I am finally back from 3 weeks in Taiwan and the best way I have found to fight off jet lag is to work on my car. My last post was "Poor Performance" and I got a lot of good T/S suggestions. To recap the issues I am having - Very hard to start when cold, long crank time, then runs rough and backfires until fully warmed up. It has also start to drop out at speed. With RPM's at 1600 and the throttle held steady the engine will cut out and then come back on when the rpm's drop below ~900.

I have a couple of questions which I have highlighted in bold type that would help me greatly in fixing the problems with this car, I feel like I am on the right track although it is a bit overwhelming at times.

Based on suggestions I acquired a full Chev. Service Manual, the Data Master software and ALDL cable.

I have tested the fuel pressure at idle it is 42PSI, however when running it drops to around 30-32psi. I talked to John at FIC and he said this is to low for the injectors and gave me some tests to do to the fuel system, I will do those today.

I tested the intake manifold pressure and it is in the range of 18-15psi during idle, the needle never stays steady like the fuel pressure, it bounces around rapidly in that range. Is that normal behavior or could it indicate a leak?

I have run datamaster once and got some interesting results I will upload the file later today. I do have a code 33 MAF lean code. I would like to clear the codes before I do another log and was hoping there was a way to do that without disconnecting the battery. Unfortunately my Prom does not allow Datamaster to clear the codes. Is there a way to clear the DTC codes without having to drop power?

Thanks in advance and I will get a datamaster run up here later today and report back on findings. Hopefully this will also help others who I see with similar issues with their C4's.

Thom

 

Do you know if it has the original injectors? Ethanol destroyed mine and the symptoms sound similar. They weren't made for today's gas.

 

Yes they are new I replaced the injectors with FIC's a little over a year ago along with a new fuel pump, filters, and rebuilt the pressure regulator

 

Your Vacuum reading should be steady..

 

Near the batt + lead is a smaller red cable with a connector. Open that connector for >30sec to clear codes w/o clearing radio/clock settings.

Have you checked leak-down rate on your fuel system. Turn the key On and the FP runs for 2sec. Fuel pressure should jump to normal setting and hold pretty steady for more than a few minutes. If it rapidly drops off there is a fuel leak in: injectors, FPR, FP or hoses.

 

I double checked the vacuum pressure and it is definatley oscilating. I will look for the lead near the battery tomorrow and see if I can clear the codes without losing all the setups.

I ran another Datamaster log today from a cold start and the idle jumped from 850 to 1300 as soon as the engine went closed loop.
I wanted to upload the 2 scan files in case someone was willing to take a look at them and tell me if they see anything unusual. But for some reason it says I can not upload files. Do I need to require additonal permissions to upload?

Does anyone know if there is anywhere I can send these files to in order to get a professional to give me an opinion? I am decent mechanic but when it comes to this level of T/S I am definately lacking experience. I just think someone who knows what to look for could cut my T/S time down and give me some more definate leads.
Thanks again
Thom

 

This is the connector you open to clear trouble codes. You only need to open it for a second or two:



Where are you measuring the vacuum? The best place in my opinion is the rear vacuum port on the plenum on the passenger side.

Error code 33 doesn't necessarily mean the MAF sensor is bad. If you lose the connection (broken wire, corroded connector pin, etc.) from the MAF to the ECM you will also get an error code 33.

 

I was measuring off of the master cylinder hose, I'll move over to the Plenum port and see what I get. Thanks for the diagram that is very helpful. Today I am going to check voltages and connections on he plenum, throttle body, etc. I looked them all up in the service manual an now need to go through them 1 at a time. While I am at it I am going to double check all of the fuses to see if any of them are flaky. Process of elimination is the only way I am going to solve this
Thom