• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

ghost reving engine please help!!!!!!!

J

jeepster89

NAXJA Forum User
Location
springfield massachusetts
alright i did a head gasket, lifters, and push rod on my jeep since i was losing a gallon of coolent every week or so.teh tear down ran smoothly. then putting it back to gether ran the same way i broke nothing and lost parts. now here is my problem:

the engine will start and idle for mayb 1-2 secs at reg RPMS then it will just rev to 3000-5000 rpms orwhenever iturn the key off. this does it all by it self no one touching the gas or opening the throttle body.i have replaces teh TPS censor the IAS teh fuel pressure regulator on the fuel rail.i cleaned the TB off the jeep with both the TPS and IAS off of it. iv been trouble shooting this for a week and icant not figure it out. i called jeep and they said it sounds like an electrical problem not mechanical. any input would be highly appreciated i just want my jeep back lol thank you

the jeep is a 1991 cherokee 4.0 HO with auto tranny
 
Last edited:
i thought about that as well. that would cause that problem? also it runs really rich like fuel is just being dumped in the engine and the comp doesnt know to stop putting fuel in it. and i know its fuel cuz the spark plugs have gas on them and the exhaust is really rich for the few secs i can let it run
 
try checking all of your lines from your hvac and your vacuum canister, the "t" fitting attched to that, i had the same problems, and one of those lines were broken, check the lines, if they are broken, replace, or seal the lines, disconnect the negative battery terminal, pump the brake to release all left over power until its hard to push, let it sit for about 10 minutes, try to turn the car on with out it hooked up to the battery(iknow, do it anyway) then wait a lil, hook everythgin back up, check lines again, try to start it.
 
thanks for that ill do that too last thing i wanna do is bring it to jeep dealer. i also read that the head gasket could be seated wrong just by a little bit like the alingment studs are seated over but not on or in the right place. this was read on a tj forum. when the head was off i did not see and alingment bolts or anything to make sure its was alinged correctly. if anyone has a picture of these it would be helpful or has a place when can see a picture thnaks
 
jeepster89 said:
i thought about that as well. that would cause that problem? also it runs really rich like fuel is just being dumped in the engine and the comp doesnt know to stop putting fuel in it. and i know its fuel cuz the spark plugs have gas on them and the exhaust is really rich for the few secs i can let it run
Click to expand...

I had another vehicle (Ford) that was running very rich and it turned out to be a bad temp sensor to the computer. It sent a signal that the engine was always cold,so it dumped lots of fuel,and of course milage was terrible. Just one more thing to check, hope this helps!
 
I'm not sure I completely understand the problem. You start the Jeep, it idles fine at first, then the idle surges to 3-5k RPM and stays there? Does it rev up and down? Or does it just rev that high just as you're shutting the engine off, idle and drive fine otherwise?

If it's running rich, check the temp sensor and O2 sensor. If it's revving too high, check for vacuum leaks. Considering you just did a head gasket, it wouldn't surprise me if you've got a vacuum leak somewhere.
 
itd take one hell of a vaccum leak to get it to jump to 5k, a matter in fact, i dont think it can rev to 5k with the throttle plate closed, 3 could be possible, id check to make sure it can close all the way, if the computer sees it open, the IAC is ignored, and its given the amount of fuel thats required to rev that high w/ the engine under load until the o2 heats up (up to 60 seconds)
 
the jeep is not driveable i shut it off since the RPMS do not drop tehy will rise until i shut the engine if i let tehm go higher tehy will just stay or go past redline and most likly dmg the engine if i dont shut it off with the key.
 
The only way I can imagine the motor reving that high is with some sort of air supply. It is probably getting a large amount of air from someplace.
The throttle plate spring? A weak throttle plate spring will let the motor suck the throttle open.
A very large vacuum leak, the brake booster or even the intake manifold. Is it possible you forgot to reinstall the MAT sensor or tighten the intake manifold bolts, or hookup the brake booster vacuum line? Maybe the TB bolts are loose and it is sucking air under the TB.
I've seen a faulty (shorted) throttle position sensor, rev the idle up pretty high on the Renix, don't know if it's possible for the OBD I.
If the IAC is stuck all the way open, it will idle pretty darned high, 3-4000 or so (maybe even a little higher than that).
 
jeepster89 said:
the jeep is not driveable i shut it off since the RPMS do not drop tehy will rise until i shut the engine if i let tehm go higher tehy will just stay or go past redline and most likly dmg the engine if i dont shut it off with the key.
Click to expand...

This happened once on my Aerostar and I opend the hood and unplugged the TPS and the RPMS settled down to normal idle and stayed normal after that. Don't know why it did that, but I cleaned the connections and luckily it hasn't happend again.
I don't know what effect it would have on an XJ if you try this. Will these engines keep running with TPS unplugged?
 
scca28 said:
This happened once on my Aerostar and I opend the hood and unplugged the TPS and the RPMS settled down to normal idle and stayed normal after that. Don't know why it did that, but I cleaned the connections and luckily it hasn't happend again.
I don't know what effect it would have on an XJ if you try this. Will these engines keep running with TPS unplugged?
Click to expand...

Sorry, but when I typed the above statements I was just getting done a 12 hour shift at work. I should have added that I did plug the sensor back in after I cleaned the connection, and the engine was running all the time. I was just suggestiing this as a way to try to stop the runaway RPMs and maybe see if the TPS is in fact causing the problem. Let us know how you make out!
 
This may be totally off the wall so sorry if it is. But is there any chance the cruise control is for some reason causing the throttle body to open up? Just a thought.
 
This may be totally off the wall so sorry if it is. But is there any chance the cruise control is for some reason causing the throttle body to open up? Just a thought.3 Hours Ago 11:53
Click to expand...

x2 My 1993 volvo would just take off on its own occasionally, I bet whomever owns it now wonders why the cruise cable is disconnected.
 
every sensor is brand new. me and my brother tested it by having the new onesplugged in on and of the TB. then by just unplugging them while on teh TB. both ways teh engine reved on its own. the TB plate does not move so i am leaning moretowards a leak below the TB or at the intkae/exhaust gasket. non of the fuel injectors are stuck open checked those. and i do not have enough time to actually test for leaking since the engine revs soquickly in about 3 secs its at 3500RPMS or higher depending on when i shut it off. so from what you have all written the major culprit asto be the area between the TB and the intake manifold or the intake/exhaust gasket area or the gasket it self. i thank you for all the replies if any mmore i dead come to mind please post them once i check those two possibilities i will post if it is fixed or not thank you all. also my cruise control is not there so thats not the problem lol
 
If the TPS is installed wrong on the Renix TB (with the TPS arm on the wrong side of the activator on the throttle plate rod) it will idle up pretty high. I can't realy picture the setup on the 91 HO though, so this may not be applicable.
 
3500 aint nothin!
icon10.gif

gotta be what mud said.
 
After I installed a new IAC it revved to 3500 rpms for about a full minute... then the computer was able to catch up to the new part and it went back to normal. Have you let it run for more than a minute or so, so that the computer can figure out what it is that you've done?
 
I used to have an '87 that would occasionally go bananas with very high idle.
I traced it to the connectors laying on top of the intake. Cleaned the pins, problem solved.
You may want to take a look at them, disconnect a couple of times, spray some WD 40, look at them.
 
the TPS can only go in one way.also the TB butterfly does not move so the comp is not controlling the air flow.and icnat let it run for more then 5 mayb ten seconds since it will go untill it redlines then hold since it can rev anymore. so i would rahter not let it rev for one min and blow up my engine lol but i appreciate all the ideas anything helps. tomm i will be trying the gasket and buying a new mopar one from jeep.hopefully that fixes it i shall let you all know.
 
You must log in or register to reply here.

Similar threads

F
Stumped on this one!
2
Replies
29
Views
4K
Bent
Bent
G
Engine low on power
Replies
7
Views
2K
Gotitjr
G
U
Overheating? Quick help please.
Replies
9
Views
2K
75SV1
7
R
2001 jeep intermittent misfire.
2
Replies
20
Views
3K
RetEBoogie
R
K
Dreaded crank and cam shaft sensor problems.
Replies
4
Views
1K
Tim_MN
Tim_MN
Back
Top