83 K20 Turbo 400 6.2L

A little background before she started acting up yesterday.

This truck was used on the oil fields until about 4 or 5 years ago. A friend of mine had purchased it for farm work. It's is in very good condition physically considering all the abuse it's most likely seen (especially since my friend and I live in Montana. So I decided to take this truck off his hands. It had a hard start. 6 glow plugs were bad and the relay was worn out. Replaced them and she was firing up much quicker. Checked the coolant temp sensor and it was reading around 3k ohms at 160ish degrees. Replaced it and the new one reads about 53-55 ohms at the same temperature. She had been running great.

When I was leaving his parents house yesterday, after helping them out, the truck made it just over a mile and it died at about 45 mph (she was at operating temp). Pulled over and restarted. Made it about 3/4 of a mile and she died again. Eventually she kept getting worse. A 7 mile trip took an hour.

During the trip, I noticed the oil level was a little low, topped off and no improvement. Well, on the final stretch home (off the highway and onto a dirt road thankfully), each little trip eventually restricted me to a 15-35' distance. Popped the hood and for 20 minutes I let the wind cool down the bay. Was able to make a 100 yard dash before she died again. Of course, each time I sat for a bit, I was on my phone doing some research. I didn't have water to pour on my IP, but I drove a tiny bit with the hood open and it made no progress with 40 mph wind hitting it. Since she died about the 4th time on that trip, a limping dog had more power in it's hind legs. No power what so ever. And if the throttle was pressed more than 1/2 way, she would spit out unburnt fuel out the tail pipes.

One of the weird things is that everytime I cranked her over after she died, it was an instant fire up. No hard starting. So, a few hours later when the engine was about 100 degrees, I fired it up and made it a whopping 80' and she died again. Just enough to pull away from my garage and near my front door.

So, hoping for a fresh start, I fired her up this morning. She had to take a little persuasion. She fired up and she will drive little spurts (never drove past 120') without an issue. However, she will not idle by herself now. If I add just a little to the throttle, she runs smoothly. Also, she has been spitting out unburnt fuel under about 1/2 throttle or more (granted she didn't reach more than 110 degrees at the heads, so it's possible that most of it was from a cold start).

I've tried running without the air filter today and yesterday with no luck. Also, coolant is full and I've checked the dipstick and oil filler cap several time and there are no signs of coolant (so it's safe to rule out a cracked head or blown head gasket).

I'm hoping that it's the Lift pump because, well, it's cheap and sounds like the culprit. Haha.

I know the primary fuel filter (attached to the intake) hasn't been changed in probably a few years (even though since my friend has had the truck, it never got over 10k miles put on it by him. The water separator (fuel filter on the firewall) is not the stock one. But it looks clean and the water is staying at the bottom of the filter (and both fuel lines are on the top).

I also read of the vent lines in the tanks are plugged, it could cause a similar issue that I had yesterday. So I took off the tank caps to allow it to vent and no change. Also tried ruling out bad fuel (last fuel added was about 4 months ago) by switching between tanks and I also put some Diesel 911 in it to try to see if it was fuel quality. No real change that I noticed.

It's also safe to say that the compression is fine because it ran great and then suddenly acted up.

That should be everything. I would greatly appreciate all plausible suggestions for this problem and would appreciate any tips for testing out components (first diesel, couldn't you tell. Haha). I'm on a limited budget as I recently moved and am still getting situated (and trying to find a job).

Thanks

 

Also, it's not my daily driver so if it takes 2-3 weeks to figure it out, it's fine by me. I just need it ready for the winter as my 300ZX doesn't provide one inch of traction on 1/4" of snow.

 

Fuel pressure test yielded around .4 psi with about 35% throttle. So there is low fuel pressure after the water separator. I did crack some lines to bleed the air from installing the fuel pressure gauge and of course tightened them while someone was cranking to keep air out. This makes sense that I have to keep my foot a bit on the throttle to idle. However, it doesn't make sense to me that with low fuel pressure I'd be spitting out so much unburnt fuel. I'd appreciate some experienced diesel owners opinions.

 

Fuel pressure is enough.

And like you say lack of fuel pressure should not result in fuel out the tailpipe.

I would look for a restriction in the fuel return line from the IP to the tank.
Perhaps run a separate line from the IP return to a canister in the truck bed for testing?

 

Pressure is .4, shouldn't it be around 4-5 psi at 35% throttle?

I'll try that out today if I've got time.

 

Miss read the pressure reading.

what type gauge was used to take it?

.4 bar is nearly 6 psi.

 

.4 psi, not bar.

Thought of this yesterday when talking about the issue with a friend. Is it possible that because it takes so long to achieve fuel to the cylinders, that eventually when the cylinders have enough fuel and it finally starts, it spits a bunch out that had ran down the exhaust when it was being cranked over? It's plausible in my opinion. I was looking at the unburnt fuel as an issue, but what if it was just an effect instead?

 

Alright, now that I'm awake and functioning (haha), a restriction in the return line would boost fuel pressure (which would benefit me at the moment), so I doubt that's the issue. I've been doing some reading and people have been mentioning testing the lift pump using the battery voltage. Could you walk me through how to do that? Didn't think it was possible with a mechanical fuel pump but apparently GM used the oil pressure sensor as a fuel shut off. If the oil pressure sensor is bad, it could explain the low fuel pressure and why it runs under light load but won't idle.

 

A restriction in the return line shuts down the IP.
It can in no way benefit you to have a return line restriction.

The mechanical lift pump is not affected by oil pressure-that is electric LP only.

 

That's good information to know about the injection pump. Thank you for letting me know that. Currently installing some new lights but I'll attempt to bypass the return line if I have time tonight before it gets dark (in about 3.5 hours). I'll post the results as soon as I can. And I didn't think that a mechanical fuel pump shut down as it is ran by the engine, thanks for confirming that as well.