Back story, bought a truck from a buddy a couple months ago. Truck belonged to his dad and hasn’t been registered or really used much since around 2015 when his dad passed. Got the truck home and had the following issues
IAT sensor (replaces)
Cam shaft position sensor (replaced)
ECM voltage low
Oil pressure gauge reads way high even before the truck is started
It goes into high idle (1000 rpm) after approx 15 seconds sitting still. Parked or sitting at a red light. No cruise control either
Power seemed to be getting lower. To me it seems like a fuel issue, either something getting stuck in a tank or line collapsing. Hired mobile mechanic and requested he check fuel pressure and check codes with a cat computer. Used the generic software and said my ecm was bad and needed and new one and that it would cure all my issues. Refused to road test it and kept saying the ecm would even fix unusual noises I was hearing. Really wasn’t happy but he left after a substantial bill for 15 mins of work.
ECM was unable to be repaired so bought a rebuilt and reinstalled that. Long story short the ecm fixed non of the issues including the power loss.
All that was leading to this. Now it’ll pull hard but then falls on its face. Hard to describe but imagine on a lower scale hitting the nitrous switch and then the immediate loss of power when you let off the button. It does that and there’s no rhyme or reason as to when, where, why and how long it’ll pull good but it’s for very short spurts. Filters were changed and tanks are full of fresh fuel.
We’re getting ready for a 7k mile road trip and I have got to get this thing reliable and ready and I’m hitting a wall
C-12 intermittent power loss
Theres a few things it could be. Best bet would be to stop throwing parts at it and take it to a kitty dealer. Have then dyno, blowby and oil test it. Also have compression and fuel checked.
Top guesses from what you have said are
1. Fuel went bad from sitting so long and filters are clogging due to the scum and grime. Replace the filters and see if it helps even for a bit. If so drop the tanks and have them and the lines cleaned and replace the filters again.
2. You are loseing boost. Check your hoses and the rubber boots for holes to see if that may be an issue.
3. Bad fuel pressure regulator. This is a known issue and if it ####s the bed then it will have trouble maintaining the 90ish PSI it needs.
4. Bad fuel pump. Pump may not be able to keep up with demand. Also a known issue.
5. Remanned ECM may have wrong flash file. Have a dealer verify it has the correct program.
Beyond that you start getting into major repairs.
Brettlester Thanks this.
Fuel contaminates would be the easiest. However, it’s weird how it will run good for a sec and then loose it again. When I pulled the old filters off, they actually looked great. Had been running red diesel was a little harder to quickly identify bad stuff. I’ll get some and try that and get some treatment for algae too just in case.
Boots are all good, no boost leaks noted but the Freightliner salesman has 4 in his truck im going to swap out anyways.
Thank you for all the tips, I’m sure it’s one of those or any combination. Supposedly the engine is a fresh reman and according to the amount of paint and lack of leaks it seems accurate. The guy a bought it from is a good buddy and wouldn’t lie. Truck has been sitting in his pasture since his dad died just rotting away and knew I’d give it a good home. He wasn’t actively trying to sell it or push it at all. Actually told me about the motor being fresh a few weeks after I got it.
I'm in no way a trained diesel tech but in my experience high idling is due to some type of air/vacuum leak which can also be tied into power loss due to poor air/fuel mixture. Maybe try spraying ether around every intake/vacuum line while it's running and see if the RPMs change at all?