FRavencroft

Hello, I'm new to this site.....I dropped this problem in another Jeep forum and thought the more input the better off and sooner I can get the problem solved.....
I have a 1995 Cherokee Sport 4.0L AW4 auto trans 4wd......the other day while driving home I noticed my Jeep was having a hard time getting up to speed. This came out of nowhere. I thought it was a tranny issue but the more I played with it I realized that the engine won't rev smoothly past 2500 rpm and it won't rev past 3000 rpm, No engine lights are on and there is no indication of any problems at all except the fact it wont rev past 3k.
It revs smooth to 2500 then struggles to get to 3k......as suggested on the other site I replaced the TPS and fuel filter no change.....tomorrow I'm going to pull the fuel pump and check the screen on it.....until then are there any other things I need to be looking at as the possible culprit??????
I pulled the tranny fuse to check shifting manually and it seems to be shifting as it should but the symptoms are the same.
I can get it to rev in both park and neutral but not in gear. It seems to shift at random time with the auto fuse in as well and if I put the pedal to the floor and make the tranny kick down it hits the 3k rpm and thats it engine wont rev past and it feels like it has a rev limiter on it and I know it does not .
Anyone have some thoughts on this I'd appreciate it.

Thanks
Frank

no rdplz

What brand TPS did you get? Aftermarket ones that aren't MOPAR are known to have a high failure rate, even straight out of the box.

HudsonN

Could be a clogged cat.

freegdr

Even though no check engine lights on does not mean there not soft codes stored. Read codes clear memory remove neg battery cable for 1/2 hour reconnect and drive. Read codes again compare to first reading and search the common ones. If there are none at least ecm functions and sensors are most likely no a issue. Concentrate on fuel,air and mechanical issues.

Another possibility partialy plug cats are same as running amarathon with a potato in you mouth .

FRavencroft

Just got back from the muffler shop Cat is flowing freely. I reved the engine up in low gear on the way home it'll hit 3500 rpm and then just goes flat I also noticed it didn't idle right it was kinda rough.
it does act like it not getting enough fuel but I replaced the filter a couple days ago now Im going to pressure test the fuel system as it may be the pump.

belvedere

That's what I'd do: put a fuel pressure gauge on it, rev it up, and see what happens.

FRavencroft

Ok so I may have found the culprit.....although at an idle the fuel pressure is like 38 psi when I rev the engine the pressure spikes for a split second then drops back to 35-38 psi and the engine wont rev any higher than 3500 rpm even in park and neutral the engine just flatlines at 3500.....Im thinking at higher rpm the fuel pressure should be greater than the idle fuel pressure so if I'm wrong would someone please correct me and fill in the correct info the fuel pressure gauge should be reading at rev up.....
Thanks
Frank

HappyTrails

Fuel pressure if from an electric pump not dependent on engine rpm. Pressure is regulated at pump or injector rail to be the same under all demand. Low pressure under high demand (load, not just rpm) would indicate a possible pump/regulator problem.

Throttle position sensors are always suspect, so fall in love with yours and learn about it.

However, lets revisit the clogged cat possibility. Could be a clogged muffler instead. Happened to me on another car. Muffler internals fell apart and clogged the output. Limited the revs, just as you describe. The telltale sign was back spitting (not backfiring) up through the throttle. Suggestion would be to remove the rubber air intake from the throttle body and rev the engine and observe for any back spitting. You will know it when you see it. Try it under the highest load you can safely do. Like have someone in the car with it in gear and firmly on the brake with the wheels securely chocked. See if you can get above 3000 rpm and look for back spitting.

When I saw this, I shut it all down and took a hack saw and cut the exhaust pipe off ahead of the muffler. Tested again. Problem solved!!! But loud. Next stop was the muffler shop.

Let us know what you find.

FRavencroft

OMG!!!!!!! I can't believe what I found that was causing all my problems......seems so simple that I could almost kick my own butt!!!!!! so I went out to pressure test the fuel again and this time I operated the throttle from the engine compartment........engine hit the troubled rpm and as it did and rpm went flat I noticed the air intake tube (Rubber) was collapsing and there it was the problem.......Air filter was plugged so bad that it was suffocating wasn't a fuel issue it was an air issue. I pulled the filter and drove to the parts house with no problems whats so ever bought a new filter and fuel injection cleaner....BAM just like that.
My dad always said to look at the whole problem and work your way through from the easiest solution and work towards the harder ones.I was on the right track with the fuel but at the wrong end of the thinking process.
Lesson learned and thanks to everyone who had an idea of what to do to track the problem down, and I hope this part of the thread will some day help someone else.
Thanks again to everyone
Frank

FRavencroft

Had a brand new muffler put on last month and thanks,I found the problem and I'm ashamed to say I over looked the simplest aspect of the fuel delivery system.........engine won't run without air.
Frank

HappyTrails

Despite all the high tech stuff on our cars, it still requires a degree from Low Tech University to solve some of our problems! Whether it be a clogged muffler or a clogged air cleaner. Who wudda thunk?

FRavencroft

Amen!!!!! Simple cheap fix and I was looking in all the hard places.

FRavencroft

Another update, I put new air filter on my Cherokee it ran great the rest of that day.
The next day it went back to not reving, so I popped the hood and reved eng from there and it was doing the same thing new filter and all.
I'm not sure why but it seems that its drawing moisture into the air box and plugging the filter. I put a Cold air intake filter system on it problem solved.
Runs like a champ with no problems. Again not sure why the factory air box is sucking moisture but it is and that was what the problem turned out to be.
Thanks again for the replies.
Frank

M Alves

Hello. This is an old thread and most of you guys are probably dead. Just kidding -I hope.
I just had the exact same problem in my 2014 Jeep Cherokee. In my case I woke up to a dead
battery. I gave it jump and it started right away. When I put it in drive I notice the car felt heavy and had
no power. I reved it up and it did t go past 3k. AWD was also unvailable. After about 15 minutes
i finally turned it off and turned it back on and Yiola! All normal again.

Just an FYI

throwmat jr

i know this thread definitely has to be dead but my friend is having this exact same problem. I haven’t been able to see if any of these solutions work but it’s on a 93 grand Cherokee. He rod knocked his old enigne which wouldn’t rev past 3k he put another engine that he rebuilt and after getting it started it doesn’t wanna start. If nothing in this thread work I will send an update.