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Restoration Project
[re: ]
22/11/2015 01:54
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Hey everyone. I bought a 1991 Audi V8 5-speed 3.6L about a month ago. I've been working on it trying to make it run. It hasn't run for 5 years and has been worked on by tons of people trying to fix it in that time. With this website and the wiring diagrams I have made a lot of headway but I need a little help still.
Initially the car would not trigger the ECU. I found the power to the ECU from fuse 29 to be broken somewhere. By jumping it, I am able to get the ECU alive and read codes off of it. I also had a dead fuel pump which I am replacing with a Walbro GSS341. The fuel pump relay does work and has power but is not triggered by the ECU. The timing sensors are both okay and I do have spark. The engine runs on starting fluid. It is not triggering the injectors though. The injectors DO work, tested by jumping them. Also bypassed the fuel pump relay to supply power to the injectors and still nothing.
I only have one code 2121 for the Idle Switch. When I try to do the output test to trigger the injectors, giving full throttle does not activate the test even though the correct code for injector one is blinking on the CEL.
Can the idle switch stop the engine from starting? And what can I do to fix it?
Thank you everyone for the help you've already provided with this forum. Hopefully I can get this cool and rare car back on the road.
Na Ja, so ist es.
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Mark Hanman
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Reged: 10/09/2010
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Loc: Costa del Poole
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Re: Restoration Project
[re: Alex Gr.]
23/11/2015 15:11
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One of my V8 projects baffled me for a while.
I managed to get the car running initially, then it simply wouldn't start again.
The final result was the ECU injection control, and which I think was damaged by either water ingress due to a bad windscreen replacement, or a complete meltdown of an Alarm immobiliser which caused a lot of damage.
Whether /if the idle switch directly stops the engine from starting, I can't remember. But the output tests ran fine for me, but the injectors simply weren't being triggered.
85 WR quattro
90 V8 Silver, 91 V8 Black, 93 V8 Lago
93 100e quattro V6. Titan, i think
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Thank you for the reply,
With the idle switch not functioning... aka the WOT switch also not functioning, I can initiate the output test where it is ready to test and blinks the code for injector 1, but I can't trigger it to perform the test. I could probably trick it into doing the test with a jump lead or something right?
Are there any known faults that keep just the injectors from firing besides roasted drivers? It is using a used replacement ECU.
Na Ja, so ist es.
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Jumped the WOT switch for the output test and the ECU was able to fire all eight injectors and trigger the idle witch and charcoal canister.
I did find discontinuity between the ECU and the fuel pump relay where it is meant to trigger the relay.
Na Ja, so ist es.
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Roy F
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Reged: 06/05/2006
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Loc: Schweiz
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Re: Restoration Project
[re: Alex Gr.]
24/11/2015 21:19
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What for god's sake is WOT?
Idle switch does sometimes do a lot to fail the start, NO signal to the injectors seems to me a bit to nasty - but not inpossible.
Did I understand you right? you used a other ECU and faild further? or do you mean you would try a other ECU?
At the moment I would say, if any responsible sensor fails there shouldn't be fire nor a signal to the injectors. Maybe I'm wrong..... I think not 
Oh... do you check the second fuel-relay?
Gruess Roy
http://roy-fuchs.smugmug.com/
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Re: Restoration Project
[re: Roy F]
25/11/2015 05:54
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Hello, haha,
WOT is Wide Open Throttle. According to the sjmautotechnik instructions, full throttle triggers each injector test.
I was able to test the injectors successfully by unplugging the Idle Switch and jumping the correct pin to ground. The ECU is able to fire all eight injectors.
What I meant was, the previous owner replaced the ECU once already as an attempt to solve this issue.
Is there a good way to test whether the injectors are firing during cranking or not? Could this be a problem with the fuel pressure regulator? I know for a fact that fuel is getting through the rail and out the return pipe but I can't say how much pressure it is under.
What is this second fuel pump relay? It is not on the wiring diagrams I have been using.
Thanks for the reply!!!!
Na Ja, so ist es.
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Re: Restoration Project
[re: Roy F]
08/12/2015 13:30
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Problem solved. No electricity to the fuel injectors due to fuel pump not firing. Not sure why the ECU doesn't trigger the fuel pump so I rigged a toggle switch to do it. Runs good now but idles at 2000 rpm. Probably has to do with the idle switch and it needing to relearn how to run properly.
On to the brakes. The line between the T connection in the rear and the whatever unit is in line to the right rear wheel is rusted through and leaking. Replacing that and bleeding. Clutch works and transmission goes in gear and moves.
Na Ja, so ist es.
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Tim A.
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Reged: 05/08/2003
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Loc: Schleswig Holstein
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Re: Restoration Project
[re: Alex Gr.]
08/12/2015 14:26
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In Antwort auf:
On to the brakes. The line between the T connection in the rear and the whatever unit is in line to the right rear wheel is rusted through and leaking
The "whatever unit" is the break force limiter for the rear RH calliper
Beste Grüße
Tim
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Re: Restoration Project
[re: Alex Gr.]
20/01/2016 00:19
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All brake lines have been replaced and are working. I have a strange problem with the engine running though.
It only seems to run on 5 cylinders. When I first start it up, it runs on all eight but after a minute the driver bank of cylinders starts to die one by one. First cylinder 8 then 7 then 6 and occasionally 5 will also stop working. If I pull the plug wire for any of these while it is running, there is no change.
I have tested and found there to be spark on all cylinders. Using a dummy spark plug.
When I listen to the injectors with a stethoscope while the engine runs, all eight are working. It seems almost like the driver side fuel rail is not pressurized enough.
Any thoughts on this? Fuel Pressure Regulator? The original fuel pump was dead so it now has a Walbro GSS341 which should be able to make plenty of pressure.
Na Ja, so ist es.
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Re: Restoration Project
[re: Alex Gr.]
20/01/2016 07:46
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What have you done to make it run after a month?
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I replaced the fuel pump and installed a switch to activate the fuel pump relay without interrupting the ECU's control of the relay. This was for testing purposes but the system works how it is supposed to still.
Na Ja, so ist es.
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Daniel Müller
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Reged: 10/05/2005
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Loc: Nonnweiler Nordsaarland
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Re: Restoration Project
[re: Alex Gr.]
21/01/2016 15:50
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If the other Bank is working fine I would try to exchange parts between both banks. Starting with the Ignition system ( Distributor with arm, cables, Spark Plugs (even if there is a spark, it does not necessary mean that the spark is strong enough)), then the injectors. At some point the fault should travel to the other side.
My guess is the distributor arm or the distributor cap. I have seen the craziest faults happening with these parts. sometimes they just stop working properly when they are warm.
I would rule out the fuel system, because as far as I know there is no difference between the two banks. Same regulator and so on. And that the Ignition valves open up to short just on one side... I don´t think so. But, nothing is impossible.
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You're right about the ignition system. With distributors, there is never certainty. The one thing I would note is that the distributors do not provide spark to just the bank they are located on. Some of the wires cross over... With my issue that means one of the malfunctioning cylinders gets spark from the driver side distributor and the other two get it from the passenger side.
I would also agree that if the fuel system is working on one side, then it should work on the other side just the same.
Thanks for the input!
Na Ja, so ist es.
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Roy F
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I think you mean injection valves alias injectors, not ignition valves 
At the rest: fully agreement.
Gruess Roy
http://roy-fuchs.smugmug.com/
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Daniel Müller
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Re: Restoration Project
[re: Roy F]
22/01/2016 10:33
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Of course, I must have been sleeping
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Daniel Müller
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Re: Restoration Project
[re: Alex Gr.]
22/01/2016 11:15
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I was not aware anymore that the ignition cables cross over. This makes a fault in the ignition system a lot less likely.
Then I would really have a look at the fuel system. Are these the cylinders the farthest away from the entry of the fuel line?
I have heard from ( very powerfull) engines breaking because the cylinders on the end of the rail where leaning because they did not get enough fuel anymore.
Maybe also something is wrong inside the fuel system that prevents the fuel from flowing easy ( can be something as easy as a swollen rubber line). The pump itself should have more than enough pressure to run the engine in idle.
Thinking about this, these are all faults that would appear under full power more than under idle....
If you restart the engine instantly after the cylinders where gone, what happens then? And, what happens if you rev the car up?
Also check the electrical connection to the injector valves. Maybe you have some sort of verdigris or so that prevents the valves from opening the whole time. Also check the side towards the ECU. As soon as the engine gets warmer, the opening time gets shortened, and then they just do not let enough fuel pass for an ignition.
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If I try to rev the engine up, I have to modulate the throttle to let it climb in RPMs. If I give it full throttle, the engine will die completely. It revs much easier when cold. The injector valves are paired from left to right according to the wiring diagram and confirmed by electrical tests with the multimeter. I would assume then that the opening time is adequete since it seems to be enough for the other side to fire. I have cleaned the contacts on the valves.
The entry fuel line, pressure regulator, and return line are all located on the passenger side fue rail, the functioning side. There are two braided lines which then cross to the driver side rail. I haven't really been able to determine a clog anywhere on those lines.
Once I have an extra set of hands, I can do some more tests. Doesn't help that everything is covered in snow now.
Na Ja, so ist es.
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Bastian P.
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Re: Restoration Project
[re: Alex Gr.]
22/01/2016 18:07
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Camshaft timing is okay?
I would check the throttle valve and the respective sensor at the front below the idle valve, especially the
connector.
Das Buch zum Audi V8
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Cylinder 5 is is firing, so Cam timing on that bank must be correct. No reason to think it wouldn't be anyway.
The Idle Valve functions as supposed to when triggered during the output test. Could that sensor really cause this? I have confirmed continuity with a multimeter between those pins on the plug and the pins on the ECU. I do still get an occasional error code for that sensor although I haven't been able to read them recently.
Na Ja, so ist es.
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Bastian P.
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Re: Restoration Project
[re: Alex Gr.]
22/01/2016 19:59
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Below the idle valve, check the connector of the throttle valve sensor (Drosselklappenpotentiometer)
Das Buch zum Audi V8
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