i took the optic sensor filter out about a month ago and it worked great, solved my problems. lately i will get a hyccup every now and again, it will also start hard sometimes and others will fire right up weather its warm or cold out. cant really find a pattern. just every now and again.

does this sound like i need a new optic filter?

No, but a OPS maybe

i think youre right doc.

truck started cuttin out last night as if it were runnin out of fuel. i figured since i was close to red and close to gas station i would fill up. ran fine couple blocks home. went to work just fine, i check the lift pump with the 30sec test and everything was fine. drove to the movie store and fine. got back on freeway and it started acting up like no more fuel, i could let up and it would smooth out but give it gas and started starving for fuel. got off and limped it to wally world. started back up and drove home just fine.

still sound like ops?

For short test only hard wire power direct to the lift pump use inline fuse & a switch for some safety, and do some diagnostic driving around, it's possible the lift pump delivers at idle but not under load, if you can hook up a gauge to the filter housing drain fitting that is even better. I've had a few pumps that work at idle but lay flat under load.

Had the same problem with mine and it was the lift pump. Acted funny, 3 months later no problems, then died on me. Got it home, it would start and run, drive around the block and then it would start surging like it was running out of fuel. The next day , no start at all. Replaced the pump from Heath and no problems since.

And a thanks to Bill for the help on the phone.

i need a guage for sure but i drove fine to work this morning. even got o it a little tiny bit and it acted fine. could the ops be quitting here and there? if i have any more problems i will hard wire with switch and fuse till i get it figured out

I replaced my ops about 3 times, and keep a spare in the glove box. I ran a fuel pressure gauge on the truck and held it down via the wiper blade ( per Bill H ) and drove it around the block. But even at idle I was only pulling like 3 psi. So for me the lift pump was definetly what it was ( and since I replaced it no problems ).

Yes it can act up, best fix is to have the new OPS control a relay (low current load) and then have the relay provide the high current power supply to the lift pump, still need to gauge check it while running though as a weak lift pump with adequate power will give same symptom, which is why I suggested the temporary hard wire to elimiate intermittent power as a possibility

well i dont think its the ops or lift pump now.:mad:

sittin in shopko parkin lot last night in high idle and it just flat out shut off, didnt hesitate or studder just dead. restarted just fine and drove home but studdered a few times. i replaced the pmd about two and half months ago so i dont think that is it. could it be the fuel solenoid itself?

anyone? pmd or fuel solenoid?

LOL. Where did you get your PMD, Dieselboy? Please tell me it's from Steaksauce?

PMD is ALWAYS a possibility. Even remote-mounted, even cooled, the fact remains: people make 'em, so there's always the chance for them to screw up.

If you got it from Heath, just get him to send a new one. If you got it from SSDiesel, better get a warranty thing going - theirs is only 90 days. Not sure about Kennedy or the others. Ebay, good luck. A1Customs, who knows? Steaksauce says they NEVER, EVER fail, and fix flat tires and top off your washer fluid all by themselves.

Yeah, it could be the freakin PMD.

i just got it from a dealer a couple months back

i just got it from a dealer a couple months back

Is you old one still on the pump? Is it DEAD-DEAD, or still intermittent?

You might try it as a spare - when your truck dies and won't start, plug it in and see what happens.

dont know about the one on the pump, i have one spare that i thought was going bad(last one) but now im not sure. maybe ill go try to swapp them. they have a one year warranty but its a little out of the way to the dealer

Don't swap them back onto the pump, but if it won't fire, just plug in the other one right there and try it. If it starts right up, you got an answer.
Don't leave it running too long (couple miutes) without a heat sink, though... the little buggers get awful hot in a hurry.

its starts and runs just fine. just happens randomly. i just pulled the pmd off and tighten the four bolts down, two werent snug anymore. i have the one i took off and thought it was the problem but never completely failed so it will work as a back up. if it fails again i will switch and see if it is the problem, i hope so cause i cant afford a new solenoid

the blazer ran fine all week to and from work with no problems, now all the sudden i ran a town over tonight and on my way home it started its crap again:o: . i was going about 50 down a old country road and it started stumblin a little then cleared up, pulled up to a stop sign and it died. fired right back up and studdered a few more times the rest of the way. pull in and switched to high idle and died after a few minutes. almost acted like it was loading up but i didnt think that was posible with diesels, true?i cant figure this out:mad:

btw i retightened the four bolts on the back of the pmd last weekend

Ding, ding, ding.... early 90's model? Shut down? Acts like PMD, how 'bout bad ignition switch under the steering column?


Tightened the mounting bolts, or the transistor screws? Bolts to IP won't help anything but keep it from falling off, but trasistor screws....

i tighteened the transistor screws last weekend. ran fine all week on the free way then running it in town did this. its on a the ssdiesel heat sync on top of the intake. brand new four months ago. would a bad ignition switch cause it to studder and hiccup under light excelleration?

It mimics the PMD failure. There are some other clues to that too, it's been awhile - I think dash gauges fail too, but don't quote me on that...

do you think there is any possibility to it being the fuel solenoid driver? its just weird that on highway driving it would be fine but a half hour of slow driving it would start acting up.

What's the location of the PMD/FSD anywho? I see heat sink, but actual location is where?

where they specify it to be, on the driver side of the intake hat. i did forget to put heat sync compound on it could this be what caused it to burn up so quick?

So this thing is still in the engine bay getting engine heat? Heat sink is only as good as the delta-T available. Hotter the space, the less effective the heat sink is, thus the hotter the PMD will be.

The side of the pump offers great cooling, with the exception of off-cycle, thus the down fall. If using a heat sink, you've gotta have a cool spot to mount, AWAY from all engine heat. If heat sink is mounted over the intake, just add some BBQ sauce to finish it off. No cooling is available there.

thanks for the bad news knkreb, jk. so if its toaste then any idea why it has done this only on in town driving and not on the highway?

In town, less air flow through the engine compartment. Fan really only engages for real when clutch gets real hot (variable to age of clutch and how well it works). In town not moving a lot of air, and fan is not locked on, because of minimal load on engine.

In town, less air flow through the engine compartment. Fan really only engages for real when clutch gets real hot (variable to age of clutch and how well it works). In town not moving a lot of air, and fan is not locked on, because of minimal load on engine.

I think Knkreb has hit the nail on the head here.

ya me too, im thinkin that goin down the highway is keeping it just cool enough to keep workin

For what it's worth, DieselBoy, When my original PMD died at about 55K, I replaced it with a FSD Cooler like on SS Diesel's page. The new one mounted on the intake didn't even last as long as the original IP mounted PMD; I got maybe 20K out of it, nursing for the last 2K or so by tightening the 4 studs. I bit the bullet and got a new PMD Isolator. So far, I have about 30K on it with no problems. Moral of the story, heat soak kills the PMD/FSD.

:idea: :ro) :cool:

:idea: :ro) :cool:

:cookoo::joke:

Same here on the intake mounted FSD.

Mine lasted all of a few hours, got stopped in traffic on Lake Pontchartrain Bridge this past summer and it stalled for the first time ever in 140,000 miles.

Cranked back up but would stumble, stall, and such until I changed it back to the original PMD.

Not to be outdone I am going to try it again when I get my extension cable which I finally ordered yesterday.

Mine is mounted inside the air filter box, good cool airflow most all of the time.

he he no more air box here:D

Where you gettin' your engine air from?

not the most recent but you get the idea

Since I don't have the truck version, I'm still lookin at which way is up.... is it drawing air from under the hood? Anyway to get cooler air to it if so? Help to keep the IAT's down in the summer, which in turn help the EGT's.

i dont have a egt problem:D

full throttle in 90degree heat only gets me 950 degree egts:cool:

intercooler baby:ro)

right side of the picture is front of vehicle

Pre or post turbo? Cooler air would getcha a few extra °F's out of it, but not noticable in seat-o-pants meter...

Saw the picture and it looks like you cut out the box part of the air box.

The amount of heat right there is unbelievable. If you shield it somewhat it could make a huge difference even if you have an IC.


This PMD thing has been beat to death but if you did have the intake air channeled through from the front of the vehicle or side or whatever the air coming in is at ambient temp. Putting the PMD out of the heat in that air flow is all around better than anything I have seen as opposed to leaving it in the original location.

The IP mounted one gets hot after shutdown where if you could channel the intake air from outside and have the PMD up there at the intake shielded from heat you could idle in traffic and it stays cool. After shutdown it's up there away from the heat.

Pre or post turbo? Cooler air would getcha a few extra °F's out of it, but not noticable in seat-o-pants meter...

pre turbo, that was up at the drags, pullin trailer up steep hill i barely touched 1000degrees

well i went and got a new pmd today under warranty thank god and im going to order the extension harness from kennedy