Our 98 Freightliner with a N14 Cummins came in with unable to get over 1500 rpm periodically. Did some testing and found if I am below 1500 rpm and keep on throttle it drives normal but if you are above 1500 and completely let off throttle then get back on before it falls a little below 1500 there is nothing there and the engine will drop to around 1500 even with your foot flat on the wood. No codes coming up. Was serviced recently with all filters and replaced a leaking fuel shut off solenoid but the whole foot feed deal doesn't directly point to any of that??? I may go through and just play with all the connectors and clean them up first.
I had an N14 in my 98 Western Star and something like that happened to me. Sounds like it has gone into "limp mode" I found that the water was low in the overflow tank. Topped it off and it never happened again. Sounds like a sensor somewhere is causing it. Mine was a low water sensor, check them all. And mine never threw a code either. George
All fluid levels are good. Coolants was a touch low but half gallon but that wasn't it. No codes on the screen or if I flip the diagnostic switch to count check engine flashes. Some readying often points to the Engine Position Sensor as causing limp mode but without a code sometimes. For $38 I have one on the way, will update.
The engine position sensor fixed it.
Well, I spoke too soon. The ran it a couple days then it started doing it again. I disconnected the battery again and drove it today and ran good for 15 miles then started doing it again so I suspect it was when I disconnected battery to work on it originally that reset something and the sensor wasn't the true fix. Still no code on the diagnostic screen or when you flip the switch to count flashes of the check engine light. I ordered a scan tool to see if there are other codes possibly that the user self diagnostic isn't showing for some reason.
This has a low probability of being your problem but I had a neighbor with an N14 that was having similar issues as yours. If I remember correctly it ended up being a speed sensor on the transmission that had gone bad. I remember it took awhile to find it's inconsistent behavior. Justm my $.02
There is a good chance of that. When researching online I see that the engine position sensor and the VSS are both common culprits. The vss is because guys would unplug it to fool the speed governor so they made it if that happens it puts in limp mode. Speedomter still works but not sure if that would be any indication. Might be worth throwing one at it unless it is astronomical $$.
I remember his speedometer still worked. I believe there are two separate sensors on the trans. I don't remember him complaining about the cost so it must not have been that bad at that time which was 3-4 years ago.
Good to know, I'll look into it more. Thank you.
Can you find out what fixed it?