Well Crud! Another '96 XJ with an Intermittent Stalling Issue

[Anak]

Had breakfast with some friends early this morning. When I left my XJ started right up and then stalled immediately. That is a new one. Tried to re-start, no go. Turned the key all the way off and tried to re-start and it started. Drove two blocks and it stalled. Took several tries to get it re-started, but it finally did. Drove two blocks and it stalled again. No re-start that time. Called AAA and got it towed home.


Immediately checked fuel pressure. None showing at the rail, but after a couple cranks it came up to pretty close to 49 psi (close enough to consider the accuracy of the gauge) but still would not start. When I shut it down it immediately bleeds down to 20 psi. Has been that way for years. Need to pull the pump assy and shim the fuel pressure regulator I think. '96 issues.


I don't think it is a fuel problem.



Moved on to CPS. Found the loom on the CPS sensor has melted. Not a good sign. Wondered if that meant the wiring has heated up. Pulled the CPS. This is how it looks:

While not ideal, the wiring itself does not appear damaged. It is just the loom that has melted. And that loom is probably aftermarket loom, not factory. FWIW I am running a Borla header. I have also been chasing an intermittent detonation issue which seems to be temperature related. That may tie in to this melted wiring loom, but I don't think it is the key to the stalling issue. Temps this morning were in the high 40s.


I did put in another CPS. I can't say new. It is a used spare. Arguably a better option than what I could buy new. Still no change. Vehicle still would not start.


Next step was to check for injector pulse. Pulled the plug off injector #1 and plugged in a noid light. Initially no start, but then all of a sudden it came to life. Threw a P0201 code (#1 injector--no surprise since that injector plug was off), but that is the only code so far.


Took it for a spin, everything seems normal.


But now I don't know what is wrong.



Did the CPS change make a difference? I decided to reinstall the CPS with the melted loom. Jeep starts right up. That suggests CPS is not the issue.


Now what?


I guess I have to wait for it to repeat the problem, and who knows when/where that will occur. Time to start carrying around a fuel pressure gauge and a multimeter. (I do that when traveling, but not usually in DD mode.) Might be time to make some jumpers to bypass some relays too.


Any suggestions?

 

[wbnickens]

My 2000 Xj did the same thing years ago. I changed the crank PS, was not the problem.
I eventually found a bad connection at the cam PS, my fault, repaired connection-fixed.

 

[Unclewolverine]

Still sounds like a fuel pump on its way out to me.

 

[Anak]

I could believe that if it would have started when the fuel pressure was at 49 psi. But with full fuel pressure it still would not start. And I gave it plenty of opportunity.

I was hoping (to the extent that is reasonable) that it were the fuel pump. The symptoms made sense. It could even help explain the detonation issue. I even have a replacement on hand for when the day comes I need to replace it. But I don't think the diagnosis justifies it. And I don't want to throw parts at the issue and end up still in the dark as to whether or not I have fixed the root cause.

 

[Unclewolverine]

Understandable. Probably the same thing that makes mine take forever to start, which at this point is either the map sensor, injectors or ecm; those are the only parts that haven't been changed on my 95.

 

[Bent]

Fixed itself, huh? Sounds British Leyland to me.

 

[Anak]

It is an annoying situation.

I am driving it around, running errands, just waiting for it to repeat conditions. I have both a fuel pressure gauge and a noid light handy so that I can immediately check both pressure and injector signal.

I would really like to pin down the problem and fix it before I find myself needing to take it on a long trip.

 

[Runnin'OnEmpty]

We need to solve these intermittent stalling
problems. They are making me nervous to
drive my 96. (It's already stranded me once.)

My thought keeps coming back to the ASD relay...?

 

[Mrpd1501]

My vote is on there being a curse on the 96 because someone at the factory got fired and called their brujo. Now we all gotta suffer.

 

[Anak]

It is indeed worrisome.

I find it somewhat ironic that while Mrpd1501 is dealing with a stalling issue that happens when warmed up, one of the theories I am tossing around is that my problem is cold related. Last Friday morning was the first relatively cold morning we have had in quite a while. My XJ enjoys the luxury of being garaged, so it would have started off its morning warmer than the ambient temperature. But when I went to leave the restaurant it would have gotten cold. And later in the day when it "fixed" itself it would have warmed back up as the ambient temperature warmed things back up.

Need more data points before I can move any theories forward or backward.

 

[Anak]

My vote is on there being a curse on the 96 because someone at the factory got fired and called their brujo. Now we all gotta suffer.

Something to keep in mind, if these numbers are accurate, '96 is the year with the highest production volume:

84-93,326
85-120,328
86-107,225
87-139,295
88-187,136
89-207,216
90-151,230
91-151,578
92-137,826
93-144,961
94-123,391
95-120,234
96-286,463
97-258,958
98-182,845
99-186,116
00-165,590
01-120,454

So, while you see more problems come up with '96s, keep in mind, there were more of them made than any other year.

 

[techno1154]

My '96 did the same thing late last year. It took a coil to get it running again. Threw everything every sensor I had at it. I have not taken it on long trips since then. I still experience hard starts intermittently. I have no idea what causes them but other than that runs really well.

Looking back, the only thing I did to it about 1,000 miles prior to it shutting down the first time was to replace the fuel pump with one off Amazon...a little different from the EOM but fit the bill. Today, my hard starts coincide with fuel pump run on. I.E., with the ignition on, the pump keeps running, fuel pressure 50 psi and yet no start. If I turn the key off, then on until the pump shuts off in the normal 5 seconds +/- the engine starts right up. My only other observation is the fact the engine is running a bit lean. The exhaust tip is a light brown color confirmed by spark plug reading. I did notice that if I disconnect the battery for a few minutes, it will start right up.

I do not want to throw parts at it, but I think I will try to get a replacement OEM fuel pump to eliminate that one item. My only other thing I plan to look at is the grounding of the pump and tank itself. I will check to see where on the body the fuel pump gets its ground. Static electricity buildup is what comes to mind.

 

[maxbraketorque]

No-start and stalling issue aside, it would be good to find the source of the melted wiring insulation. Sensor signal wiring is not high electrical power, so something besides a short circuit caused the insulation to melt.

 

[techno1154]

No-start and stalling issue aside, it would be good to find the source of the melted wiring insulation. Sensor signal wiring is not high electrical power, so something besides a short circuit caused the insulation to melt.

Too close to the exhaust manifold.

I forgot to add, pinging at certain RPM and load. Never at wide open throttle. Could it be the TPS purchased from the local discount parts store?

 

[Anak]

For maxbraketorque: Wiring is not what melted. Wiring loom melted. Apparently I need to find the high temp wiring loom. The stuff I have been getting at the auto parts store is only fit for use under the dash or some such place. I peeled the melted plastic off the wiring and the wiring is still pliable, the insulation un-harmed. I put that CPS back in and am continuing to run it, but I added an extra zip tie to pull it closer to the firewall.

For techno1154: I don't know if it would be that TPS or some other sensor. I think (and I could be wrong--someone who knows please chime in) that at WOT the computer runs entirely off a programmed table, without using input from O2 sensors and such. If that is indeed the situation then it would suggest that you have a problem with the inputs the computer is using to calculate timing and fuel. The challenge is to figure out which input. TPS, MAP, IAT, O2, Coolant temperature...am I missing any? All of those are potential suspects.

 

[Runnin'OnEmpty]

My '96 did the same thing late last year. It took a coil to get it running again. Threw everything every sensor I had at it. I have not taken it on long trips since then. I still experience hard starts intermittently. I have no idea what causes them but other than that runs really well.

Looking back, the only thing I did to it about 1,000 miles prior to it shutting down the first time was to replace the fuel pump with one off Amazon...a little different from the EOM but fit the bill. Today, my hard starts coincide with fuel pump run on. I.E., with the ignition on, the pump keeps running, fuel pressure 50 psi and yet no start. If I turn the key off, then on until the pump shuts off in the normal 5 seconds +/- the engine starts right up. My only other observation is the fact the engine is running a bit lean. The exhaust tip is a light brown color confirmed by spark plug reading. I did notice that if I disconnect the battery for a few minutes, it will start right up.

I do not want to throw parts at it, but I think I will try to get a replacement OEM fuel pump to eliminate that one item. My only other thing I plan to look at is the grounding of the pump and tank itself. I will check to see where on the body the fuel pump gets its ground. Static electricity buildup is what comes to mind.

Here's my theory:
The ASD relay powers the coil, fuel pump, and probably
the injectors upon startup and while running. Since
your fuel pump continued running after the timeout,
I believe the contacts were sticking closed in the
ASD relay. High resistance at the contacts could also
affect the voltage to the coil and fuel pump, possibly
causing the detonation too. Since so many systems
depend on this relay, I'd take a good hard look at it.

 

[maxbraketorque]

For maxbraketorque: Wiring is not what melted. Wiring loom melted. Apparently I need to find the high temp wiring loom. The stuff I have been getting at the auto parts store is only fit for use under the dash or some such place. I peeled the melted plastic off the wiring and the wiring is still pliable, the insulation un-harmed. I put that CPS back in and am continuing to run it, but I added an extra zip tie to pull it closer to the firewall.

For techno1154: I don't know if it would be that TPS or some other sensor. I think (and I could be wrong--someone who knows please chime in) that at WOT the computer runs entirely off a programmed table, without using input from O2 sensors and such. If that is indeed the situation then it would suggest that you have a problem with the inputs the computer is using to calculate timing and fuel. The challenge is to figure out which input. TPS, MAP, IAT, O2, Coolant temperature...am I missing any? All of those are potential suspects.

ok on the split loom stuff.

By WOT, I imagine you mean open loop fuel control. Both open and closed loop fuel control calculate a target fuel pulse width based on input from TPS, MAP, IAT, RPM, coolant temp, and battery voltage. The fundamental difference between the two modes is that in closed loop the calculated target fuel pulse width is modified by O2 sensor feedback to actively maintain 14.7:1 AFR. Actual WOT wouldn't be any different than open loop, i.e., no use of O2 sensor feedback. Ignition timing on the XJ doesn't have closed loop. Always relies on the same things - TPS, MAP, IAT, RPM, coolant temp, and battery voltage - without feedback from a knock sensor (sadly).

 

[maxbraketorque]

I keep forgetting the Renix XJs have a knock sensor...

 

[Anak]

ok on the split loom stuff.

By WOT, I imagine you mean open loop fuel control. Both open and closed loop fuel control calculate a target fuel pulse width based on input from TPS, MAP, IAT, RPM, coolant temp, and battery voltage. The fundamental difference between the two modes is that in closed loop the calculated target fuel pulse width is modified by O2 sensor feedback to actively maintain 14.7:1 AFR. Actual WOT wouldn't be any different than open loop, i.e., no use of O2 sensor feedback. Ignition timing on the XJ doesn't have closed loop. Always relies on the same things - TPS, MAP, IAT, RPM, coolant temp, and battery voltage - without feedback from a knock sensor (sadly).

Thank you for the clarification.

I knew there was a closed loop mode, just not exactly what was/was not in play.

 

[techno1154]

I have swapped the relay around several times and have the same results with each relay. Is there a difference in relays? I am going to throw a few sensors at it to see what helps.

Anak,
I throw my experiences in your post to see if we have something in common. I did clean the grounds in the engine bay which did not make a difference. My next move is to see where the fuel pump is grounded and renew clean/it. Not sure that will help but it is worth a shot.