Cm870 running on back 3 cylinders

[BrianL]

Hello, I need help on where to start. My 2003 Isx only running on the back 3 cylinders.
Here’s what I have done. Swapped the timing and fueling actuators front to back with no change, still runs on the back cylinders. Next I got the injector leak tester and found the #1 injector to produce bubbles on the compression stroke so I replaced the injector, still no change, it only runs on back 3. Next I sent the ECM to {aftergarbage ecm repair shop} for testing and they determined it was bad and not repairable so they sent me a remanufactured one for $1300 and guess what, the truck still only runs on the back 3! Any ideas where to start next?

[hhow55]

https://rawze.com/forums/showthread.php?tid=591

[Pd6cas2]

How old is Your main engine harness! After yrs of service, there’s wire gremlins.

[Rawze]

You know this thread crossed my mind today, ...

I remembered one time about another CM870 that went to Mr.Hags shop, that would not run for s#it on the front bank.. especially cylinder #1 and #2.

I went over there to help find the issue and we ended up pulling the intake manifold, ECM and cooling plate, etc. off the intake side of the head.

We found the intake of the head behind the ecm cooing plate was so totally packed up with carbon and soot, that it was causing cylinders one and 2 not to be getting any air much at all into their intake valves. #3 did not look much better.


Just a thought. Seen a CM871 like that once too.

[Andre_The_Giant]

What did u guys do with the carbon? Pick/ scrap &vac it out? Or take head off

[Rawze]

(06-26-2023 )Andre_The_Giant Wrote:  What did u guys do with the carbon? Pick/ scrap &vac it out? Or take head off

in the case for the carbon packed intake,
we ended up inframing it + putting a new head on it because once we cleaned out all the carbon and soot buildup, we found that intake valves were also not sealing any more and the engine was loosing compression real bad.