Starts, No tach, rpm maxed at 1000-1500 rpm

[Griffeod]

Help please! I’ve tried it all have no clue any more!

99 24 valve, starts fine, runs, rpm gauge not working, won’t go pass 1000-1500 rpm, guessing on that because no rpm.

things I’ve done 

no stock lift pump has air dog

new apps

new crankcase sensor

new cam sensor

new fuel filters

new(refurbish) ECM

what happened

Was driving and just wouldn’t go pass 1000 rpm, no tach, replace crankcase sensor, didn’t fix it, unplugged it, plugged it back in and it fixed it, worked for couple days, then same thing happened, went and got another sensor, replaced it, didn’t work, check the wires to the sensor to the ECM all good, and voltage was like 4.98. Then replaced ECM, first try started same problem turned it off, started it again worked great.. lasted two days, sent ECM back they tested sent it back I installed it, same problem, read only to use Cummins CKS, ordered it put it in same problem, on to apps installed new one, no change, today installed new Cam sensor, same results

only thing I did notice is the fuel pressure gauge which usually stays at 15 will now climb to 18-20 then drop back to 15 then climb again then drop... lost no idea anymore 

[dripley]

Scan it for trouble codes and see what comes up.

[Haggar]

You need to use a scan tool to help you.  No display of RPM could be 2 problems but you can't sort it out without seeing the live data from the ECM and PCM.   Same with the engine only going to a low RPM.  The map sensor may be lying to the computers.  Since it works sometimes when you wiggle wires and then quits, it is possible you are starting to have grounding issues for the sensors.   again that should show up in the live data because the signals from those sensors should be unrealistic.

 

GL

 

Hag

[Griffeod]

Checked all the grounds, going to check the ground wires to the ECU tonight, have a new Map sensor may install that, if I can figure out what size socket it is, much larger then the new one and not in an easy spot to put a wrench on it, guess I may have to buy a scan tool, I have a cheap pocket scan but it wouldn't link, Im really lost on this thing

[Mopar1973Man]

31 minutes ago, Griffeod said:

hecked all the grounds, going to check the ground wires to the ECU tonight,

 

ECM, PCM and VP44 are ground through the passenger side battery terminal. If you do the W-T ground wire mod then the ground will be on the gear case next to the VP44. 

 

32 minutes ago, Griffeod said:

Map sensor may install that, if I can figure out what size socket it is, much larger then the new one and not in an easy spot to put a wrench on it

MAP sensor has zero to do with idle state. 

 

Need error codes there could be a...

• AC noise issue from the alternator flooding the ground with noise. 
• Could be a damaged VP44 and/or ECM being the idle software is damaged in the ECM or the VP44 is not listening correctly.

 

 

[Griffeod]

How do I check for AC noise? Then I know I have a ground issue. Would a new alternator fix it, the truck was running  like a champ, can’t get codes it won’t link

[Griffeod]

Ok did the w-t mod, still not fixed, is there a way to test the ECM or vp44? I have a cheap code reader but it won’t link, or no comms, any thing helps thanks

[dripley]

You could go over to Blue Chip diesel and checkout his VP44 trouble shooting page.very good info on the VP there.

 

I see you have a refurbished ECM. Have you spoken to them about it? Is it still under warranty?

 

Reread your op and see you sent the ECM back in. Who did the rebuild?

Edited March 17, 2020 by dripley

[Griffeod]

Auto computer exchange, sending it back today to see if it’s the problem