Intriguing problem

[6.5TD Burb]

My Suburban will somewhat randomly stall. Today on the way home after some 75-ish highway driving (guessing 10-15 minutes) I come to a stop and pull out onto another road and it died just as I was pulling out. It did it before in the exact same spot. Most of the time when it stalls it's after I just start it up but not when it's cold. If I hard wire the lift pump (done by P.O.), give it a few seconds to bleed the air out of the injector lines with the accelerator on the floor it will eventually start backup after a few seconds of cranking. With usual driving there is no excessive black smoke. Doesn't seem to be lacking any power and mileage is est. 16mpg. The only abnormal thing that I can see is that in the morning when cold it'll puff a rather large amount of white-ish smoke. There are no codes other than the occasional 78, which is odd because there is a brand new Delco solenoid that I just put on there. The PMD is a brand new Dorman unit with well less than 1K miles (SSD relocated/heat sink) with a #9 resistor. Other than that it's all stock that I can see. OPS has been replaced within the last 2000 miles with a Delco unit; at speed and op. temps it's reading 30psi IIRC. Any ideas?

[6.5TD Burb]

Forgot to add the lift pump is a new AC Delco also with less than 2000 miles on it.

[jasondmann]

Sounds like a bad PMD, I know your's is new but it is possible that it is bad, it happened to me. Shouldn't be too hard to try a new once since it's relocated.

[6.5TD Burb]

That's what I was thinking but ruled that out for a few reasons.
1) It's not hard to start after the air is "bled" out of the injector lines. I don't have to wait for the unit to cool down or what have you.
2) Even though it's sporadic I can almost put my finger on when it is going to do it. The conditions are rather..specific for lack of better words.
3) The predecessor to this PMD did the same thing; it also had less than 3k miles on it. Possible I could get 2 quick failing units in a row but I think it to be a little unlikely.

Forgot to mention this earlier but I don't know if this is a symptom or not. If I pull the fuse for the lift pump while the truck is running it will stall. I read on here that the injector pump is capable of running the truck by itself without the lift pump so I was thinking that this would be a problem, no?

One other thing. When I got home last night I pulled the wire and popped the fuse back in. Suburban started and drove with no problem. Turned it off and it started right back up. Started up with no problems this morning. Does this every time. It'll stall, hard wire the lift pump till I get where I'm going, pop the fuse back in and won't have a problem till it does it again.

[Robyn]

Are you sure your lift pump is running all the time the engine is.

If the Oil pressure switch is shot the lift pump may not be running constantly which can cause a condition of fuel starvation.

With the hard running and then slowing down, everything is hot and the transfer pump in the IP can't keep up without the lift pump to help and the slow speed will allow fuel starvation.

Have you replaced your OPS recently??

The OPS could be having an intermitent issue too due to heat.

Keep us posted

Robyn

[6.5TD Burb]

OPS is new, haven't seen any signs of it being defective.

Dad thought it may have been the FP relay so I have a new one of those on it as well. Delco of course.

As far as I can tell lift pump runs with the motor. When running if I pull the fuse for the lift pump the Burb will stall. New fuel filter. If I open the purge valve with the hose off I get a nice strong stream of fuel (haven't put a gauge on it yet) with the lift pump hard wired. Haven't tried it on the fuse yet.

[JohnC]

If pulling the fuse for the lift pump makes it stall I'd bet either the filter is plugged or there's a hefty (suction) air leak between the lift pump and the injection pump.

[Burning Oil]

If pulling the fuse for the lift pump makes it stall I'd bet either the filter is plugged or there's a hefty (suction) air leak between the lift pump and the injection pump.

I agree and put a gauge on it to see whats going on with the LP.

[6.5TD Burb]

Well I don't think the filter is plugged, it's brand new. Maybe 1500 miles on it and still looks clean. I'll try to put a gauge on the bleeder this weekend if it's not raining.

[6.5TD Burb]

Could the stalling from pulling the LP fuse be caused by a weak IP?

[JohnC]

If pulling the fuse for the lift pump makes it stall I'd bet ...


I'm retracting my previous statement. I'm not sure about the '94, but I'd bet that fuse powers more than just the lift pump. (On the '95 it's called "ECM-B")

[Robyn]

The transfer pump was never designed to do the job of pulling fuel from the tank but only to pressurize it internally to the IP.

Now have you made sure that the in tank sock/filter is not plugged or sucking air

These little devils can and do cause issues from time to time.
A plugged sock will raise hell with LP delivery.

NORMALLY the transfer pump will keep the rig running BUTTTTTTTT the thing is gonna lack power and performance under high demand.

Best

RC

[6.5TD Burb]

Apparently, jasondmann (http://www.thedieselpageforums.com/tdpforum/member.php?u=22362) was right. Got home today and let it have it's couple minutes of cool down time before I shut it off like I usually do. Tried to cut off on the way home from work (same spot) but I threw it in neutral and kept the revs up to try and keep it running. Anyway, didn't have the right size t-fitting for the fuel pressure gauge and I didn't feel like going any where else at the time so I called it quits....fast forward 1 hour. Hop in the Burb about to take off to go peruse the local salvage yard (hopefully for a complete 93TD). Won't start. Spend maybe 15 minutes trying to get it started to no avail. Hard wire the LP, nothing. Open the bleeder valve and theres still nice pressure so I know it's not a fuel problem. Checked codes and pulled a 13 and 78. Odd. Cleared the codes and pulled the fuel solenoid. Turned the key on and the plunger comes up. Key off plunger down.....shut off solenoid is good. What gives? Couple hours later and it STILL won't start. Guess I'll be ordering ANOTHER PMD at work come Monday.

What could cause rapid PMD failure? It's currently mounted on the SSD heat sink unfortunately still on the intake. I keep reading vibrations kill them most often, but this is a little much. The PO said the same thing happened to him which is why he ended up selling the thing.

I have thought of the sock and dad did mention it but it's not a constant problem like a sock would present. Sometimes it runs so smooth with no problem.

[6.5TD Burb]

Another update.

Started it early Sunday morning to find out if I needed to take the Jeep to church or not. Took a couple moments but it started. Let it run for 20 minutes +/- then shut it off and restarted it 3 or 4 times. No problem. Church let out and it fired up no problem. No problem this morning coming to work either. I am getting a little misfire (term.?) Don't know if I mentioned that or not. Only happens for a couple seconds at a time then it goes away. Happens sporadically. I guess when I drive the tank down I'll drop it and check the sock...I'm not about to drop a full 42gallon tank; I'm crazy not stupid. With this thing I can't be sure of anything it seems. Would a clogged sock cause a no-start for 4 hours?