The 1947 - Present Chevrolet & GMC Truck Message Board Network - Most base model truck you've seen? 1989 Cheyenne K2500 4x4

So I thought I’d give a little update on the actual work that’s been going on with the truck. I originally bought it with a poorly running engine, and it was fairly obvious that someone had shotgunned parts at it. Supposedly, the fuel pump has already been replaced but I’ve seen no signs that has been done. The TPS, IAC, CTS, thermostat, water pump, alternator, and tensioner were all new. The heads have been off the engine at some point, as the head bolts are Vortec style. It ran very rough at all times, didn’t seem to be firing on all cylinders, and had a lean pop at highway speeds. I decided to at least hit all the basic failure points in order to start from square one and see where I was really sitting at with the engine.

Number one - throttle body rebuild! Right away I already knew what I was in for, as the line fittings did not have Teflon seals and instead had PTFE tape sealing them.

https://i.postimg.cc/zBpggCgv/9-F3-E...94-E8-AE85.jpg

Aaaaand here we go. Aftermarket regulator at some unknown adjustment. Injector body spacer torqued so tight that it broke the body. Injector o-rings all improperly installed. I had to source a new injector body in order to replace the broken one and obtain stock regulator parts.

https://i.postimg.cc/k4MVq2pm/13-A38...C098-A8-F4.jpg

All rebuilt, correctly this time!

https://i.postimg.cc/90rrwv2g/9135-A...-F77-FC6-F.jpg

I also came across this premium repair, which was actually shorting out on the throttle body.

https://i.postimg.cc/66m7x5Vk/5-E0-B...-A1-AD38-F.jpg

And a few other parts - air filter, fuel filter, oil change kit, distributor, rotor, plugs, wires, and coil. I didn’t do the distributor and coil right away since I needed to drive it ASAP for two weeks for work. The engine picked up quite a bit, but still had a pretty significant miss. At this point, I was suspect of at least a partial ignition failure as it would occasionally instantly cut out and come back, like hitting a kill switch.

https://i.postimg.cc/hPQXDWpf/F8-CE3...21-E1-B261.jpg

I didn’t get a chance at a picture, but during this time, the battery light came on during one drive home. A quick test with a Fluke had revealed that a diode failed internally and was introducing AC voltage into the system. The crappy reman alternator was traded in for a NEW one which solved that problem. It ran a little better again, but the ignition issue still persisted. So, this weekend I swapped out the coil and distributor.

https://i.postimg.cc/jSVLCgFv/791827...9-FE3-C710.jpg

https://i.postimg.cc/Vkj5t9yw/E5-BD4...DBE33-DFFE.jpg

The old distributor definitely had some pickup coil issues, with significant wear. A No-name ignition module was installed. It also didn’t help that the rotor was improperly seated and almost wore a hole in the cap. So, great call on a new distributor assembly!

https://i.postimg.cc/Dzn0PWFX/CDFEC9...FBA3-DE773.jpg

Fast forward to yesterday, the truck sounds and idles tons better. There is still some shake and major stumbling right off idle, until about half throttle. Past that, it runs excellent. I’m suspecting a cylinder with low compression or two cylinders sharing a blown head gasket. This is backed up by the fact that #4 and #6 spark plugs had a lot of build up on the spark plugs when they were removed, and that the MAP sensor defies the laws of physics and actually gains vacuum upon acceleration. Next chance I get, I will be removing all the new spark plugs to gauge if that pattern follows on the new ones, and also performing a compression test.