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4.0L wont perform

#1 User is offline   Sissyjeep1 

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Posted 12 December 2012 - 06:56 AM

Looking for some guidance.I have a 4litre runs perfect at idle in neutral and revs.If you try to run down the road misfires and major backfire through exhaust.Any thoughts would be appreciated.

#2 User is offline   JeepinIan 

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Posted 12 December 2012 - 07:07 AM

What year, how many miles? Any changes to vehicle before the poor performace?
Ian Stewart

If you don't fight for the trails, there won't be any trails to fight for.

What you get by achieving your goals is not as important as what you become by achieving your goals.
Zig Ziglar

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling that thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself." ....

John Stuart Mill

#3 User is offline   drshame 

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Posted 12 December 2012 - 09:10 AM

Plugs..Fuel Injector Cleaner....Bad Gas....clogged air filter/gas filter..
How's your general maintenance been?
My 4.0 WJ's up to 164,000 and had it's share of hiccups, but I have changed filters/plugs/routinely including the gas filter at the tank..which is often ignored.
Sounds like some fuel system issue, imho.

#4 User is offline   Sissyjeep1 

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Posted 12 December 2012 - 09:18 PM

It's a 91 yj. I put a throttle sensor on it and a new distributor as it acts like a timing issue. It used to only happen occasionally shifting into second but now much worse. When it was first happening I ran it with fuel pressure gauge on it and saw no fluctuation.

#5 User is offline   Krocker 

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Posted 12 December 2012 - 09:29 PM

oh it's sad it got worst, maybe you miss something...
best-selling brands of Rubicon Express and Pro Comp Tires

#6 User is offline   JeepinIan 

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Posted 13 December 2012 - 07:39 AM

HAve you had a code scanner put on it? Chances aer it is a sensor, and just replacing sensors w/o knowing which one is a waste of money.
Ian Stewart

If you don't fight for the trails, there won't be any trails to fight for.

What you get by achieving your goals is not as important as what you become by achieving your goals.
Zig Ziglar

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling that thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself." ....

John Stuart Mill

#7 User is offline   Sissyjeep1 

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Posted 13 December 2012 - 08:07 AM

View PostJeepinIan, on 13 December 2012 - 07:39 AM, said:

HAve you had a code scanner put on it? Chances aer it is a sensor, and just replacing sensors w/o knowing which one is a waste of money.

Thx for the input.

#8 User is offline   Krocker 

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Posted 17 December 2012 - 09:32 PM

exactly, but there are no other option I guess.
best-selling brands of Rubicon Express and Pro Comp Tires

#9 User is offline   drshame 

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Posted 02 February 2013 - 01:32 PM

+1 for scanner/error codes.
CPS/ TPS?
Fuel Filter?

Pulled plugs lately? Whatever the cause I'll bet they're fouled or need to be re-gapped.
My 4.0 WJ is up to 167,000 and has needed multiple sensor changes and obviously new plugs too.
Let us know what'cha find.

#10 User is offline   Sissyjeep1 

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Posted 20 August 2013 - 05:41 AM

I am still trying to repair my 4.0 litre yj.I dont have a code scanner and doesnt have a ck eng light to flash codes at dash.I have put a timing light on ignition and confirmed that it loses spark if you shake the whole jeep by the rear quarter panel.Does anyone know if there is automatic shut down sensor of somekind?I have searched and shaked all eng harnesses I can reach.When it stalls turn the key and starts right back up.If you dont touch it will sit and run perfect.This is a 90'yj with a 91' 4.0ltr efi in it.Any thoughts?

#11 User is offline   JeepinIan 

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Posted 20 August 2013 - 01:21 PM

Maybe a bad ground. Run it by an autozone, they can put a scanner on it.
Ian Stewart

If you don't fight for the trails, there won't be any trails to fight for.

What you get by achieving your goals is not as important as what you become by achieving your goals.
Zig Ziglar

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling that thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself." ....

John Stuart Mill

#12 User is offline   Big Red One 

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Posted 22 August 2013 - 02:55 PM

Sounds like a bad ground... computer controlled stuff are sensitive to poor connections, if all else fails get a 4.2 with a Carter BBD... mine never let me down and a piece of string/paper clip and some Duct tape were all I ever needed to fix ANY problem... :horsedead:
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#13 User is offline   SuperDave1984 

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Posted 23 August 2013 - 11:11 AM

Does it still have the catalytic converter on the exhaust? Mine got clogged with crap after a day of wheeling in water and mud. Would idle all day long, but you couldn't go anywhere.

#14 User is offline   Sissyjeep1 

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Posted 27 August 2013 - 05:12 AM

I cant run far enough to get to an Autozone for a scanner.It doesnt have a cat converter on it and that doesnt account for the loss of spark when you shake it.Does anyone know how the auto shutdown relay functions?

#15 User is offline   JeepinIan 

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Posted 27 August 2013 - 02:49 PM

With it running, shake the harnesses and when it quits, check that harness for loose connections.
Ian Stewart

If you don't fight for the trails, there won't be any trails to fight for.

What you get by achieving your goals is not as important as what you become by achieving your goals.
Zig Ziglar

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling that thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself." ....

John Stuart Mill

#16 User is offline   Sissyjeep1 

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Posted 15 April 2014 - 07:46 PM

View PostBig Red One, on 22 August 2013 - 02:55 PM, said:

Sounds like a bad ground... computer controlled stuff are sensitive to poor connections, if all else fails get a 4.2 with a Carter BBD... mine never let me down and a piece of string/paper clip and some Duct tape were all I ever needed to fix ANY problem... :horsedead:

Finally found problem after almost two years! Previous owner or mechanic repaired cps with blue but splices and put back in wire cover with electric tape.What a nightmare.As it turns out many of you were right in different ways.thx.

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