RPM issues, 87 4.0...no rev over 3400

[JeepcoMJ]

I've got a friend with a 1987 mj, 4.0 auto.

 

won't rev above 3400 rpm.

 

have swapped ECU, TCU, ALL engine sensors including TPS, IAC, IAT, ICM, and distributor.

 

the only thing I haven't done is swapped the CPS. haven't ohm'd it out or anything, either.

 

the odd thing is that the CPS appears higher on the bellhousing than typical. there are two different positions (approx. 1/2" difference) where it can mount on this bellhousing. this jeep originally came from colorado and so I'd assume that's a high altitude thing, but don't quote me on that.

 

 

anyways, I'm thinking I need to put the CPS in the lower of the two mounting positions, but wanted to get your guys opinions. and no, I don't have pics of the CPS locations...nor will I have any.

 

Thanks,

 

Pat

[Geonovast]

I would like to see this bellhousing...

 

But of there's nothing mechanically wrong with the motor.. I'd say that could definitely be it. I would think that if there was a valvetrain problem, the motor would complain quite a bit when you tried to rev it higher.

[Justin_k]

Could the cat be plugged off bad enough it won't allow that much rpm? Or do those old ones have a cat?

[JeepcoMJ]

no cat.

 

no funny noises from the motor.

[Eagle]

The high-altitude Renix models just used a different CPS -- it mounts in the same place. I'm running a high-altitude CPS in the '88 XJ. It allows more advance when the engine isn't under load, which in theory should help gas mileage.

[asm4mcc]

I HAD THE SAME PROBLEM IT WAS MY CPS ON THE BELL HOUSING

[kro10000]

Please turn off the Capps lock :thumbsup:

[Oizarod115]

have you gone through and checked all the engine ground straps?

[JeepcoMJ]

yep, they're brand new.