• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Engine cuts out at highway speeds on a hot day

lordoeuf

NAXJA Forum User
Location
Vancouver Island
For the last 10 years or so, my '99 XJ has had the issue of the engine momentarily cutting out on a very hot day at highway speeds (100 kph). It doesn't get very hot where I live, except for a few times a year. On average, the problem occurs once a year. When the engine cuts out, it feels like someone is stepping on the brakes. The duration of the stall is about 1 second, then the engine resumes.

In the past, I had upgraded the ignition coil to an ACCEL branded one, but it didn't fix the problem. Replacing the spark plugs, wires, and dist. cap didn't help either. I measured the resistance of the 6 ignition coils when the car is cold and get the expected 12 ohms. I still need to measure them when the car is hot.

Anyway, I am leaning towards needing to replace the fuel pump module (pressure reg., pump, fuel filter, strain, etc). That is a rather involved job for the occasional home mechanic with the XJ being the daily driver. But before I begin this horrific task, I was wondering if anyone else had any other ideas as to what the issue could be? If you think it's also the pump, would Delphi be the best replacement brand?

I am the original owner of the '99 XJ and generally have had the habit of running the tank nearly empty before filling it. So I've been doing that for 20 years. I'm guessing that this caused substantial sediment built-up in the fuel filter or pump and running the tank low caused the pump to heat up leading to its wearing out.

Thanks!
 
Since you have a plastic tank there isn't much of a chance very heavy accumulation of stuff unless you think your getting really bad gasoline. I recent did the ZJ tank up-grade and my tank on my 2k was spotless inside. Most likely problem is with a wiring connection and your CPS.
 
For the last 10 years or so, my '99 XJ has had the issue of the engine momentarily cutting out on a very hot day at highway speeds (100 kph). It doesn't get very hot where I live, except for a few times a year. On average, the problem occurs once a year. When the engine cuts out, it feels like someone is stepping on the brakes. The duration of the stall is about 1 second, then the engine resumes.

In the past, I had upgraded the ignition coil to an ACCEL branded one, but it didn't fix the problem. Replacing the spark plugs, wires, and dist. cap didn't help either. I measured the resistance of the 6 ignition coils when the car is cold and get the expected 12 ohms. I still need to measure them when the car is hot.

Anyway, I am leaning towards needing to replace the fuel pump module (pressure reg., pump, fuel filter, strain, etc). That is a rather involved job for the occasional home mechanic with the XJ being the daily driver. But before I begin this horrific task, I was wondering if anyone else had any other ideas as to what the issue could be? If you think it's also the pump, would Delphi be the best replacement brand?

I am the original owner of the '99 XJ and generally have had the habit of running the tank nearly empty before filling it. So I've been doing that for 20 years. I'm guessing that this caused substantial sediment built-up in the fuel filter or pump and running the tank low caused the pump to heat up leading to its wearing out.

Thanks!

change the filter and see if that helps, but usually a clogged filter will give much more problems than an occasional power loss. clogged filter usually dont get better on their own.

a fuel pressure gage and flow rate test might clue you into fuel delivery problems. Id check that out first. but heck after 21 years yes the fuel filter could be getting dirty, but that does not fully explain the symptoms.
 
change the filter and see if that helps, but usually a clogged filter will give much more problems than an occasional power loss. clogged filter usually dont get better on their own.

a fuel pressure gage and flow rate test might clue you into fuel delivery problems. Id check that out first. but heck after 21 years yes the fuel filter could be getting dirty, but that does not fully explain the symptoms.

The only filter on a 2000 is in the tank on the bottom of the fuel pump. Yes, you could check your pressure but it's not likely to be the problem.
 
On my 1990 filter in on the frame. Golly inside the tank, what are they thinking, it sure aint ease of service!

what about fuel flow volume? I figure a clogged filter or bad pump will reduce the flow rate, so a flow volume test would indicate problems. but again, this problem is intermittant, unusual for a clogged filter to act this way.

Now a rag or leaf in the tank could float around and intermittantly clog the outlet, but that is not common since the advent of unleaded fuel restrictor fillers. On my older cars you can run your arm down the filler pipe it is so large, so all sorts of things can find their way in!
 
ps.... it is a 99 xj not a 20 xj if that matters for filter location.

in tank pumps and filters, For repair shops I guess if you charge by the hour a simple replacement job will earn good money. What if the filter or pump fails with a full tank? now you need to remove 16 gallons of fuel, yikes stupid design, just plain stupid. probably saved jeep 50 cents in manufacturing costs I reckon.
the only thing that should be inside the tank is the level float. Heck I got cars that dont even have that, no gas gage! simple rules!
 
I replace the fuel pumps on 2 of my XJs recently. A weekend job, or even a day. I used a Carter Fuel pump. I think the Delphi is good too. You didn't list the mileage. One I had it cut out in traffic. Not fun and fortunately someone stopped and helped push it so I could roll down to the gas station. I was at an intersection and dealing with other autos. The other had starting problems, so I changed the fuel pump. I ended up replacing the ignition key relay to get it to start in the end.
It could be the O2 sensor. I had a Tempo that would cut out at speed, then go again. Replaced the O2 and ran fine. Still, problems like yours could be anything. I might even think about the CPS.
 
There is a screen inside the fuel pressure regulator mounted on top of tank it is connected to fuel pump could be contaminated only option is replace the Fuel pressure Regulator screen is not sold separately.
 
If I am going to go to the laborious task of removing and draining the fuel tank, it seems that I just as well replace the whole fuel pump module. This is not something I want to engage in unless absolutely necessary. The Jeep is the daily driver.

I had replaced the O2 sensors at the interval the manual states. I think that was like 10 years ago. Didn't help the problem. But as the problem is so infrequent, it is hard to troubleshoot.

As for mileage, in MILES, It is at 107,500. I live in a small town now.

At one point I lived in a hot climate and it was more frequently stalling on the freeway at 120 kph. I took it to the dealer (it was under extended warranty). They claimed that they had to drive it around for hours with the OBD II meter plugged in. They claimed the issue was the ignition coil and replaced it. I moved away from that climate zone not long after so I don't know for sure if it was the ignition coil or not. But 8 years later I replaced their ignition coil with the ACCEL unit and I can say that this was not the cause of the current stalls.

I will look into the CPS related wiring. That does sound like a possibility and is easier than removing the tank, though the sensor itself is very difficult to bolt on due to access.

16 years ago I took the Jeep to the sand dunes in the middle of summer. Temperature was around 109 F. After 2 hours of duning, the engine shut off and wouldn't start again. It was under extended warranty and they replaced the crank sensor. Solved that problem. So apparently heat kills these crank sensors? The stalls I receive now are only on the hottest day of summer at 100 kph.

I do have an extra Mopar crank sensor I've been meaning to install, but I'm afraid of stripping the nuts that hold it on. Access is VERY difficult. The dealer even mentioned the nut may have stripped after their replacement 16 yrs ago.

But perhaps I can just pull the connector and spray in some contact cleaner? If I can reach it.
 
Any time I touch a electrical component connector It gets a squeeze of "De-ox" grease to prevent corrosion.
 
You could be experiencing heat soak

Heat soak is a starting issue. It wouldn't have anything to do with cutting out while your are on the road!
 
Thanks for the tip. I don't have any de-ox and amazon Canada wants $40 for it. I do have some electrical contact cleaner and some carbon conductive grease from MG Chemicals, so I will try this route and report back after next summer when it's hot. I know this hill on the highway that it surely will cut out on when the temp is 30 C, which is only that hot once a year.

I'm trying to decide if I want to pursue the swearing required to change the crank sensor. Would a faulty crank sensor cause this issue? I was under the impression that a faulty crank sensor will either work or not. If it is not likely the crank sensor, then I'll just clean the contacts, assuming I can reach the connector.

I was getting a rock auto order together, but I guess I'll hold off on the fuel pump module. I've been putting that off for 10 years anyway.

I checked the injectors while the engine was warm and all the resistances are at 14.5-ish ohms. I used the shop ears to listen to each injector. Some of the sprays (ticking sound) are much louder on some injectors and much quieter on others, even with the stethoscope rod on the same location of each injector. Is this normal? I didn't hear any alterations in the pulse pattern though.
 
If you are going to shotgun random parts at an undiagnosed problem, start with the most logical suspect, the Crankshaft Position Sensor. Crank Position Sensors can have intermittent “thermal failure”. The CPS/CKP fails when the engine gets hot, but works again when it cools back down.

Once you get a good system for installing the CPS, the whole job takes less than 20 minutes. You can gather up about 3 foot of socket wrench extensions, or you can drop one end of the front driveshaft.



BTW I wouldn't buy a Carter fuel pump, or a generic parts store Chinese fuel pump if you gave me a thousand dollars and said I could keep the change. I only buy Bosch fuel pumps, NTK O2 sensors, and genuine Jeep OBD engine sensors.
 
Last edited:
Thanks for the tip. I don't have any de-ox and amazon Canada wants $40 for it. I do have some electrical contact cleaner and some carbon conductive grease from MG Chemicals, so I will try this route and report back after next summer when it's hot. I know this hill on the highway that it surely will cut out on when the temp is 30 C, which is only that hot once a year.

I'm trying to decide if I want to pursue the swearing required to change the crank sensor. Would a faulty crank sensor cause this issue? I was under the impression that a faulty crank sensor will either work or not. If it is not likely the crank sensor, then I'll just clean the contacts, assuming I can reach the connector.

I was getting a rock auto order together, but I guess I'll hold off on the fuel pump module. I've been putting that off for 10 years anyway.

I checked the injectors while the engine was warm and all the resistances are at 14.5-ish ohms. I used the shop ears to listen to each injector. Some of the sprays (ticking sound) are much louder on some injectors and much quieter on others, even with the stethoscope rod on the same location of each injector. Is this normal? I didn't hear any alterations in the pulse pattern though.

Carbon conductive grease...NO! Not on the electrics! Use Dielectric silicone grease. You dont want conductive grease, it can short things out. The dielectric grease wont short things out, it is made for this kind of application.
 
I may or may not have the non-carbon conductive grease. The carbon grease I have is for electrical connections. It is particularly for sliding metal contacts. Packages states:

MG Chemicals
Carbon Conductive Grease
Improves electrical conductivity
Lubricates and protects
A high purity silicone oil loaded with branched carbon to produce a highly conductive lubricant capable of operating over a broad range of temperatures. Lubricates and improves electrical connections between sliding surfaces, while providing protection from moisture and corrosion.
Electrical resistivity = 117 ohm-cm
Electronic grade, premium quality, will not harden

What's wrong with using it on the crank sensor's connector? As long as I don't put so much that it bridges the connections (there are 3), is there any harm? Based on the wording on the packaging, it seems ideal. Just a small dash on each conductor.

I was at Canadian Tire today and grabbed two 20" 3/8" extensions. 20" was the longest they had. I'll give it a go at replacing the crank sensor just because I have a Mopar unit on hand. The dealer got me a spare one 15 yrs ago after I got stranded in the dunes.
 
I have replaced the crank sensor. It wasn't pleasant. Here's some notes for the next guy:

You want to have the distance from the end of your 6-sided 11 mm socket to the end of the ratchet in the 41-42 cm range. You don't need a swivel. Remove the pinion side of the front drive shaft and bungy cord it to the PS upper control arm. I torqued the two bolts to 120 in-lbs, which is 10 ft-lbs. Beyond that, I felt like the housing the bolt went into may be stripping, even though I read online the torque range for these bolts is from 8-12 ft-lbs. Perhaps this is what the dealer meant back in 2003 when they said "the bolt is stripped, you won't be able to get it out again". Is the housing aluminium?

When I inspected the two bolts, there was some silver gunk between 2 full threads which had the consistency of metal. It was rather difficult to pick out. When I tested one of these picked out silver chards with a multi-meter, I got an open circuit, so now I'm not sure if it was indeed aluminium. Metalic coloured thread lock?

I inspected the connector. There are three very macro conductors with a plastic wall individually separating the conductors. I was not at all concerned about lightly dabbing in the carbon conductive silicone grease. I would think it would offer a better connection for the case that the connector's spring contact wore out.

The Jeep turned on. I'll try to remember to report back after the heat of next summer to see if this fixed the problem.
 
Brief update: I don't think the issue was the crank position sensor because I've had the Jeep cut out a few times now, and it's winter. The issue is more likely to happen with the tank at half full or less. So I'm back to thinking I need a fuel pump module.
 
My first question is what brand CPS did you use?
Could be that aftermarket bad out of the box CPS thing you always read about on the forums.
Cause I am thinking thermal failure just happens when the Jeep gets up to operating temperature.
At least that was my problem. And that the time of year wouldn't matter.

That being said it is my understanding that fuel in the tank helps keep the fuel pump cooler.
So I can see why you think that. The pump is also experiencing thermal failure.
 
The CPS was from the dealer and had the Mopar markings on it.

Well, it was cutting out only 1 minute after I turned the vehicle on. I had left my driveway and got onto the main road and was accelerating; then the engine choked in/out a few times.

It is winter here, so the car was definitely not up to temperature in 1 min of run time.
 
Back
Top