RB20DET won't rev over 5500 RPM, any ideas

[underground]

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

[boj01]

Coil packs or AFM??? Also sounds like it is hitting the factory boost limit/cut. How much boost is it running and is it running an Electronic Boost Controller??

[meggala]

have you checked the cooler for leaks?

also your waste gate actuator could be faulty

[blind_elk]

Crook fuel pump? Gets hot after 15 minutes and won't pump properly. Causing detonation by leaning off mixtures.

[underground]

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]

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]

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]

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]

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.

[underground]

Anybody got a manual RB20DET ECU? How would we know if it was a manual or auto ECU? We bought a motorset...

[R31 POWER]

I don't know if it helps but my ecu has a silver with blue tag

22

23710 04U01

MEC-R126 1 0315

[BlueRB240]

I Have a auto ecu in my car and it's a 5 speed. it revs all the way out without any problem.

[Leeroy94]

I have this problem. I want to fix this problem!

Has this since been resolved??

Any ideas?

[GTSBoy]

10 to 1 odds says that the original problem here was faulty knock sensors or a faulty AFM. But good work for necro-ing a thread from 2004!

[Leeroy94]

I really need to find someone in the Gold Coast area that has extended knowledge of the rb20det engine because I think mine has been played around with and it's just not performing.