94 6.5L TD Hesitation Stalling Issue

[SeattleSilver]

Posted first in the wrong forum, I think. Sorry for the mulitiple post.

So, I've been dealing with this issue for a couple of weeks now. The truck will stall at any speed, cough, hesitate and have low power, then after 15-30 sec, and a belch of black smoke (or a trail if i'm getting on it a little bit)pick back up again. If I'm restarting from a stall, it turns right over and starts again. There are no trouble codes. I replace the filter in the seperator ~8 months ago, I've pulled it and it looks fine. Air filter is a K&N. A little while back I was having stalling issues with code 42, but I replace the harness to the optical fuel sensor and that fixed that problem. Work in the last year includes all new glow plugs.

Any help would be great.

Drew

[FordeatinZ71]

my first guess would be the PMD (pump mounted driver). i would get the relocation kit and the heat sink...relocate the new one with the heat sink and you should be ok...

[chrisk1500]

PMDs are expensive. Check the simple things first.

Test fuel pressure first. Make sure LP is putting out around 7 psi at idle and around 2 psi at WOT.

Try taking your OS filter harness right out of the equation by disconnecting it and plugging the harness directly into the OS.

Also, clean and ensure all grounds are tight on the battery, block, and inner fender.

If none of this helps the situation, you may want to borrow a spare PMD from a friend to test first. Then dump the coin on it....fire me a PM later to get your PMD mounted properly...

[SeattleSilver]

The truck died completely on me after work today. I drove it to work, it was really rough, parked it, came back to it after work, and it wouldn't fire. I opened the bleeder valve on top of the fuel filter, and pulled the fuel solinoid fuse, and it wasn't pumping any fuel at all. I tried it with the fuse in, and out, the valve wide open and just barely, and with the gas cap off and on. Any idea what happened?

[GM Guy 1]

the lift pump piggybacks off of the Oil pressure switch, so that could be part of the issue as well.

[98crewcab]

PMDs are expensive. Check the simple things first.

Test fuel pressure first. Make sure LP is putting out around 7 psi at idle and around 2 psi at WOT.

Try taking your OS filter harness right out of the equation by disconnecting it and plugging the harness directly into the OS.

Also, clean and ensure all grounds are tight on the battery, block, and inner fender.

If none of this helps the situation, you may want to borrow a spare PMD from a friend to test first. Then dump the coin on it....fire me a PM later to get your PMD mounted properly...

I didnt know you could bypass the optical sensor harness?
how long can you run it like that ?

Are the PMD difficult to replace ?
I have a friend with same issues...

[SeattleSilver]

I went back over my receipts, and they replaced the OPS. What about the lift pump under the drivers seat? How much of a PITA is that?

[chrisk1500]

Lift pump is easy to replace - similar to gasser fuel filter.

The LP in the 94 only pumps when the truck is running or there is adequate oil pressure to the OPS. It may also run during cranking.

Try unplugging the LP and jumping it with 12 volts to see if it pumps properly.

[chrisk1500]

I didnt know you could bypass the optical sensor harness?
how long can you run it like that ?

As long as you want.




Are the PMD difficult to replace ?
I have a friend with same issues...


Depends.

If you get a complete unit from Heath, it should take about 15 mins.

If you are putting the new PMD back on the pump, it can take around an hour to take off the intake, clean things up, and bolt it back together.

[SeattleSilver]

OK good advice. Now that I come to think of it, I haven't heard that pump running like I'm used to. I'll get under there today and see if thats it. Thanks everyone.

[SeattleSilver]

It was the Lift Pump. All better now, thanks for the help. You folks rock!:happy:

[chrisk1500]

No problem.....remember - simple cheap things first.

Most folks immediately blame the PMD without doing any troubleshooting first.....