P1688 But Truck Still Runs

[wish4hemi]

I’m getting a recurring P1688 controller failure on my VP44. However, it’s easily cleared and the truck runs just fine. Could it just be the PSG is slow to boot up?
 

Codes: 1688, 1693 companion

Code reading/clearing method: Edge JwA

 

Two scenarios

1. Turn the key on, 1688 is active, clear it, then start the truck without ever turning the key off. CEL never reappears as long as the truck is kept running. Idle is 800 RPM, idle load is 5% with new RV275s from DAP. The 1688 will never come back until the truck is turned off and back on. Runs great.

2. Turn the key on, 1688 is active, do not clear it, start the truck, leave the CEL on. Idle is sporadic from 860 to 1,000 RPM, engine load always shows 0% at idle. Truck can still be driven but acts very strange at idle while that 1688 is there. 

At this point, I’m just clearing the code before I drive it each day and have had no issues. Sometimes when I shut it off (like a fuel stop) then turn it back on, the code does not reappear. But 90% of the time it does come back after a key power cycle. It does not seem to be time sensitive as I’ve had it stay away for both 5 minute and 5 hour shutdowns. 

 

2002 Dodge Ram 2500

Edge Juice w/ Attitude CTS, Cummins reman ECM (been installed for years), reman VP44 (been installed for years), factory PCM, 197,000 miles, good lift pump pressure of 20 psi (in-tank Carter), W-T mod is done, alternator charge wire goes straight to the passenger battery via fusible link, batteries are new, APPS is 0% at idle

 

Another reference thread with similar issues? 

 

Edited May 10, 2023 by wish4hemi

[Mopar1973Man]

P1688 code is more or less the checksum of the PSG is no longer matching so the code is being thrown. This is showing there is a software issues internally.

[Great work!]

Yep like @Mopar1973Mansaid. Internal software checksum, failed check points or watchdog triggering.

 

Sounds like just speculating,  problems loading calibration data so it uses default values just so it runs but not optional. 

Edited May 10, 2023 by Great work!
Clairty

[Mopar1973Man]

Exactly. @Great work! is right on the money. All the computers or electronics have limp modes to keep you rolling to get home. So sadly your going to need to replace that VP44 soon.

[wish4hemi]

I do have a spare VP44 that should have good electronics. Maybe I’ll try swapping out just the PSG. 

[Mopar1973Man]

No you can't. The PSG must be calibrated to the pump. Swap the entire unit. This is why the price is that high it takes 3 hour of the test stand to calibrate one VP44.

Edited May 16, 2023 by Mopar1973Man

[wish4hemi]

“No you shouldn’t,” I think is the more appropriate verbiage lol. Once the current pump does die electrically, I think I’ll give the PSG swap a try and drag along the fuel solenoid, timing solenoid, fuel temp sensor, and tach sensor. The spare pump has a stuck timing piston and is mechanically defunct anyway.

 

I wonder how much of the calibration is to make up for solenoid manufacturing differences and how much is related to the tolerances in the machining of pump internals. No matter; I’ll run the current 1688’d pump until it gives up the ghost either way. Many thanks for the input. 

[Max Tune]

Keep us posted on how it goes....

[Great work!]

You shouldn't do it but I have done it. The calibration is a lot of solenoid dead time versus battery voltage. Then there's default timing solenoid setting in case of loss of crank position sensor.

 

You'll need steady hands and you can leave it on the motor. Stagger cut the wires on the back so all your splices won't be in a big wad. It's  tight to use but splices .maybe solder and heat shrink if you can.

 

Be VERY careful when removing the top there is a thin ribbon cable in there that goes to the speed/position sensor. Rip it and you're screwed.  Tie the top up with string or tape so it doesn't get yanked.

 

Pack some wads of aluminum foil around the sensor so the screws won't drop into the pump. Don't use cloth keep things clean. You need a good quality torx # 9 (i think) bit and a magnet to un screw the sensor from its mount . You don't need to un solder the ribbon cable .

 

It may take a few runs for it to smooth out the pump seems to have an ability to learn things as it goes along.

 

Tag the wires on the back if the insulation is crumbling slide some heat shrink over them.

 

Do not attempt to remove solenoids while on the motor they will get broke. The pump needs pressurized with air to assist removing the injection solenoid.

 

Fortunately Cummins didn't  marry the VP and ECU together with the k- line like most of the European companies did so you can swap with junk yard parts.

 

Good luck this might help with the wiring. Don't forget and leave the aluminum foil in there.😫

 

Edited May 17, 2023 by Great work!
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