Yesterday in the process of doing coolant cleaning and flushing, probably the first time this truck has gotten up to temperature in a long time, it started running very rough and blowing smoke out of the tailpipe. At idle it was evident that it was missing hard, hard enough to shake the doors on the somewhat worn out strikers that they will bang against the body.
The process to actually get this thing up to temperature was to maintain 2500+ RPM for 15-20 minutes just to get it into the beginning of normal. No thermostat is installed, and despite putting cardboard in front of the radiator as much as I could, getting it hot wasn't easy. Between the Restore and Restore + flushes it probably ran for 60 - 90 minutes at 2500 RPM just sitting in the truck footing it myself, and at least another 90 - 120 minutes idling while hot.
I did a contribution test and got codes for cylinders 2,4,6. Suspicious that they're on one side, and all at the same time. That said, this truck doesn't have the single connector VCH but the dual connector kind. I then shut the engine off and did a buzz test right away, and all the injectors sound the same. Visible blow-by on this engine is minimal.
I'm leaning towards just having dead injectors. I did recently do cups, injector o-rings, shims on the injectors, UVCH, and replaced all the VCH pigtails. But just because it's been done doesn't mean it's good, however with the buzz test identical across the board by ear is it a solid conclusion that I'm not looking at wiring problems? Anything else to look for before blaming injectors? The truck does start easy, I mean practically instantly. I've never had such a short cranking diesel, but it sure runs like crap!

 

How many miles on those injectors?
Did you swap internal orings too?

 

No idea on the miles, I assume 200k+.

I did not do anything internal, just external when I was doing the cups and the shims on the injectors; there were no orings involved for those.

 

Without a thermostat it will be hard to get one warm. Why is it missing one? I would not trust the temp gauge too much. The cooling system on these are very robust. I don’t think mine ever gets past “N” on the gauge but the heat is hot in winter so that is fine with me. If it runs fine, it runs fine, when are you trying to get it hot?

you can also do a wiring test from the IDM connection to verify injector wiring integrity.

If you let it cool down and restart it, does it still miss?

 

I know the injectors are recommended to be replaced after 200k. Or at least rebuilt.

Is it possible some wiring is crossed, causing a misfire? That'd cause those issues.

 

Like mentioned with no thermostat it will be difficult to get to temp. The dash temp gauges is only to tell you something is majorly wrong like if it goes all the way hot obviously. Not a fine tuned tool by any means

 

I would just quick verify the connections.

 

Thermostat is out because I was chemically flushing the cooling system, and removing the tstat is part of that procedure. Yes it's difficult to get the engine up to temperature without a load when there's no thermostat installed. Operating temp was monitored via oil temp through the OBD port. I only ever got oil temp as high as 190, so coolant temp would have been in the 160-180 range depending on oil cooler performance. Still not "hot" but got the job done. Yes the miss is still there after cooling down. I don't think wires could have crossed themselves mid-running, and still with crossed wires the buzz test would be impacted would it not?
Thanks for the documents and I'll look in to the wiring tests. Checked the morning and the ODO is in the 280k range but it's difficult to read because the LCD is messed up. I recall when I did the shims, while checking unshimmed clearance every single one was super tight and needed the maximum shims. I've always known that was just a band-aid. I've been working through a lot of things to get this basket case back on the road.
​​​​​​​
​​​​​​​

 

LCD is kaput on my '92 also. Sad for me. Maybe try to wiggle the connector to the valve cover at idle and see if quality of idle improves?

 

Good idea, I did try that while it was still missing but had no effect. I also checked the body of that harness for rubbing but it's well off of everything.

 

Do you have a spare ECU or spare IDM?

 

Definitely do the pin test. When you put everything back together, you may have pinched a wire under the valve cover

 

I don't have either. They would be very handy about now!

Will do

 

I have spares of both, when back in TX late Nov we can test unless you have figured out the issue by then.

 

I appreciate it!