Misfire misfire misfire

97 Sport- 4.0, AX, NP 231, not that the trans and Xcase should matter since it feels like its a fuel supply or air issue.

First of all no codes or CEL. Now for the problem, it almost feels like the same thing as when the TPS was shot. It sort of surges, not really throttling up by itself, but power will drop off for a split second sporadically then jump back up real quick. Just happened this mourning on the way to work, then again on the way home. Both times it did not present itself while idling to warm but while it was on its way to operating temp while driving. While idling at a light it kind of stumbled a bit when it wasn't up to operating temp as well. Once operating temp was met it ran like a champ. CEL never came on but I figured I would stop by and see if there were any stored codes from when it was acting up that just didn't trip the CEL, no codes. I'm gonna go down and clean the IAC right now but figured I'd post this in the meantime and see what kind of responses I come back to.

Also, as of late I have been noticing my fuel mileage gas been dropping, which I would expect with a misfire, but mileage was dropping before misfire presented itself.

Other thoughts I have(please rule these out if they don't seem right):
O2 sensors
Cat clogged
IAC
Fuel pressure
CKP(but don't these typically fail once warmed up)

Any other suggestions throw them out there.

Thanks, Josh

the odb2 system will hold a set of codes that might be a problem but it will not save them once the key is turned off. if you bring it somewhere to get checked. drive around for a wile. then do not shut off the jeep just hook up the scan tool and look at pending codes.

*Test your throttle position sensor
*Verify fuel pressure is solid with a GAUGE
*Test your coolant temperature sensor
*Always be sure tuneup hardware is fresh when chasing a symptom. Plugs, wires, cap, rotor

This does not sound like a crank sensor or a clogged cat.

birchlakeXJ said:

*Test your throttle position sensor
*Verify fuel pressure is solid with a GAUGE
*Test your coolant temperature sensor
*Always be sure tuneup hardware is fresh when chasing a symptom. Plugs, wires, cap, rotor

This does not sound like a crank sensor or a clogged cat.

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couldn't say it better myself.:laugh3:

My buddies Dakota had the exact same symptons... and no codes... tune-up fixed everything. Start there.

thanks for all the responses.

Sooo, a little bit of an update. After it started acting up the first time I let it be for a few days and came back to it. The symptoms pretty much were non existent, so I drove it for a few weeks and now (yesterday) it is doing it again...

here is what has been done:

-tuneup was completed- no change, no big deal cause it probably needed done anyway, its been a while.
-CTS was swapped with a brand new NAPA unit (needle was getting wavy in the weeks I have been driving it lately so I just swapped it)
-MAPS and TPS were swapped with known working units, problem persisted
-fuel pressure with a gauge tested good
------

I have yet to check the O2 sensors, but aren't they open loop until the vehicle gets to operating temp.
IAC wasn't touched so i have look at and clean that.

Other than this, I have no clue... so any other suggestion are welcome

Maybe i missed it but have you performed a compression test? Wet and Dry

i haven't actually, would make some sense that it goes away after heating up i guess.metals expand and contract causeing it to diminish once it reaches operating temp. ill test comp when i get home just to rule that out. im still leaning toward a bad sensor though, just got to get off my ass and test stuff

finally got around to testing stuff and it turns out the upstream 02 sensor was sending a signal before the engine got to operating temp and was throwing it out of whack... so for future refence i thought i would throw that up here so people experiencing the same thing might have a place to start

gremlins.

the o2 should go closed loop as soon as the coolant temp gets up. make sure you t-stat is good as well. otherwise if it is weak you can have driveability issues as it will go closed loop on a cold engine which is not optimal as it can cause lean misfires...

amcjeep said:

the o2 should go closed loop as soon as the coolant temp gets up. make sure you t-stat is good as well. otherwise if it is weak you can have driveability issues as it will go closed loop on a cold engine which is not optimal as it can cause lean misfires...

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The engine heats up as it should and the t-stat is good. I just serviced the whole cooling system and threw in a stant super stat (its all ill use beside OEM). The problem was present before and after I did the cooling system, its weird but it appears to have been just the O2 sensor cause its been running good for three days now.