V8 Soarer (SC400) Won't rev past 3800RPM

[buttocks]

My new V8 SC400 (1991 model) has a small problem, it drives perfectly but it hits a rev cut at 3800rpm. Its an ECU type cut, and no metter what i'm doing full throttle or part throttle or even at idle it still does it.
I've posted this on australia toyota forum and they haven't come up with anything solid yet
You can read it for yourself for information
http://www.toymods.net/forums/showthread.php?t=10007

There has been alot of comments but nothing has worked so far, its goto be something simple as other than that the car is perfect.
Thanks Guys

 

[Lextreme II]

Can you tell us how does your car drive from idle to 3800 rpm? Is it sluggish and very slowly reaching 3800 rpm? Sounds like one of your ignitor is out. Its most likely the top one. You can unplug the spark wire and test the for spark on either #2,3,5 or 8 cylinder (Top ignitor) Spark plug # 1, 4, 6 and 7 would be the lower left ignitor. Once again, I would test the left banks because its the easiest to remove the plugs and wire. You should test # 4 and 6 which is the 2nd and third on the left bank. Please let us know if it would help. http://lextreme.com/forums/showthread.php?t=5886

 

[GSMnow]

Is your check engine light coming on at all? Does it have any error codes stored? I don't know about the Lexus 1UZ's, but I know several other cars go into a rev limit to protect the engine if it thinks something is wrong. If it sees no vehicle speed for example, it might think you are stalling the torque converter. If it sees the Park/Neutral switch it may think you are revving it with no load. If your SPD (vehicle speed signal) has noise on it, it may think you are at the 155 mph speed limiter. If there are no codes stored, it thinks it is doing the right thing for you. In that case, monitor th injector lines and IGT lines to see if it is cutting fuel and/or spark. If they are both there, and it still quits, then it could be faulty ignition failing to fire the cylinders. Good Luck

Gary M.

 

[buttocks]

See heres the problem. The car runs perfectly upto that point. No hesitation good power everything is fine, and now that you meantion it , it does feel like the speed limiter, but its at 4000rpm and in every gear, well about 3800rpm anyway

 

[Nick M]

Did you check the obvious? Make sure the throttle plate opens all the way and the cable is not binding?

 

[Zuffen]

Could it be the fuel pump stops when it switches to high speed?

If you have a faulty Fuel ECU it could do that.

 

[buttocks]

If it was as something like the throttle plate or a cable it wouldn't just stop reving at 3800rpm, its some kind of rev cut, its like instead of 7500rpm rev cit i have a 3800rpm rev cut

 

[Lextreme II]

Could it be the fuel pump stops when it switches to high speed?

If you have a faulty Fuel ECU it could do that.

Second stage fuel pump is a good lead.....

 

[buttocks]

And that could cause the rev limit to be at 3800rpm and not at 7500rpm?

 

[GSMnow]

YES, if the fuel pump is stopping at 3800 rpm instead of going to full power. It normally runs at about 9 volts, and should go to full battery voltage. I didn't even think of that one, but it sure makes sence.

Gary M.

 

[buttocks]

How do i check that?

 

[Zuffen]

You should be able to check its operation with a multimeter.

You can do it at the Fuel ECU (behind the right hand drive passengers seat) or at the fuel tank.

I don't have the wiring diagram in front of me but you should be able to check the voltage running to the pump in low speed, it should be around 9 volts, and it should shut down at some point. You can then check the high speed circuit, which should be battery voltage. This one should come on stream when the low speed circuit turns off. If it doesn't come on try and borrow a fule pump ecu to try in its place.

 

[cyberdiamond]

You can also test by jumping B+ and FP in the diagnostic conector with a paper clip or simular.

NOTES....
Use a THICK piece of wire if you don't use a paperclip as the fuel pump probably draws 7-10amps.
DO NOT LEAVE IT IN THERE PERMANENTLY!!!! for safety reasons (fuel pump will not cut off in the event of an accident)

Far easier and it will tell you if its the fuel pump ecu.

 

[buttocks]

So once i jump these 2 curcuits, what am i looking for?

 

[cyberdiamond]

So once i jump these 2 curcuits, what am i looking for?

Nothing if its revs over 4000 and works properly then its the Fuel Pump Ecu.
Just a quick way to rule it as the cause or not.
What it does is basically give the fuel pump a constant 12v

 

[Nick M]

If it was as something like the throttle plate or a cable it wouldn't just stop reving at 3800rpm, its some kind of rev cut, its like instead of 7500rpm rev cit i have a 3800rpm rev cut

For future refrence, it most certainly can. On a normal operating car, can you hold the RPM to 3800 and keep it there? Yes. So can a stuck cable.

edit:Toyota switches to B+ from 9V under high load.

 

[buttocks]

I jumped fp and B+ and it still has the problem

 

[Smitherz]

Dude, I would buy another ECU pronto! Don't waste your time. If that takes care of the problem you just saved yourself a ton of troubleshooting hassles. If it doesn't you can just turn around and sell it! You sound like you've spent a lot of time on this unique problem that could be solved by swapping out a $100 part. :rambo:

One time my friend that owns an automotive repair shop had a customers truck that just WOULD NOT operate correctly. The owner had taken it in to a few different shops before his. The truck was just a complete mystery and he tried everything including getting a loaner ECU from the stealership. Are you ready for the cause of all of this? Well I went to take a look at it for the shop owner (I studied electrical engineering in college and there was an aftermarket speaker (unshielded!) near the location of the ecu! I drop kicked that speaker right out the shop door and the truck ran just like it should from that moment on. For some reason the trucks ECU ran fine for a couple years before it was effected. They were pretty shocked. Work smarter not harder I say :22: Ground leads and magnets are huge weakpoints for electronics and are overlooked by almost everyone. Good luck.

 

[Nick M]

I say Ground leads and magnets are huge weakpoints for electronics and are overlooked by almost everyone. Good luck.

I say you are absolutely right about that.

 

[buttocks]

We unpluged the AFM (air flow meter) and it still ran the same and still had the problem