Any Diesel guys in the audience?

So here's the thing.

One of our trucks has a 2001 3126 CAT. It's got about 200k miles on it and normally runs like a champ. On days where it's 50* or warmer, while pulling a hard hill once the coolant temp gets up just a touch the throttle gets cut back and holds the rpms at 1500 and the "Check Engine" and "Engine Protect" lights come on the dash. I'm thinking this could this be a faulty EGT sensor? Sometimes the coolant temp doesn't even have to rise, it just does it after a bit of a hard pull. Thus, that makes me think it's a result of EGTs but I don't know if a 2001 3126 CAT has such a sensor. Any input?

What is the boost gauge reading when it looses power? If its still reading good boost I would look at the fuel filters for the chance of a quick/easy fix but Im guessing its not reading full boost. If the EGT valve is bad it would probably not spool up since I think it cuts fuel if it thinks the exhaust temp it to high. Thats just a guess. I really have no clue. I can ask my dad tomorrow.

The above is probably completely wrong. lol

D-Rod wrote:

What is the boost gauge reading when it looses power? If its still reading good boost I would look at the fuel filters for the chance of a quick/easy fix but Im guessing its not reading full boost. If the EGT valve is bad it would probably not spool up since I think it cuts fuel if it thinks the exhaust temp it to high. Thats just a guess. I really have no clue. I can ask my dad tomorrow.

The above is probably completely wrong. lol

Unfortunately, it doesn't have a boost gauge. lol The turbo sounds like it's spooling as it's should, the ecu just cuts the throttle back and even if you hold it at WOT, it sticks at 1500rpm. But the turbo sounds like it's spooling for whatever throttle input would be needed to hold it at 1500rpm.

I forgot to add that if you pull it over, shut it off and wait a little bit and fire it back up, it works fine until the next pull heats it back up.

I don't know much about diesels, but I know from experience on my supercharged car, if I get bad gas the same thing happens under boost, especially up hills. Also happens if the knock sensor goes faulty. I am not sure if its possible to get bad diesel, or even if they have knock sensors but I would assume its something in that area, possibly a faulty sensor, but something is setting it into limp mode. Just a thought from a different direction.

I don't think they have knock sensors sinse the purpose of them in a gas car is to pull timing when it gets knock. In a diesel you can't pull timing since there is no spark.

D-Rod wrote:

I don't think they have knock sensors sinse the purpose of them in a gas car is to pull timing when it gets knock. In a diesel you can't pull timing since there is no spark.

Exactly. That and (This is still a mystery), I'm pretty sure diesel engine can't have "pre-detonation" because there's no ignition to ignite before.

Thats what I figured since its compression ignition, but never knew for sure, but some sensor is definitely telling it to go to limp mode, whether something is really wrong or not. No clue what other sensors would be. Another thing that does it on mine is its boost level sensor, and I'm pretty sure you'd have one of them.

Tygur wrote:

Thats what I figured since its compression ignition, but never knew for sure, but some sensor is definitely telling it to go to limp mode, whether something is really wrong or not. No clue what other sensors would be. Another thing that does it on mine is its boost level sensor, and I'm pretty sure you'd have one of them.

I'll have to look into that. The engine doesn't feel sluggish and the turbo doesn't change pitch before it does it. It's just out of the blue cutting back on the throttle.

Is it a variable Turbo? If so....You might want to check the egr valve and the related components. The Ford 6.0L was bad about EGR problems. Just a thought.

dlinsbeck wrote:

Is it a variable Turbo? If so....You might want to check the egr valve and the related components. The Ford 6.0L was bad about EGR problems. Just a thought.

I don't think it is.

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