Injection pump failure?

[crashz]

Sorry to post this question, but I'm next to my truck now and have no internt other than my phone.

My 87 1 ton dump with 6.2 is not starting easily and when running has a miss that gets steadily worse. It will start and run fine with your foot on the accelerator, idle fine with cold advance, then stumble at warm idle. It stumbles, catches back up, stumbles harder, catches, stumbles and dies. Re start is hard.

First thought is air.

This afternoon I put a new fuel filter on, bled it out with a vac pump, and put a clear tube on the fuel return. Fired up, reved smooth, bubbles disappeared and ran clear, idled good for 10 minutes, and dies. Further tries had it dying sooner and sooner. Not a bit of air in the return after the initial bit from the filter change.

The truck is completely stock, and likely the original IP. It has 26k miles or so the previous owner thought, but could be 126k.

When my IP in the 83 went, it was all of a sudden, and would not re-start. This seems more like air problems, but nO evidence. Any thoughts?

Thanks,
Leo

[Yukon6.2]

Hi
Have you tried the other tank?
Lift pump leaking?
Thomas

[crashz]

Just a single tank, about 1/2 full. Brand new mechanical lift pump. Great fuel pressure if you open the bleeder on the filter base.

[DmaxMaverick]

Verify the fuel quality first. Then....

Sounds like retarded timing. Check the pump flange for tightness or pump movement. Otherwise, it could be the pump starting to go away, and/or timing set wear (although this won't happen quickly). The HPCA and throttle will compensate for retarded timing. Add in some tired injectors and colder weather and it becomes exaggerated. The mileage of the truck is really irrelevant, considering its age.

[crashz]

Thanks Dmax!

Fuel looks clean and clear from the filter, but i know its old. Plenty of stanadyne fuel conditioner in it too.

The pump and lines are tight, but good call on the timing. I'll try adancing it a little.

Could there be an issues with fuel pressure in the IP housing? Seem like it gets worse after ever restart.

[DmaxMaverick]

What do you mean by "worse"? Fuel pressure in the housing should be minimal after the HPCA disengages, if the return is not obstructed. If your HPCA isn't working for whatever reason (failed solenoid, bad temp sender, etc.), the timing may be too advanced. Meaning, enough advance for a good cold start, then too advanced after it warms up with no means to retard. In this case, it usually causes a really bad rattle, but the other symptoms could be similar. To test the HPCA, start cold, then immediately disconnect the rear wire on the pump. It should stumble, smoke and run poorly. If no change, the HPCA isn't working. If the engine is warm, supply Batt+ power to the HPCA connector, and it should run like too advanced. To test the temp sender, start cold with it/them disconnected (simulates coldest starting condition, assuming the rest of the system is functioning).

[crashz]

DMax

The truck will re-start hard, run, stumble and die quicker and quicker each re-start.

Then again, by that time, the truck is warm enough that the cold idle is no longer active. I think the temp sensor is working because the high idle solenoid on the throttle side of the IP is working.

[diaric]

check that your return line isn't plugged. If the problems start in a short time of running, its probably a return line issue. If its in miles of driving, its probably the fuel cap not venting.

[crashz]

Thanks!

I haven't been able to get back to the garage (the trucks sits 130 miles away from my house) since I first posted, but I was thinking plugged return line as well. Maybe.

I did try removing the fuel cap once before without any change. New one on it now.

So my plan of attack next time I'm up there is to:
- take the fuel cap off;
- remove the clear tube and try blowing some low pressure air through the return line (~5psi);
- if it seem like it's restricted, I'll fix or replace the line;
- Try running it;
- if it doesn't change, I'll try advancing the timing by 1 line width

If none of that seems to work, I'll pull off the IP and send it to a local Stanadyne shop. Might as well have the injectors refreshed too. And with this amount of work into it already, I might as well change the timing chain as well. I feel kind of stupid, as I replced the harmonic balancer and thought nothint of the timing chain.

[crashz]

Just a quick update:

Today I checked the return lines (5 psi through the line back to the tank) and they are not blocked.

I then advanced the pump by a paper thickness, started the truck (glow plug controller died, so I started it off of WD40 and Ether). Started with a grumble, ran beautiful at cold idle, when low idle kicked in, it began to stumble. I gave it a little throttle, it bogged without revving up, and died.

I noticed that the pump might have not been tightened down enough, as after it died, the timing lines were back inline. So I put the batteries on the charger and also plugged in the block heater, and advanced the pump by a full line thickness. Tightened it down better too.

It wouldn't start again without a snort of ether. I found that odd, especially when it was running and warm. With a sniff of ether, and foot to the floor it roared to life. Cold idle again for a bit, ran beautiful. Low idle ran good with barely a hint of a stumble or fishbite. It was rattling a bit more, but seemed really smooth. I let it idle for a bit and again goosed the throttle at the pump side. It bogged and died. My father was watching and couldn't believe how it went from running smooth to dead.

I'm stumped. It looks like the original IP, so I'm going to have it rebuilt. Going to have the injectors tested, rebuilt and balanced if I can as well.

Will report back once I have the new pump and injectors in.

[crashz]

Well, I got the pump off, and had it rebuilt by a Stanadyne shop. BTW it is a DB2 4544.

When I took it off the final straw was the metal shavings I found when I pulled the return check valve. See photo.

It was confirmed with the build sheet. They replaced everything. Head, rotor, lift pump, advance piston, gaskets seals, you name it. The guy at the counter was surprised.

This weekend I'll install it, and hopefully see the fruits of my labor. Then comes the task of stopping this rig.

[john8662]

Sounds like a good idea to rebuild the injection pump because of the shavings.

I'm curious about your 5psi on the return above. I've been wondering how much pressure these rigs normally see on the return side.

Of course much of this is determined by the fuel tank cap.

J

[crashz]

Sorry John,

I re-read my post and it sounds like I measured the return pressure. What I meant to say is that I applied 5 psi of air to the clear return hose after I removed the end at the pump and it blew through without a problem. Gurgling tank and all.

So the metal shavings have me thinking a little. Recently I read a report conducted by the militarty on fuel lubricity and failure of the DB2 pumps. All pumps failed, at least in part, at the internal lift pump or housing charge pump. I thought nothing of this until I pulled mine of the truck.

I can verify that my truck had a failed mechanical lift pump. The truck ran (low on power) and started fine before I changed the fuel tank (leaked). After that, I was chasing leaks and could only get it to run when I primed the fuel system with a vacuum pump. No fuel at the bleed screw on the FM was also a good indicator.

Replacing the lift pump helped starting and fuel pressure, but the damage was done. I think over working the internal charge pump to act as the primary lift pump, cooked it. In doing so the rotor wore into the housing and caused the metal shavings.

I'm convinced that the failed lift pump is the real culprit. I'm debating with myself on removing the mechanical pump and installing an electric pump. Or maybe both. However I will be installing a fuel pressure gauge so that I can monitor fuel pressure while running.

BTW - do you guys know what the "Feed the Beast" mod is, and should I do it? It looks just like a larger inlet fitting on the IP. Is that right?

[john8662]

The FTB mod is just a larger inlet on the injection pump and a modification to the FM100 round filter housing found on 92+ 6.X.

The shavings were also probably from the advance piston below, it wears badly.

If the head/rotor were technically bad, you're getting a new pump now.

I agree that fuel starvation from a bad lift pump does no good for the injection pump in the lubricity department as there isn't sufficient flow through the pump to lubricate and cool the pump either.

J

[crashz]

I had a productive day yesterday and got the injection pump on, the injection lines on, and the intake manifold back on. Vacuum lines, CDR, fuel lines, guage, e-pump, manual glow plug solenoid and switch are left. I may even ditch the FM and and go with a Racor unit while I'm at it.

John - thanks! And yes, I think its a different pump altogether. This one has the half circle and line on the timing cover flange. My old one only had the line.

So much more work to do to this old truck to get her back on the road, but it will be worth it.

[crashz]

Update:

Got her all finished up, minus the new fuel guage and filter assembly. I couldn't wait any more.

I used a vacuum pump to pull fuel through the filter housing and all, then cracked the injectors and went to town bleading the system. I pulled the glow plugs so that the engine would turn over easier. It took a little while, but got fuel at each injector then tightened them up.

With the block heater and no glow plugs, she fired off so nice and runs so unbelievably smooth, its hard to imagine its the same engine. I've never felt or seen such a smooth diesel. All of my previous 6.2's had a louder clatter and would shake a bit at idle. This one is smooth as butter.

Now to address the brakes, lights and transmission and get ready for state inspection.

[DmaxMaverick]

It's always a good feeling when something finally works.

If it seems too smooth and quiet, the timing is probably retarded. It should clatter, some.

[crashz]

Thanks Dmax!

It probably is a bit retarded. It runs as smooth and quiet as a gas engine of similar vintage. Almost no smoke at all either. I'll probably adjust the timing a bit once I get all the other little things done.

BTW- do you have to pass CA emissions with your Blazer? Do they perfrom the opacity test by snapping the throttle 3-5 times?

[DmaxMaverick]

No smog for the 85. Smog tests for 1998 and later Diesels only. An opacity test on a N/A diesel is essentially useless. If it doesn't smoke, it's broke. It's the nature of the mechanical Diesel fuel system. Black smoke is soot. Even the latest "clean Diesels" smoke. If they didn't, the DPF wouldn't be such a big deal.

When properly tuned, it should puff a bit of black on hard or snap acceleration, and a light haze under heavy load. White/blue smoke should only be seen for a short period during a cold start.

If yours "runs as smooth and quiet as a gas engine of similar vintage", I suspect it's a lot retarded.

[crashz]

We have emissions for any vehicle over 10,000 lbs and that is the opacity test. It used to apply to all light duty diesels here in MA, but now only over 10,000 lbs GVWR.

I was just curious. In quoting the MA emissions testing regs, I realize that the inspection station should not have tested my truck in the first place. It has a GVWR od 10,000 lbs. Not over.

As you stated the opacity test is useless. And if you've seen it done, it seems abusive. Somehow, my truck passed with its dying injection pump, as it was fish biting even then.

I'll put pump timing on the priority list. Thanks again Dmax! :)