Engine/Transmission (1998.5 - 2002) 98 1/2 Misfire at idle only when at operating temp.

[JLandry]

The only thing that I question with the injectors is: Why if i bring up the rpms by as little as 50 rpms does he miss go away?

That's a good question and I don't have an exact explanation, only guesses. For starters, if the pop (opening) pressure of a particular injector has changed in relation to the other injectors, that would mean it would start spraying fuel earlier or later. This could be felt as a miss at a low rpm and could be masked as the rpm increased. Another idea is possibly you could have an injector which didn't close off the injection pulse cleanly, so it could leak or dribble. Essentially any difference between individual injector opening and closing pressures, or their spray patterns, will be felt as increasingly rough running engine the lower the rpms.



Again, using a DRBIII or Cummins Insite software to selectively kill individual injectors helps troubleshoot this sort of thing. Also, pulling out the individual injectors and testing them for pop pressure and spray pattern could be revealing. If the injectors checked out OK, then I'd start suspecting the VP44next.



Regards,



John L.

 

[EthanWhite]

Alright! Thanks for the info. I might be headed to the dealer (damn) soon. I wish I had a Dodge DRBII

 

[JLandry]

Alright! Thanks for the info. I might be headed to the dealer (damn) soon. I wish I had a Dodge DRBII

One thing to consider...



You'll probably pay a minimum of $100 for a dealer to troubleshoot this problem (probably more). Any parts or repairs will still be on top of that.



A set of new Bosch RV275 injectors is only $360 on Amazon and you can easily install them yourself in a lazy afternoon. By installing them, you'd absolutely eliminate the injectors as the source of the problem, and you'd get slightly better performance and fuel economy to boot. If turns out there was nothing wrong with your stock injectors, you can sell them on eBay for $50-60 to recoup some of your costs and still have the nice new RV275 injectors in your truck.



I'd be very tempted to skip the dealer for now and just replace the injectors.



Best regards,



John L.

 

[EthanWhite]

To follow up, year ago when I was having this problem, I replaced the injectors with NEW bosch 300HP Marine injectors for the 5.9 ISB used in marine applications. I actually found the best price on amazon through thedieselstore.com. But then again, that was 5 years ago. I paid 300.00 US for six brand new injectors.

After their replacement, the truck ran (and still does) run perfectly smoothly.

I thought I would follow up,..... 5 years later.