RevZeroX

https://www.cherokeeforum.com/f2/tps-readings-27275/

00xj-classic

whats going on with the limited??? havent heard from you in a couple days, just wondering if you fixed the problem.. let us know, glen..

Zeustopher

Ok, I spent another few hours on the Cherokee yesterday. We were having a heck of a time getting all the injectors to stop leaking, etc. I finally got that all figured out and i am leak free! We replaced the IAC and the TPS and neither of those made a difference. Now the Cherokee is idling slightly high but I haven't tried to adjust that yet.

My problem is still there and I have no idea what else it could be. It still backfires at around 1750 RPM alot and then dies off at about 2250 RPM and runs like normal. It idles very steady. There is no exhaust leak in the manifold (There is a tiny one we discovered right before the catalytic convertor but we'll patch it.)

We have checked the Spark plugs - all fine, wires - all visually fine, Cap and Rotor - showing small signs of normal wear but still very nice (replaced not too long ago), Injectors - all clean and not leaking, Fuel Rail pressure - right up to speck, fuel filter - replaced, IAC- Replaced, TPS - replaced. I do not see any Vacuum hoses that are broken.

So I have no idea where to check next. Any suggestions? Thank you all for all the support and suggestions this far. I really don't know what I would have done without you guys!

Zeustopher

Anyone have any more suggestions for me to try tomorrow?

Zeustopher

No suggestions?

Jamie57

Although your wires may LOOK fine they could be damaged inside where you cannot see them. The only way to check them is with an ohm meter and a chart to tell you what the readings should be for the length of the wire you are testing. They are not really WIRES but a length of carbon rope. If you used real copper wire you would have noise like you wouldn't believe coming from every car radio from a block away.
Wires will "Work" if there is no load on them. as your RPM increases from idle they are experiencing an electrical load and will break down if they are damaged in any way. After you get to the higher RPM they are pulsing so fast that the back fire seems to disappear. It hasn't but is happening so fast you don't hear it.

Much easier (and cheaper)to buy a brand new set of wires.
Have you checked the spark plugs? What shape are they in?

The only thing after that would be the compression test everyone else told you to do.
This could tell us if you have a burnt valve which will also give you the same symptoms you are suffering.
Good luck. I hope it's just the wires.

Zeustopher

Ok, that is good to know about the wires. I'll look into getting some new ones. I checked the spark plugs and they look actually pretty good. They had very little carbon build up on them, all the gaps were correct, and there wasn't one spark plug that looked different from the rest.

The compression test is a difficult one for me. I've been trying to track down a compression tool. I think I've found someone who I can borrow theirs. Even at Autozone they were out of them and i couldn't even "rent" one from there. So I haven't forgotten about that compression test, it is just taking a while for me to get the gauge....

Thanks for the help. Just out of curiosity, what would be involved in changing a burnt valve?

Jamie57

It would require removal of the head from the block. It would also be wisest to get the head rebuilt than to just change out the valve. The compression test will also tell you if it's advisable to even change the head, because if the piston rings are shot all your going to do is driver compression gases into the oil pan..
I know this is starting to sound VERY expensive but there are ways around that.
This jeep community sounds like the best group I've been involved with. Well maybe except for the nostalgic drag racers I hang with.
I'm sure they would be happy to help you solve your problems with some enginuity and elbow grease.

Lets eliminate the simple stuff first and worry about bad case later.

Zeustopher

Yeah that does sound expensive... But I'll trust you to worry about the other simple small problems first and then I'll start worrying about the larger, more difficult things.

I have been very impressed with this forum/community as well. I couldn't believe how many posts i recieved after just the first hour! It was unreal to me!

Jamie57

Don't get spoiled! Sometimes it's not so fast. Must be a lot of bored guys like me on here today! LOL

Zeustopher

Alright I have been really swamped the last few days with school starting. I haven't checked the spark plug wires yet. I am planning on hopefully doing that tomorrow afternoon. i haven't done the compression test either but it will come shortly. I do have something interesting happening though now.

The fuel system is all cleaned out, now and I am having a much clearer feel for what it is doing. I'll explain:

Car is idling slightly high at right around 1000RPM (How to adjust?)
When gas is pressed it lags ever so slightly and sputters. At almost exactly 1750 rpm it backfires and sputters. Between 1250 rpm and 2250 I have a lack of power as well. When rpm reaches 2500 rpm I gain a ton of power and it runs as though there is nothing wrong. Also, I found out that if i am traveling at 2000 - 2250 rpm constant then the jeep seems to jerk a little bit or pulse... The rpm, at the exact same throttle position, wil go up and down between 2000 and 2500 rpm. I never noticed it doing this before so I don't know if that helps us to narrow down even farther what is going on or not.

Thanks for everyone's support right now. I wish I didn't have school so I could spend a few more long days on the jeep but it just isn't happening right now.