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-   -   Won't Accelerate! (http://www.jeepforum.com/forum/f13/wont-accelerate-1549756/)

trev52890 07-16-2013 12:49 PM

Won't Accelerate!
 
I have a ZJ 4.0L that won't accelerate past 30mph. It WILL shift fine but once it gets close to 30mph it starts to bog down and sometimes it will stall. Then once i throw it in neutral it will start right back up and then do the same thing near 30mph. rpms seem normal until it starts bogging down then the rpms will stay the same or will drop a bit. No codes. New upstream o2. No Catalytic converter. Newer CPS/CKS. I take good care of it. clean icv. newly rebuilt engine. Please help!

My transmission pan seems extremely hot after driving it untouchably hot. Could an overheating transmission be causing this? (my fluid levels are fine and its a remaned tranny not a year old)

dellis 07-16-2013 12:59 PM

Check for a bad Throttle Position Sensor or a stuck throttle.

Also, read this post from Oldfrog that we were discussing yesterday, and see if his symptoms match close to yours. His was a defective TPS.

==========

As for the transmission, if the problem is happening when you first start out driving (when the tranny is cold), then it isn't related to an overheated transmission.

trev52890 07-16-2013 01:06 PM

Cant be a bad tps because i can rev it in park to any rpm without it bogging. and throttle cable is fine.

PolkaPower 07-16-2013 03:05 PM

Quote:

Originally Posted by trev52890 (Post 15683589)
Cant be a bad tps because i can rev it in park to any rpm without it bogging. and throttle cable is fine.

That is not a valid way to test the TPS.

trev52890 07-17-2013 10:56 AM

Tested it and then replaced it. the problem still persists. i also tested the cks and it says that the resistance is 5.6 Mega ohms which is 5600000 ohms.

dellis 07-17-2013 11:33 AM

Quote:

Originally Posted by trev52890 (Post 15687283)
Tested it and then replaced it. the problem still persists. i also tested the cks and it says that the resistance is 5.6 Mega ohms which is 5600000 ohms.

The TPS was bad? If so, try resetting your PCM after replacement so it can re-learn stuff (reset by disconnecting your battery for about 10 min).

On restart, I've heard that you should not touch the gas pedal and let the Jeep idle up to operating temp so the PCM can learn idle through the new TPS.

sebian 07-17-2013 11:51 AM

Quote:

Originally Posted by trev52890 (Post 15687283)
Tested it and then replaced it. the problem still persists. i also tested the cks and it says that the resistance is 5.6 Mega ohms which is 5600000 ohms.

Sounds like you found the problem. The CKS should have no resistance, or as described in repair manuals, open resistance.

BeDifferent 07-17-2013 04:01 PM

a little help please; what is the CKS and where is it located? :o
thank you.

trev52890 07-17-2013 05:02 PM

I reset the PCM still having the problem. Sebian i thought it should have infinite resistance when your ohm meter is set to 1000 to 10000 ohms? So in that case wouldn't it be infinite resistance? Also i just tested the CKS by watching the voltage as i rotate the crankshaft and the results were normal.

To expand on this issue a bit more. it is now happening at any speed. whenever i touch the gas peddle to accelerate it starts to hesitate and sputter
but as soon as i left off the gas or just let it idle it runs fine. the rpms will flutctuate a little but not more than 100. also when it dies it always has NO problem starting right back up. When it is in neutral or park i can rev the engine and it seems fine, it only tries to die in drive

ZeeJay1997 07-17-2013 06:01 PM

Sounds like a fuel delivery problem. Check fuel pressure at rail. Should read 49 plus or minus 5 throughout throttle range.

Kingr98 07-18-2013 05:33 AM

Could the overheating transmission and the stalling both be symptoms of a problem with the transmission?

I am not a transmission guy, but if something is causing the transmission to bind up it could bog down the engine. And after driving it for a while, the trans would get hot from the added friction. Once its in neutral, the resistance isn't there and it idles fine.

dellis 07-18-2013 07:14 AM

Trev, I agree with ZeeJay as far as your testing process. I believe that the common non-transmission causes are TPS, clogged cat, air supply and fuel supply. Though it may seem less likely, you should test your fuel pressure to eliminate your fuel system as the cause (more fuel is delivered under load than just reving) ... I don't think you have a vacuum leak or other air supply problem because your TPS and idle seem good.

Second, yes, your testing of the CKPS makes me believe that it is good ... plus, a failing CKPS would likely have problems in neutral and while reving, and not merely under load.

Finally, if you paid a shop to install your remanufactured transmission in the last year, then call the shop that installed it and ask them if your symptoms are consistent with transmission problems.

dellis 07-18-2013 07:36 AM

Quote:

Originally Posted by BeDifferent (Post 15688404)
a little help please; what is the CKS and where is it located? :o
thank you.

Crankshaft Position Sensor, often abbreviated as CPS or CKS (I use CKPS, and I don't like to use "CPS" because that acronym can get confused with the Camshaft Position Sensor).

The CKPS is on the top of the transmission's bell housing.

trev52890 07-18-2013 11:20 AM

thanks for your help so far guys but still stumped and loosing my cool. here is an update. At idle it is acting a little funny like it wants to start to die but in a split second it jumps back to a normal idle. Never dies from an idle though. Checked grounds and vacuum lines, all good. recleaned icv. checked cks and tps sensors. still bogs down when its given gas but only while in drive. both o2 sensors are unplugged. fuel pressure is at 50psi. I'm stumped guys.

sebian 07-18-2013 11:26 AM

Quote:

Originally Posted by trev52890 (Post 15688623)
I reset the PCM still having the problem. Sebian i thought it should have infinite resistance when your ohm meter is set to 1000 to 10000 ohms? So in that case wouldn't it be infinite resistance? Also i just tested the CKS by watching the voltage as i rotate the crankshaft and the results were normal.

To expand on this issue a bit more. it is now happening at any speed. whenever i touch the gas peddle to accelerate it starts to hesitate and sputter
but as soon as i left off the gas or just let it idle it runs fine. the rpms will flutctuate a little but not more than 100. also when it dies it always has NO problem starting right back up. When it is in neutral or park i can rev the engine and it seems fine, it only tries to die in drive

IIRC your OHM meter should be set to 20k ohm if available. And during the check, it should read "0" ohms, indicating that there is no resistance in the circuit. Double check your multimeter specs to make sure it will read open resistance like that.


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