I have an 85 Camaro 2.8L, manual trans. The car runs really when it is first started cold, but then once it warms up it is very sluggish and runs pretty bad, so i guess its not a mechanical problem... I have changed the following parts so far: throttle position, O2 and MAF sensors, Ignition Coil and module, cap, rotor, EGR Valve. All vacume lines have been fixed of leaks. I have cleared the computer of codes, and none have popped up recently. I have posted about this problem before, and someone suggested testing the coolant temperature sensor. I had a hard time getting leads to the sensor to test it with my multimeter, so I decided to just change it out anyway because it was a pretty cheap part. The car did run slightly better, but it still has the problem. Any ideas on what to check next?

Thanks
Joe

 

Typical, once at GM spec op temp, it just sucks the life out of these engines.

Keep the temps well below 200F and it will be a pleasure to drive all the time.

 

If you got a cheapo reman CTS, it may still be wrong (mine is, just don't feel like spending the money to do anything about it when I have a GM 3-wire ready to go in).

Also check the IAT... It's got the same job except for it works with the incoming air. And the fuel filter is how old? Spark plugs, plug wires?

 

I'm pretty sure the CTS isn't a reman...what range should the IAT sensor be in? Atleast I can get to that one with the meter and test it. Plugs and wires are relatively new, I have been meaning to change the fuel filter.

 

I'd like to say, make sure you're CTS is giving a correct voltage reading, because many of the parts that you get from chain parts stores, such as Autozone are mad in bulk for a number of cars, so the voltage they operate at is kind of a rolling estimate of all the years that the part fall under. For example when I did work at Autozone, I had a longtime customer come in and rant about a coil pack not working in his truck. Now, like many other parts stores, there's a no return policy on electrical parts, but the guy clearly showed us the the coil pack was running under a lower voltage than needed according to the Haynes manual he pulled out from aisle four.

 

With the engine cold (I mean COLD, as in not having been run yet for the day), both the IAT and CTS should have about the same resistance reading. It's not the volts that come out that matter, it's the resistance. There is a resistance chart floating around either here on the V6 board or in either the Electrical or Tech/General Engine boards. The same chart applies to both sensors.

 

Whoops, definitely meant resistance.

 

I know its a older thread but some of the details are similar to the issue I"m having. My 2.8 runs worse after warm up. She runs like a a champ until then. Mild acceleration she is ok but when you need to get going she really. She bogs and even a occasional backfire through the intake.

I'm unsure if my IAT is bad or if I am reading it wrong. To measure the resistance I have the dvm set on 20k and get a reading of 2.93 without side temp at 78". At 200k it reads 2.9.

I will be checking the CTS when I change the thermostat to a lower temp. possible 180".

 

And how old are your plug wires, and how are the wires at the coil and ignition module in terms of corrosion and whether they are solidly connected or not? Ignition problems can be nonexistant cold and crop up when hot because plug wire and other wire resistance changes with temperature. I had a module that tested fine cold and failed the tests when run through a few times to get hot.

 

Never tested while hot. I can do this weekend. In the last two weeks I replaced with AC Delco parts..plugs/wires/cap/rotor/coil. I also replaced all the O rings on the fuel rail, new injectors. I was debating on the FPR.. pressure while running reads around 60?? A key on prime reads 38 to 40 steady. I am getting closer to the goal of having a sound running engine, I just the trip woul end sooner rather than later. I have alot more work to do on the inside that I could justify spending more $$. At least she can see the progress then and not just hear me talk about it.

 

I'd double check your running fuel pressure first before you go anywhere else. Seems funny that the system primes at 40 or so max and then hits 60 running. When my fuel return side of the replacement fuel rail was clogged, the system hit around 56 PSI on the prime and stayed high. Worse comes to worse, get a security torx bit and remove the FPR before putting a blow gun in the brass fitting in the middle of the FPR chamber and blow the crap all the way to the fuel tank (if there is any).