The Project Pad

So, The engine is in the URQ. After I got it wired up a couple weeks ago we started it 10+ times and had it running for more than 10-15 minutes a couple times to get it up to temp and now it refuses to start.

After some time with a power probe it seems like my ignition/injector trigger(the wire from pin 3 on the ECU) is STUCK to ground. With the battery connected and the key off the pin is to ground. This wire should only ground when the ecu sees the criteria for ignition(cam/crank position sensors) correct?

Is this the cam sensor short to ground fault?


Ive been trying to pull codes but I havnt gotten it setup yet. It seems like the check engine light isnt getting power because it doesnt come on when the key is turned to the on position.


Any help would be appreciated because Ive been pulling my hair out.

And Ive tried 2 different ecu's(ive had both in the S6 and they are fine). Also made sure I didnt have a short to ground in the harness for pin 3.

Mentosman42 wrote:And Ive tried 2 different ecu's(ive had both in the S6 and they are fine). Also made sure I didnt have a short to ground in the harness for pin 3.

try to communicate with it via vagcom with ONLY power and ground supplied to it (on the bench, or with all plugs disconnected), but since this is a swap I'd do it on the bench). just to validate you haven't been frying ecus.

I cannot imagine that the ECU is fried because I have swapped the ecu between the S6 and the quattro and there is no problem(did this when the car wouldnt start originally). The S6 is currently running with the ECU I originally put in the Quattro and the Quattro has the s6's ECU currently.


A couple days ago I went out in the morning and tried to start the Quattro and it started 3-4 times in a row and then would not start(i only ran it for 10 seconds each time it started). This was all within a couple minutes.

I guess tomorrow Ill swap the ecu's again just to make sure. This is all really wearing on me. Its like every night gnomes go and screw everything up. We had the engine starting for a week straight no problems and then it suddenly wouldnt start, we poked around it started, then a couple days later it wouldnt start again.

And just for clarification, I am using the wire from pin 3(ecu ground trigger) to ground the original fuel pump relay coil in the car and my new relay coil for the ignition/injectors.

Ok, so yesterday I swapped the ECU over to the s6 and it runs fine. I also found the wire for pin 3 in the s6 harness and it also goes to ground like the urq is so that isnt the problem.


Going to run to radioshack and pick up some parts to build the CPS test light. Gone through my wiring 10x and it is all fine. If I dont find a problem with the CPS I dont know where to go from there.

This is a shot in the dark - but I had similar symptoms with a crank angle sensor on my 3b. It worked for a little bit but then stopped working completely and wouldn't start. I replaced it and it has been good ever since.

Been digging deeper.


Seems that I do not have 5v power to my cam sensor/TPS/alt sensor. I continuity tested pin 12(power for them) on the ecu plug with my power wire to the CPS/TPS/altitude sensor and the wiring seems fine(no resistance and had continuity).


One strange thing that I did find is that one of my grounds at the intake manifold(I believe it is ground 15) has 12v in it with the ECU unhooked. So that is where I am starting although I dont know that will have anything to do with not having 5v at my CPS because the CPS ground doesnt have voltage in it(it is ground 16).

Anyone know why pin 12 wouldnt output 5v? I know this isnt an ECU problem because like I said I have swapped this ecu into a running car and it worked fine.

Ok, as far as the ground, unhooked the o2 sensor and the voltage went away. Can the heater element like short out and pass the power straight to the ground?

Update:

CPS problem fixed. My stupid error. Had a wire labelled wrong so it was going to the wrong location.


That being said I dont know how this engine ever started and ran. The wire that I had labelled wrong was the 115 fuse aka keyed power to ECU and ignition and I had this on my new relay(on 87) that is powering my fuel injectors, evap, n75, ect. The ecu and ignition was getting its keyed power supplied essentially through the fuel injectors(power was pulsing with them). Also because of this I was not getting the 5v supply at the cam position sensor constantly. It was also being powered with the fuel injectors. Wired like this the car started 15+ times and idled fine and had been reved to 2000-2500 rpm.


Tomorrow I will have everything back together to try and fire it again.

RIght on!!!! Let the Port Rose live!!!!