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RB20DET won't rev over 5500 RPM, any ideas

underground

By underground,
in Engines & Forced Induction

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underground Collaborator

underground

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Hey Guys,

I'm buying a 89 240SX with RB20DET swap for my little brother.

He currently is having problems with the rev limit.

The motor won't rev past 5500RPM.

He has installed three different RB20 ECU's. After about 15 minutes after each ECU swap he's done, the computer trips and wont let the car go past 5500RPM. But, it will rev fully for about 15 minutes after he swaps them.

I have been ragging my mind trying to think of what could be causing it.

I have had this problem on cars with bad boost sensors, where they are overboosting, and the ECU puts a clamp on RPM.

But, the guy I am buying the car from is saying the RB20DET doesn't have a boost sensor.

I have never swapped one and don't have any experience with that motor.

List of things checked/replaced:

ECU (3 different ones)

NEW ECT

air control valve

aac valve

MAF (3 Different ones)

CAS (2 different ones)

Compression tested (145-160 psi across the board)

scoped bottom end (no damage)

igniter chip (2 different ones)

tested all coil packs

Any ideas?

Chris

underground Collaborator

underground

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Heres when he started having problems:

"When I took it to emissions, it was sitting there about 15 minutes, when the water started boiling in the recovery bottle. I turned off the car and let it cool down.

Driving it home, the intercooler hose, hose between pipe and hot side of intercooler, blew apart."

He had somebody tow him home. He had it parked for 3 weeks. Installed the Hybrid FMIC and has had problems ever since.

underground Collaborator

underground

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  • Author
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He mentioned that when in neutral he can rev all the way to redline. It's only when he's underload, driving, that he has this problem.

I just can't figure out why its not sending a code to the ECU. It doesn't make any sense.

I'm wondering if it might have something to do with the wiring on sensors on the transmission.

blind_elk Grand Master

blind_elk

Posted
Posted
He mentioned that when in neutral he can rev all the way to redline. It's only when he's underload, driving, that he has this problem.  

That doesn't mean much - I once had a truly blocked fuel filter that would allow the engine to free-rev till the cows come home, yet it was virtually impossible to get the car to move from stationary.

Check the available fuel pressure when the problem is happening.

Revhead Grand Master

Revhead

Posted
Posted

What happens when it gets to 5500? Does it bounce hard off a limiter, does it gradually get slower as it approaches 5500, then just not go any harder? Can it go past 5500 using part throttle or going down a hill? All of these will help to narrow down where the problem lies.

I doubt the transmission or the wiring to/from it is the problem. Basically if you're getting a speed reading, your reverse lights work, and (if it's auto) the idle compensation works when you click it in/out of gear, then it's all working fine.

R31 POWER Mentor

R31 POWER

Posted
Posted

I think I know the prob.

Are you trying auto or manual ecu's?because someone I know had the same prob with his manual RB20det with a auto ecu,we put my manual one in and she rev'ed to redline. :)

  • 9 years later...

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