popping sounds

[damonleehill]

I have a '95 gt v8 that has a problem no one can find .When the engine is running,and driving. as long as a constant speed is kept it has a popping sound ,as in missing.It happens at any speed and when you press on the gas it does'nt hesitate at all and runs fine without the popping sound untill its held at one speed.
Checked all the simple things,plugs,wires ,fuel pump pressure.replaced distributor,sensors.
HELP
Thanks
Damon

 

[AznStanger3v]

exhaust leaks have done this to me before. and i know someone will chime in with "but they tick", i know this. they also produce other sounds as well.

 

[1TallMF]

Try running a cylinder balance test with a code reader, its the step after the KOER test. This can help you narrow it down to one or two problem cylinders, if that is the case. That "popping" sound could be runing rich, possibly caused by an injector stuck open or something. this test should give you an indication if that could be the case. If this test checks out, I'd say check your TPS voltage at closed and wide-open throttle, should be roughly 0.85-0.99V at closed and I think ~4.25V at WOT. If you're seeing more than 1.0V at closed throttle, that also could be your problem.
If that checks out, check the MAF voltage, but since you can't really reproduce engine loading while under the hood, this will only give you an idea if the voltage is way out of whack, and clean it reagardless. As mentioned above, also check your fuel pressure with vacuum on and off. Lastly, if nothing else helps, it might not be a bad idea to check the engine vacuum if you have a gauge to do so. Should be no lower than 15"Hg at idle for a stock motor.
Good luck