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Old 11-05-2013, 07:30 PM   #1
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94 yj misfire under a load

Only happens under load under 2500 rom any higher it clears up and also has low idle after warmed up seams to run good until then no check engine light previous owner replaced a ton of sensors and got frustrated and sold it to me any help would be greatly appreciated thanks in advance

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Old 11-05-2013, 08:33 PM   #2
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Any codes being thrown? May be low fuel pressure too.

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Old 11-06-2013, 08:42 AM   #3
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No codes fuel pressure is at 35 psi key on engine off and 50 at idle no change when I unplug fuel pressure regulator which has also been replaced engine has good vacuum and I can't get ahold of a obd1 scanner
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Old 11-06-2013, 08:52 AM   #4
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Tried blowing thru the return line to the tank and it seams as if it's blocked hooked a hose to the return line and out it in a bucket and now fuel pressure is at 33-35 at idle gonna try to see what I can find out to clear or replace the line
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Old 11-06-2013, 09:27 AM   #5
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You don't need a code reader to get the codes. You just need to do the "key trick" and watch the CEL while counting the flashes.
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Old 11-06-2013, 12:03 PM   #6
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Yeah no codes cleaned the line have good fuel pressure now still missing under load low rpm replaced the cap and rotor again had some buildup on the inside of cap still no change
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Old 11-06-2013, 08:36 PM   #7
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Is the cap and rotor good?
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Old 11-06-2013, 09:34 PM   #8
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Replaced with new
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Old 11-07-2013, 08:19 AM   #9
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I'm wondering if there is a vacuum leak somewhere. Since you stated the PO replaced a lot of sensors already, either the seals/gaskets may be leaking or a vacuum line broken or disconnected somewhere.
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Old 11-07-2013, 09:07 AM   #10
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Vacuum is good steady at 19 at idle checked with carb cleaner no leaks everything is in order I just ordered a new distributor pick up coil should be in this afternoon
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Old 11-07-2013, 07:49 PM   #11
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We'll pickup coil didn't work I'm at a loss anyone else have any suggestions everything tests fine at idle only misses after warmed up under 2200 rpm
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Old 11-07-2013, 08:26 PM   #12
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timing chain? bad/clogged injector? Could be many things. When my old xj did something like this, I took off the throttle body, removed all sensors and cleaned it up in carb dip, couple new gaskets and the problem vanished. Might have to take it to someone who knows their stuff before you dump a ton of money fixing stuff that isn't broken
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Old 11-08-2013, 04:57 PM   #13
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How about the plugs?
If idle changes after warmup it could be faulty temp sensor. A vacuum leak should give you a faster idle.

How old is the o2 sensor?

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