92 with a low power/idle issue

[Develdog1106]

I have a 92/auto that runs perfect when cold. Once the truck gets to operating temp, the idle drops way down when stopped and in gear- it feels like the torque converter is trying to lock up (I know that's not what the problem is, just what it feels like). When I take off from a stop, it feels like the truck is dragging a battleship anchor for a couple seconds, belching a lot of black smoke, and then takes off like a scalded cat. When stopped and I put it in neutral, it idles perfect. There are several threads with similar, but not identical, problems; this is what I've done so far:



-Transmission filter and flush (done every year with full synthetic)

-TPS checked, good

-Computer swapped with a known good spare one I have

-External 12v applied to KSB (and tried removing the wire also)

-Lift pump replaced (from Cummins)

-Injectors bled (twice)



Everything I've done so far has made absolutely no difference. I did stop by a local diesel performance shop and explained the problem to him. He had a quick look at the truck and assured me it wasn't a pump problem.



Just got the truck back from the local Cummins Dealer, who put two hours of diagnostics ($220) in it and found nothing wrong. I declined their request for two more hours. They checked air filter restriction, leaks, air in the system, fuel contamination, transfer pump, and overflow valve. All checked good. Their next step was to adjust valves and pump timing.



Anyone have a direction to send me? I would seriously appreciate any help- this is getting extremely frustrating!

 

[Fordiesel69]

Sounds like a boost problem. Some part is heating up, expanding and then leaking. It truly *could* be a pump issue, but the back smoke and no power sounds like a turbo boot issue.



Why not check you valves just for the heck of it.

 

[cerberusiam]

Pump timing. When it gets warm the timing backs off, cold it advances.



Also adjust the idle and smoke screw and see if that will effect it.



Another possibility is a problem in the pump itself once it gets warm.





That enough to keep you busy for a while?

 

[Develdog1106]

I'm going to dive in, do what you guys suggest. I'll let you know what happens. Thanks for the help!

 

[dpuckett]

I was also thinking timing and idle speed; cerberusiam explained it.



It cant be determined to NOT be a pump problem without running the pump on a stand. Period. I hate it when people say "Oh, with only XXX mi on the engine, it cant be a pump issue. " BS. I have heard of pumps going south in 30k; others going 500K+ with no issues. It's all in the fuel put through them and hwo they are used. If they have adequate supply volume and pressure, the harder-worked rigs actually run better than the cream puffs.



Your injectors are probably due for a refresh.



TPS and computer wont affect engine running. TPS is for OD only; computer controls the KSB.



Do you have any leaks you can see on the pump or in the fuel lines going to and from the pump?



I'd still check out the timing and idle speed. Any decent diesel shop will have a photo tach to check idle speed. Timing is a little more involved, but the easy way is to advance the pump about 1/16" on the gear housing and see if that makes any difference. Info on timing advance is easy to find with a search.



Daniel