Here we go (stall) again (sigh)

[billschall]

The stalling issue has returned. Began several weeks ago. I've re-read everything I could find here on TDP. But not certain if it's the PMD or IP.

Symptoms:
- only stalls when warm/hot.
- does not usually throw code(s), but has thrown DTC35 one time since this headache began.
- will stall when cruising, accelerating or coasting, the latter being the most common.
- once it stalls the first time, repeatedly stalls until I get home.
- will occasionally "surge" before stall as though I hit the throttle a couple of times.
- always, always restarts right away(I've mastered key-off, key-on, glow cycle wait while coasting).

items checked - remedies taken:
- fuel pressure gauge teed off at input line on top of pump - gauge attractively zip-tied to windshield wiper. Fuel @ 5 PSI at idle, drops to 1 PSI under foot-stompin acceleration, and maintains pressure during & after stall.
- all grounds examined for looseness and checked with ohmmeter.
- fuel filter replaced last week
- new PMD replaced last summer with heat sync initially mounted on intake plenum but relocated behind driver's side headlight during top end rebuild this past winter.
- PMD extension cable examined and seems OK.
- electrical harness on firewall examined and appears OK.

One other thing that leads me to think it may be the IP is that fuel mileage still sucks. Only getting 13.7 running B100 / 14.5 running petro. Would have thought the mods (intake, 4"exhaust, rebuilt injectors) would have jumped it more than it did as I was getting 11.5 on B100 before the rebuild.

This is becoming soooooo frustrating I'm about ready to cut my losses and sell the damn thing. Are there any bench tests that can be done on a PMD to determine its functionality? Should/Can a new PMD fail with less than 6,000 miles on it?

[sturzam]

It surely can. Just went through the same symptoms.

I had replaced the pump and PMD last Sept. (Brand New Staynadyne) figuring I should be good for awhile. I just replaced the PMD again three weeks ago. Only 8 months old and 4200 miles on the speedo. So far so good.

The shop that I bought the pump set-up from did bench test the complete unit, after a day of testing they said there was no problems & would not warranty the unit but after repeated failures they finally gave in gave me a replacement PMD, so my guess is that the bench testing is not an accurate everyday accurance. Maybe they just didn't do the testing they said???? Good Luck.

[Robyn]

I would certainly try a fresh PMD before yanking the IP out.

Another issue could be the filter harness.
How old is the rig??
The filter harness is the little short wiring harness that plugs into the top rear of the IP and has a small rectangle shaped box in it.

If the filter goes sour it can allow for some wierd operation and "possibly stalling"

Usually if the rig starts right back up when hot its not the PMD.
You very well may be seeing the IP having some internal issues.
How many miles on the IP since fresh??

Robyn

[billschall]

I would certainly try a fresh PMD before yanking the IP out.

Another issue could be the filter harness.
How old is the rig??
The filter harness is the little short wiring harness that plugs into the top rear of the IP and has a small rectangle shaped box in it.

IP harness replaced during headjob, truck is a '95.


If the filter goes sour it can allow for some wierd operation and "possibly stalling"

Threw out a perfectly good looking filter and replaced it with another $23 filter to rule out filter blinding.


Usually if the rig starts right back up when hot its not the PMD.
You very well may be seeing the IP having some internal issues.
How many miles on the IP since fresh??

Robyn

IP has never been replaced that I know of. Just bought this headache last year w/ 113K on it, replaced heads (amongst other numerous things - see sig) @ 123K and now has 125K on it.

[Robyn]

Check the PMD and see if a fesh one gets it going.
If not the fickle finger is starting to point at the IP.

Check the colored ID tag on the IP and check with your local pump guys that do the Stanadyne pumps and see what they can tell you.

May be the original and time for a freshen up.

Keep us posted

Robyn

[93_Burrito]

Mr. Bill, you've got e-mail... I've got a good spare PMD and am local.


Andy

[tommac95]

I agree to try new PMD/FSD before FIP.

Since it is '95 a new IgSwitch might be a good place to start.... it feeds LP and FSD and FIP , etc. ... and when coasting the system voltage dips a bit.

When you replaced fuel filter did you purge and bleed air ... and check for the small cylindrical nylon mesh filter screen on the tubes inside?

Good job using the fuel pressure gage for monitoring!

[billschall]

I agree to try new PMD/FSD before FIP.

Since it is '95 a new IgSwitch might be a good place to start.... it feeds LP and FSD and FIP , etc. ... and when coasting the system voltage dips a bit.

When you replaced fuel filter did you purge and bleed air ... and check for the small cylindrical nylon mesh filter screen on the tubes inside?

Good job using the fuel pressure gage for monitoring!

Well the problem came back the other night, only this time everything was relatively cool. Go figure.

After reading numerous posts here, I'd thought about the ignition switch, but I've wiggled it and smacked it repeatedly - and never once does the engine shut off. Maybe I should look at the circuit from the ignition to the IP & PMD. Although I'm not quite sure how to do that while driving - perhaps a volt meter?

I don't know why, but I've never had to purge the air after changing fuel filters. The possessed little beast seems to purge O-2 all by itself. Change filter, turn the key and it always starts & runs.

Where is this mesh filter screen that you mention?

[tommac95]

Its' good practice to drain the conditioner before remove filter , then wipe out cannister. After install new element open the plastic drain-nut thingy atop filter element [ LP-- ON ] , to bleed out any air in can... open until fuel runs out of top. If not , only the bottom 1" of element will be immersed, decreased filtration capacity. {due to fact conditioner tubing connects at bottom cannister}
* * *
After removing filter element from conditioner hsg (and wipe clean) look down inside housing. You see two tubes (StainlessSteel), one (taller one) nested inside the other. There should be a cylindrical yellowed nylon ring (actually cylinder) around the smaller/taller SS tube, resting upon the top edge/lip of the shorter/fatter tube; this is a filter screen... they sometimes are inadvertently withdrawn when removing a filter element , and accidentally discarded. Not sure how critical , but there for a reason ! They partially clog , too.
Replacements available mailorder from Gomers/US Diesel Parts.