Engine Misfire at Operating Temp

[Crossthreaded Nut]

Hi, my name is James and I'm new to this forum.

I've got a problem with my engine that maybe you guys can diagnose.

I bought the truck a few months ago and it had a distinct mis most all the way through the RPM range. I've had good luck working on my 94 PSD so I thought I could track down the problem quickly. So much for that.

I figured it was injectors so I saved my pennies and had them rebuilt into baby swamps. This made a significant difference as all needed new barrels and plungers. After this modification, I no longer hear or feel the mis over 2200 RPM's. Since the problem didn't completely go away, I changed IPR external o-rings. This also made a fairly large improvement but it still runs rough after the engine oil temp gets over 190f.

The scanner shows that injection oil pressure is between 500 psi at idle to 2,470 psi at WOT. It's my understanding that these are acceptable numbers. The buzz test passes all cylinders. The cylinder contribution test consistently faults cylinders 2 and 3. Fuel pressure at idle is 67 psi.

What would you look at, replace, modify, monitor next? I'm not giving up, but I don't know what to do now.

Thanks for any information,

James

 

[94f450sd]

this is what you could do.swap those 2 injectors with 2 other injectors and see if the faults follow them.when you swapped the injectors you did make sure you sucked the oil and fuel from the cylinders before installing them,right?made sure you could turn the engine over with a breaker bar or by hand twice before you tryed to start it right?if not then you may have abent rod/s

 

[94f450sd]

also how long have youdriven it after the injectors were installed?you couldstill have some air in the HPO system and fuel system

 

[Crossthreaded Nut]

Thanks 94!

Great suggestion! I'll swap injector holes to see if the faults follow the injectors next weekend.

Yes, I did suck out the fuel and oil before installing the new injectors to avoid hydrolock. Now, having said that, apparently someone has previously been in the engine to replace injector o-rings. I guess it's possible that they could have damaged a rod. Are we talking push rod or connecting rod?

Thanks,
James

 

[94f450sd]

i almost forgot,welcome to the site

yes i am talkin about a con rod.if somebody has been in there then it is not entirely impossible for you to have a bent rod.but if the faultsfollow the injectors then you have an issue with those 2 injectors.

 

[MUDWHISTLE]

I have a similar problem, How would a person go about find out if they have a bent rod?

 

[DaveBen]

Measure the piston height at the top of the piston stroke and compare it to the others. They should be very close in final height.

Dave

 

[95_stroker]

Hmmmmm, how long could an engine run efficiently with a bent rod?

 

[94f450sd]

it depends on how bent the rod is.they can run OK for a day,weeks,months or years if you dont hammer it like i do

 

[MUDWHISTLE]

I have had this problem for two years (it did this when I bought it) and has not caused me a problem other then the way it runs, My next question is would it only run like this when it is warm or wouldn't it do it cold too? Mine runs perfectly smooth when it is cold. and it will not act like this till the throttle pot sensor is at a certain position. As for measuring piston height would that be done by removing the injectors and measuring that way?