Trying to figure out 1991 K1500 5.7 issue

[Chopper16]

Over a 2 year period of time the truck would miss on hills occasionally, sometimes on the same hill sometimes not, until it became common place. Switched cap, rotor, wires,plugs and the problem stopped for about 2 months.

Then it started coming back, so I changed part after part, fuel filter, o2 sensor , map sensor, knock sensor,coolant sensor, coolant sending unit, cap, rotor, plugs , wires, distributor, coil, the fuel meter in the throttle body, I think thats what it was called? I think a few more sensors as well? Fuel pump too!

And nothing , so I took it out to a hill that it can barely climb and loosend the distributor and turned it a little at a time until it could climb the hill with no issue's, I think I was retarding it. But then it slowly came back to the hill issue.

Now for it to be able to drive down the road without missing I have the distributor turned so it runs a little rough at the start but once warmed up it runs pretty good even on some hills. But again it will miss some days on a hill but not the next day on the same hill. At factory timing setting it starts fine but hills cause same issue.

I did get injectors for it and put them in and it could barely run, so I put the old ones back in with the new o-rings and it seemed a little better, but who knows, it is so hit and miss? That was over a year ago, the issue has worsened since , after changing a lot of the parts mentioned. Sometimes you can smell a little gas at starting but I figured it was from the timing being off in order to run down the road decent? Never an engine light, had a mechanic at work run it on a computer and everything was normal. Thinking timing chain, cams shot?

[diyer2]

I had a 93 silverado.

I would not change the timing, set to oem spec and check EGR valve. Mine had poor power and a bog at low end, new EGR valve fixed it. Guess $50.00.

[Chopper16]

Forgot, EGR was changed ,twice. I changed so many things that its hard to remember off hand. It did have an EGR problem about 10 years ago, kind of puttering around in parking lots, but normal speed was fine. The EGR change did fix it then but I have changed it twice in the past two years, just to make sure I didnt get a bad part and no difference.

Thanks for the idea though!

[diyer2]

If set to OEM specs and it starts good, idles smooth and runs without missing except under conditions you mention I don't think it's cam, timing chain or lifters. This would affect all running aspects IMO.

I don't know the name of the part but it's under the distributor cap, sets on the distributor plate for plug firing I think.

Have you checked all grounding points? I tend to believe it's not mechanical.

[desrtrat]

well it's a 1991 could be just worn out. maybe be time for a upgrade..

 

good luck

[Chopper16]

I have not checked all of the grounding points. I am planning to reset the timing and go from there. Before I changed it the truck would start and idle nice but even driving down the road it would do the missing, kind of bucking thing. By turning the distributor it idles a little rough at start up and will still miss on hills but normal driving is fine and it idles decent after heated up but not perfect.

The plate at the bottom of the distributor was mentioned by my neighbor, that is something I will look into now as well. I am not convinced its mechanical either, but just running out of idea's

It just throws me for a loop that when I changed the cap, rotor, wires and plugs it had no issue's for about two months? Maybe that plate? Also why did the new injectors make it run so bad it wasnt even able to be driven? Bad parts, I dont know?

As for upgrading, well it has 368,000 plus on it, I was working a high paying job so I put in a crate engine and transmission about 190,000 miles ago, Just because I wanted to upgrade it, it still ran fine. If I could find a like new 1991 K1500, I would buy it in a an instant. I am not fond of trucks too much past that point. Rust has taken my trucks from me not really mechanical issue's, otherwise I would still have them.