Engine/Transmission (1998.5 - 2002) Low speed engine miss

[Jetflyer]

Okay guys, my truck is having a low speed engine miss at 800-1000 rpm, and past that it clears right up. When driving down the road it does the same, los speed miss and more throttle it clears up and runs great. The shop has currently diagnosed this to the #6 cylinder as they swapped the #6 injector with the #1 injector and the problem remained at the #6 cylinder. All filters were replaced, fuel pressure is good as well. The injectors are good (tested). The VP44 was replaced 12 months ago. I'm out of ideas. Thanks.

 

[JLandry]

Did the shop do a compression test?



John L.

 

[cerberusiam]

Number six cyliner is the usual problem if it scuffed one. Run a compression and leak down test to see if that will show any differences.



Could still be a pump problem but check cylinder first.

 

[Jetflyer]

Ok they did do a compression check and they're all good so I called Blue Chip Diesel and am going to send it in to them as he said it could be a fuel delivery valve inside the pump. It just seems odd that it has this miss at low rpm and engine speed but you can drive out of it, and with more throttle pressure the truck runs great. Thanks for the help.

 

[cerberusiam]

Low fuel delivery pressure to the injectors will cause a rolling miss at an idle. Almost impossible to track down and find on the truck, totally impossbile to find on a test bench.



A lot of times these miss fires are also accompanied by more than usual hazing of the exhaust at an idle. The bigger the injector the worse the hazing and the more critical delivery pressure is.

 

[Jetflyer]

Well the exhaust is clean at idle, just a puff a start up and idles smooth, and like I said when you put a little throttle throttle pressure into it that's when it starts missing and when you put more throttle pressure it clears right up and runs great, just when off the throttle and light pressure does it do this. Just to be clear, fuel pressure is 15psi idle, injectors just reworked from F1 diesel, compression good, and still scratching my head. Thanks again for the replys.