Hi, the service engine soon light comes on now and again. The car has had an oil change and oil filter. Is this just a Corvette thing?. My car is a 1988 C4 . John.

 

No, not just a Corvette thing, could mean a lot of things, but generally emissions related such as leaking vacuum lines, bad 02 sensors, etc.

Pull the codes http://www.corvettebuyers.com/c4vettes/codes.htm

 

Thank you for those codes.Further to the issues I have been having. Today my new pressure gauge arrived. On tick over, 680 to 720 rpm, the gauge held at a steady 40 psi. With the pressure regulator vac taken, it rose to 50 psi. With engine switched off, the gauge rose to 46 psi and dropped to just over 45 psi after 10 minutes. I found 1 plug lead off prior to carrying out the test. I then took the car out and the miss firing started again. I was able to clear it after feathering the accelerator pedal. This happened several times.The car is fitted with Summit Racing electronic ignition. Numerous other engine mods have been carried out by the previous owner with paperwork and receipts for various parts and work carried out. This might account for what seems to be higher than stated fuel pressure for a 1988 Corvette. The car is thought to be running around 400 bhp according to the paperwork I have with the car. It certainly shifts when running as it should. The fuel pressure regulator looks similar to a standard item but appears to have an adjusting screw with lock nut on the top. This has not been touched by me. The vacuum pipe was dry when removed and had good suction. I would be grateful for any thoughts any of you might have. Car show season is up and running in the UK and I need to be able to get it there and back. I just can't trust the car at the moment. Kind regards John.

 

The plug that had the wire off is probably fouled so it will not fire when adding alot of fuel, and will fire when easy on throttle,try new plugs.

 

Thanks for that. I have checked that plug and it is ok. The misfiring I refer to is not one cylinder, it is probably all 8. I am thinking it is possibly a sensor problem as fuelling proven ok. I am advised that the coolant temperature switch is a likely culprit . I will replace that. The next port of call if required will be the co2 sensor. If that does not work, I will check the EGR valve which I am thinking of deleting any way. The car starts and runs perfectly on my drive and only plays up when I take it on the road and it starts to warm up. This is when one of the two sensors could influence what is being sent to the fuel injectors. I had a similar problem with my Sierra Cosworth which wouldn't run properly and that was a temperature sensor that had failed. I will have some new parts in a couple of weeks . I will post how that goes when fitted. Kind regards John.

 

Has distributor been removed to prime oil pump, or for any other reason? Do you have access to another known good distributor? I t could be the problem,just looking at all ignition parts that could be causing your misfire problem.

 

Ignition not touched . Electronic Summit Racing kit fitted. All leads and 4 plugs checked and in very good visible order. As I said, car starts great and revs cleanly through range on my drive without a hint of a misfire or problem. I have been in touch with the owner of UK based Eurovettes and it is he who has experienced problems with customer cars in the past which have been traced back to bad sensors. I live a fair way from him so taking the car to him for a proper look is not an option.He is in the US until the end of the month and will send me parts I have ordered upon his return. I will post updates on this forum regarding progress as parts are fitted. Thank you all for your constructive help and thoughts.