Engine/Transmission (1994 - 1998) Engine Miss

[Jfam]

I did research the FAQ’s and searched under engine miss…



I have a miss only at idle. Researching the forum, I found one source that said he used a heat gun to check temperature at the exhaust manifold to determine if there was a weak injector. At normal operating temperature I pointed the laser to a small flat spot on the manifold that is couple of inches from the block. The outdoor temperature was 25 F. The readings were as follows:

Cylinder 1: 145 degrees F, #2 175, #3 180, #4 200, #5 195, #6 170.

I tried a couple of other spots and the relative difference between #1 and the rest remained approximately the same.



Does this indicate a weak injector for #1? If not, what else could it be? I do not see how it could be a valve, though possibly an out of adjustment specs condition? That does not seem likely to me either. If it turns out to be an injector, I assume it would be wise to replace all. If that is so, what would the ballpark cost be?



Anthing else it could be? I replace both high pressure and low pressure pumps a couple of years ago.



Thanks…

 

[WDixon27]

i have not had to do this on my cummins but have on many other diesels to find the missing cylinder, while it is idling crack injector lines loose one at a time till you find the one that doesn't effect the idle quality, or doesn't effect it as much as the other 5, that may help narrow the search down to one cylinder

 

[hsmith]

Not unusual for the center cyl's to read a tad warmer due to the mass.

 

[bmoeller]

Temps seem 'bout normal. The way the air enters the intake valves, the back 3 tend to run hotter. That is why it is recommended to install the EGT probe in the rear side of the divider.

 

[Jfam]

Well I tried the simplest thing first... Good rule, but generally Murphy will get you and it will turn out to be the most difficult problem that is the cause. Anyway, I let some fuel out from the filter and it ran MUCH better... almost normal. So I changed the fuel filter and it runs 90%better. Water in Fuel indicator does not come on. Still a mystery as when cold at idle there is a minor miss.



Could be an air leak, but the symptoms and "cure" so far would indicate not so.