Weird rough idle

[hktpmd]

Hey guys I'm kinda new here. I been reading for months and now I have questions lol. So I got a couple 12v trucks which I love and now I bought a 24v. So far I like the truck but the electrical issues are driving me nuts. My truck still has the warranty installed in tank lift pump. I recently had the vp die so I put a good one on. Changed filter as well. Truck ran mint after. The next day i get this rough idle. So i check fuel pressure its around 13psi and never goes under 10. Scanned it and did the key trick. I have a 1693 with key trick and two 1688 with the scanner. EGT low and EGT high...there is no egt on this truck soo im confused there..  the truck runs mint just at idle it sounds like its got a cam in it lol. So i thought it was electrical problem. I did the WT ground wire mod and the blue wire fuse at the pcm. So I had the batteries disconnected for a bit doing that. I also installed a 150 amp breaker like mopar1973man suggests. Now after doing all this I started the truck and it was fine. Drove it for a day with no problems. Next day the rough idle came back. Also somehow it tripped the 150amp breaker 😬. What could cause that? I followed the instructions on WT ground wire mod simplified and never had any shorts or anything. If I go and unhook my batteries and then do a TPS reset the truck will be fine and runs and idles perfect for a day and then this comes back. Please help guys. I'm at a loss here. I love the truck but I'm starting to wish I stuck with a 12v. This trick is a work truck + my daily. I run my own excavation company and need this truck so quick reply are 100% appreciated.  Thanks guys 🍻

[Tractorman]

59 minutes ago, hktpmd said:

Also somehow it tripped the 150amp breaker 😬

 

You are not the only one to have this problem after installing a circuit breaker.  Likely that you have a weak 150 circuit breaker.  Prior to the W-T ground wiring mod, there was a 145 amp heavy duty fuse in the distribution center.  Try a better quality 150 amp circuit breaker or fuse.

 

I use a 150 amp fuse and I have never had a problem, but I also have a manual grid heater switch control, which means there is no post-cycling of the grid heaters - a lot less work for the alternator after the engine is running.

 

The 1688 code is more serious:

 

- John

 

 

[hktpmd]

Ya I got that on my scanner too. The weird thing is that if I reset my tps it runs fine. I'm going to go see a buddy later that has the pump jumper cable and see what happens. I was thinking maybe a bad alternator?? It's charging fine and everything tho. Also it don't matter if it's cold or hot. The engine when I first start it up and it's reving around 900 at idle doesn't act weird but as soon as the idle comes down a bit it starts rough idling again. Also if I put it in drive or reverse and hold the brake it doesn't act up. If I put it in drive and just let it move under its own power it rough idles but the second I either give it a little throttle or hold the brake it goes away...

[Tractorman]

When it begins to act up, turn off the engine and disconnect the alternator output cable.  Restart the truck to see if the problem is still there. 

 

You can perform an AC voltage test on the alternator output with everything connected and engine idling.  The test should be done after the grid heaters have finished post-cycling and there are no heavy electrical loads present.  The reading should be around .05 volts AC or less.

 

Double check your work regarding the W-T ground wiring mod.  Make sure all connection points are clean and tight.  Make sure you didn't miss a ground connection.  How is the condition of the cross-over cable?

 

- John

[hktpmd]

Cross over is in good shape. All battery terminals have been cleaned and gone thru. With no wires hooked up on alternator I get 0.002-0.004 sometimes gets up to 0.010 but usually it's sitting around 0.002- 0.004 on AC setting. If it's the injection pump I just want to know. I can replace the pump in an hour or so so not that big of a deal to me. I work on all my own equipment and trucks so hard work is nothing new to me. I just wish it would say to me hey fix this lol. What do u guys think about the in tank lift pump? What if I put another lift pump on the side of the engine where the original was with leaving the in tank one in?

Edited October 4, 2023 by hktpmd

[Tractorman]

11 minutes ago, hktpmd said:

With no wires hooked up on alternator I get 0.002-0.004 sometimes gets up to 0.010 but usually it's sitting around 0.002- 0.004 on AC setting.

 

All alternator wires need to be connected for the AC voltage test.  The test is not valid if the alternator is not working.

 

I suggested disconnecting the alternator output wire to check if your rough idle disappears - not to check for AC voltage.

 

15 minutes ago, hktpmd said:

What do u guys think about the in tank lift pump?

 

The factory installed in-tank lift pump is fine - I had one installed under warranty for over 150,000 miles.  It was still working fine when I replaced it with a frame-mounted lift pump for easier access.

 

If you end up replacing the VP44, be sure to purchase one that gets a new (not rebuilt) PSG and that the PSG is calibrated to the pump on Bosch 815 test stand.  Don't know the quality of your current VP44, but it may be sub-standard, especially considering the 1688 code set.  

 

25 minutes ago, hktpmd said:

What if I put another lift pump on the side of the engine where the original was with leaving the in tank one in?

 

I do not recommend two lift pumps in series.  It will work fine, but it complicates the system and there is no benefit.  Plus, it is another component that can fail.  I would either continue to use the in-tank lift pump or remove it and install a frame-mounted lift pump.  I think the frame-mounted lift pump is the best option because it becomes a pusher pump and its location is easy to service.

 

- John

[hktpmd]

10 hours ago, Tractorman said:

 

All alternator wires need to be connected for the AC voltage test.  The test is not valid if the alternator is not working.

 

I suggested disconnecting the alternator output wire to check if your rough idle disappears - not to check for AC voltage.

 

 

The factory installed in-tank lift pump is fine - I had one installed under warranty for over 150,000 miles.  It was still working fine when I replaced it with a frame-mounted lift pump for easier access.

 

If you end up replacing the VP44, be sure to purchase one that gets a new (not rebuilt) PSG and that the PSG is calibrated to the pump on Bosch 815 test stand.  Don't know the quality of your current VP44, but it may be sub-standard, especially considering the 1688 code set.  

 

 

I do not recommend two lift pumps in series.  It will work fine, but it complicates the system and there is no benefit.  Plus, it is another component that can fail.  I would either continue to use the in-tank lift pump or remove it and install a frame-mounted lift pump.  I think the frame-mounted lift pump is the best option because it becomes a pusher pump and its location is easy to service.

 

- John

 Thanks john.  So I got 0.115 with the truck running. Sorry I thought you meant without any wires hooked up. I didn't get to the hot wire test yet maybe tomorrow.  I got a lift pump and tps coming tomorrow as well. Hopefully it's fixed but I'm not counting on it lol