4.0 High RPM cutout

[87manche]

So, Now that I've got all the fluids and such changed today was the first time I pushed the truck hard. A WOT run through the gears wasn't as much fun as I thought. At about 3200 RPM it's like somebody just turned off the ignition. RPMs came back down below 3K and the truck runs fine. I've done most of the tune up stuff already.

Plugs, Wires, Cap, Rotor.

I need to do the fuel filter yet, I suppose it could be not enough flow, but it really seems like an ignition cutout.

I'm going to check all the sensor wires and such, make sure they've got good connections.

Could it be the coil failing at high RPMs?

[87manche]

SO, A few updates.

I replaced the fuel filter, it was rusty so it needed to go anyway. Problem is still there. I've narrowed down the circumstances.

Doesn't matter what gear, as long as it's WOT, accelerating and above 3500 RPM. This includes if I lightly pedal up above 3 grand and punch it to the floor. The cutout happes the instant the pedal is all the way down. I think it may be a TPS issue. It works fine a 7/8 pedal but not full pedal. I think for some reason the ECU is cutting the fuel. I'm going to track down all th sensors tomorrow night, and recalibrate the TPS. Hopefully that fixes it.

[Pete M]

The computer does different things at WOT, but only above 3k? Thats odd for sure.

Jeep on!

--Pete

[Bounty Hunter]

What's the Renix 4.0L rev limiter set at? Anybody know about the HO or the 2.5L MPFI limiter settings?

[DirtyComanche]

5200 for the renix, I think...

[Pete M]

I'd never thought about a Renix rev limiter, but I'm quite familiar with the limiter in my mom's PT cruiser and it cuts the power pretty abruptly. Feels like I pushed the clutch in and let off the gas, but I haven't yet. Angers me to no end too 'cause that turbo 2.4 really likes to sing and the limit is found before the tach even gets to the red.

Jeep on!

--Pete

[DirtyComanche]

Oh, wait, I "think" the rev limiter is 5200... I've hit 6grand because my trans has a few issues...

 

 

I've never actually just left it in first and kept on it until it hit the limiter. So, I dunno. I'm not very helpful as far as that goes.

[Bounty Hunter]

I've hit the limiter on my '95 2.5L a few times, but I'm never looking at the tach :shock:

[87manche]

I don't think it's the limiter. I left it in second and slowly eased the RPMs to about 4K. About half pedal. It got there just fine. as soon as I stabbed the pedal to the floor it bucked, let off the pedal to about 3/4 and it accelerated again to about 4500.

It's a very odd problem. I'm going to get out the service manual and start troubleshooting sensors and such, I really think it's a computer problem. It's like the fuel just got shut off.

[DirtyComanche]

Hmmm, TPS? Try cleaning it, if that helps, buy a new one.

[87manche]

TPS was the first thing I thought. Maybe the voltage at WOT flips it out. It does idel a bit lower than the 600 RPM mark, about 450. I'm going to get out the DVM and look into that.

The fun of owning a jeep :)

[Bounty Hunter]

Have you tested the TPS? It's pretty simple to do on the truck.

[87manche]

No, I haven't yet. I'm going to do that tonight. I'm going to test and possibly recalibrate it. Maybe I can get my idle to where it needs to be.

[87manche]

So I tested and adjusted the TPS sensor. It was a little off. Read about .95V at idle, I adjusted it to .83. Manual says .85 is where I want to be. Problem is still there. I was putting together theories of why the ECu wold be cutting fuel. Reading in the Renix EFI manual it says that during startup if the pedal is pushed all the way in then it figures a flood condition and will cut all injector cicuits. So I'm going to see if the ECu isn't reading sensors properly and thinks that it's still in start mode. I don't see how, but I suppose it's possible.