PMD relocate, #9 resistor, sluggish, POOR mileage

[LeadHead]

Ok, so a few months ago my '98 Sub was having a problem of stalling while driving, so I ordered a 6' PMD relocation harness, grabbed the PMD off my previous, dead IP and mounted it in front of the radiator for max cooling. To save on labor we left the bad PMD (and original unknown resistor) on the IP. Since I didn't know what number of resistor was on it I got a #9 from a local shop (freebie, can you believe that?!) for the newly relocated PMD.
This is the wife's vehicle and it sits in the driveway most of the week so I cannot say for certain that the poor fuel mileage and laggy performance happened at the same time of the relocation, but it was during that approximate time frame that this truck went from 19-21 MPG to 11-13 MPG. It has new glow plugs, but when starting it cold (even as warm as the 40's) it kicks out a pretty good amount of a combination of light and dark gray smoke and runs a bit rough for a few seconds, sort of like it's missing one cylinder. On the road especially when climbing a hill it feels like it's running on 7 cylinders and has about the same performance level.
Now, I have a couple questions: 1. Would dropping a #9 resistor into the PMD cause these problems, depending on what resistor was in the old one? This truck is driven with a light foot but still SUCKS $4.19/gal fuel. #2. I have read about needing an additional ground wire when relocating the PMD. The directions that were included with my relocation cable mentioned nothing about this and I assumed that plugging the new cable into the pump would essentially keep all wiring the way it was. The heat sink is bolted to the vertical bracket in front of the radiator/AC condensor, so is that a sufficient ground? Could this lack of a specific ground wire give me these problems?
My suspicion at this time is the injectors, and a new set of Bosch's should be arriving in a few days. The vehicle has 290+k miles and I can personally vouch for the fact they have not been replaced for the last 125k. Maybe they've never been changed, but who knows. Is this more likely to be the problem than my previous concerns? It's getting to the point where we can't afford the feed bill for this beast.

[LeadHead]

Forgot to say, the IP was replaced 2 years ago, thanks to an incompetent dealer mechanic who ruined my old one. These problems began late last summer before the stations switched to winter blend, so that's not the problem. At one point I used some Lucas fuel conditioner/cleaner and it seemed to help fuel mileage a little, but if there was any improvement it quickly went back to the same MPG horror.

[grancito]

The #9 resistor is not the problem, you need a ground from the PMD to the IP, but when I didn't put one, there was no problem for 2 years, then some no starts occured some times. The starting and running on 7 cylinder problem, sounds more like a bad injector.

[jasoncooperpcola]

Ground wire from PMD to the Injector Pump???? I didn't do that on mine. The instructions didn't even mention it! BUT i bought my PMD from Pensacola Diesel.

[LeadHead]

Please bear with my ignorance, but if the IP is grounded to the truck and the PMD is grounded to the radiator bracket, why do they call for an extra wire to the IP?

[grancito]

IP is grounded to the engine, engine is grounded to the battery, then a ground from there to the body, radiator is connected to the body, pmd is connected to the radiator. The number of connections to become bad are many.

[LeadHead]

Sounds logical, thanks.

[Racer5551]

The fuel solenoid is the only ground that needs to be clean and well connected.

The PMD does not need a ground at all and in a recent post elsewhere it's reccommended that it is not grounded.

The reason the fuel solenoid ground is moved with Walts setup is so thet the harness is able to reach the intake mounting location-if you left the FS ground on the IP the harness would not reach.
A much better practise is to extend the FS ground wire and leave it connected to OS screw on the IP to allow the PMD harness to reach the new location.

[grancito]

Try disconnecting the PMD from it's mounting, the engine will not start, it has to ground through the mounting bolts.

[Racer5551]

Try disconnecting the PMD from it's mounting, the engine will not start, it has to ground through the mounting bolts.

Heath ran his system submerged in a pail of water with only the extension harness connected-no ground to the heatsink.
It ran just fine.

Also a good many nubies run the pmd hanging in the air without a heatsink and ruin them.
No ground required for the PMD.

[grancito]

Heath ran his system submerged in a pail of water with only the extension harness connected-no ground to the heatsink.
It ran just fine.

Also a good many nubies run the pmd hanging in the air without a heatsink and ruin them.
No ground required for the PMD.

I have 2 PMDs and neither of them work if they are not grounded.

[jimclemjr]

Amen on the ground. When I installed my extension harness and new PMD it would not start. Added a extra wire to parallel harness from solenoid ground to heat sink and it fired right up. Obviously the low voltage signals or something need this positive circuit completion.

[6.5 Knuckle Buster]

I find I rarely disagee with Grant... but on multiple occasions to check the PMD of an truck that was running poorly or not, I connected mine trucks PMD
with the ext cable to another truck not even touching mine and they have run. I have alway sat back and wondered what all the whoopla was about grounding the PMD. I admitt it, I grounded both my heat sinks on the PMD to the battery because I was in fear of the unknown I guess

[Racer5551]

It seems I misunderstood another post I read that did in fact say that grounding was necessary,often the PMD screws are enough to complete the ground but not in every case.

[grancito]

Here is a posible answer, the ground wire that was connected to the IP gets moved to the heat sink, someone said it is the fuel shut off ground, so then we extend it to the relocated PMD, if the PMD is not grounded then the fuel shut off solenoid won't work. This would explain why I had to ground the PMD.

[Racer5551]

The ground on the IP is the fuel solenoid not the shut off solenoid.
When it gets relocated to the heatsink it can have a poor ground due to the anodizing or powdercoat and not complete the fuel solenoid circuit.

The ground for the PMD can be affected the same way and an extra ground wire would help from the PMD base to a chassis or battery ground,it helps with electrical noise generated by the PMD.

It is said that a light sanding of the heatsink to remove the coating where the PMD mounts and the heatsink to intake mount in the case of the SS Diesel direction would help with the problem.

[grancito]

The ground on the IP is the fuel solenoid not the shut off solenoid.
When it gets relocated to the heatsink it can have a poor ground due to the anodizing or powdercoat and not complete the fuel solenoid circuit.

The ground for the PMD can be affected the same way and an extra ground wire would help from the PMD base to a chassis or battery ground,it helps with electrical noise generated by the PMD.

It is said that a light sanding of the heatsink to remove the coating where the PMD mounts and the heatsink to intake mount in the case of the SS Diesel direction would help with the problem.

I called it a shut off solenoid, but there is only one, the fuel solenoid correct?

[Racer5551]

There are actually 2.
The fuel shut off solenoid that looks like a stack of 50 cent pieces on the top /front of the IP and the fuel solenoid on the rear of the IP in the center of the fuel lines.

[grancito]

OK, understand, so does the PMD need to be grounded, since there is a controversy over that.

[Racer5551]

Apparently it does need to be grounded to drain away the electrical noise it generates.
It was reccommended that sanding the heatsink and pinching a stranded light gauge wire between the PMD base and the heatsink was a good way to do this.The other end of the wire should connect to good clean ground-body,frame,engine or battery ground.

[grancito]

Good info, thanks.

[Racer5551]

Not a problem.
I just wanted to clear up what I had said earlier in the thread about no ground being needed.
The original poster I was taking the info from was very hard to understand untill he re-posted in plain english.

[BeelzaBubba]

Pinching anything between the PMD and the object it is secured to is a poor idea and impacts the ability to transfer heat from the PMD effectively. It requires a flat surface and creating any sort of air gap, even if you use transfer compounds, defeats the purpose of using anything as a sort of heat sink to preserve a PMDs lifespan.

[Racer5551]

The approach explained would be to create a grove in the heatsink and the PMD base only deep enough to create an interference fit to eliminate the air gap.
But as previously mentioned often the PMD screws can supply the needed grounding effect.

[Bazaromcmullen]

When my black wire broke that is the external ground on the PMD relocation from Walt, my truck would not run. I also thought this was a parallelled ground from the PMD to the IP. Now I know that this ground is for one of the two solenoids and the reason the truck would not start was because the Sol was not grounded after the wire broke.
Thanks for clarifing. I too had been stumped by why the PMD would not ground through the mounting bolts. Now I know the black wire grounds the SOL.
As Paul Harvey always said," And now you know ...the rest of the story."

[jimclemjr]

My PMD heatsink had a tapped hole and I extended a parallel wire from the IP Sol ground point where the factory location was and it fired immediately. Just for any nubies or others wondering- Grounding 101 - based on my experience as well as the factory example is that ground connections are best served by fresh star washers- preferably stainless- that bite between the chasis or ground point and the cable connector. Make sure washer is correct size and has full perimeter bite to both layers. Don't put a star washer under the bolt head but between the ground points. Coating with dielectric grease is good as it won't hurt connection as the prongs will bite thru the grease and keep the hole mess from corroding.