2001 XJ dies at highway speed

[BattlebornXJ]

Hello all,
I'm an old guy and have little experience with forums so go easy on me.
I have two nearly identical XJ's. A 2000 and a 2001. The 2000 is just fine, it's the 2001 that is giving me a migraine. I say this because I'm swapping known working parts between the two to eliminate possibilities. That being said, here's my problem...
It's hot here now in Nevada, 108 degree average afternoon high (my problem definitely occurs way more often when the weather is hot). My jeep will die at freeway speed if driven at 65mph+ for 10-20 minutes at this temperature. I pull over and turn off the key. It will re-start immediately, but will hesitate and stutter if I don't let it sit and cool for at least 5 minutes. After 5 minutes it will start and accelerate normally back to 65mph, but will die again in a mile or two. If let it cool (with the hood up) for 20 minutes, I will make it another 10-15 miles before it dies again. If I can get off the freeway and take surface streets, it will drive all day with no further issues. So as see it, driving constantly at freeway speed in the heat causes it to die. And letting it cool down definitely helps, so heat must figure into the problem somehow. But at the same time, driving on surface streets where the jeep runs at a higher temp and in a hotter environment, it will run fine. I have swapped out the following parts that I know are functioning properly from my other jeep: Crank position sensor, TPS, ignition relay. I tried the PCM but the 2001 has a skim key and it destroyed the PCM from the 2000 (or so i'm told). DON'T try a PCM swap unless you know what you're doing! The fuel pressure at the fuel rail is good, and fuel will squirt from the test port schrader if pressed immediately after the jeep dies. I've been beating my head against this rock for a few months now with no solution. Any suggestions would be greatly appreciated. Thanks


2001 XJ, 4.0 engine, 140k miles, AW4 transmission, NP 231 transfer case. 3.5" lift but stock in every other way

 

[Tim_MN]

Is, or was the Check Engine Light ON ? Have you checked for any current or pending trouble codes with a trouble code reader ? If you do not have one, most auto parts stores will loan you one, but you should own one yourself. It would be a really good idea to buy one with Live Data so you can see what is going on instantly.

What is missing when it stalls, spark at the plugs or fuel pressure ? A small squirt of gas does not mean you have good fuel delivery. You should be seeing 49 +/- psi when running. The OBD-II engine sensors are typically the root cause of stalling or other running issues, but they can all be tested with a basic volts/ohms multi-meter.


Any engine sensor that is not a genuine Jeep part is suspect no matter how recently purchased or installed. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.

 

[Runnin'OnEmpty]

Good advice from Tim.
Fuel pressure was mentioned, and I think you indeed have a faulty fuel pump. Especially if there's no MIL illuminated. Basically the brushes wear down and the pump stops running when it gets warm, and being submerged in fuel it cools quickly and then starts up again.

 

[BattlebornXJ]

Thanks for the responses guys.
No check engine light, no stored or pending codes. Fuel pump is a few months old (best one I could buy at NAPA). I changed the fuel pump because the jeep wouldn't start on the first crank no matter how long you cranked it, but always stared quickly on the second crank. The new fuel pump fixed that issue and now it starts immediately on first crank. Fuel pressure while running is about 48psi. I tested the CPS using a method found on this forum and the numbers say it is good. I also know it must be working because my other XJ runs fine with that CPS. Although kinda pricey, buying a diagnostic computer with live data seems like my last option. If i'm going to buy one, it should be a GOOD one. Still can't figure the fact that is runs trouble free in town but not on the highway.......

 

[CJR]

BattlebornXJ,

Seems like you have trapped heat in the engine bay that may be causing "vapor-lock" in fuel lines,etc. As you are well aware, the intake manifold sits over very hot exhaust headers. Try insulation on the intake manifold, injector lines,etc.. Also, there is also insulation tape available to wrap around the headers.

I increased the flow of hot air out of the engine bays on my 88XJ & 00XJ by simply using riser blocks to raise the rear of the hood at the cowl. I simply used two(2) 1"x1" aluminium spacer bars and drilled two(2) holes, in each bar, and mounted the bars between the hood and the rear hinge hood brackets. The raised rear of the hood significantly increased the flow of hot air out of the engine bays and solved my problems.

Best regards,

CJR

 

[Anak]

Several possibilities come to mind. One is that your new fuel pump is not a good fuel pump, and under constant load it loses the ability to keep up with the engine. You would need to drive with a fuel gauge hooked up and watch to see what fuel pressure is doing at the point it stalls out.

Other possibilities involve wiring. I had my Jeep die on me suddenly one day because the wiring for the O2 sensor got close to the exhaust, melted the insulation and shorted out. I am not sure how this would play out in your instance. In mine it stayed shorted out. I had to trailer the Jeep home in order to figure it out. If I had known then what I know now I could have gotten things back up and running in very little time.

The other possibility is a poor ground leading to high resistance leading to overheating of some component or other. For more on that, see this thread: https://www.naxja.org/forum/showthread.php?t=1148570

 

[maxbraketorque]

Verifying that fuel pressure is steady (or not steady) when this happens would be my next step.

 

[Tim_MN]

Heat soak that leads to vapor lock only causes starting issues. Once running, the fuel flow does not allow vapor lock to occur.

Good suggestions to confirm fuel flow meets the engine needs at speed.

 

[RCP Phx]

When my 2000 started doing that it was the CmPS.

 

[CJR]

Tim MN,

With all due respect, I disagree with your statement on "vapor lock". I suggest you review;Taylor, Charles Fayette (1985). The Internal-combustion Engine in Theory and Practice: Combustion, fuels, materials, design. M.I.T. Press. p. 140-142. ISBN 9780262700276.

Best regards,

CJR

 

[Tim_MN]

8 XJ's over 20 years, and a CJ-7 for 25 years, I think I might be somewhat correct. YMMV.

 

[maxbraketorque]

I'd be surprised to see vapor lock happening at highway speeds. The combination of airflow through the engine bay, air flow through the intake manifold, and fuel flow should be sufficient to keep the fuel below the boiling point, if the fuel pressure is at the specified value.

However, the thing is that boiling is suppressed by holding the fuel at pressure. In an '01 XJ, it could be a combo of a sub-spec fuel pressure and hot engine bay, so perhaps it could be vapor lock even at highway speed, but it would still tend to point to a bad fuel pump.

Perhaps a good way to test for vapor lock would be for the OP to bring an IR gun, and when the engine dies, measure the fuel rail and injector temperature. Another option would be to bring a spray bottle of water, and as soon as the engine dies, thoroughly mist the fuel rail, injectors, and manifold. Then try immediately starting it.

 

[Anak]

I too would be surprised to find vaporlock at highway speeds, but if any vehicle could achieve it, a 2001 XJ would be a good candidate. Combine a return-less fuel rail, pre-cats and the perennial underhood heat issues of the XJ platform and you have a great starting point.

 

[CJR]

To further discuss this problem let's list some issues;
1. Air temperature was stated to be 108F. The road air temperature was most likely hotter than 108F before it entered radiator to remove the BTUs from the radiator.
2. At cruise speeds, fuel consumption is low, i.e. fuel flow slows down or pauses periodically,
3. Fuel/injector lines in the engine bay are over the hottest part of the engine,i.e.exhaust headers. Take a laser temperature reading of the headers at hood-open idle and realize that closed-hood engine bay temperatures may be higher than this headers temperature.
4. When I bought my used 2000XJ it had a large plastic cover, under the engine, that sealed off the engine bay and the engine bay was at a higher temperature than normal. I removed that cover and improved cooling.
5. The incoming high temperature road AIR picks up the BTUs,dumped into the AIR from the radiator, and then dumps these additional BTUs into the engine bay AIR. Likewise, the hot headers are dumping incredible amounts of BTUs into an already hot engine bay. So, if this hot AIR can't get-out/flow-out of the engine bay fast enough, the temperature in the engine bay rises dramatically. Since the intake assembly sits over the hottest part of the engine, vapor-lock is very likely to occur when fuel flow slows down. Cool-down typically clears the vapor-lock, but this cycle continues to repeat itself on very hot days..

Best regards,

CJR

 

[Tim_MN]

2000 XJ bought 20 years and 150,000 miles ago. No vapor lock when running, 4-low on the Jeep trails, or 85 mph on the highways.

 

[BattlebornXJ]

Thank you everyone. Got her fixed. It was indeed the fuel pump. The problem got worse and worse to the point where it was quite predictable. I hooked a fuel pressure gauge to the test port on the fuel rail with a long enough hose to reach the passenger compartment which allowed me to monitor fuel pressure as I drove (poor man's live data). Sure enough, pressure would drop for just a few seconds to about 10-20 psi, causing the motor to die, but then quickly come back. I guess this is why it was tricky to detect with he fuel pressure gauge under the hood. By the time you pulled over, got out and opened the hood and re-started, the gauge would be back to normal. This is the third fuel pump ("top of the line" from NAPA) I have installed in the last year and a half. The other fuel pump failures were were catastrophic and easy to test for, and I really didn't want to believe that supposedly quality replacement parts were just as low quality as cheap parts. In my gut I knew this, but three in a row???? Lesson learned...Thanks again.

 

[Anak]

Are you replacing your fuel filter at the same time you replace the pump?

 

[RCP Phx]

Are you replacing your fuel filter at the same time you replace the pump?

It's one in the same on a 2000!

 

[Kapt. Bob]

Glad you found out what was the issue.

Try a Bosch fuel pump the next time.

 

[jeep ride]

Thank you everyone. Got her fixed. It was indeed the fuel pump. The problem got worse and worse to the point where it was quite predictable. I hooked a fuel pressure gauge to the test port on the fuel rail with a long enough hose to reach the passenger compartment which allowed me to monitor fuel pressure as I drove (poor man's live data). Sure enough, pressure would drop for just a few seconds to about 10-20 psi, causing the motor to die, but then quickly come back. I guess this is why it was tricky to detect with he fuel pressure gauge under the hood. By the time you pulled over, got out and opened the hood and re-started, the gauge would be back to normal. This is the third fuel pump ("top of the line" from NAPA) I have installed in the last year and a half. The other fuel pump failures were were catastrophic and easy to test for, and I really didn't want to believe that supposedly quality replacement parts were just as low quality as cheap parts. In my gut I knew this, but three in a row???? Lesson learned...Thanks again.

Do you remember the brand name of the pump you got from Napa?