1/4 tank limp mode

[Adam Buel]

Recently converted my truck to a manual NV 4500. With the conversion we found the truck would go into limp mode (2000 rpm max before dead pedal) if the tank is at a 1/4. Truck runs perfect otherwise. Tested it today with running it down to 1/4 tank and did not have the issue until it was powered down. Thinking it maybe an electrical issue from the float assembly to the pcm. Fuel pressure is 15 psi solid. We also noticed today when fueling that the fuel remaining should have be appox 8 gallons, but the tank only took 22 gallons, it should be a 35 gallon tank. 

Previously we tested it by being at a 1/4 tank and going to the fuel station, we left it running and fueled, as soon as we started driving the issue did not return until we were back at a 1/4 of a tank. The tank does have a sump system instead of a draw straw. 

Additional info: The only other time it is in 2000 rpm limp mode is when it is initially started until I change gears.  No issues when the truck was still an automatic(48RE). ECM was remanufactured, pcm is the stock auto. Contacted several places and have been told they will not issue me a manual PCM because of VIN.

 

Any ideas?

Edited January 28 by Adam Buel

[Mopar1973Man]

21 hours ago, Adam Buel said:

The tank does have a sump system instead of a draw straw. 

Bad idea. Sumps are going to be very expensive when you have to replace the entire fuel tank when it starts to leak. Draw Straw is the best option. Not to mention sumps and bottom draw are illegal in all 50 states because of fire danger and safety issues. They are fine for track purposes not for street.

 

21 hours ago, Adam Buel said:

Thinking it maybe an electrical issue from the float assembly to the pcm. Fuel pressure is 15 psi solid. We also noticed today when fueling that the fuel remaining should have be appox 8 gallons, but the tank only took 22 gallons, it should be a 35 gallon tank. 

The sender loses accuracy over time. The only way to gain it back is to replace the sender on the sender basket with a factory replacement. You can check the ohms of the wires from the sender to the PCM connector. You can jump the pins of the wiring and check for a zero ohm connection to be sure the wiring isn't adding ohms where it shouldn't. Possibly a corroded pin at the fender on the driver's side or at the fuel sender. Yes if the pin in the sender is damaged you can replace the entire sender basket which @dieselautopower sells as well.

 

21 hours ago, Adam Buel said:

Additional info: The only other time it is in 2000 rpm limp mode is when it is initially started until I change gears.  No issues when the truck was still an automatic(48RE). ECM was remanufactured, pcm is the stock auto. Contacted several places and have been told they will not issue me a manual PCM because of VIN.

Well, you talked to the wrong person I know I've had several members go to @Auto Computer Specialist and had custom software written for both ECM and PCM to do transmission swaps and I had done one in my yard just 2 years ago and Auto Computer Specialist handled the reprogramming for me.

[Adam Buel]

Thank you for the reply.  I sent Auto Computer Specialist an email regarding the ECM PCM. 

Do you think the sender is the culprit? because when I i am at 1/4 tank its limp mode  does not matter what gear I am in. But I can leave the truck running at the fuel station fueling up and the problem is gone until I hit 1/4 tank again. I am lost on this one. Could the sender hit 1/4 tank and send a problem signal to the PCM? 

I do have codes from the swap.

P0500 from spinning tires in the snow.

P0753

P0713

P0720

P01763

That's all the codes I came up with via the ignition trick 3 times.

Thank you again for your time. 

[Mopar1973Man]

Let's just say all the error codes will cause a limp mode. Output speed sensor,  transmission temp sensor high, etc. Fix the codes and limp mode will go away.

 

Fuel level doesn't affect anything to cause limp mode... Unless the ground for the trans is dependent on the fuel sender ground because the trans ground is junk then that would be why the level affects the limp mode.

 

Master ground for that should be passenger side battery terminal and driver side kick panel. Which that is why the trans temp code for high volts because the ground is missing back to the PCM.

Edited January 29 by Mopar1973Man

[Adam Buel]

Can I add resistors to the tans wires that are left over from the swap? I have have 2 connectors left over 1 is for speed sensor and the other is a circle connector that plugged in right above the pan. That I assume is for all other codes.

[Adam Buel]

Thank you Mopar1973man for the lead on the ECM PCM. I sent them out this morning.