Engine/Transmission (1998.5 - 2002) Rough running under load

[Gotdsil]

Here's the issue. I've had an intermittent, now constant issue under load. It may be a "miss", feels like you're driving on washboards when it happens. It's noticeable under load 3&4 gear uphill pulls, anytime with trailer. Runs fine at idle and cruise.
Here's my rig: '99 2500 w/205k. Free flow intake and exhaust, rv injectors, Tst 10 level box with remote and system on/off switch. Remanufactured vp44, other mods to drivetrain.
Here's what I've done so far: no thrown codes and nothing a basic scanner picks up, had a loose ground/negative wire. Fixed, problems went away. Now it's back and worse. Checked wires and all "splices/taps" for fueling box. Cleaned and reconnected, no change. Replaced MAP, no change (had spares).
Have gauges in cab for ex temp, fuel press, and boost press and all in range of normal. Problem is very bad with fueling box on, very slight with off.
Any thoughts?

 

[klcammie]

when "miss" happens what does the tach do? remain steady? jump around? Stop working all together? On my 01 had similar issue, long story short can position sensor was going south. Changed and no more issue. also check connections for map and oil pressure they can cause the same issue.

 

[Road Dog]

I call that a shudder and I get it occasionally with a camper in the back. I think it's in my [automatic] transmission or maybe the carrier bearing on the driveshaft (2 piece on a 3500).

 

[B.G. Smith]

Here's the issue. I've had an intermittent, now constant issue under load. It may be a "miss", feels like you're driving on washboards when it happens. It's noticeable under load 3&4 gear uphill pulls, anytime with trailer. Runs fine at idle and cruise.
Here's my rig: '99 2500 w/205k. Free flow intake and exhaust, rv injectors, Tst 10 level box with remote and system on/off switch. Remanufactured vp44, other mods to drivetrain.
Here's what I've done so far: no thrown codes and nothing a basic scanner picks up, had a loose ground/negative wire. Fixed, problems went away. Now it's back and worse. Checked wires and all "splices/taps" for fueling box. Cleaned and reconnected, no change. Replaced MAP, no change (had spares).
Have gauges in cab for ex temp, fuel press, and boost press and all in range of normal. Problem is very bad with fueling box on, very slight with off.
Any thoughts?

If you have auto trans it is trying to tell you that the converter clutch can't handle the power that is being produced. Had that with a 99 I had. Worked ok stock as long as you keep the rpm's above 17 or 18 hundred. With a small fueling box it could be reproduced at will. bg

 

[Gotdsil]

Thanks for the input. Here's an update. Drove across CA, west to east, and problem was present as the "miss" under load, not noticeable at cruise (5th gear, manual), but maybe present. After my visit, I checked connections again where fueling box is spliced, cleaned IAT, and then adjusted APPS to label (it was off a couple volts). APPS volt curve seemed to be ok with truck off and parked. Drove home, and problem was manifest as "dead pedal". While you accelerated up through the gears, you would get virtually no power or acceleration for a moment when depressing the pedal, and then the power would come on strong. Happened with TST box on and off. Occasional miss. Thanks to Blue Chip's great page on VP44 issues! Next is to wire in a voltmeter to the APPS and watch voltage while driving.

 

[KATOOM]

You need to check the AC noise coming from the alternator too. Its not uncommon for the alternator to produce too much AC noise which will cause the torque converter to unlock and re-lock rapidly and cause a shudder. An clean alternator is best but some people will also install a filter.

 

[mfurrh55]

You need to check the AC noise coming from the alternator too. Its not uncommon for the alternator to produce too much AC noise which will cause the torque converter to unlock and re-lock rapidly and cause a shudder. An clean alternator is best but some people will also install a filter.

I think he has a manual transmission, he said fifth gear manual

 

[KATOOM]

Didnt catch that. Thanks.

 

[JR]

Are you using scotch locks? Those things are the biggest POS's, sometimes they can lose connection even though they look like they have a good bite. I'd switch to either a positap or solder them together.

I'd completely disconnect the box though while you are troubleshooting

 

[KATOOM]

Are you using scotch locks? Those things are the biggest POS's, sometimes they can lose connection even though they look like they have a good bite. I'd switch to either a positap or solder them together.

I'd completely disconnect the box though while you are troubleshooting

Great advice right there. ALWAYS disconnect any electronic devices on the engine when diagnosing running problems to assure they're not the culprit.