I had borrowed the IP off my 1991 and put it on my 1990 to determine if the other trucks IP was bad. I was going to leave it on my 1990 but it has bigger issues and will probably be pulling a head, as I had compression coming out of #7 injector back into the IP. I found it when I was bleeding injector lines, every compression stroke you could hear it pusing out the injector.

I reinstalled the good IP back into the 1991, I never should've touched it to begin with as it was running just fine before I removed it. Since reinstalling it, I have plagued with a rough idle, and sounds kinda power stroke or clacky. It really starts to ckack at highway speeds.

The IP was new a year ago and may have 50K on it

Here is what I have done to try to fix it;

installed 8 new injectors with Viton orings,

replaced the return lines,

rough adjusted the timing to about 1 deg Past TDC (yes towards the passenger side).

Even tried advancing the timing, to try to cure it.

checked the IP timing gear to make sure I am not off, and I am not!!!

I have gone over every inch of the hard fuel lines and the return lines looking for an air leak.

Listened to every injector with a mechanics stethoscope, thinking I may have a bad injector. I know even a new injector can be bad, if there is a bad one I seriously do not know what I am listening to.

With all that throw the ideas at me, what have I missed?

 

It sounds like your cold advance might be stuck on.

 

I don't think it is the cold advance; when I cold start the truck, it will idle up for a few minutes and then kick back down to normal. I am just trying to Trouble Shoot the rough idle.