'91 Cummins won't idle/start.

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'91 Cummins won't idle/start.

Postby Mark Nixon » Wed Jul 28, 2010 10:39 am

Firrst off, I have a fair idea of WHAT may be causing this, because I've checked everythinng 6 ways to Sunday and the problem is very consistent.

Okay, so the truck was running fine when I first acquired it.
As time progressed it developed a surge at idle, then went to no-starting unless the throttle was depressed.
On a longer trip recently the truck just died when the accelerator was at idle, BUT FAILED TO RE-START.
After some hair pulling and tapping on the pump head, it fired up.
It has shut down and failed to re-fire numerous times since, even after I replaced the solenoid plunger and gave it more fuel via the fuel screw to get it to idle.
Last night, after having tinkered with the pump for 4-5 hours on Monday to get it to idle, it was dropping the idle out and stalling again.

The consistent part is that it WILL stall out if I let off the pedal and it will, 90% of the time, only re-fire after tapping on the pump head.
My fuel pressure to the pump is adequate, both cranking and running, no leaks in the supply lines, doesn't white smoke at any point, it just won't idle.

One other thing, this truck was being run on straight, filtered (supposedly), USED vegetable oil, but I have found signs of congealing in the OLD filter and the filler neck, as well as a light brown, waxy, substance coating the lines post-filter.
The fuel level sender also does not work at all, which I suspect is because of the WVO.
Is it possible to partially block the pump inlet and still have high-speed function of the injection pump, yet lose flow to cause stalling at lower rpms?

I'm also not ruling out a worn out injection pump, the truck has 230,000 miles SHOWING on a dead odometer and the pump appears to be the original.

So, any thoughts, anyone?

Mark.
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Re: '91 Cummins won't idle/start.

Postby BobS » Wed Jul 28, 2010 4:53 pm

Replace the lift pump if it's the diaphragm stock type. WVO has a tendency to destroy diaphragm type pumps. If it has a piston type lift pump check the pressure output. If it's all ok then look for a deteriorated rubber fuel line hose. Make sure the tank is vented. if all that's ok then I would start looking toward the injection pump.
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Re: '91 Cummins won't idle/start.

Postby PToombs » Wed Jul 28, 2010 5:11 pm

Because you say it will start after tapping on the pump head, it leads me to believe that the pump is all gummed up with the WVO crap. Something is sticking inside, when you tap it, it releases and will start. I don't think it's in the fuel inlet. Time for a pump redo.
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Re: '91 Cummins won't idle/start.

Postby Mark Nixon » Wed Jul 28, 2010 5:40 pm

I do have a pump that's been worked over a little, 3200 spring, fuel screw played with, but I need to re-install the AFC lever, which I did get with it.
I'm also looking at putting my PODs in it, along with a 16cm housing.
The truck has an automatic transmission that works really well, but I'm wanting to put a few extra ponies to it, because it's a slug and I think 50-75 HP won't hurt the situation.
Might throw my PacBrake and a 4 inch D/P on while I'm at it. :twisted:

I will be swapping out the fuel tank, because my suspicion is that there's a nice, thick, layer of plant, chicken and french fry residue lurking in there. :lol:

On installing the PODs, where do I get the thinnest sealing washers at and how thick are they?

Where do I get a boost referenced regulator?
I want it so I can run my 2nd Gen HP-L/P and filter set-up.

Don't worry, I have guages. :lol:

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Re: '91 Cummins won't idle/start.

Postby PToombs » Thu Jul 29, 2010 7:19 pm

Washers; fuel shop, .020 thick. ;)
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Re: '91 Cummins won't idle/start.

Postby redneckroot » Fri Jul 30, 2010 5:41 am

I agree with Pete that the tapping on the pump leads me to think its the pump. But I wouldn't be suprised if the guy just poured the wvo in the tank with minimal filtering before hand. That said maybe the screen on the end of the pick up in the tank is getting coated over with junk.
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Re: '91 Cummins won't idle/start.

Postby SNOOT » Fri Jul 30, 2010 7:33 am

Check your connections at the fuel shut off solenoid. If they get dirty or loose it can cause this problem.
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Re: '91 Cummins won't idle/start.

Postby cougar » Sun Aug 01, 2010 9:49 am

Even jelled diesel fuel can play havoc with the injection pump for a while after. You may want to try pushing a high concentration of PS Injector Kleen and/or Seafoam through the system to break up the sludge.
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Re: '91 Cummins won't idle/start.

Postby Mark Nixon » Sun Aug 01, 2010 10:34 am

It most definitely is NOT an electrical issue, nor is it a supply issue, thoroughly checked both.
I just did a 500+ mile roundtrip and before I left I checked the tank, and there is no build-up on the bottom that I could find by repeatedly sliding a stiff looped wire across the length of the floor, from the filler tube opening.

I filled up and hit that fill with diesel-911, drove then filled again and gave it a shot of injector cleaner, for good measure and it's still not starting.
I also found that no amount of tapping on the pump will free it up if it runs for an extended time.
It's like extra heat just compounds the problem.
I HAVE to give it a whiff of ether before it'll fire off.

I was going to just swap the pump out, but I need to put the AFC lever back in the pump I want to use, yet I'm missing the tool to remove the top cover bolts, so it didn't get done.

Plus, I thought maybe it could be done chemically, so much for that. :roll:

If it truly is the result of bad B/D, or congealed WVO, it's some really stubborn stuff. :evil:

I haven't found any (100%) BioDiesel to try to run through it to see if that'd free it up, or not.
My suspicion is "not".

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Re: '91 Cummins won't idle/start.

Postby Mark Nixon » Thu Aug 05, 2010 8:57 pm

Well, pulled the top off of it to-day.
I found a light coating of a substance that resembles, for the lack of a better description, varnish.
The odd part of it is that it's all over the steel parts, but ALL of the aluminum pieces are clean as a whistle.

I also found an issue that's hard to describe.
The best I can describe it is that when I move the shutdown lever forward, to "run", then as I push the fuel lever forward, there's a slight "snap" and it "gives" and it continues to slide forward to full fueling.
I can drop the fuel lever back and move it forward again and it wlll "snap and give" again.
It's repetitive, but I don't think it's supposed to do it.
The governor moves freely, not a sign of binding or sticking.

I'm thinking it's a mechanical malfunction or wear, rather than fuel contaminant related.

I'm going to put the AFC lever back in Dale's old pump and stick it on to-morrow.

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Re: '91 Cummins won't idle/start.

Postby cougar » Sat Aug 07, 2010 8:24 am

Hey Mark, just some thoughts on the pump.
http://www.dieseltruckresource.com/dev/ ... l?t=231863
If you look at the third picture, #s 111 and so on are the governor. If the sliding sleeve (#115) is sticking in the de-fueling position, that may be the culprit. The fly weights may move freely but the sleeve may not due to that varnish. The problem gets worse as heat expands metal.
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Re: '91 Cummins won't idle/start.

Postby Mark Nixon » Sun Aug 08, 2010 10:42 am

That's all fine and well, but as I mentioned earlier, when working the fueling arms, the arm that runs the throttle had a definite sticky spot to it, but it wasn't like gummy, it felt like a physical catch from wear or damage.
I have the pump totally removed and baking in the sun to evaporate the remaining fuel out so the dissection can begin later to-day. :twisted:

The replacement pump is mounted up, the fuel plumbed up, and primed, for a "pee test" and it did "pee" on all 6 during that test.
Kinda neat how they go "around the clock" in reverse. :lol:

Next is to remove the POD injectors from their current engine and inspect them.
I may take them someplace to get them cleaned, popped, and reset before I put them in, if I can find a place to do it.
If I do that, then I'll work on a turbo to put my 16cm housing onto while I'm waiting for the injectors.

I can't believe I'm doing all of this work to a lousy AUTOMATIC truck. :cry:

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Re: '91 Cummins won't idle/start. UPDATED!

Postby Mark Nixon » Tue Aug 10, 2010 10:03 am

Well, I shortcut it, needed to get it into service, so I didn't do the PODs.
I'm baffled by something, though.

I basically removed the idle screw and intended to turn the full power screw to compensate the idle back up, but once it was together and running, it idled too low, even with the FPS bottomed.
Then I re-indexed the thottle lever and it ran too high, but when I adjusted the FPS to compensate, it now feels like it's soggy on power and barely even smokes.
Truthfully, I haven't even messed with the AFC, yet, but normally I don't have to, the power, and smoke, increase is usually noticeable just turning the FPS.
FYI, this pump does have a 3200 spring in it.

Also, I bumped the timing about halfway to the head from it's original position on the old pump, maybe a move of .125-.250?

It might not help the power "feel", but I'm dragging about 7,000 pounds behind the truck while doing the drive test, but you'd think that would make it SMOKE a bit more.

This thing ran better with a malfunctioning pump and the same load. :oops:

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