Smokey, Rattly SOB

Hey guys, Newb here. To the forum and diesels, although I have driven this 92 G30, 6.2, 4l80E for ten years all I did to it was oil changes and brakes.
Couple years ago I had to put an Injection pump. Got a used one from my local wrecker. Fairly straightforward job ( I am an automotive tech in real life, tons of experience) Eyeballed the pump timing per my junker's advice. It ran good so I left it alone and drove it. It had always been tough on cold starts, I recently learned right here that that was probably caused by the temp sensor in the passenger head that had been bypassed.

Going to try to cut to the chase here, just want you guys to know the vehicle. Couple of weeks ago it developed an even rattlier rattle on the freeway. that was easily found to be a loose flexplate. Managed to tighten it without dropping the trans. Next day there was an emergency lunch date 20 miles from work, so I was running to beat the clock, 85 mph speedo pegged. by the time I got back to work it was rattling just as bad as before, and smoking. a lot. I ignored the smoke and ordered up a new flexplate that I installed the next day. The old one wasn't broken but the bolt holes at the crankshaft were hogged out. Changed the oil while it was in the air. Rotella.

Now it is smoking out of one tailpipe all the time, rattles more than what was previously normal, and has a noticeable miss at idle. A couple guys that thought they knew said it was an injector knock, changed four in the smokey bank, bled thoroughly and it's unchanged. I have been told: Head gasket, defective injector, hung valve, stuck rings, and a few to dumb to mention. I was hopint you guys could lend some insight before I get greasy again. Thanks!

BTW, she shows 290,000 on the clock. Don't know any prior history except the Goodwrench reman sticker on trans. please help.

An easy way to trouble shoot the 6.2L with a miss/rattle is to get the engine to normal operating temp, and with the engine running, loosen one injection line at each injector one at a time to determine if "killing" that cylinder makes a difference (similar to pulling a spark plug wire on a gasser).

For example, if "killing" the injector makes no difference to the engine running, then you have found your dead cylinder. However, if that process causes the engine to miss and run worse, then you can move on to the next cylinder. This also applies to the noise. If "killing" the injector causes the rattle/knock to go away, you have found your suspect. This can then narrow down further diagnostics needed for that particular cylinder.

Once you have found a particular cylinder giving you the trouble, another easy check is to swap injectors with a known good cylinder. If the problem follows the injector, you know you have a faulty injector. If it remains with that cylinder, then your issue lies internally.

I had a 6.5L once that was running really rough. This process quickly led me to a problem with cylinder # 1. A follow up compression check found almost zero compression on that cylinder. Turned out to be a broken piston.

Casey

Welcome aboard!

Step one: Change the fuel filter and verify the fuel supply to the injection pump (lift pump, fuel line condition, fuel quality/condition, etc.).

Step two: (rarely needed, but available as necessary)