Which Resistor to use? Or No Resistor at all?

[drgerry]

I did a search for this and came up with nothing. Searching "resistor" found too many to search through.

Which resistor should be used in the PMD/FSD? I've seen #5 and #9's
What's the difference?
Can you run without one at all?

Getting the old resistor out is a booger. I'm thinking that if mine dies on the road (I have a spare), can I run the new one without a resistor if I am unable to get the old resistor out at the time?

Should I purchase a new resistor? if so which one and why?

[Yukon6.2]

Hi
Getting the resistor out is easy with the right tool.
There is a hole in the resistor that you can hook with a wire with a 90 bend near the end.
I believe that the #5 is a happy medium.And yes you need the resistor.

[JohnC]

IIRC there are two holes in the resistor. A paper clip bent into a "U" shape with a tiny hook at a right angle on each end will pull it out.

The resistor tells the ECM the pump's calibration. The value is stored in the ECM. Usually, the ECM won't notice if the resistor is missing. Only when it decides to read the value will it complain. If it can't read the resistor it will default to the lowest fuel map.

The right resistor for your new PMD is the same as the one that came with the pump when it was last calibrated. This should be the one in there now, unless someone in the past changed it.

Using a higher number than spec will increase the fuel rate slightly, if you also force the ECM to read the new value. The easiest way to accomplish this is to force a TDC offset learn cycle. However, if you go too far from the correct value the throttle will get touchy and the engine may surge. I had a pump that called for a #4 and when I tried a #9 it was beyond annoying. I want back to a #4, although a #6 probably would have been fine. The power increase is small, though.

So, bottom line, if you have no resistor, you should be fine for a while, and even if it is detected, it will still get you home. To avoid problems all together, either dig the resistor out of the old PMD (easy if you have a remote mount) or get a new one of the same value. If it is not remote mounted, or you can't get to it, you can always read the value stored in the ECM with a Tech II.

[Robyn]

If you have the old PMD off the rig you can look into the plug socket on the PMD and see the tiny circuit board that the resistor is on..

The will be a number from 1 through 9 on the little circuit board.

I sacrificed a small screwdriver to make a tiny hook that can be inserted into one of the outer holes in the resistor board and lifted alternately from side to side and the resistors come right out.

Do not be tempted to use a #9 (Unless that is what yours had originally) as the computer will usually scream after it finds it.

[More Power]

Here's a link to a piece we published some time ago about this topic.

https://www.thedieselpage.com/t/fsdresistor.htm

[drgerry]

You guys are great (assuming you are guys) :)

Thank you, and as I read you comments I began to remember a little about this.

I may find one online somewhere. PMD's don't go bad too often so I'll probably be good for a while. What happened was (wha' had happn' wus) I made an offer of $175 for a $200 DTech on ebay didn't think they would take it. I needed the truck over the weekend and just bought a Dorman from Oriely's.

Sure 'nuff, they accepted my offer and I couldn't back out. Now I have an extra PMD.

Sleep well everyone, be good and have fun!

[Kennedy]

Makes no difference initially and even when it does change you'll never measure any difference.

Try no resistor. It will not care until you do TDC learn or some point months or even years down the road it will suddenly set a DTC when the ECM decides to check it.

[trbankii]

Using a higher number than spec will increase the fuel rate slightly, if you also force the ECM to read the new value. The easiest way to accomplish this is to force a TDC offset learn cycle. However, if you go too far from the correct value the throttle will get touchy and the engine may surge. I had a pump that called for a #4 and when I tried a #9 it was beyond annoying. I want back to a #4, although a #6 probably would have been fine. The power increase is small, though.


Do not be tempted to use a #9 (Unless that is what yours had originally) as the computer will usually scream after it finds it.

I just went out and looked at mine. Apparently the PO installed a #9 at some point. It also had a Diesel Rx PMD (which I've since swapped out for a Flight Systems/D-Tech PMD) and an SSDiesel Supply FSD Heat-Sync.

Regarding a #9 being "beyond annoying" or making the computer "scream," what exactly should I be looking for? A DTC being set? JohnC mentions a touchy throttle or engine surging?

I'm just wondering if I should replace the #9 resistor for better reliability or if there are definite signs that the computer is having issues with it.

[JohnC]

A #9 resistor won't set a code. The effect depends on what the pump really calls for. If the correct one is not too far from #9, say #6, the effect is smaller than, e.g. if the pump calls for a #3.

Mine called for a #4. Now that I think about it, the one I couldn't live with may have been a "#13", the largest resistor the PCM will except without setting a code, and larger than anything Stanadyne used.

One exercise you could try is, if you can get your hands on a scanner, see what resistor the PCM thinks is installed. If the PCM thinks it's #9 and driveability is good, just let it go. If PCM says something other than #9, you could force a TDC offset learn, which will also learn the #9 resistor, and see how you like it. If you don't like it, you'll have to get a different resistor and relearn again.

I don't think you can do anything with the resistor that will have an effect on reliability. Driveability would be an issue way before that.

[trbankii]

Much appreciated, John. I was just concerned from the comments about #9 resistors that the truck could have issues if it was "choking" on dealing with the #9 resistor.

[JohnC]

No. The resistor tells the PCM that the pump under delivers, so the PCM calls for more fuel to compensate. This can make the throttle touchy as the incremental change is out of proportion with the change in throttle position.

[DmaxMaverick]

No. The resistor tells the PCM that the pump under delivers, so the PCM calls for more fuel to compensate. This can make the throttle touchy as the incremental change is out of proportion with the change in throttle position.

This is the way I interpret it. It changes the linear correlation between the APP and actual fuel delivery. "Idle" speed is a preset default value, adjusted by the PCM according to actual engine speed, and is held static and precisely adjusted only as required to maintain the preset engine speed (such as an A/C load, etc.), within a very narrow margin. The problems come in when there is a human input, which is anything but static, and is (normally) constantly changing.

I have the "#13" experimental resistor John referenced (thanks John). I've used it for testing but never put it into normal use, on 2 trucks, both 95's (running perfectly, otherwise). As John said, throttle response becomes erratic, and essentially a 2-position throttle with little predictability according to foot-pedal input, which becomes more prominent as the resistor value departs further (greater) from original. It's OK at idle, on cruise control, significant load (acceleration), but is difficult to hold a steady manual speed. Any pedal fluctuation causes exaggerated increase and decrease of engine speed response. This was with an original calibration resistor #7. The same test with an original #3 resistor pump was as John described. Anything off idle just wouldn't be happy at any input. The original #3 with the #13 resistor did set a bunch of codes, but they were more related to the erratic running than the actual resistor complaints (misfire, cylinder balance, crank sensor). Definitely not streetable behavior. If there is a power advantage, it may be useful for competition when you want/need a 2-position throttle, but I couldn't tell, seat of the pants. We didn't do any timed acceleration runs (maybe should have, in hindsight). Also, downgrading the value (original #7 to #3) did nothing noticeable, other than what seemed like a little longer cranking time to start, but that could have been anything or nothing. It was a fun adventure, but yielded nothing of use, other than to confirm that messing with it is a waste of time. Time and money is better spent on a custom chip/program and other proven upgrades, which will offer some real world results.

Bottom line: If you don't know the original resistor that should be used, just throw in a #5 and worry about more important things.

[JohnC]

Yeah, that is what I was trying to say... ;)

[arveetek]

It was a fun adventure, but yielded nothing of use, other than to confirm that messing with it is a waste of time. Time and money is better spent on a custom chip/program and other proven upgrades, which will offer some real world results.



That pretty much sums up the same conclusion I came to when messing around with the "optic bump." It even messed up my cruise control: it could no longer hold steady RPM when going down hills. Took me a long time to get it back to normal operating parameters. Then the IP failed and I replaced the whole thing anyway.

Casey

[trbankii]

Many thanks for the explanations. Always better to understand what is going on than just a simple "you should do this" or "you should do that" like most of the other forums.

[ronniejoe]

Do not be tempted to use a #9 (Unless that is what yours had originally) as the computer will usually scream after it finds it.

This isn't true in my experience with several trucks.

[Robyn]

I have tried the #9 in a few, and depending on the original resistor that was used issues came up.

Seems that if the original was greater than #5 it would likely not complain.

If the resistor was on the lower end of the scale a complaint was more likely.

I used a #9 in my Dahooooley, but it had been chipped and the new programming did not care, and it was probably designed to use the 9.

[Kennedy]

Any resistor 1-9 can be used in any pump without issue. It's when the resistance exceeds the range of #9 that you have issues, BUT again only when TDC learn is performed. The #13 resistor was something developed by an ill informed vendor thinking that he could market something unique. We even fell for it for a while. With a #13 as soon as you do a TDC learn the ECU will set a code.

Again there is apparently some sort of a random check timer that looks in on the resistor periodically. This is evidenced by the truck that suddenly sets a DTC for the resistor years after the PMD was replaced without a resistor. Ron would have to verify, but as I recall when Michael developed the Scan Soft program for the OBD1 trucks it would show the value of the resistor. This value would not change no matter what you did until TDC Learn.