will not rev over ~1500 rpm

I have a 88 Cherokee with a 4.0 in it. It is new to me and is a project. The first project is to get it to run. I have put in new plugs. The old plugs where carbon black. I have changed out the fuel filter and air filter.

The problem is once it starts it will not rev past 1500rpms. Idle is rough as well. Please give a list of issues that could cause it and any way to test them. I have a multimeter and know how to use it!

Thanks in advance for all your help. I will do my best to answer all questions to help diagose this.

Do a search on distributor indexing. That is most likely your problem.

Won't rev over 1500?? I had a co-worker with a CJ that did the same thing....turned out to be a plugged cat. Certainly worth a try!

carboned plugs and won't run above 1500 RPM--

rich mixture or insufficient ignition would be most likely causes. In no particular order, I would check:
--coolant temp sensor (may think it's always real cold)
--air charge temp sensor (again too cold?)
--internally leaking injectors (dumping gas into cyl)
--crushed/collapsed fuel return line (will increase fuel pressure)
--O2 sensor (can be reading leaner and thus telling ECU to richen mixture)
--CCV system blocked off (allowing internal engine pressure to pollute intake
charge out of useable range-- below 12.5:1)
--distributor timing/indexing (spark at the wrong time)
--distributor cap, rotor, and wires (high resistance = low spark voltage)
--plugged exhaust (wouldn't account for high carbon, but would limit RPM)

run a search on each and determin where to start and post any questions you've got-- hope this helps!

--Shorty

I didn't see anyone mention a crankshaft position sensor (CPS) either. My 90 wouldn't go above about 1300 when mine went bad.

I did the TPS and new cap rotor plugs. No difference. I think I may have to try the CPS next. Does anyone know the resistances off hand for the coolant temp sensor?

Could the ingnition get off that far without being taken apart?

my experience with the cps is if you are in gear pull to a stop and you stall or stumble the cps is dieing.

experience with cats are they love to be petted. but seriously just pull the cat and muffler off and if its revs higher then 1500 problem solved. mine limited me from going over 50mph. didnt know the 4.0 had so much power until i cut a slit infront of the cat and sounded like i had s turbo and point of least resistance was the slit.

ive never had problems with coolant sensors and im about to have a problem with my oxygen sensor bexause im running rich but im spending any money on this engine anymore.

Also the renix owners best friend is a chiltons and a multimeter. damn great system but one thing dies ive been under the hood for a couple hours testing things.

I picked up the Haynes. First one I could find, it isn't very helpfull. The exhaust is well open before the cat. The manifold to downtube is on my list.

When I say that it doesn't rev over 1500, it won't stay at 1500. It goes between 1000 and 1500 on a fairly regular cycle with mild backfiring.

Fuel injectors are currently out. They are getting an ultra sound bath in the morning.

Really sounds like a timing issue to me. (CPS etc)

If you had the timing chain off you could have it out timing one tooth. I did that on a yota one time.

EGR valve?