PMD resistor question

[mobilevet]

Ok, well I have found out some interesting information on my truck. When I bought it it had two PMD's, plus the one on the pump (presumably dead).

The newest PMD (#1) was in use and mounted on the intake (with heatsink) and was close enough to use the factory wiring harness.

The older PMD (#2) was mounted on the firewall using a wiring harness extension, with a heat sink and small electric fan.

(I know these are not good places for mounting - I am reworking the mounts finally)

Right after I got it, I dismounted #1 and rehooked up #2 presuming that it would be better to use the one farther from the engine. Not long after the truck went dead; remounting and using #1 got it going again and so I just ran it like that for a couple years until last week when #1 died (should have moved it earlier). Anyway, I now have a new PMD (#3) and "5" resistor.

So, I took off the #1 and #2 PMD's and found out that: #1 had a resistor with a "9" printed on the board; so, I'm guessing the "9" means it was the "upgraded" resistor. But the #2 did not even have a resistor at all!

My #2 PMD - which is still working and what I was running for the last week will be again relegated to backup after I install the new one (#3), but now I have a "5" and a "9" resistor.

So the question is: Do I go ahead and get another "5" resistor, or just put the "9" into #2 PMD and if the new PMD fails not worry about it being a bit different on the resistor until I can get back and deal with the problematic PMD?

Also, the truck is a 4x4 so I have the skid plate option for mounting, but it would seem difficult to get to if you needed to switch to a backup out on the road.... what about behind the driver side battery?? maybe mount both side by side for easy switch??

worth putting the electric fan back on?

[More Power]

Whew... so many questions.... :eek:

Not having a resistor at all in one of those modules pretty much answers the question of whether a variable resistor (mounted somewhere else) would make any difference. Actually, the resistor value is "looked at" while performing a TDC-Offset, but not otherwise - though some believe the 1996+ systems look at it periodically... I don't know.

For the least possible problems, I recommend a #5 resistor if you don't know what the original module was equipped with. A #9 can work, but there have been instances where it set codes.

I'd mount the module where it's easy to get to - like you were thinking. Behind the driver's side battery is a reasonable location because there is a hole in the radiator support for incoming airflow.

Fans on modules might be a option, but fans are unreliable, especially those not made to work in a hostile under-hood environment. These fans are usually sourced from an indoor electronics application (i.e. computers).

[mobilevet]

Thanks. I'm sure I was making this more complicated than necessary but just didn't want to waste time and have to go back and redo. I"ll just go with the #5 in the primary and stick the #9 in the backup since it won't probably matter for the short time of use. I have mounted in front of the battery without the fan and will just go with that. Both primary and secondary are mounted side by side for easy switch if necessary (just will be tight to get your hand in there to unhook the harness).

Thanks to all of the TDP users and their advice.

[Robyn]

Here is what I have done and it has been a good plan.

The lower swing down skid pan is a lovely cool place to mount a PMD.

Sadly, getting to it on a nasty dark and wet night is a real PITA.
I have always mounted my PRIMARY PMD down under on the inside of the skid pan. (actually its not a skid pan but more of a water/splash and dirt shield.

I have kept my spare mounted on a manifold mount unit and stored in the rig along with a little wrench that can allow me to quickly attach it to the engine if need be.

All thats needed then is to get the rig home, and the engine mount set up is quick and easy and will get you home.

The other option would be to have both your primary and secondary units mounted on the lower splash pan and two cables run up topside.

In the event of a failure, a simple roadside swap of the cables would be all that was needed to get you up and going.

I agree with Jim, stick with the #5 resistor.

If you are using a Heath, Kennedy or ??? Programing that will make use of the #9 resistor and not set codes or otherwise complain it can be a plus, but on an otherwise stock setup, stick wth the #5.

Good luck

Robyn