1994 jeep wrangler misfires

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  #1  
Old 08-23-02, 05:33 AM
anees rahman
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Question 1994 jeep wrangler misfires

I've got a 1994 Jeep Wrangler with a 2.5L, 4-Cylinder engine.
It misfires out of the exhaust. In fact, it has blown open my muffler. No power left! Replaced Dist. Cap, Rotor, Plugs and Wires. Did not help.
Thinking it could be an intake manifold leak or a bad cam shaft???? It idles rough but does idle. Can't hear any intake leaks. Should I do a vacuum test? Compression test? Could it be anything else??
 
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  #2  
Old 08-23-02, 07:27 AM
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You didn't say how many miles on it, but if the O2 sesnor has never been changed that might be a good place to start. Not sure what maladies are common to that motor; should be some knowledgable soul along for more enlightenment.
 
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Old 08-23-02, 09:35 AM
anees rahman
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1994 jeep wrangler misfires

Sorry, it has 127,000 miles on it.
I hooked it up to a scanner (Snap-On 2500).
No code for the Oxygen Sensor came up, but code 15 did come up and it's for No Speed Signal???????
Don't know if that could cause the problem?
 
  #4  
Old 08-23-02, 12:52 PM
Joe_F
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Could have a bad crank sensor if so equipped, common problem on Chryslers of this vintage.
 
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Old 08-23-02, 01:14 PM
anees rahman
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1994 jeep wrangler misfires

Thanks for the input.
Would a bad crank sensor give a code?
How do I go about checking it?
 
  #6  
Old 08-23-02, 03:09 PM
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Before you throw more parts at this animal.Do a compression check dry,then add oil to each cylinder one at a time and retest.Record results before and after.Do a vacuum test noting idle and part throttle readings and any jumping of the vacuum guage (specific amount needed)disconnect and plug your egr hose if equipped,before you do the vacuum test as it may affect part throttle readings,record results.Remove one plug wire at a time and start or attempt to start and note if one cyl makes less change than others ,record the cyl that makes little or no change in your idle,then reply here and Ill take a stab at saving you time and money,good luck,rahman
 
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Old 08-23-02, 03:44 PM
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Good suggestions from davo since the compression and vacuum tests are zero cost items.

On the O2 sensor - can be bad and not give a code. The one on my wrecker craps out about every 50k miles just like clockwork without getting a code.
 
  #8  
Old 08-23-02, 05:52 PM
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The o2 sensor would not go to a preferred cylinder because it measures all fuel pulses,and in 1994 it cant differentiate between the ignition pulses to compare,if you had a bad 02 it would be totally rich or lean.If you had a bad o2 sensor.OBDII would detect a misfire or other catalyst damaging problem.
 
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Old 08-26-02, 06:55 AM
anees rahman
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1994 jeep wrangler misfires

Thanks for all the input.
Unfortunately I got the latest posts this morning.
I did however do some more work on it this weekend.
Hooked up the scanner to it again.
Noticed that the timing is all over the place.
The timing ranges from 13-19 degrees. Never steady!
My immediate thought was a bad distributor or timing chain.
Took the distributor out. Don't see much play in it. Can't really tell if it's bad or not.
The timing chain does have some "normal" play in it.
I'm kind of leaning at replacing both, but don't know if I should or not. I don't have money to throw around.
Am I on the right track with all this timing stuff, or is it normal for the timing to move around so much? On this Jeep, the timing is controlled by the computer.
I'm all confused.
 
  #10  
Old 08-26-02, 09:01 AM
Joe_F
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Have you read the links and posts below in my signature file for guidance?
 
  #11  
Old 08-26-02, 09:43 AM
anees rahman
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1994 jeep wrangler misfires

I have checked the links, but could not find anything for this problem.
I did however find other interesting items that have nothing to do with my problem.
 
  #12  
Old 08-26-02, 03:31 PM
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I'd go with the timing!! You said it misfires so bad it blew a hole in the muffler.It's probaly actually backfiring which is a sure sign of a timing concern.
My first step would be to make sure it hasn't jumped time.Use a good repair manual and check your timing marks as well as the distributor setting to make sure their ok.
 
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Old 08-27-02, 11:51 AM
chilango69
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Exclamation map sensor??????

hey I'had read what you had experience with you jeep and if you don't want to spend to much just change tha map sensor las time I'had the same problem with my jeep 89' and was the map sensor just give it try!!!!!!
 
  #14  
Old 08-29-02, 06:37 AM
anees rahman
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1994 jeep wrangler misfires

Ok, here is the latest.
I've checked the compression.
Cylinder 1-170psi
Cylinder 2-170psi
Cylinder 3-165psi
Cylinder 4-165psi
All cylinders are firing ok.
No vacuum leaks noted!
Have not put a vacuum gauge on yet.
Checked timing chain. It does not have excessive slack.
Replaced distributor-still the same. Timing fluctuates from 13-19.
Have not tried the map sensor idea yet.
Checked all timing marks. Distributor/rotor, piston and dampner all line up ok at tdc.
Also, I installed a new muffler.

Jeep still starts hard, idles good and backfires.
 
  #15  
Old 08-29-02, 10:37 AM
Joe_F
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I still say go back to autolibrary and start there. They have how to check the various sensors.

Chryslers of this vintage had problems with bad crank sensors and other troubles...test the parts before damning them as bad.
 
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