I just inherited a 90 gmc 1500 from my uncle with 220,000 on the v6. The truck has been taken care of and is in really good condition except for two things. Any help would be awesome. Upon startup the truck runs great. Then eventually(usually cruising on the freeway or if the a/c is on) something seems to trip and the check engine light comes on. It usually happens at low RPM and under more load on engine(uphill or a/c). From that point on the engine feels like it's constantly missing every few seconds. Turn off the motor and it's fine again for a bit. My uncle said it's been happening for a little while and the mechanic he took it to said he couldnt pull any useful data from the computer. All the easy maintenance things have just been replaced(oil/filter, fuel filter, plugs/wires, cap, rotor, thermostat[it was sticky]) and altough the problem is not AS bad, it is still definitely there. It just takes a little longer to happen each time.

My other question is small and not as important to me but kinda interesting. With the stereo off(everything is stock), no noise comes out of the speakers obviously. But with it on the speakers whine pretty loudly in corollation with the speed of the engine. The weird thing is that the whine volume has nothing to do with the volume on screen. even if the music is faded all the way to the front right, the back left speaker will whine. Dont get it.

THANKS FOR ANY HELP!!!!

I have a 90 GMC 1500 but with the 5.7L.

Figure out what code is being set when the check engine light comes on. See http://www.troublecodes.net/GM/ on how to read the code(s).

As for the stereo question. Mine did the same thing until one day I got nothing but static out of the speakers. Eventually, your stereo will go out. I got a CD player from Crutchfield.com that included everything you need to install the new stereo.

//2000CAYukon

Have you tried running a good fuel injector cleaner through it? Apparently these engines have an issue with the injectors gumming up and causing problems. I was having issues with a MIL light and rough idling. I had the codes read and one of the cylinders was missing. I ran a bottle of injector cleaner through it and it straightened up. I now try to make an effort to run a bottle through every now and then and haven't had any more issues.

Another thought, have you had the fuel pressure checked? Your fuel pump could be going bad and it might not kick a code. That happened to my brother's truck.

Thanks a bunch. I will check those things out. That website looks like a good resource.

Just as a note, the method of getting the trouble codes mentioned on the website listed above will only work for pre-OBDII vehicles.

That whining noise is the ground... check your wires make sure they are taped up and not touching the metal of your car