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running without a resistor?

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5akman

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I'm in AK for the summer job and need to get my '96 6.5 running. Last year it did the PMD thing which I replaced with a new unit the prior owner had purchased but never installed. I remote mounted it but forgot about the resister. It ran fine for a few weeks then just died numerous times in the way a PMD failure will do. I headed back to CA and let it sit.

I put a new resister in today but couldn't get it to start due to bad batteries. My question is, will a missing resister eventually cause running problems? Interesting that it ran without it for most of the summer.....

Lance
 
it should not cause an issue on your OBD-II, OBD-IIs run with the stored value until a TDCO learn is initiated, I intentionally ran mine sans resistor to prove a point for 6 mos never an issue. Now if your batteries drained possibly the PCM did a reset somehow and it is noticing the missing resistor, but ther should be a missing resistor code popping up if that happened, also I've had PCMs unplugged for over a year and the truck starts up and all stored valuse are still in the PCM.

Your sig says remote mounted where/how is it remoted; was it a new driver when installed, or used but good driver that was once located under hood, I only have used drivers as spares , if a driver has been mounted under hood for any time as far as I'm concerned they are suspect and not worthy of being a primary use driver.
 
If the driver is a Stanadyne and especially as Doc says a "USED" one, all bets are off.

Get a fresh DTECH PMD and make sure the remote mount uses a good quality heat sink with heat transfer paste between the PMD and the cooler.

Out of the engine bay is the best place for the PMD.

The swing down pan below the radiator has a lovely spot on the inside that allows a cooler to be mounted easily.


I have seen new out of the box, factory type stanadyne PMD's fail within 2 weeks so ????????? ya never know.


Missy
 
I am pretty sure both of my trucks are sans resistor.... maybe thats my fuel mileage problem??

):h ):h ):h ):h ):h
 
The PMD was in a new box in the glove compartment and looked spotless so I assumed it was new. The PO said he'd bought it but never got it installed. The remote mount is on a large alum finned heat sink, with the Silver paste mounted into the opening in the bumper. Batteries have gone dead every winter as I don't have a way of keeping them charged up. I have the charger on them right now and will know more later today.

I do hear the lift pump running under the drivers seat and I opened the T handle drain next to the thermostat yesterday when I got it running for a few minutes and diesel poured out and it stalled the motor. I then did not have enough battery power to get it started again.

Lance
 
The engine shouldn't stall with the water drain open. On obd2 the pump should run with the ign on, try that and see if it pumps fuel.
 
On OBDII LP will run with ign during the WTS cycle, so not for very long with just IGN on. Then it should keep pressure while running so it doesnt stall like NVW says.

I thought the resistors worked the opposite way. OBD1 only checked resistor value every 50th start or TDCO relearn, so it didnt have to be there all the time. But OBDII it checked to make sure it was there every startup. I dont have an OBDII so I cant check and I dont know that for sure.

TDCO and resistor value is stored in non-volatile memory in the PCM, even on OBD1 so it is never lost even with chip changes or unplugging it. Why you have to do TDCO relearn when you change out a whole PCM.
 
Nope it will run without resistor OBD-II, I ran that way on purpose 6 mos sans resistor to debunk steak boys assertion the variable fuel control works by adjusting the value of the driver resitsor as a real time on the fly adjustment, I ran 6mos that way, PCM only looks/looked at it when I did the TDCO ko/ko learn command. Your thinking was mine for a long time Buddy, until I did it by accident leaving one out, then again on purposed, once ko/ko happens truck does not start and you get a driver resistor error code

I don't know where the value is stored in OBD-II either as it holds the value even with a PCM out for a year + ??? as that was how long I had one in the back of the truck I was playing around with.
 
The reason you do a TDCO with a PCM/IP swap is for that PCM to learn the current location of the IP & optic sensor, same PCM out and back in up to a year+ that I know of in mine has not required TDCO learn.

Matt B was with me when I swapped 2 different PCM tunes 2 PCMs and we did not relearn them, both PCMs operating on the stored TDCO/resistor values within the PCM

this is another area of physical/actual operation that does not quite match up with text found in GM manuals
 
You have to run TDCO relearn when you swap a PCM, because it doesnt come to you with the value you set in it a year ago. If you set it in your truck, then took it out, then yes it will save it for when you put it back in your truck. If eveyone set it to -1.94 then it will always be the same. But if you buy one it will most likely come with no value, or a stored value of -.5 or something and if you have your pump at -1.94 then it wont be right. Thats why you have to run TDCO when you get a PCM from somewhere else to replace yours. And it learns whichever resistor you have then too, otherwise it operates on whatever was stored from factory or previous owner.
 
I have gotten PCMs from Bill or junkyards with a TDCO value stored in them, truck will start/run & runs like crap sometimes, smokes on start but the stored value remains until I initiate a TDCO learn so the IP position & PCM TDCO positions match, junkyard PCMs have been un-powerd for ??? Yet they still have a stored TDCO value in them I've seen some at factory setting, & some at higher than factory.

Last PCM I got from Bill came with a TDCO of -1.5 in it truck it was laggy on acceleration I did the learn and it went to -1.98 TDCO based on current location of IP, and I was getting the odd timing error code and heavy smoke at start, when I moved IP to driver side and relearned TDCO I was -1.85 all issues cleared up.

I have put PCMs from my vehicles in others to test if PCM was acting up in others, or theirs into mine the TDCO does not change.

Yes you must match your truck to the replacement PCM, but once the TDCO for your truck has been put into it, that value stays regardless how long it stays out, or any other vehicle it goes into.
 
On re-read I think we said exactly the same thing in different way, one twist to PCM swaps if you have theft deterrent 97+ truck you also have to learn that value which seems to also stay in a non powered PCM for 1 + year
 
TD sorry for the confusion, I clarified because you seemed to have tried to clarify my post and make it seem like doing TDCO relearn on a PCM swap is not required, like it was optional, which its not, unless you like running with the wrong TDCO value. I originally explained why you have to do a TDCO relearn, because the value is stored in non-volatile memory (like Flash) on the PCM PCB, and it stores the value until you run the relearn. I apologize it seemed like I stated a question, but I meant to say "That is why" and not "Why?"

Yes there is a TDCO value in them, but its not your TDCO value, unless it was set in your truck and not reset in that PCM later. So it should be done when anyone actually replaces a PCM. There is a difference between replacing PCM and troubleshooting by temporarily putting another PCM in. Obviously a TDCO relearn is not required for the truck to run, because truck needs to be running to do the relearn. Thats a given.
 
Ok, did I read one of the replies correctly in that the truck should not have stalled when I opened the T handle? If so, what does that mean? Faulty lift pump? Filter was new last summer and I only got about 1000 miles on it before the truck died and I parked it.

Lance
 
most likely faulty lift pump, its a very important thing to know and check often, because you should flush the filter bowl at least each oil change, but in the case where you dont drive it 3000 miles in a year the bowl should be flushed out occasionally anyway because the fuel will settle crap in the bottom. And oil should be changed annually even without 3000 miles on it.
 
I hope that is the solution. I just happened to bring a new Walbro -5 with me on this trip!
Lance
 
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