My beast has been off the road for some months now because every time I take it out it stalls after 10 minutes driving and won't restart until it cools down. I checked the CPS, coil (replaced coil) ignition amp all ok so I went to the cooling fans which were not coming on, I bypassed the switch with the engine on and both fans worked but when I did the same with the engine running it died immeadiately and would not restart. Now, is there a circuit breaker in the fan supply line and the sudden power draw causes it to trip and causes the ECU to shut down or is it the battery, with the power draw causing the supply voltage to drop below 11.5 volts. it is a new battery but it has gone flat a few times and was a cheapy. Any suggestions? The A/C system is disabled (no belt to compressor) and never used and has been like that for years (air conditioning in Wales!!) and might have some revelance but I will await some words of wisdom before I start messing with it.

 

I don't know how the fan circuit is wired. I believe there is a section up in the stickies with manuals, you could probably find a wiring diagram there. Ill just throw out a couple of things. Are the battery terminals tight? While its running does it seem "normal?" Has the quality of the running changed lately? When it dies is it electrical at all, or is it fuel- flooding or starving? Could it be the fuel pump getting warm? It sounds like you have determined that its sensor related. Have you already ruled out the fuel system?
Just throwing it out there- Good luck.

 

Thanks Jerry,
the engine was only running for minutes and was cold when I bridged out the switch, maybe the fan relay is shutting down the ECU because when this happened last time on the road the nice man from the AA found no supply to the coil or to the injectors, and when it dies, it's instant, no spluttering or staggering. As for the wiring diagram, it's as much use as a chocolate teapot, everything links back to the ECU. what I can't understand is how come a battery reading 11.7 volts will start my diesel Rover 75 but not the jag, there must be some sensor in the circuit that kills the starting circuit below a certain voltage but I can't find anything about it.

 

I'm not sure about the exact voltage but it is true that the car won't start if the battery is low.

Have you checked your fuseboxes ? If they haven't been re-flowed, there's a chance this could be the source of all electrical issues - fuse boxes are a major failure point on late model cars.

Larry

 

Hi makula,

I'm sorry to hear your XJ40 is misbehaving. Unfortunately, sudden stalling is often the result of more than one component or system malfunctioning, so it's a matter of methodically narrowing things down one component and system at a time.

My first question is whether you have checked the Vehicle Condition Monitor (VCM) for any stored Diagnostic Trouble Codes (DTCs)? To do so, turn the key to position II (ON) but do not crank the engine. Depress and release the VCM button on the trip computer panel to the right of the steering wheel, then watch for any message to be displayed in the small window below the speedometer. DTCs are displayed in the form of the letters FF followed by a two-digit number, such as FF29. If you find one code stored, there may be others. Let us know and I'll share how to read any additional codes.

As far as battery voltage goes, Jags do need strong, healthy batteries. If the battery voltage sags much below 11V while cranking the engine, the ECM will not trigger the ignition to fire.

If your new battery has gone flat a few times, it is almost certain that either the charging system is not working properly or you have excessive quiescent current draw, probably due to a parasitic drain. It sounds as though you have the '93-'94 Electrical Guide, but if not, you can download it here:

http://www.jagrepair.com/images/Elec...Electrical.pdf

Regarding the stalling, how long has it been since you gave the car a good tuneup? Things might improve simply by ensuring that basic tuneup components are all functioning properly.

Here's my tuneup list:

Spark plugs

Spark plug wires (if they're several years old or more or otherwise suspect)

Distributor cap & rotor button

Air filter

Fuel filter

Check engine coolant; flush and drain as advised

If there is any question about the coolant thermostat, replace it

Clean the CPS and its electrical connector.

Adjust the throttle cable to remove any slack that has developed:

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Check the transmission fluid. Low transmission fluid can cause stalling by preventing the torque converter from releasing when slowing to stop or turn. To check the fluid: with the car parked on a level surface after a drive to get the gearbox hot, leave the engine running and engage the hand brake and depress the brake pedal. Move the gearshift lever through every position of the J-gate and pause at each gear/position at least 3 or 4 seconds for the gear to fully engage. Return the lever to Park and release the bonnet/hood and raise it. Confirm that the transmission fluid comes exactly to the HOT line on the dipstick and that the fluid looks clean and red. The best fluid I have found for the ZF 4HP24 gearbox is Redline Oil D4 ATF, which has a viscosity index very close to the Dexron III that was originally specified but is no longer available. Dexron VI has a much lower viscosity and does not perform optimally in these transmissions.

Clean the battery power connections throughout the car (especially the battery terminals, as Jerry mentioned, plus the jump start terminal on the bulkhead/firewall and the connections at the alternator).

Clean the battery ground connection to the body.

Clean the grounds in the engine bay including the two on the intake manifold and the one on the bulkhead behind the cylinder head and the engine ground strap.

With the battery ground cable disconnected, remove each relay on the bulkhead panel and clean its terminals and socket with a small wire brush and zero-residue electrical contact cleaner spray. Do the same to the fuel pump relay, which is in the boot/trunk right hand side near the tail lamp behind the carpeted trim.

Consider pressure-cleaning the fuel injectors (see photos at the link in my signature) or having them professionally cleaned.

A few things on my tuneup list that are not the cause of your stalling:

Check the front wheel bearings and re-grease and adjust if necessary

Replace the windscreen/windshield wiper rubber

Top up the windscreen/winshield washer fluid

*****

If you've had any signs of rich running, three things I can think of that can contribute to stalling due to overfueling are the Coolant Temperature Sensor (CTS), Fuel Pressure Regulator (FPR) and carbon canister purge valve.

The CTS is mounted on top of the thermostat housing and its resistance changes with temperature, informing the ECM of engine operating temp. If the CTS fails at its COLD resistance, the ECM will continue to apply cold-start fuel enrichment even after the engine has warmed up, leading to rich running.

The FPR is a metal cylinder mounted at the front end of the fuel rail. If the diaphragm fails, raw, unmetered fuel can be inhaled into the intake manifold via the FPR vacuum hose, causing rich running the ECM cannot correct. To check, pull the vacuum hose off, crank the engine, then check for signs of wet fuel at the vacuum hose fitting.

The carbon canister purge valve pulses open and closed to allow fuel vapors stored in the canister to be inhaled into the intake manifold under certain running conditions. If the valve fails in its open position, the fuel vapors are inhaled by the engine at all times, contributing to rich running the ECM cannot correct, since it can't shut off the failed valve.

Since your car is a '94, the other thing worth checking is the wiring harness between the fuel pump relay and the electrical connection on the evaporative flange at the top of the fuel tank. There is a short section of harness with an electrical connector behind the battery that loosened and burned from arcing on our car. See this link for photos:

Welcome to Jag-lovers - Members Photo Viewing Page

Also, the fuel pump electrical connector at the evaporative flange is known to deteriorate and have problems. It's not easy to access or even to see because it is squeezed between the fuel tank and parcel shelf, and disconnecting the electrical connector must be done mostly by feel. But if you don't see any problems at the connector behind the battery, it would be worth checking this connector at the top of the tank for signs of burning or deterioration of the plastic.

Please keep us informed.

Cheers,

Don

 

Thanks Don and Lawrence for your input. Lawrence, I have taken out the passenger side fusebox and checked all the connections and all seems to be well apart from a bit of green gunk at the bottom which I cleaned.
Don, I did a full tune up just before I retired when I had access to a workshop and a ramp, since then I've done 200 miles (weekend warrior). The stalling occurs whether I am doing 70 or just idling and as I said it's instant, no stumbling or stuttering. What has me flumuxed is why the fans will run (bridging out the switch) with the ignition on but will instantly kill the engine when it's running. As for the flat battery, I traced that to a dodgy sunroof switch which was giving an earth to the Aux relay which then powered the blowers and the radio even with the ignition off and the car locked! It looking like I will have to bite the bullet and climb under to remove that stupidly placed fan relay. I just needed to check if those deviant gits at Jaguar had installed some exotic safety link into the circuit. Again thanks for all the advice and will keep you posted as to who wins, an ancient Jag or an ancient Fitter. (by the way no codes on the VCM)

 

Thanks again everyone for your input but after some investigation coupled with some heavy meditation I think I have found the fault. The lower cooling fan (I presume it's the lower temp one that comes on first) seems to be the culprit. I stripped and flowed the passenger side fuse box (doing the board links certainly requires high sphincter control) put it back and voila! still the bloody same. I then pulled the fans out and unplugged the lower fan returned the fans and tried again and by the blessed underpants of Joseph, it worked! I ran the engine, bridged out the fan switch and the engine didn't miss a beat. How the hell a dodgy fan can shut down the engine is still beyond me, maybe it puts the ECU down to earth, who knows. I would have though the fuse would have blown.
Anyway, the car is now on a final warning, one more problem and it's going to China to be an ashtray.
Thanks again to everyone

 

Keep the phone number of the tow truck handy then!

 

Back again, still the same problem. I've replaced the temperature sender and the fan switch but still the damn thing stalls when it gets hot. Now I have a theory (and please feel free to giggle) but I recently changed my battery, which according to the supplier is the correct one for my car but it's only a 70AH. Is it possible that the sudden draw of the cooling fans is enough for the voltage to the ECM to fall below the threshold causing it to shut down? I know that the alternator should supply enough power when the battery demands it but is it possible the voltage monitor on the ECM kicks in before the alternator can compensate? Desperate times require desperate thoughts.
Just to reiterate, the engine runs fine until it reaches full temperature and if I keep it idling so that the temp gets high enough to trigger the fans, it shuts down instantly, no coughing or spluttering and it will not restart until the engine cools down again so it definetly seems to be linked to the cooling fans. Can anybody out there help, it's driving me crackers (the wife's been on ebay looking for a jacket that ties at the back and i'm not allowed near sharp things)

 

I still think you have a bad connection somewhere.

If this was my car, I'd clean all the grounds, reflow the fuseboxes, clean all the relay and relay bases on the firewall & re-plug the ecu a couple of times.

Larry

 

Thanks for that Lawrence, I know you're right but being an orthodox lazy git I've been putting it off but I will bite the bullet and get it done

 

Very Interesting! I had that same problem recently- Him being right and me being a lazy git!