This is the first winter since I bought my '94 Z28. When it gets cold out and I go to start the engine, it will fire and then die immediately. It will then fire right up and run fine. Sometimes it will stay running the first time, but idle really rough and stall when I try to drive. Also, sometimes if I hold the throttle open a little while I start it, it will stay running on the first try. I checked the fuel pressure and it was 42 psi static (and did not bleed down for 5 min.) and about 35 psi while running. When I rev the engine it goes up to about 44 psi. What should it be? Static seems correct to me but the running pressure should be a little higher I would think. Plugs and O2s look good and no check engine lights. This only happens when the air outside is cold (below 40°) and the car is cold (sitting for more than a couple hours). If I have been driving and stop at the store or something it fired right up on the first try. I am going to try and get a datalog of the cold start tomorrow morning, but anyone have ideas for now?

 

Have the same problem. I think it's just something with the LT1's. Someone else on here mentioned that they like to run hot. A co-worker suggested to prime the key three times before starting just to get fuel pump to pump to the engine first. Never bothered to try this, though.

 

sounds like your runnign rich or have weak spark. test for a weak spark. test the temp sensors, intake air temp and engine temp sensors. what plugs are you using? have the injectors ever been cleaned and tested?

 

Priming the pump multiple time does not seem to help any. My car does not run hot at all. The previous owner put a 160 t-stat in and with the cold air the car barley sees 170 degrees.

Plugs were put in by previous owner, but they look very good. I have no check engine light and I just cleaned all the sensors over the summer. The injectors Ohm out good, and I have run injector cleaner through them twice in the 5 months I have owned it. Could a bad temp sensor cause this issue and not throw a code?? Could the fact that my car never seems to reach a good operating temp factor in as well?? I tried data logging this morning but the laptop battery dies on my drive and didnt save the file. If it is cool enough outside here tomorrow I will try again in the morning.

 

You should try testing and or replacing the ECT sensor and the IAT sensor. The PCM first looks at these two sensors before starting the engine and adjusts the fuel mixture for the coolant and intake air temperature. If these sensors are sending the wrong info, the computer won't be able to adjust the mixture for the ambient temp and the engine will run poorly. The PCM is not smart enough to detect if the data received is correct, so it won't light the MIL (garbage in= garbage out). Your fuel pressure is good, and what you are experiencing is not because the engine is an LT1. You may also consider taking a good look at the IAC valve, as it controls idle speed.

 

Thanks! Thats the information I was hoping to get from my datalog, if it had saved. Since the coolant sensors are not that expensive I may go ahead and just replace them, and clean the IAC valve.

 

Ok, it wasnt cold enough to do it yesterday, but it stalled when I went to go to work this morning and of course I didnt have my laptop. I went ahead and bought the IAT and ECT sensors and will clean the IAC valve and see if that fixes it. Since my MPG has been declining in the cold weather I am almost positive its those sensors, I just wasnt sure since there was no code.

 

UPDATE:

So far I have replaced the IAT and ECT sensors, and I took the throttle body off and cleaned that as well as the IAC valve. The TB and IAC were pretty dirty, but even after cleaning the car does the same thing.... Im stumped.

 

I can't think of anything that hasn't all ready been mentioned.

I will say this though, we finally got snow the other day, not much but it was near 20 degrees out. The Camaro had been sitting for 12+ hours that night. Got in, turned the key and fired up no problems. No pumping the throttle, no stalling, nothing. Next day it was a bit warmer, and had the usual troubles.

 

I cant really think of anything else. Mine happens all the time.