starts stumbles and dies

[dhartley]

i'm back my 94 suburban is driving me crazy. now it starts stumbles and dies when started after sitting all day or night. it has new injectors,the glow plugs are working and has a new fuel filter. on the weekend i put in another block heater 1000watts it is so warm in the am i can feel the heat coming out under the hood. it is about -15 c the truck has been showing a code 35 i have not coded it in a few weeks. i will do that tonight. the 35 has been showing for months. truck works excelent once it is going have cleaned all the grounds and the batts test good on my home tester.i have to give it throttle to start and it misses for 5 secs or more and smooths out and runs fine for the rest of the day. my wife tryed to start it last night after work {not plugged in } and it barely got going. i was not there at the time.compression ranges from 340 to380 with one at400. pmd is 1 to 2 years old. i have put in at least two in 6 years truck has 485000 kms thx Dana

[Robyn]

Be sure your lift pump is working on the starting circuit.

Check the fuse in the junction block over by the AC housing under the hood.
The fuse is in a little holder on the far RH side of the little compartment.
If your lift pump is not starting until the engine oil pressure is up this could very well make for a tough startup.

The lift pump is wired up two ways. The first is activated when the ignition switch is turned to the start position. Once the engine has oil pressure the Oil pressure switch closes a set of contacts that continue to power the pump.

The DTC 35 is "Injection pulse width error" (responseTime short)
This is an IP trouble code and may be indicative of a failing pump but also can be agravated by a PMD that is taking a poop.

If your pmd is easily accessable (remote) I would swap the little sucker out real quick to eliminate that as an issue.
Another little gremlin can be the filter harness. This little wiring device plugs into the square plug on the top rear of the IP. The harness runs between the optical sensor and the main engine harness. You can remove it easily after taking the air plenum off the intake to get some room.. (GM Item) (About 6 inches long with little black box in the center of it that the wires run through)

The filter can cause stumbling and other issues.

Check the fuel pump for start up delivery, then try a fresh PMD and then replace the filter harness.

If these do not correct the issue then the IP is very likely the culprit.

Both the PMD and the filter harness can possibly agravate the system to trip a 35.

My 94 Burb was showing 35's and it was the Sol D (PMD replacement) that was causing it to do it. Replaced with a remote Stanadyne PMD and no more issues.

Issues with the PMD are usually not at cold start but more prevalent when the engine is HOT but anything is possible with this stuff.

The filter harness will usually cause a "Fish bite" stumble like missing symptom when running and not just at startup. BUTTTTTT again anything is possible.

The DTC 35 is an issue though and is pointing to a problem that needs resolving.

**** Another thing***** If your PMD is remote mounted make sure that the original ground wire that went from the PMD harness is still connected to the IP. If it is not then get it back there even if you have to splice in an extension. This is a very important ground****** Many of the remote mounts came with a screw and instructions to ground the wire to the cooler/heatsink.. This is a bad idea and can cause issues.

Good luck and let us know.

Robyn

[dhartley]

its definatley not the lift pump checked it this am if it is the pump where is the best place to get one?

[bickj]

I have a 95 2500, doing the same thing. When I turn on the key after sitting there is no pump running, if I put it in Drive and turn key to start pump runs. I believe that the pump is running fine when started, the truck runs fine the rest of the time. When I start it after sitting even around 0c, pugged in starts, stumbles and dies, then takes some spinning to restart runs ruff smokes then smooths out. Warm starts are ok, but it does spin a little more than I think it should. Have put new ends on battery cables and cleaned have checked other connections. Computer not throwing any codes. I do remember the pump running briefley when I used to turn on key now it is not so I think this might be the problem. Now my 95 does not have a junction block on the ac side under the hood so where is that fuse on mine. Thanks very much for your time!

What a great place to be...
95,2500,4wd,ext. cab, lb,3.5 banks exhaust,airbox mod,remote mount, 488,000km, stuck wastegate overboosted broke block and crank @ 471,000, found out after I got gauges, my advice to to anyone get boost and pyro, was making 18 psi but engine light would not go on unless over 2800rpm to give overboost code

[Robyn]

Most parts stores sell replacement lift pumps for these rigs.
I have purchased them at NAPA before as well as the MA General store..

The 95 will find all the relays and fuses for this stuff on the LH side of the engine bay in the little square Box behind the ABS setup. 92-94 had the stuff on the RH firewall and the 95 on went to the other arrangement.

The 96 and latter uses a slightly different wiring on the lift pump and the OPS is not in the loop as far a supplying power.

The fuel lift pump does not come on when the key is turned to on. It only comes on when the key is switched to the start position and then once the oil pressure switch closes the pump is powered though that circuit.

With the tranny in D and the key switched to start the engine will not crank but the Lift pump works.
This is the best way to prime a new filter. Just have a helper to do it and bleed everything out.

As far as the stumbling and dieing, this may be an air leak , bleed back issue.
Install a clear plastic tube from the top of the IP to the return line and then run the truck well to clear any air. Let it stand over night and then observe the clear line when you do a fresh start. If there is a large amount of air then I would suspect the check valve in the Lift pump as beeing bad.

If the CV is bad then the fuel can suck back to the tank leaving an amount of air for the IP to deal with.
The return line is not submerged so air can enter the IP from this route if the fuel is draining back.

Try parking the truck with a major nose down attitude and see if this helps.
If this helps then the check valve is the issue probably.

If the system was allowing air in on the promary side of the system then the truck would run crappy all the time.
A very small amount of air will really screw these things up and make then run like crap.

The optical sensor will do wierd stuff if there are bubbles going through the system too.

The injection system must be totally free of air to function right.

Give these things a check and let us know.


Robyn

[DmaxMaverick]

Try loosening the fuel filler cap at a hot shutdown, before it sits overnight or for a long period. If this helps in any way, replace the cap. They're cheap, and very often the source of much grief.

[dhartley]

Im back , sorry lots going on. i replaced the pmd[and remote mounted it] and that is the end of the code 35 but it is still stumbling and dying . i put it in the garage tonight and put clear hose on the return to check in the am for bubbles. but i will try the gas cap and priming the pump by putting it ing and turning the key. it sounds as if this will work on a 95 only , but maybe i will get lucky, i will follow up.a lot sooner than last time, i promise