Limp mode. Can't get above 4,000 RPM

[richord]

I don't know how long the car has been in Limp mode since I've been driving locally at less that 60 MPH. I tried to rev it above 4,000 RPM yesterday and it stops at exactly 4,000.

1. No error codes.
2. No warning lights.
3. I did a lot of work on the engine cooling system, new radiator, cooling hoses, thermostat, both belts, the rear cross over pipe (without removing the supercharger.

Truck runs fine except the 4,000 RPM limitation.

Any suggestions on where to begin to trouble shoot. I have the GAP IID tool and the Icarsoft tool. Any suggestions of what parameters to look at since there are no error codes.

 

[itsaguything]

Odd. Limp mode is a response from the ecm, as a result of a code.

Unless, something is supposed to be reporting and its not. Of course I would expect a code in that situation too.

 

[Nechaken]

That's weird behavior. Does it do this in Park/Neutral as well as when driving ?

If you have the GAP tool, perhaps try logging pedal position % vs. throttle opening ?

 

[itsaguything]

Now that I think about it , you may be right. Doesn’t limp mode restrict the engine to 3000 rpm??

 

[powershift]

Are you in park during this time? Is there reduced power too? I've noticed that on mine it wont rev past 4K for some reason, but in gear no problems past 4K.

 

[richord]

Are you in park during this time? Is there reduced power too? I've noticed that on mine it wont rev past 4K for some reason, but in gear no problems past 4K.

Thanks for mentioning this! I drove the vehicle today and sure enough it will drive above 4,000 RPM but it is rev limited at 4,000 in park or neutral.

I could have wasted a lot of time chasing down a problem that didn't exist.

I was testing the vehicle for coolant leaks and rev'd the engine up, that's when I "discovered" this anomaly.

For those interested I then went to ChatGPT to get advice. It was adamant there was a problem! Last night I checked Gemini and DeepSeek and they at least warned me that there was potentially a rev limiter. I know not to use AI for health advice, investment advice and now I can add car repair advice to my warning list

Thanks for the input folks!

 

[itsaguything]

Think of AI as a friend. Sometimes friends need correcting. The AI response is only as good as its knowledge base .
As for revving an engine, without load past 4000 rpm, that can’t be healthy for an engine.

 

[greiswig]

You know, people should use AI to ask it how best to use AI and what the limitations are. It is sometimes pretty spot on in this area.

I have seen more people trust outputs of a LLM without knowing what the heck it’s doing behind the scenes and how a probabilistic word generation engine derives answers… it’s like giving someone a plane with autopilot and expecting them to be able to fly it.

Glad your problem is solved, though.

 

[richord]

You know, people should use AI to ask it how best to use AI and what the limitations are. It is sometimes pretty spot on in this area.

I have seen more people trust outputs of a LLM without knowing what the heck it’s doing behind the scenes and how a probabilistic word generation engine derives answers… it’s like giving someone a plane with autopilot and expecting them to be able to fly it.

Glad your problem is solved, though.

I agree with your advice regarding LLM’s. I work in IT and began using neural networks in the early 90’s. I experienced their limitations early.

I am also a helicopter and fixed wing pilot and although I use autopilot, every 2nd or 3rd flight I hand fly the plane because there were occasions where the technology screwed up. The one occasion where that habit was a life saver is when my engine failed due to a loss of oil pressure. Hand flying the plane to an “off airport landing”. Plane was destroyed but I was unharmed.

At least with a Land Rover I can leave it at the side of the road

 

[powershift]

Yeah, generative AI is terrible. For the 4k RPM limiter, I've never had that on any of my cars/trucks, but I suspect Land Rover deemed it abusive to sit there and rev the engine. I like doing it, but with the side window down I can hear a lot more engine noise above 4K RPM while in gear.