dirty obstructed fuel filter

Colin

SGKent Mon Oct 03, 2011 4:26 pm

every set of manifold runners that have come my way from buses that L-jet was pulled off after the owners pulled out their hair had bad leaky cracked injector seals. I asked myself, were these less than $10 parts and less than an hour to change parts the reason the bus engine failed to run properly - and the source of so much frustration for the PO? And when the high pressure fuel line crumbles in your hands - spooky.

SGKent Tue Oct 18, 2011 7:53 am

L-jet specs and troubleshooting manual

http://www.thesamba.com/vw/archives/manuals/afc_fi...Manual.pdf

SGKent Tue Oct 18, 2011 7:56 am

jonspin wrote: 1978 Westy. I know I probably should have left it alone. If it's not broke don't fix it but I thought putting in a compu fire would be a good idea. But in the process I messed something up in the Fuel Injection. The bus would turn over and begin to start then die. I put the points back in and had the same exact problem. So I read up a bit and the cold start injector is working and that gets it to begin to start but when the signal to a relay located on the wall by the gas tank and above #3 piston is suppose to tell the injectors to start working, they don't. At least I think that is what's happening. I am very new to the FI so I'm having a tough time with this one. Everything else with the coil, distributor, vacuum hoses all connected wires all connected and timing is right I triple checked all of the that. I forgot to disconnect the battery before doing any of this. Did I fry the relay or do I maybe just need to reset the system somehow? I can here what I think is the relay clicking a couple times as it dies. Any help would be greatly appreciated.


Look at the wires that supply voltage pulses to the ECU. It attaches to the coil. You may have it on the wrong side.

borninabus Tue Oct 18, 2011 8:50 pm

jonspin wrote: 1978 Westy. I know I probably should have left it alone. If it's not broke don't fix it but I thought putting in a compu fire would be a good idea. But in the process I messed something up in the Fuel Injection. The bus would turn over and begin to start then die. I put the points back in and had the same exact problem. So I read up a bit and the cold start injector is working and that gets it to begin to start but when the signal to a relay located on the wall by the gas tank and above #3 piston is suppose to tell the injectors to start working, they don't. At least I think that is what's happening. I am very new to the FI so I'm having a tough time with this one. Everything else with the coil, distributor, vacuum hoses all connected wires all connected and timing is right I triple checked all of the that. I forgot to disconnect the battery before doing any of this. Did I fry the relay or do I maybe just need to reset the system somehow? I can here what I think is the relay clicking a couple times as it dies. Any help would be greatly appreciated.
make sure the double relay is supplying power to the fuel pump while the starter is operating AND when the AFM flap is open.
you say that your points & such are spot on, but just a friendly reminder that the manual sez to make sure ignition is in order before you delve...

SGKent wrote: Look at the wire that supplies voltage pulses to the ECU. It attaches to the coil... ...on the negative side.
it's white with a gray sheath and runs directly into the main harness just below the ECU plug on the right of the engine.
incidentally, you can test for pulse from the coil @ ECU plug # 1 (the one at the the "bottom") with a test light connected to it & to ground.
it should pulse with the points.


on a side note:
the manual linked above by Ol'Beetle is essentially the same as the "troubleshooting guide" i linked in the original post; just not in VW specific lingo :wink:

the manual linked above by SGKent is the exact same "training & troubleshooting" manual that is noted in the first post...

SGKent Wed Oct 19, 2011 9:11 pm

Hi Brandt - First you should replace the fuel filter. While it is off, connect a hose to the end of the pump and see if it will pump fuel back into your gas can. If it does with force - don't spill any for fear of fire, then you know that fuel can come from the tank. It is not uncommon for the fuel filter to be plugged with rust. The filter is a tighter weave than regular filters because it is for FI so it is easier to plug up. Next check to see that the white wire in the gray sheath is connected to the coil on the distributor side. That wire supplies the ECU the pulse it needs to figure how often to fire the injectors. Here is a link to the FI troubleshooting manual. Last - that high pressure line is probably old. Be very wary of it because if it ruptures you will have a fire on your hands of epic proportions.

http://www.thesamba.com/vw/archives/manuals/afc_fi_training_troubleshooting_manual.php

SGKent Fri Oct 21, 2011 7:46 am

drober23 wrote: I have seen people asking where they can get Multi Fuel rated FI hose to use with late bay FI Type IV motors in the past.

The 5/16" Gates FI hose I bought from NAPA the other day is rated as Multi Fuel. Though I would pass it on.

Still not sure where to get a good 50mm hose (for the line between the fuel filter and fuel pump) though.

rustbus Fri Oct 21, 2011 8:58 pm

Guys -

Does anyone know of a online L-Jet parts lookup that will tell you the year range for the various FI parts? for example, if i have 2 decel valves, with differing part numbers, can i find out what year range they suit?

EDIT - http://www.type2.com/library/fuel/fuelibo.htm
thats a start



another great link for this thread, on "Late FI Bus EEC Valve Fix",

from Amskeptic

http://www.thesamba.com/vw/forum/viewtopic.php?t=476758&highlight=eec

airkooledchris Mon Oct 24, 2011 9:27 am

SGKent wrote: drober23 wrote: Still not sure where to get a good 50mm hose (for the line between the fuel filter and fuel pump) though.

Scott at germansupply.com has this 50mm hose. The good stuff, not the braided ones...

SGKent Tue Oct 25, 2011 8:55 pm

tootype2crazy wrote: mikewire wrote: tootype2crazy wrote: Ok I pinched off the return line and operated the flap and the fuel pressure jumped up to 100! The gauge definitely is not at fault. Could it be that I have 2 bad pressure regulators on my hands? What are the odds of that?

If you pinch the return line, then fuel can't return to the tank, and pressure just builds in the line so it would make sense that your FP would jump to 100. Just operate the flap with the fuel system open, no pinched lines. You should be running about 35psi.

Didn't you notice in my first post I did what you just said and the psi was 20 on two different regulators? By pinching I was doing what the others said to do.

you have a clogged fuel line, fuel filter, bad pump, or clogged outlet in the tank

When you pinch the line a tiny amount of fuel can push the pressure really high. When the return is open the pump can't supply enough fuel to keep the pressure up. Turn a garden hose on at a dribble and hold your thumb over the end. Eventually you will get enough pressure to get a high pressure spray but it will be small. Take your thumb off and it will fall back to a dribble. The way to test it is do a flow test into a bucket. If the filter hasn't been changed - and I am not going to read the full topic again to see because I have other things to do, change it first. Good luck.

SGKent Tue Oct 25, 2011 8:59 pm

White99z wrote: How would I test the cold start valve? It's been suggested before in this thread! Can't find much on Ratwell.

It is the T that both hoses connect to between the rails and is bolted to the plenum. There are two ways - Just install a new one - they fit many cars and can be found new for as little as $30 - $40 or pull it off and see if it dribbles after the initial spray. If you haven't had your injectors cleaned you may want to do that too. Also you want to check your fuel pressure.

tootype2crazy Tue Oct 25, 2011 9:05 pm

SGKent wrote: you have a clogged fuel line, fuel filter, bad pump, or clogged outlet in the tank

When you pinch the line a tiny amount of fuel can push the pressure really high. When the return is open the pump can't supply enough fuel to keep the pressure up. Turn a garden hose on at a dribble and hold your thumb over the end. Eventually you will get enough pressure to get a high pressure spray but it will be small. Take your thumb off and it will fall back to a dribble. The way to test it is do a flow test into a bucket. If the filter hasn't been changed - and I am not going to read the full topic again to see because I have other things to do, change it first. Good luck.

FYI the tank is freshly cleaned and coated and the filter is brand new. I will check the supply line for kinks and so on. If there are none the the process of elimination would implicate the pump I suppose.



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