engine studder...

'97 xj, 4.0, ax-15, 231

on the way home from a bit of wheeling im cruising down the highway. suddenly i got a violent jerk, jeep gets kicked out of cruise control, and CEL comes on. the engine continues to studder, and then i pull over. i double check everything under the hood i can (found a rats nest in the air box). no improvements. all fluids are fine, no leaks, all connections are good. so i stumble home... all of 125-150 miles.

during the drive, i caught onto something. the stumble comes on the deceleration. the motor runs through the RPMs fine in nuetral. but on the road the "jolt" typically comes when the vehicle comes from pulling under power and then dropping RPMs. say im traveling up hill, or accelerating, everything is fine. but as soon as i crest the hill and start going down or simply lift off the gas i get a pretty violent jerk.

when i pulled in the driveway i pulled all the plugs, and everything looked fine. its 3am, and im stumped and tired. can anyone in the world of naxja help me out?

a couple notes, idk if they are relevant or not:
- oil pressure was all over the place.
- tranny has a lot of grinding (ive been meaning to replace the master/slave cylinders).
- voltage was at normal levels or below, very quirky.
- im sure im forgetting something...

- havent opened up the distrubutor to look at it.

its 3am, bed sounds nice. F the heep. itll still be there in the morning.

If it is related to gas pedal position, like backing off at the crest of a hill, I'd check the TPS for smooth continuity with an analog voltmeter.

i woke up this morning, i think its worse than i thought. i found this behind my jeep:


the bigger splatter is new, think it blew out when i started it this morning. my guess would be that the finner spray is from the night before. this would attribute to wacky oil pressure i suppose. engine temp ran 210. runs like complete crap now.

F my life...:rattle:

i added half of a quart last night when my oil pressure dropped. i managed to get home with fairly good pressure. checked the oil this morning and its well into the "FULL" area. doesnt look like its got coolant in it.

but the coolant looks fairly dark and merky. what are the chanes i cracked the head?

Is that black soot on the ground?

oil.

are you sure it's oil?? It looks like soot from an extra rich mixture or a dead cylinder. Check the vacuum line to the MAP and make sure you've got a dry distributor cap. Good luck!

Eliminate all of the simple solutions first before you start exploring the complicated solutions. 97's are not known for head gasket/cracked head issues.

Shorty said:

are you sure it's oil?? It looks like soot from an extra rich mixture or a dead cylinder. Check the vacuum line to the MAP and make sure you've got a dry distributor cap. Good luck!

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well... it was liquid. i didnt think to check and smell for an odor. i didnt think soot right away, as im not aware of it being in liquid form. i could by all means be wrong though. distributor was checked on the side of the road last night.

i will take a closer look though, and check for deposites. will check vacume lines as well.

xjtrailrider said:

Eliminate all of the simple solutions first before you start exploring the complicated solutions. 97's are not known for head gasket/cracked head issues.

Click to expand...

any suggestions on where to start. im stumped, in the last 13 years shes never given me a fit like this.

VAhasnoWAVES said:

well... it was liquid. i didnt think to check and smell for an odor. i didnt think soot right away, as im not aware of it being in liquid form. i could by all means be wrong though. distributor was checked on the side of the road last night.

i will take a closer look though, and check for deposites. will check vacume lines as well.


any suggestions on where to start. im stumped, in the last 13 years shes never given me a fit like this.

Click to expand...

Condensation mixed with soot? A lot of moisture comes out of a tailpipe. Wipe your finger around the upper 2/3 of the tailpipe--sooty?

:idea:

Shorty said:

It looks like soot from an extra rich mixture or a dead cylinder.

Click to expand...

well... now that you say that. last night i did smell a very strong odor of gasoline. almost as if it was flooded. it was deffiantly liquid this morning though. like i said, i didnt notice a particular odor. maybe gasoline making its way through? spark plugs looked fine like i said.

so what would be the best course of action... compression test?

Test the MAP sensor first, but yes a compression test and vacuum test will tell you worlds about the condition of the engine. Pull the dipstick and smell the oil.

sorry our wheelin trip turned into a repair job for ya ha. I am gonna go along with the map. What you are describing and what I see from your pics is a VERY rich mixture if I had to guess. Esp with all that water flying up in there... it may have shorted the sensor out. That is what happened to an XJ I had. There are plenty of write ups online about how to check it. Here is a pretty good one: http://www.cherokeetalk.com/forum/f64/map-sensor-test-procedure-1261/

Now if all checks out there a compression test is worth a look. But the tough thing about it is you say the plugs looked fine. can you define fine? Normal brown on the insulator? Black insulator?

And just a random side note: the cruise uses vacuum. You saying it kicked out of cruise makes me wonder if a vac line popped off... there are a few FREE things to check before you spend money. Vacuum is the biggest PITA to track down but look at the places that are obvious first.

the MAP sensor is the little guy on the drivers side of the throttle body correct? ill have to give it a proper check.

fine as in expected/desirable looking. no signs of carbon deposites or anything. never checked the gappage though. hell... i dont even know what the gappage is supposed to be. :wow:

the cruise kicked out as soon as the CEL came on. i could be wrong, but i think the CEL deactivates the cruise function in order to discourage from long travel.

VAhasnoWAVES said:

the MAP sensor is the little guy on the drivers side of the throttle body correct? ill have to give it a proper check.

fine as in expected/desirable looking. no signs of carbon deposites or anything. never checked the gappage though. hell... i dont even know what the gappage is supposed to be. :wow:

the cruise kicked out as soon as the CEL came on. i could be wrong, but i think the CEL deactivates the cruise function in order to discourage from long travel.

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I have had 2 XJ's with the CEL on that the cruise worked just fine in... too bad it didn't happen here. I have a scanner in my jeep ha. However we may both be right. Maybe certain codes disable cruise? But I have never seen one personally for what it's worth.

The gap I wouldn't worry too much about. It is supposed to be .035, at least on my XJ it is. But if the plugs look alright that wouldn't give you the sudden reaction you spoke off.

The MAP sensor will have a little vacuum line running into it. I am going to assume your 97 is the same as my 96 in this department. On mine it is the sensor on the left side (drivers side) of the throttle body.

Another thing to look at would be the TPS. I have never had one go bad. But Ben said his TJ kicked out more than one from minimal amounts of water. From what he knows the 97 had a different design TPS than others. Don't quote me on that since its second hand info but its another thought.

I just went through the exact same scenario. To make a long story short, my header (APN) was cracked in 3 places with a done-in motor mount.
New motor mounts and header install = All my power back, no more rich condition, better gas mileage and a big f*ckin smile on my face!

redxj_07 said:

I have had 2 XJ's with the CEL on that the cruise worked just fine in... too bad it didn't happen here. I have a scanner in my jeep ha. However we may both be right. Maybe certain codes disable cruise? But I have never seen one personally for what it's worth.

The gap I wouldn't worry too much about. It is supposed to be .035, at least on my XJ it is. But if the plugs look alright that wouldn't give you the sudden reaction you spoke off.

The MAP sensor will have a little vacuum line running into it. I am going to assume your 97 is the same as my 96 in this department. On mine it is the sensor on the left side (drivers side) of the throttle body.

Another thing to look at would be the TPS. I have never had one go bad. But Ben said his TJ kicked out more than one from minimal amounts of water. From what he knows the 97 had a different design TPS than others. Don't quote me on that since its second hand info but its another thought.

Click to expand...

like i said, thats what i had heard about the CEL and cruise. but dont take that as gospel.

and yes, i identified that MAP on the throttle body on the drivers side. but here is where im stumped... i fail to see any vacume line, connected or otherwise. and i also fil to see were one would go.

VAhasnoWAVES said:

like i said, thats what i had heard about the CEL and cruise. but dont take that as gospel.

and yes, i identified that MAP on the throttle body on the drivers side. but here is where im stumped... i fail to see any vacume line, connected or otherwise. and i also fil to see were one would go.

Click to expand...

It is under the sensor... pretty much in the center. It is just a little elbow that goes from the throttle body into the sensor. Again its pretty small so you will have to feel around the bottom to find it.

any engine codes?

sounds silly, but try disconnecting your 02 sensors and see if it runs better. The o2's went out on my jeep (98' 4.0 ax-15) a few months ago and it resulted in the feeling of a miss fire at idle, and a very rich smell. I've had o2 sensors on other cars literally spit raw fuel out the tail pipe... so i'd check into it.

Though by the symptoms it sounds like it would have been the TPS, when mine went out i got a bucking at cruise speed every few minutes, and at idle it would want to stall/wouldnt idle, and when giving it gas it would hesitate for a second and then slam on the power.

anthony- really? i failed to see it. ill double check tomorrow. i went through trying to check the MAP today and all i concluded was that it was getting the power it needed. im sure there is some differences between years, and the link you gave me didnt seem to match mine. it could have been operator error though. haha. my manuel is MIA, so i couldnt find the wiring chematic for my particular year.

banditt007- sounds exactly like my symptoms. there is a code, but i havent pulled it. the jeep made it home and its sat there since. i question the O2 sensors as well, but have not messed with them. though i also hear an exhaust leak around the manifold, guessing a cracked header... my cat is rotted out and sounds like marbles, and i found holes/cracks in my muffler as well. im sure NONE of that is helping.




i need to get the code read, thatll be a good starting point. will update as i get more info.