Jeep Wrangler Forum

Jeep Wrangler Forum (http://www.wranglerforum.com/)
-   YJ Tech Forum (http://www.wranglerforum.com/f218/)
-   -   dead cylinder? (http://www.wranglerforum.com/f218/dead-cylinder-255554.html)

jeepermatt 07-13-2013 03:33 PM

dead cylinder?
 
I was told i have a dead cylinder,but compression tests on all 4, yes it is a 2.5 come up normal...only problem is it will idle like it wants to stall,then come back up to normal and run fine...any suggestions? I just replaced cap,rotor,plugs,wires,ecm and all sensors

Defcon 1 07-13-2013 03:35 PM

Are you sure it's only coming from one cylinder? How did you confirm that? Could be possible clogged fuel injector or partially clogged, could be any fuel related issue. Also could be insufficient air getting to the engine. How does it run above idle? Are you sure you are getting spark to each plug-point? Do you notice that the engine is running on the cool side? Give us more details and we can point you in a better direction, you haven't really eliminated any system yet if that's all the troubleshooting you did so far.

jeepermatt 07-13-2013 11:06 PM

Fuel injectors firing great,hasnt run any cooler than normal,great spark,runs like a scalded dog when you are on gas,but when you get to a stop,it will drop to about 450-400 rpms then slowly go back to 1000 with air on or 850 without air,run great then do it again at the next stop...only happens at a stop

Ole4Cyli 07-13-2013 11:11 PM

Try cleaning your IAC and throttle body. While you're in there, clean out all the sensors and plug-ins.

Defcon 1 07-14-2013 07:10 PM

Quote:

Originally Posted by Ole4Cyli (Post 3959712)
Try cleaning your IAC and throttle body. While you're in there, clean out all the sensors and plug-ins.

X2, the airflow passing threw the TB at idle is crucial. The IAC is directly in charge of that, if its working slowly, or if that passageway is a little clogged, you will have big idle issues.

jeepermatt 07-15-2013 06:52 PM

Alright..cleaned out the iac and throttle body...still have rough idle...but found out what pain is! Forgot i had a cut and got cleaner in it!

Defcon 1 07-15-2013 07:53 PM

Quote:

Originally Posted by jeepermatt (Post 3965731)
Alright..cleaned out the iac and throttle body...still have rough idle...but found out what pain is! Forgot i had a cut and got cleaner in it!

Lol pain is part of the game man. Are you sure the the IAC is working correctly? If the plunger is slow to retract/extend it will not allow the correct airflow to pass around the butterfly-valve. A simple check, is to remove the IAC from it's housing, (but dont disconnect the electrical connector), then have a buddy "key-on" the ignition, and by "key-on" I mean don't crank, but engage the electronics. The EEC tells the IAC to retract the plunger at start-up, (allowing air to bypass the butterfly-valve), you can physically check if this is happening. If it doesn't retract when you key-on, it's a bad IAC. You can feel this retraction in your hand as a buddy keys-on.

As the engine RPM's increase, the EEC will tell the IAC to begin to close, (a message relayed from the TPS), so as you increase in power the butterfly-valve will begin to open and the IAC plunger will start to extend to "plug" the bypass idle-air in the TB. The TPS and IAC work together, if it's not the IAC, troubleshoot the TPS, it could be relaying an incorect butterfly-valve angle, such as " not equal to 0 degrees ", which could also be part of your idle issue. If the TPS is telling the EEC " im not a zero degrees " (when it actually is), the fuel-injected into the cylinder will be miscalculated for that given degree marker. You can eliminate the TPS by 1: getting an ohmeter and doing a bunch of electrical checks at different RPM settings, (aka long and boring), or 2: "Borrow" a new TPS from an auto-store and see if anything changes lol.

jeepermatt 07-19-2013 07:38 AM

Alright..plunger on iac was sloooooow...went and replaced it and throttle body position sensor.. still no change....still stumped!

Defcon 1 07-19-2013 08:06 AM

Take off the battery cables and let it sit overnight, the computer still thinks the old sensors are installed, and adjusts the delivery based off the old information, this could be a problem. Once the capacitors are all drained out, the computer will relearn the new sensors for the next set of startups.

Did you do a thorough cleaning of the TB? I mean not just spray it but actually take it off and soak it in carb-cleaner and scrub it down? The valley in the IAC chamber is always full of sludge/grim, mine was partially blocked. Take off the accelerator cable, unbolt the TB from the intake manifold, take off the sensors then clean the heck out of the TB, reinstall with a new gasket. After that you pretty much eliminated the airflow being the issue, (if you did the simple things like check for clogs in the airway or blockage at the filter). Maybe you should re-check the electrical system before the fuel system, you said you were getting the correct rating for the spark at the plug-points? Are you getting any codes btw?

jeepermatt 07-19-2013 03:31 PM

Only code i got was a 12 for the iac...replaced it already with a brand new 1. I went ahead and replace both sensors, and I scrubbed out the throttle body with throttle body cleaner and reinstall with a gasket and still does the same.

AllMudd 07-19-2013 03:46 PM

Quote:

Originally Posted by jeepermatt (Post 3981126)
Only code i got was a 12 for the iac...replaced it already with a brand new 1. I went ahead and replace both sensors, and I scrubbed out the throttle body with throttle body cleaner and reinstall with a gasket and still does the same.

You should have gotten 12 if you disconnected the battery. That's what code 12 is, you should have also got 55 which is end of codes

jeepermatt 07-21-2013 09:50 PM

Alright...replaced the iac and disc.the battery overnight...still does the isle down to 500 rpm at a stop,then back to 850.cant seem to track this down...i wanna keep her,but might have to trade her if i cant get this sorted out! Help me save my jeep!!!!

Ole4Cyli 07-21-2013 11:14 PM

Could something be clogged on the fuel lines somewhere, Causing the engine to die down when it demands more fuel but can't get it? Clogged air intake tube? Did you make sure the plugs are on the correct firing order? Just naming things that would obviously cause problems...

jeepermatt 07-21-2013 11:32 PM

We replaced fuel filter,cleaned out air tubes,checked fuel pressure and did a by the book tune up...only sensor we didnt change is the one on the throttle body...all vaccum lines were replaced just in case.dont know where to go from here...i am totally stumped.

Ole4Cyli 07-22-2013 01:28 AM

A sensor on the throttle body can do weird things, mine had a bad connection and the engine would buck and the RPM's would shoot up sometimes when hitting a bump in the road. Since that's the only thing you haven't changed, wouldn't hurt to check it out.

Defcon 1 07-22-2013 05:16 AM

Quote:

Originally Posted by jeepermatt (Post 3988715)
only sensor we didnt change is the one on the throttle body


Can you post a pic of this sensor? I thought you said earlier that you replaced the IAC and TPS

jeepermatt 07-22-2013 08:14 PM

On a 2.5 its the one that sits at the back of the throttle body.we only cleaned it really good when we removed and cleaned the tb

Ole4Cyli 07-22-2013 10:39 PM

Yeah that's the same one that gave me issues, I would really consider replacing it since it's the only thing that hasn't been replaced. I really have no idea what the problem could be, if you've already replaced all that stuff it seems like it'd be running better than new!

jeepermatt 07-22-2013 11:04 PM

Oh how i wish! She runs smpoth as hell down the road,its only when you come to a stop that she does this....cant figure her out..therefore her name is ENIGMA

Buz 1 07-22-2013 11:12 PM

i've got the exact same issue i've been chasing 4 over a year now.. does it @ every stop, & after 2-3 seconds it returns to 800 rpm & will idle all day long... i've replaced every sensor under the hood except the map... gonna try cleaning the air passage the iac blocks off with a pipe cleaner in the next day or 2,but i'm out of ideas.. runs great otherwise.. i hauled a '97 xj on a 2000lb trailer 30 miles up Interstate 75 last week @ 65mph,,, no problem.. i will post a fix it i ever find 1.. good luck with it...:popcorn:

Defcon 1 07-22-2013 11:47 PM

Quote:

Originally Posted by jeepermatt (Post 3991690)
On a 2.5 its the one that sits at the back of the throttle body.we only cleaned it really good when we removed and cleaned the tb

Quote:

Originally Posted by jeepermatt (Post 3979612)
Alright..plunger on iac was sloooooow...went and replaced it and throttle body position sensor.. still no change....still stumped!


There's only 2 sensors on the TB, the TPS and IAC, if you replaced both then there is nothing left to be replaced. You said the IAC plunger was actuating slowly so you replaced it, you must be talking about the TPS. If that sensor isn't telling the EEC "I'm at 0 degrees" the engine won't idle correctly.

Please post a picture of the sensor that you didn't replace and we'll tell you not only what it is, but what it does.

jeeptjrider 07-22-2013 11:58 PM

My 4.0 had the same problem with cylinder 6 check ur cap n rotor at night and all lights off see if maybe u its arching somewhere mine was u will see a blue flash.. Also check O2 sensors my old 2.5 ran like total shit everyone said no it can't be that just unplug them n see what it does if it runs better there is ur problem.. Good luck


All times are GMT -5. The time now is 10:09 AM.