96' Xj stumbling and dying (I have searched and read for hours)

Hey guys, I'm a very long time lurker here and have learned many helpful things here and used many of them to keep my jeep on the road.
I have unfortunately run into a problem that's kicking my rear and I cannot seem to figure it out.

First off:

Plugs and wires are brand new and gapped to .35
Dist, cap and rotor are brand new
Fuel pump, strainer and filter are brand new
Fuel pressure reads 51 psi all day long
New upstream 02 sensor (xj had no cat, a cherry bomb and no downstream 02 sensor when I bought it and I haven't changed it yet as there is no wiring for the downstream 02 sensor)
Just performed an engine swap now I have this problem
Intake and exhaust manifold gasket is brand new
Coil is about 6 months old
Cps is about 6 months old

Now, as stated in the header I have read and searched for hours a day looking for things to try without an oscilloscope or serious equipment having to come into play.($$$)

After the engine swap (96 xj engine with 130,xxx to replace my 96 xj engine with 200,xxx) the first two days of driving went great everything running smooth as butter. Day three I went out to start my jeep and it started right up but stumbles randomly every few seconds, sometimes several stumbles in a row and it will randomly die even if idling smooth. It starts right up every time it dies without hesitation or extended crank, except for when I'm driving it sometimes takes a few tries and some coaxing with the skinny pedal to start. It stumbles at any rpm (stumbles worse when driving) and will sometimes die as I am slowing down and coming to a stop. I cannot figure this one out and I am on a college (poor) budget so I am trying to pinpoint this rather than throw parts at it. The thing that confuses me is it doesn't feel or sound like a misfire it feels like all 6 cylinders want to shut down for a second then it catches and keeps going.

Specs: 96' xj 4.0 197,xxx on the body and 130,xxx on the engine. It also has a 3 inch lift but that doesn't matter with my problem.

Can anyone give me some tests to run to help diagnose this?

Thanks,
Trent

Check your ignition coil

I've had similar happen a few times for different reasons. CPS, new doesn't mean good and also the CPS wires and connector are always suspect. Be sure and check the CPS wires aren't cooking on the exhaust manifold.

IAC, usually happens when your foot is off the gas pedal, it can't seem to make up it's mind now to adjust the idle and the motor dies. This doesn't sound like your issue though, as you said you tried to coax it back to life using the gas pedal. In most cases when this happened to me there was some sort of charging issue involved and the IAC wasn't actually at fault.

I had an issue with a splice in my 96 that would limit the voltage to the ASD relay coil and likely other functions on the same ignition run circuit. I had a hunch about that circuit when my 96 was acting up, it finally crapped out in the middle of an intersection in 18 inches of snow. I started shaking harnesses and got lucky.

I had an O2 sensor wire cooking on the exhaust that eventually dumped battery voltage into my the O2 ECU sensor circuit. It acted a lot like a bad CPS. No idea what actually happened, I just know the ECU would randomly act up, I'd get a serious misfire and motor would barley run.

Something easy you can check, pull and re-seat all your spark plug cables at the plugs and the cap. Check and make sure all the wires are properly crimped onto the spark plug cable. You may want to ohm check all the wires, there are only seven of them. High resistance in a high voltage circuit (or a moisture path to ground) may only act up occasionally. Once the spark jumps to the wrong spot it tends to stay on that path, but may only jump to the wrong spot occasionally. A little WD-40 or something similar (I use silicon) on the end of your finger and rubbed on the insulated part of the plug or distributor cap contact towers (not the metal) really helps when seating the cables and helps avoid the cables back sliding into the boots and helps to make sure they are seated all the way in and making good contact.

Could be another sensor, something really necessary for the motor to run, like the MAP.

Have you checked our MIL codes? My 96 has the key method, flashing check engine light code function. It may steer you in a fruitful direction, but don't count on it as being the last word when troubleshooting, it will fool you.

8Mud said:

I've had similar happen a few times for different reasons. CPS, new doesn't mean good and also the CPS wires and connector are always suspect. Be sure and check the CPS wires aren't cooking on the exhaust manifold.

IAC, usually happens when your foot is off the gas pedal, it can't seem to make up it's mind now to adjust the idle and the motor dies. This doesn't sound like your issue though, as you said you tried to coax it back to life using the gas pedal. In most cases when this happened to me there was some sort of charging issue involved and the IAC wasn't actually at fault.

I had an issue with a splice in my 96 that would limit the voltage to the ASD relay coil and likely other functions on the same ignition run circuit. I had a hunch about that circuit when my 96 was acting up, it finally crapped out in the middle of an intersection in 18 inches of snow. I started shaking harnesses and got lucky.

I had an O2 sensor wire cooking on the exhaust that eventually dumped battery voltage into my the O2 ECU sensor circuit. It acted a lot like a bad CPS. No idea what actually happened, I just know the ECU would randomly act up, I'd get a serious misfire and motor would barley run.

Something easy you can check, pull and re-seat all your spark plug cables at the plugs and the cap. Check and make sure all the wires are properly crimped onto the spark plug cable. You may want to ohm check all the wires, there are only seven of them. High resistance in a high voltage circuit (or a moisture path to ground) may only act up occasionally. Once the spark jumps to the wrong spot it tends to stay on that path, but may only jump to the wrong spot occasionally. A little WD-40 or something similar (I use silicon) on the end of your finger and rubbed on the insulated part of the plug or distributor cap contact towers (not the metal) really helps when seating the cables and helps avoid the cables back sliding into the boots and helps to make sure they are seated all the way in and making good contact.

Could be another sensor, something really necessary for the motor to run, like the MAP.

Have you checked our MIL codes? My 96 has the key method, flashing check engine light code function. It may steer you in a fruitful direction, but don't count on it as being the last word when troubleshooting, it will fool you.

Click to expand...

I appreciate the input and I will get to checking those things out, sounds like I need to go get some t pins and get testing. I just found this:

Cyl 1 105 psi
Cyl 2 110 psi
Cyl 3 120 psi
Cyl 4 120 psi
Cyl 5 120 psi
Cyl 6 120 psi

Thoughts? Blown head gasket between 1 and 2 cylinders? I wont be able to do a leakdown test until tomorrow. Keep the suggestions coming guys.

Edit: Put an inline spark tester between coil and dist. cap and it has a strong spark coming from the coil. Although I'm not sure how effective a test that is, I do know that it has a spark.

I had a similar issue once. I described mine as a violent shutter though.

You could see the tach bounce to 0 and back.

I just wouldn't be so fast to discount the lift. Did you lower the transfer case?

If so...you could be pinching the wiring harness at the firewall.

This could also occur because of engine swap....

I found bare wires that were touching after pulling on harness while idleing.

Easy enuff check it.

I'm about to start ripping hair out... I have wiggled and visually inspected every wire and connector and harness and I cannot get the stumble to happen at will. It is still completely random. A couple things I have noticed are sometimes once a little warm it will drive okay for a few minutes at a time (this is driving me nuts.) Also I drove it last night and got it up to 45 mph and when it stumbled at 45 it was very violent, the jeep lurched hard forward and I immediately let off for fear of driveline components. I will physically take my grounds off and clean them and see if it helps.

I know the feeling(hair pulling). Is the tach bouncing from 0 to whatever rpm you were at? Mine would happen mostly when I hit a bump. Seriously INSPECT the shit out of the wiring harness behind valve cover by the firewall. Get your ass in the air and do it!

greychalet said:

I know the feeling(hair pulling). Is the tach bouncing from 0 to whatever rpm you were at? Mine would happen mostly when I hit a bump. Seriously INSPECT the shit out of the wiring harness behind valve cover by the firewall. Get your ass in the air and do it!

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No, the tach will only drop about 300-500 rpm and then it will catch back up or it will just die. Yup, back to inspecting the wiring. Bottoms up...:moon:

LOL. I have never seen that emoticon.

I had a similar issue, turned out to be an intermittent cps failure. Spark looked good when I.checked it, but would cut in and out once I wasnt looking

souske said:

I had a similar issue, turned out to be an intermittent cps failure. Spark looked good when I.checked it, but would cut in and out once I wasnt looking

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I call it chasing a ghost... This one is kicking my A**. I get paid Tuesday I will get an oem one instead of the idiotzone cps I have installed and see what happens.

Update:

Replaced cps with a new unit, no fix.
Replaced ASD and fuel pump relay with no improvement.

My gut keeps telling me I have a fuel problem, when I install a fuel pressure tester and it stumbles the fuel pressure goes up 3-5 psi. (Is this bad?) Also when I shut the jeep off the fuel pressure drops to 20 psi in 30 seconds and is at zero within a minute and a half. Bad regulator?

I just cannot seem to find a problem with any connections, wires or harnesses which makes me think fuel delivery as its been a battle with the fuel system with this jeep ever since I bought it. Stupid ethanol :smsoap:

I have seen a few fuel related issues where the short hose from the fuel pump to the mounting bracket was cracked or came loose. Does it do it worse when the tank is almost empty?

The compression numbers are not great, but that shouldn't be your problem. Compression causes an overall low power and doesn't come and go. If you had an EGR I would blame that. I would possible put a vacuum gauge on it and run it up and tape it to the windshield so you can read it while you drive. It will tell you a lot.

When it stumbles, does it make any funny noises? Things that come to mind are a sticking valve, a vacuum leak on the intake somewhere, a leaky hose to the MAP, a CAT with broken up matrix that sometimes restricts the flow, a flakey fuel pump/hose. Are you sure you don't have a spark plug wire arcing over to another wire or ground?

An intermittent O2 sensor can drive the ECU crazy trying to compensate for a problem that isn't there. I'm a Renix guy and am not that familiar with the newer systems.

old_man said:

I have seen a few fuel related issues where the short hose from the fuel pump to the mounting bracket was cracked or came loose. Does it do it worse when the tank is almost empty?

I've been down this road, it was one of the first things I checked.

The compression numbers are not great, but that shouldn't be your problem. Compression causes an overall low power and doesn't come and go. If you had an EGR I would blame that. I would possible put a vacuum gauge on it and run it up and tape it to the windshield so you can read it while you drive. It will tell you a lot.

I will do this today.

When it stumbles, does it make any funny noises? Things that come to mind are a sticking valve, a vacuum leak on the intake somewhere, a leaky hose to the MAP, a CAT with broken up matrix that sometimes restricts the flow, a flakey fuel pump/hose. Are you sure you don't have a spark plug wire arcing over to another wire or ground?

Now that you mention it I can hear a small noise coming from the front of the engine (sometimes) but only at idle and when it really dips low in the rpms like its going to die. Its just a quick rattle. Also I think I hear a small vac leak and I'm having trouble locating it but I will keep at it. Can't I use carb cleaner to spray around and find a leak?
An intermittent O2 sensor can drive the ECU crazy trying to compensate for a problem that isn't there. I'm a Renix guy and am not that familiar with the newer systems.

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I will re- check my codes. Thank you

Someone suggested the ignition coil, have you replaced it?

RedHeep said:

Someone suggested the ignition coil, have you replaced it?

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I tested it with a DVOM and it checked out although I have read that test is not 100%...maybe its time for a new one.

redxj94 said:

I tested it with a DVOM and it checked out although I have read that test is not 100%...maybe its time for a new one.

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It's a $15 part prone to failure from heat, water, etc. And it's often intermittent.

I had similar issues, but for me it turned out to be a coolant temp sensor located in the thermostat housing. It was difficult to diagnose until I saw the water temp gauge fluctuate and wander.
Maybe running it disconnected will give you a clue. Im only guessing here, but at least it could be another lead for you.

CaliGold said:

I had similar issues, but for me it turned out to be a coolant temp sensor located in the thermostat housing. It was difficult to diagnose until I saw the water temp gauge fluctuate and wander.
Maybe running it disconnected will give you a clue. Im only guessing here, but at least it could be another lead for you.

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If he's got a '96, the sender in the tstat housing is for the computer and the one in the head is for the gauge.

I had very similar problems with my 92 w/ 230K but without the dying. My problems were the 2 pcv intakes under the valve cover. They were completely clogged giving the computer a false reading and fattening the motor. Cleaned them and now it runs like a top. Pull the PCV elbow off and look down in. If it looks like there's a bunch gunk in there I would pull cover and check. Hope this helps