Tired, broke, fed up, and ready to drive it into a tree

A while back I posted here about error code 24.
http://www.naxja.org/forum/showthread.php?t=18362
1996 XJ, 4.0L, AW4, 160K miles. My check engine light is on and the jeep doesn't have any power when you drive it past 2K RPM. Starts, idles, revs fine. When under load though it has NO power.

-I pulled the codes, got code 24 - TPS and MAP voltages don't match.

-Replaced TPS - $30 with no effect

-Replaced MAP sensor - $90 with no effect

-Brought it to a local shop - they scrached their heads and said they don't know where to start.

-Bought a handheld code reader - $155 which didn't help any more than my volt meter

-Finally broke down and took it to jeep thinking "yeah, they're the pro's... they'll know what's wrong with it". It sat there for a week and a half. Finally they said it needs a cat. converter. I said "are you sure??" They said they were. I told them to make SURE and cut the cat off and drive it. They wouldn't do it -- said they were SURE. $585 for a cat - installed. I said no thanks - I'll get my own. They still charged me $80 to look at it.

-Bought and installed a new cat - $170 with no effect. The rattle they heard were just pebbles trapped under the head shield. My cat wasn't clogged at all! While I had the old cat out, and I was swapping the O2 sensor to the new one, I decided to test it. It tested bad. Of course the dealership didn't mention this...

-Bought and installed new O2 sensor (at the cat) $70 with no effect. Tested the front sensor, tested fine.

Check engine light is still on, I still have no power. Local shops are clueless and even the f|_|cking DEALER couldn't fix it. I have thrown a total of $600 at it and haven't made ANY difference. No one can help me, not even the f*uckers that made this POS - JEEP.

I would just like to know if anyone has any suggestions on things I should try before I take a sledgehammer to this damn thing?

Thanks


BTW, I have 3 XJs and one MJ. This '96 has given me more problems than all 3 other jeeps added together.


SimpleXJ

Shot in the dark here but might as well try it, how about the ignition system?

XJguy

Would it start, idle and rev fine? This problem only present when driving in gear, but I'll try anything now... In my past experience with bad coils, the vehicle ususally doesn't start/run. This pile starts and runs great, just doesn't drive.

Anyway, what should I test?

SimpleXJ

Coils......I replaced the coil in my 94 XJ a couple of months back. It was running fine, but I was tracking down radio interference. New coil solved it. May be something to consider.

SimpleXJ said:

Would it start, idle and rev fine? This problem only present when driving in gear, but I'll try anything now... In my past experience with bad coils, the vehicle ususally doesn't start/run. This pile starts and runs great, just doesn't drive.

Anyway, what should I test?

SimpleXJ

Click to expand...

I would go down the line and test the resistance and continuity on every thing. FSM, or Chiltons can guide you if you need it.

XJguy

I've got both an FSM and a chiltons. I can't perform a lot of the FSM tests because they require a $3000 snap-on scanner. But on the ignition system, to test the coil, FSM only lists a no-start test. Since mine starts, I assume the coil is fine. What other components need to be checked?

Thanks

SimpleXJ

SimpleXJ said:

I've got both an FSM and a chiltons. I can't perform a lot of the FSM tests because they require a $3000 snap-on scanner. But on the ignition system, to test the coil, FSM only lists a no-start test. Since mine starts, I assume the coil is fine. What other components need to be checked?

Thanks

SimpleXJ

Click to expand...

You dont need that thing, a simple voltmeter with resistance function will allow you to see how things are doing. Off hand, you can check the coil, the wires, the plugs...you can also inspect the cap and rotor, you can check the ignition module and pick up coil (dont know if the 4.0 has these, check FSM).

If all checks out fine I think the next thing I would look into is fuel delivery, make sure injectors are good, pump and filter. Good luck.

Xjguy

XJguy said:

You dont need that thing, a simple voltmeter with resistance function will allow you to see how things are doing. Off hand, you can check the coil, the wires, the plugs...you can also inspect the cap and rotor, you can check the ignition module and pick up coil (dont know if the 4.0 has these, check FSM).

If all checks out fine I think the next thing I would look into is fuel delivery, make sure injectors are good, pump and filter. Good luck.

Xjguy

Click to expand...

I just remembered, an EGR valve that is not working properly can also give the low power you describe.

XJguy

I had 94 pontiac sunbird with similar problems - started and idled fine. New wires and plugs fixed it.

Kenny

Would any of these things cause a check engine light and error code related to the TPS and MAP? I'm kinda confused.


SimpleXJ

Isn't there a vacuum line going from the manifold to the MAP sensor? What kind of shape is it in?

All right, I own a 96 XJ myself, and I work on Jeeps every day. So here is an off the wall question. Does your cruise control work? I know, what the hell has cruise control to do with this? If you replaced both the MAP and TPS, and the same code is still setting, something is causing the code to re-set. You said it had code 24. Do you have the P-code for the failure? Code 24 covers the TPS voltage high and low, as well as the TPS does not agree with MAP faults. The P-code will be more specific as to the exact fault. OK I'm rambling now. Back to the criuse control issue. The PCM shares inputs for various systems, this is internal within the PCM itself. DC does this to save money on manufacturing the controllers. One of the shared circuits is for the TPS and the cruise control switch inputs. I have seen a shorted clockspring bleeding voltage from the horn circuit to the cruise switch circuit and causing a high voltage reading at the PCM for the TPS. It may seem far fetched, but I have repaired several vehicles just by replacing the clockspring. An easy check would be to disconnect the dash wire harness side connectors from the clockspring and road test it again.

That being said, what is you fuel pressure? How about checking your fuel pressure while it is acting up. Pressure is important, but fuel volume is too.

Recheck the basics, sometimes we can miss the easy stuff while expecting something really complex. It happens to all of us at one time or another.

XJguy said:

I just remembered, an EGR valve that is not working properly can also give the low power you describe.

Click to expand...

91 and up 4.0l XJs do not have EGR valves.



Bryan

A restricted air inlet would not be noticed at low rpm and become noticeable as rpm increases. This could result in high manifold vacuum which might show up as a MAP fault.

karstic: checked the rubber elbow from the intake to the MAP - its in good shape and has plenty of vaccuum.

PaulJ: checked the airbox and plumbing for a restriction - found none.

BryanC: I did borrow a friend's pressure guage and I stuck it on the fuel rail. I don't remember what the measurements were in, but it read a steady 50 idle or revved. I don't know how I'd test it while driving though. Whats the pressure supposed to be at anyway?

I played with it some more this morning - started to think maybe the tranny or the torque converter are binding up. I went for a drive and when the thing acted up I threw the shifter in nuetral - it revved up a bit but rather slowly. I stopped, put it in park, then floored the piss out of it like I never have before. It revved up to about 4.5K RPM and sat there. Not like a rev limiter when it bounces up and down; but this thing just sat very steady at around 4.5K, and I had it floored.

So the problem is definately in the motor, and now I know it does it while not driving as well.

The specific P code I got from my handheld scanner was P0121 - "TPS voltage does not agree with MAP".

Bryan, where is this clockspring you are talking about located?

Thank you so much all!

SimpleXJ

PS
I guess I went too far when I said I was gonna drive it into a tree... and take a sledge to it and whatnot.... but when you throw $600 worth of parts at it to no effect, it'll do it to ya. Maybe I won't drive it into a tree but a carburated intake conversion definately crossed my mind. That is if no one can fix it.

Actually, I just found in my FSM that the fuel pressure should be at 49.2 psi +/- 5psi at idle - so my fuel pressure is within spec.


SimpleXJ

Clock spring is in the steering column. Has something to do with the air bag I think. I know you have to pull the sterring wheel to get to it tho. Im stuck at work and dont have a manual handy to give anything more specific.

Well guys, I fixed it

Before I tell you what the problem was, I'd like to tell you a story that happened a few days before the problem, that I thought had nothing to do with my error code 24.

Since its been so nasty and slushy here in VA with all the snow, and I was due for an oil change, I decided not to get wet lying on the ground and (for the first time) take it to Jiffy Lube. I usually do my own oil, but I was lazy.

Anyway, when I picked up my jeep JL said that I had a small power steering leak. Nothing serious, just some dripping. They said they topped off the reservoir and... I quote the guy - "I found a nice spot for the quart of PS fluid under the hood, if you need it again."

Not thinking twice about it, I said thanks, paid my bill and rolled home. Well, the next day or so is when I started having the problem... but what does having an oil change done have to do with code 24 (tps and map voltages don't match)? Well, nothing! The oil change itself had nothing to do with it... it was the guy's "nice spot" under the hood for that quart of PS fluid!



As you can see, the quart bottle sitting in front of the airbox, is clearly blocking any air trying to get into the engine. When I pulled the damn thing out of there, and went for a drive, the jeep had all the power in the world and the check engine light is out.

I mostly blame myself, but I don't know whats more embarassing -

-the fact that it took me 2 weeks to figure this out... when I glanced over this bottle a million times before, while trying to find the problem

-the fact that jiffy lube thinks this is a "good spot" to keep fluids

-or the fact that the JEEP dealer thought it was the cat. converter and charged me $80 for a misdiagnosis when the problem was right in front of their faces! Sorry, I don't have much sympathy for them... they have all the tools, skills and etc needed to have figured THIS out. Or at least not tell me a lie that cost $170 (cat.)

-or at last, the fact that I threw $600 at it in parts trying to fix it.

Anyway, live and learn right? This was so stupid that I don't know if I should go to Jiffy Lube and see if they wanna pay some of that $600 or if I should just forget it and learn my lesson.

No wonder all the sensors read within spec and everything I tested was fine... because it really was!

Thanks to all of you for your help

Best Regards,

SimpleXJ

PS
I guess driving it into a tree seems a bit extreme now huh?

well hey man just look at it this way, now that you put 600 bux worth of crap into it, its gonna run REALLY good for a while now LOL, congrats on the "find"

Isn't there supposed to be a little square tube that goes from the airbox through the front crossmember?

karstic said:

Isn't there supposed to be a little square tube that goes from the airbox through the front crossmember?

Click to expand...

thats only on earlier XJs (my 87 had it, my 96 doesn't)

im not sure when they eliminated it