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Unread 04-02-2011, 12:30 PM   #1
kc10er
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1991 YJ Wrangler 
 
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Miss firing cylinder?

Ok, so like the rest of us, I have spent a lot of money making the jeep look good and run right. Now I have another problem.

To start the jeep is a 91 yj, 2.5 4 cyl.

It seems as if the engine is running on 3 cylinders. That might not be the problem but it is the best way I can describe it. For the past few weeks, especially when cold, I would be driving and get that 1 second loss of power, like a miss. Felt like the engine would lag or bog down for one engine cycle (a split second) and be fine. When it got up to running temp, it would be fine.

NOW, cold or warm the engine idles and runs rough. Like I said it feels like it is running on 3 cylinders but I am not sure. It accelerates normally but with a loss of HP obviously. Idles fine (rough) and does not die. Engine shakes a little, typical of a missing cylinder.

So, I heard the fuel pump might be going bad before with the intermitted lag/miss while driving. Could it be that I don't have enough fuel pressure anymore to run smooth? I replaced plugs and wires last month. I don't see any way to adjust the distibutor cap on this one as it only has two screws to hold the cap down. I hope I did not burn a ring, since it leaks oil pretty bad and it was low yesterday. Engine had a little thin white smoke coming out of oil fill when I added oil yesterday (pulled over).

I have not checked fuel pressure, what should it be at?

I don't think it is plugs or wires what do you think?

Any ideas on what I should check before replacing all kinds of stuff?

Sorry for long post, thanks for help in advance.. I have a trip to Uharrie planned on the 8th, need this thing running.

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Unread 04-02-2011, 01:33 PM   #2
MJMPC
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You can check for codes.

http://www.jeepforum.com/wiki/index....k_Engine_Codes
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Unread 04-02-2011, 02:52 PM   #3
kc10er
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my CEL is not on though...
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Unread 04-02-2011, 05:21 PM   #4
Mark05059
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there can be codes even if the light isnt lit.
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Unread 04-02-2011, 11:16 PM   #5
04WJny
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Try checking the plugs, see if there gapped right. i had a problem a few months ago with my spark plug being gapped at 0.009" instead of 0.045" which made made only 5 cylinders fire most of the time, and my engine sound terrible. i would suggest by checking the simple things first. Have you done any work to the car recently?, Ex. tune-up etc... if so, re-check what you did and make sure everything was installed properly. Next, check the spark plugs, plug wires, distributer cap, rotor, fuel injectors, and make sure they are all working properly.
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Unread 04-02-2011, 11:33 PM   #6
kc10er
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ok so i checked codes. got the following:

13=no change in map from start to run.
Changed map sensor, did not fix.

33= a/c. I have no a/c (removed) so duh on that code.

41=Alternator field control circuit open or shorted. I will replace alternator later as final resort. I have changed batteries and have a new starter, Alternator was tested and is tossing out 14 volts so it should be good.

55=end of codes.

My timing is computer controlled i think as the distributor cap can not rotate (only two screws to hold it to the rotor). I will be replacing the injectors and bought a new fuel filter. These will go on tomorrow. Will gap the plugs and check compression. Updates tomorrow.

Thanks for the suggestions so far.
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Unread 04-03-2011, 12:53 AM   #7
moonshinefuel
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Check all of your vacuum lines, and vacuum line connections. Just comb through all that, make sure there are no leaks, or anything like that.
You are asking good questions, the fuel pressure can be easily tested, it is not difficult. Post the compression results when you get them.
I would not be so quick to change out the fuel injectors just yet. My original injectors have over 316,000 miles on them, and they are fine.
Spray out the throttle body, with throttle body cleaner, put some fuel injector cleaner into the gas as well.
Adjusting the timing is not something you do by turning the distributor. It is basically not adjustable. Not in the traditional sense of turning the distributor.
Try to track down the oil leak, and start replacing gaskets, needless to say, running low, and losing oil is not a good thing. The head gaskets are very durable on the 4 cylinders, but any head gasket is prone, if overheating occurs.
Keep posted here on your findings, and results.
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Unread 04-03-2011, 01:51 AM   #8
kc10er
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Head gasket is in the parts bag already, and the intake gasket is gonna be done as well. I have already seafoamed the fuel about 2 weeks ago, but only one can in nearly 18 gallons. Wonder if i should dump a lot more in there cause I have a full tank now. Will do compression check tomorrow and post results. Just to be clear, cylinder order on this is 1234 from front to back? or staggered 1324 like an import? Thanks!
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Unread 04-03-2011, 04:45 PM   #9
kc10er
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ok so here is the update of tests in total:

Changed map sensor = did not fix.

Gapped plugs to .045 = did not fix

Checked to make sure I had spark on all 4, I do = did not fix

Compression test results in order from front to back (if that is right):
1-130psi
2-124psi
3-129psi
4-130psi
Compression good = did not fix

Replaced fuel filter = did not fix

Cleaned sensors in the throttlebody and intake manifold = did not fix


So, all i can think of is, bad injector, clogged injector, bad fuel pump, bad sensor in throttle body / intake mani.

I guess next i will change all the sensors in the TB/ mani and then buy one injector and test it in each position to see if i have a bad injector.

Am i missing anything?? Should i do injectors first or the fuel pump? RALLY don't wanna drop tank as i have a full tank and nowhere to drain/store gas. Much less do i wanna drop the tank for obvious PITA reasons.

Thanks to anyone that has more easy tests/ suggestions.
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Unread 04-03-2011, 06:14 PM   #10
NonRubicon
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According to the Haynes Manual, the plug gap for the 2.5L should range 0.033 to 0.038.

The 0.045 gap is for the 4.2L running with the Team Rush upgrade.
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Unread 04-03-2011, 06:21 PM   #11
moonshinefuel
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Quote:
Originally Posted by kc10er View Post
Head gasket is in the parts bag already, and the intake gasket is gonna be done as well. I have already seafoamed the fuel about 2 weeks ago, but only one can in nearly 18 gallons. Wonder if i should dump a lot more in there cause I have a full tank now. Will do compression check tomorrow and post results. Just to be clear, cylinder order on this is 1234 from front to back? or staggered 1324 like an import? Thanks!
Actually it is 1-3-4-2
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Unread 04-03-2011, 06:31 PM   #12
kc10er
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Quote:
Originally Posted by NonRubicon View Post
According to the Haynes Manual, the plug gap for the 2.5L should range 0.033 to 0.038.

The 0.045 gap is for the 4.2L running with the Team Rush upgrade.
well i can regap em, but that is what they were at before i widened them, still no fix so at the advice of a friend i am gonna replace the plugs all together. Even though i just put new plugs in and they all spark he said one might have fouled and not sparking consistantly. worth a shot for 10 bucks.
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Unread 04-03-2011, 06:36 PM   #13
kc10er
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Quote:
Originally Posted by moonshinefuel View Post
Actually it is 1-3-4-2
wait, so my wires to distributor are not in the right order?? What i ment by post is the cylinders are named 1234 from front to back, not firing order. i have from front to back arranged on the distibutor clockwise as follows:

distributor plug number one (front most plug on dist.) goes to FRONTMOST cylinder.

next in line clockwise (outer passenger dist plug) goes to THIRD from front cylinder

next one (rear plug on dist.) goes to far REAR cylinder

next one (closest to block) goes to the SECOND from front cylinder.

Confirm?? Hope that is not too confusing.
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Unread 04-03-2011, 08:12 PM   #14
moonshinefuel
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Quote:
Originally Posted by kc10er View Post
wait, so my wires to distributor are not in the right order?? What i ment by post is the cylinders are named 1234 from front to back, not firing order. i have from front to back arranged on the distibutor clockwise as follows:

distributor plug number one (front most plug on dist.) goes to FRONTMOST cylinder.

next in line clockwise (outer passenger dist plug) goes to THIRD from front cylinder

next one (rear plug on dist.) goes to far REAR cylinder

next one (closest to block) goes to the SECOND from front cylinder.

Confirm?? Hope that is not too confusing.
Ok cool, well, you mentioned cylinder order, I was thinking firing order. Your compression looks really good. I would be very happy with that.
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Unread 04-03-2011, 08:17 PM   #15
moonshinefuel
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If you think it is running on three cylinders, and it might be an injector related problem. I might be tempted to just disconnect one injector at a time. If you unplug any given one, and it is still running the same, then you have something there.
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