Hello
Note this is long with lots of details but I believe it is important to understand what is going on.
I posted a couple of months ago about my 1984 Gti Rabbit. I originally thought that I had fuel pressure problems.
The car would start immediately and then die 2-3 seconds later, I could restart it and then again it would die 2-3 seconds later. If I started it with my foot on the gas pedal it would start and run at about 2000 rpm however I would need to keep the rpm up for several minutes and then it would be ok. I ruled out losing fuel pressure because of this situation where it would take minutes of holding my foot down a bit and keeping the rpm up at about 2000 rpm. If it was losing fuel pressure like when you change a fuel filter, the idle stumbles for a few seconds or so upon restarting but after about 10 seconds or so the system pressure is built back up.
In my case it takes a couple of minutes of holding the gas pedal down at
2000 rpm before I can release it and then the car can idle by itself. I also noticed that at this time after about two minutes when the car can finally idle by itself the rpm is about 850-900 rpm. After driving it for 30 minutes on the freeway the idle is about 1200 rpm. This may be an indication of the problem, the idle increases as the car comes up to temp.I checked for vacuum leaks, changed the idle air bypass screw oring, fuel filter, injector orings and injector holder inserts. I also had a spare warmup regulator sitting around and I swapped that too. None of this made a difference.
One it is warmed up it starts and runs fine. I only have this problem after it sits for a while.
I've been driving with these conditions daily for a few months now, freeway driving to and from work about 20 miles each way. A couple of months ago when all this started to happen one day I started it up and the car had all kinds of power like never before also all kinds of throttle response, it was undeliverable, this lasted for about a week and then it went back to normal running conditions, and then my problems started shortly after. Was this a sign a something failing? The frequency valve control unit?
Recently I started to think that, the car starts immediately and then dies, so it must have fuel and then it runs out. I was thinking maybe the frequency valve was not working upon a cold start up. So today after work I dove into it and checked out the O2 sensor and the frequency valve. (Note I do hear the frequency valve buzzing, however I need to check it in the morning cold when the problem exists and listen to see if the valve buzzes for the few seconds that it does run.)
So this is what I measured tonight when I got home, car was up to temp, etc.
I hooked up the dwell meter to the test plug near the cold start valve to measure the dwell of the frequency valve. Upon starting the car the dwell went to 45 degrees steady and the car was hot. This is like open loop conditions however the car was up to temp. After about 1-2 minutes the dwell then went to 50 degrees and heald steady for 3 seconds then it went back to 45 degrees and held steady for 2 seconds then it went to 50 and swung between 50 and 54 degrees. I turned the car off and restarted it and it did the same thing, went through this weird cycle where it looks like it goes open loop and then up to 50 (solid) back to 45(solid) then swings between 50-54 and pretty mush stays here swinging between 50-54. I was surprised I thought that it would be either open loop or not, is there some sequence it goes through even if the car is up to temp? The fan was coming on.
So I took a voltmeter and measured the ox sensor voltage with it still connected, and I measured .4-.6 Volts as the dwell swung between 50-54 degrees. I then disconnected the ox sensor and grounded the green wire (the one that goes to the control unit), the dwell slowly increased (within about
5 sec) went up to 74 degrees, stayed there for a few seconds then slowly went down to 36 degrees, the ox sensor read .8 V. I read that, upon grounding the wire to the control unit that this would simulate a lean condition .8V - 1V and that the dwell should go to 75 degrees or higher. My dwell increased but then cycled back down? Is this normal?I read on a Volvo web site a CIS discussion that upon grounding the wire the system would compensate for the lean / rich condition. As it compensates the lean rich condition will eventually swing the other way and the entire procedure will start all over again? Is this true, that if you disconnect the green wire from the ox sensor and ground it that the dwell will swing up and then back down? I've read previous posts on this group stating that it would swing up to 75 degrees and stay there. Why would the dwell go up and then come back down with the wire ground. I would think that it would go to one extreme and stay there.
Lastly, if you are still with me, another odd thing I noticed. This is the last test / experiment I did. The car was up to temp; I disconnected the ox sensor temp switch. This switch opens above 77F and shorts below 68F. So I ohmed out the switch and it was open as expected therefore leaving the connector off the switch made no difference. The car was idling and the dwell was between 50-56 degrees. Just for the hell of it I took a small piece of wire and I shorted out the connector. This would simulate a below
68F water temp and put the system into open loop? Well the wire shorted across the connector the dwell went up to 60 degrees and stayed there. What give? Shouldn't it have gone open loop to 45 degrees?Do I have a bad control unit?
I repeated all of the above tests 3 times and got the same results.
Thanks for you time.
Ideas?