RB20DET won't rev over 5500 RPM, any ideas!

[underground]

Hey Guys,

I'm buying a 89 240SX with RB20DET swap from ProjectRB240SX on the boards 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, and after about 15 minutes after each ECU swap he's done, the computer trips and wont let the car go past 5500RPM.

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, Christian (ProjectRB240SX) is saying the RB20 doesn't have a boost sensor.

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

Any ideas.

Thanks!

[underground]

List of things checked/replaced: ECU (3 different ones)NEW ECTair control valveaac valveMAF (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

[BoostFab]

might be wiring problem?

[gani]

check your tps voltages i had to fix an sr20 with the same problem a while back

[Joe]

if its limiting RPM there is a code, the only other thing it could be is the igniter, but its been replaced already.

try to pull them, even if the light isnt on. some CEL's wont trip the light till they have happened multiple times but will still have the code stored in memory and can be pulled.

[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 this problem ever since.

[PROJECTRB240SX]

I've tried checking codes and I have been getting nothing... I'm going to try the method sean told chris to do in one minute and I'll let you know what I get.

I'm racking my mind and will be peeling apart the wiring job we did to see if there is any shorts.

Joe if you want to give me a hand and take alook... a set of project virgin eyes may be helpful. I'm going to be digging into this caruntil its fixed and any help possible would be much obliged!

[PROJECTRB240SX]

code 55 in both modes.... wiring to maf is good. No Loose connections, no slit wires grounding out.

I'M LOST!!!!

[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.

Any help from my wonderful NICO family is much appreciated.

[PROJECTRB240SX]

Ohh one more thing I noticed on my last run.... It backfires when it hits this limiter.

[PROJECTRB240SX]

I'm trying to get this car near perfect for chris upon pick up.... any help would be greatly appriciated! This is a mind bogling problem.

[underground]

Christian, I really do think it's overboosting. This would make sense as the hose off the FMIC blow off. In addition, you mentioned the wastegate was stuck open. All of these things make me think that the overboosting is causing your knock sensor to trigger the ECU.

While I don't know why the ECU is not reading, that may never be determined.

I figure that when it trips the ECU, the ECU pulls timing, and sets maximum RPM to the 5500 Range (Default perhaps)

This would also make sense of why when you are in neutral you can rev all the way to redline.

When the motor boosts over 5500 RPM, I figure it is also probably leaning out the injectors and probably causing detonation as well.

I dont know, but after reviewing your problems, this is what I am thinking.

We really need to find that boost gauge. Surely, somebody in AZ would be gracious enough to part with one for a price.

Chris

[underground]

Basically, the overboosting is causing havoc on the motor.

[Joe]

if the wastegate is stuck CLOSED it will overboost, stuck open will cause no boost because its bleeding all the boost off.

and HELL YES that can cause this problem, that is a serious issue. its probably not the knock sensor its the fact the MAF is maxing out and the ECU limits the RPM because it dosent know how much air is going into the engine. Krayton had a problem like this because his wastegate line was hooked up wrong. i also had this issue but with the R34 maf and mines ECU i never hit this odd limiter, just full boosted to 17psi.

you should have said something about the wastegate sooner, a wastegate not working is not something that should be written off.

[PROJECTRB240SX]

That was on the old turbo.....

We replaced the entire exhaust side of the engine. This is a different wastegate off of a properly Running engine.

[Joe]

so does it boost properly when it works?

[underground]

Yeah, he said the boost is coming on at the appropriate time, around 2800 RPM.

We are trying to find somebody that might lend us or sell us a boost gauge. This will sum up whether that is the issue or not.

Kamin, do you have a boost gauge we could use or buy?

[PROJECTRB240SX]

Joe could you meet up sometime early this week to just get another set of eyes to look at this car and give an opinion... Also I'd like you to drive it so you can experience the phenomenon yourself, Well that is if Chris says its alright.

[Joe]

Christian i would do it but my schedule all week looks like this, school from 6:30-1 work from 2-9. you can bring it by my work and ill take a look if you want to come out to ahwatukee.

i dont have a boost gauge you can borrow eithre, its not here in phoenix sorry.

[underground]

It's still your car big man, so you can do whatever you want until I sign that title, lol.