86 S3 just started not starting a few weeks ago. Went through Dougs checlist and all good. Checking noid today and fuel pressure but think they are OK. Will also try some starter fluid in AFM and see if she runs a bit

But was reading old pist where guy had similar situation and stumped everyone. Turns out he got water in fuel!

I have to run with drive side gas cap not clised due to cligged vent and there was a massive rainstorm recently

But even if I switch to other tank, which in theory should be water free if that is indeed the issue.. it does not start

I cannot recall if I tried started on possibly corrupted tank but wondering what to do? I was thinking of switching to non corrupted tank, disconnect fuel line at rail and flush a couple gallons. Maybe the rail and line had corrupted gas??

I know water sinks to bottom of gas so I expect if I was trying to start on corrupted tank it probably pulled some mix fuel

Thanks!!

 

I think the flush idea holds promise. Pump the output into a clean container. If there's water, it'll be evident

Cheers
DD

 

Hello Doug and all

Well update! She sputters and runs for a couple moments on starting fluis so as I diagnosed spark is there

My noid lights arrived and wouldn't you know, they did not light... Tried several and nothing. Checked 12v at resistor pack and good as before.

So did this as picture shows. Put probe into 12v side of injector connector and hooked to noid light. Then ran other noid pin to ground and sure enough she lit!!

So unless bug spray and beer has clouded my brain, seems to me the injector is NOT getting ground signal from ECU

Anyone agree with my debug?

I have an unknown spare ECU so will pop it un and see

Thanks!!

Randy

 

 

 

Now I am stumped!

Swapped out for another ECU and same issue. Noid lights not lighting on crank

I might pull an injector to see if there is any spray but at this point appears 12v to injector is good but no ground signal from ECU

Very bummed since that is kind of worst case situation

 

Cranked motor for couple 15s bursts... Pulled plu and bone dry. No fuel being sprayed by injectors I believe.

Double checked noid.. no light but if I ground noid pin directly and crank she lights up so 12v from resistor pack seems good

Is there ANYTHING else that would prevent the ECU from grounding brsides a bad ECU???

I will check fuel pressure since I bought bloody tool but dont feel fuel supply is issue

 

The ECU has four connections to ground which are pins 5, 16, 17 and 35.

All of these run all the way back to the engine and appear as black wires in that cluster of earths on the back stud of the inlet manifold. They go through those white multi-pin connectors for the injector harness to get there.

I would suggest checking you have good earth there and good contacts in the pins of the multi connector. Then use a multi meter to check for continuity of the four earth wires from car ground to the four pins on the connector to the ECU. Chances are you have either got a bad contact or fractured wire somewhere among them.

 

At the rear of the water rail is a bundle of ground wires, a half dozen or so. These are the grounds for the FI system. Make sure none are loose or broken, check for corrosion, etc

Cheers
DD

 

Thanks for tips. Will dig into the wiring. I cleaned all ground connections last year when I revived car and all has been good since then... But I suppose anything can happen at any time☹️

I should know that by now!

 

After lots of reading and pondering, it seems possible that if NONE of the injectors are getting ground from ECU then maybe the coil trigger pulse is not firing to the ECU

So what is best way to verify trigger pulse is firing. If I crank and have voltmeter on neg coil what should I see?

???

Thanks. Randy

 

1. as you have spark, the trigger is working/ but, one way to verify, is to crank and watch the tach. it is ulse sensitive. If the needle bouces, thee is a pulse. if it lies still, there is none

1. down and under. At the transmision engne connection on the right side is a braided ground strap. It is in ahostile enmvironment insofar as connectivity os concerned. Clean and/or rrplace/

3/

 

Randy, there is a bullet connector from the coil to the multi connector (white wire with black stripe) at the rear of the motor. If you disconnect this connector and then make and brake the connection with the ignition on you should hear the injectors clicking every three connections. This should be confirmation that the injectors are firing. Did you confirm that there was no water in the tanks?
Con

 

Last post got chopped off.. let me try to add what got removed...

Con -
My - coil WB pulse wire has no bullet connector, but I did remove from the - coil post and tapped a dozen times to - coil post. Still no noise from the injectors with ignition on.

So this leads me to my next observation. With ignition on, the + coil post was 12v, but the - coil post was only 1.7 volts. I am not sure what that voltage reading SHOULD be for the "tap" suggestion you mentioned above. And if I crank the engine, the - coil post voltage reading on my
DVM just says "L".... I cannot remember what that means on the DVM but it is a good Fluke 77 unit.

I made a detailed drawing of the wiring and plan to methodically verify voltages and continuity. I am pretty sure I have an issue with no injector
pulse to ECU pin 1 or... not ground signals from ECU to 6 injectors. As such, I am not concentrating on the possibility of water in gas.

Thanks