As some of you know by reading my previous posts that I am trying to find a good solution for the engine stalling problem on the X300 4L machine. To recap briefly the engines will stall, very infrequently, when starting up following a stop for a red light or such. It last for about a second and if you are quick to let up the throttle the engine will recover and keep running. Sometimes it will stop completely and you will have to go through the standard engine start proceedure and it will start normally. Mine has never failed to start normally.

Several people have blamed it on the throttle position sensor(TPS). As I have also. I tried to find an alternative to the Jag (FORD) unit which cost around $500. The Ford Scorpio was a candidate. I bought one and found it rotated in the wrong direction. Square one again. The theory was that the wiper was worn and not making good contact near the idle position and would loose contact when the throttle was initially advanced. Well, once before I goofed and ran the car for a short while with the TPS disconnected following cleaning the throttle body. The engine idled fast but otherwise ran OK. So that theory is beginning to be shot. And just this afternood I did a test. I started the engine and let it warm up good. Then I reached down and disconnected the TPS. All the engine did was start to idle fast, 1300 to 1400 rpm. Plugged it back in and it returned to normal idle.

As a result of my test and experience I am beginning to question if the TPS is at fault at all. When the engine stalls it feels like a momentary shut off of the fuel for about a second or less. The reason I say fuel instead of ignition is due to the fact that a quick release of the throttle will recover the engine. Also, normally it only does this at or near idle. But I have had it do the exact same thing at 60mph for just the split second of time and recovered by a quick release of the throttle.

So all these words explains where I am. What I would like from the members is some input. Most of us when we solve a problem we are so elated that we forget to get back on the form and tell all. If any one has had the stalling problem and solved it would you PLEASE respond to this thread and tell us what the malfunction was and what you did to solve it. Right now I am running out of ideas. The fuel issue is something I will give a lot of thought to. But that is it for now.

Come on guys. Need input

 

It does sound like a fuel issue and if so, then that's where I'd start looking. Have you changed the fuel filter recently? A possible candidate. Another candidate might be the fuel pump, missing a beat perhaps. Might be worth checking power supply, relay (in the boot fuse box I think) fuse and any connections and earths. I had an issue similar to this, which occurred a few times when decelarating, (usually more suddenly than usual). It happened a few times over a three week period and then cleared itself up before I got a chance to investigate further. It hasn't happened since. Not a lot of help, but I would strongly suggest an interruption to the power supply to the fuel pump.

Others will chime in about fuel rail pressure and the like, but I always try to eliminate the simplest things first.

 

EZDriver, considering all you have been through, I have a suggestion. There is a little thought of function of the X300 that gets very little attention, but can ruin the performance of the engine. That is the adaptive fueling system. Unfortunately, there is only one device that can reset these adaptions if they cause problems. That is the now antique Jaguar PDU. The best explanation of the adaptions and resetting them is in the attached bulletin. Forget the codes it refers to, and pay attention to the adaptions, how to assess them and reset them.

You will have to hunt down a dealer that still has a PDU operating, which may be a chore, but could it could make a difference. Over the years, I have 'repaired' several X300's simply by performing this reset, one of which would barely run.

I've brought this up before, and I'm usually poo-poo'd. But I thought I'd throw it out here. I'll add that my 1995 XJR routinely starts getting lower MPG a couple times a year; that's my que to reset the adaptions.

Good luck! I hope you get to the bottom of it.

 

check your coils

 

Thanks for the response. As far as the filter is concerned that was the first thing I attacked. And as far as the coils I don't think so. The stall is instantaneous on all six cylinders for about one second. Coils just don't act that way.

The other thing I can throw out is that the car runs great with essentially the same mileage it has always had. I have a test section of highway that I travel frequently at a certain speed. Get between 26 and 28 mpg. I attribute differenct due to gas variation. If it was not for the stalling once in a great while (sometimes a couple of weeks will go by and then two or three over the next few days then OK again) the car would be running perfect like it always had for the nine years I have had it.

I will look into the PDU idea. Maybe Motorcar man has one.

What I'm looking into is a way to monitor fuel pressure with a guage in the cockpit. A blip in the reading at the same time as a stall will get me a new fuel pump. Of course just putting the guage in might just solve the problem. Come to think of it there hasn't been a stall for more that a week!!!

Thanks guys. Hope someone chimes in that has had exactly what I have and fixed it. Oh well, I can hope can't I.

 

I would lean toward something electrical. Specifically something in the electrical for the fuel injection system. Start combing the wiring looking for one that might get pinched, interrupting the connection. Since the stall is occurring at acceleration, it makes sense that something is getting in a bind somewhere. Let off the throttle, the bind goes away.
I cannot think of anything on the fuel flow side that would only stop for a second, and then recover after a quick release of the throttle.

 

You make a good point which is why we started with the TPS. But disconnecting it while running has essentially no effect like a total one second shut down. Also, I had this stall once while cruising at a constant speed of 60 mph again for about one second.

 

I wouldn't be too quick to discount ignition coils, though I sorta thought at this point you had covered that possibility. X300 coils have a history of causing some intermittent feedback, sometimes in a wild manner, and messing with the engine management and instruments. Sometimes it can be spotted as a light show seen through the epoxy at the top of the coils. I keep a cardboard paper towel tube around so I can look down on the coils and block out the light. If you see any flashes going on in the coil as the engine runs, that's a coil to get rid of.
I've seen and heard of weird stuff attributed to coils. Stalling, hesitation, instruments that light up like a Christmas tree or needles going haywire. You need to cover all the bases.

Cheers,

 

Having been a partner in a carburetor remanufacturing company for 25 years+, (I sold out in 2000) I have had my share of the TPSs developing cracks in the carbon traces. A crack in the traces on the low side would create a dead spot during acceleration, it would quickly recover as the contact swept past the crack. The only time it would cause a lingering problem would be if the throttle were held to the spot of the crack. Even then, the engine would revert to idle (as yours did when you disconnected the TPS) as the ECM would not be receiving the control voltage return.

I'm talking about inspecting the actual wiring and connectors over the entire system. Look over everything from the fuel pump to the power supply to the ECM. Anything and everything electrical that may be interrupted during acceleration. Specifically, wiring around something that has movement, i.e; the entire engine and transmission have movement (hopefully, not much) due to the motor and crossmember having rubber mounting. Any wiring in the vicinity of these may be susceptible to chaffing.

I am not too up on the Jaguar electrical systems, as I have just recently acquired mine. I am just throwing this out there from my general automotive knowledge and having dealt specifically with a diesel truck with a nasty wire chaffing problem with symptoms very similar to yours. It took me over two months on that one, but I finally tracked the open wire down.

 

What about the Air Injection Pump!!

Over the last year or two I had an occasional (and disturbing) stall in the XJ6. It was becoming more frequent. It would happen soon after a warm start, or perhaps during normal running while idling at a stoplight, or decelerating, during closed throttle. Not too cool! After a stall, it would restart just fine, like nothing happened.

Occasionally while at freeway speed, a "miss" would occur for less than a second, but was easily felt through the drivetrain.

I have not had a miss or stall during acceleration, as you have, but your problem may be similar to mine, especially since you have not found a culprit yet.

About 4 months ago, I disconnected the air injection pump. There has been no recurrence of a miss, stall, or hesitation. The car runs great! It is reliable again.

The MIL comes on about once a month to remind me that the air pump is disconnected (secondary air "incorrect flow"). After a reset, the OBDII secondary air monitor will clear even though the pump is still disconnected!

My theory: The exhaust manifolds are probably cracked, allowing some air into the exhaust. The O2 sensors are original to the car (old). This, in addition to the adaptive fueling, results in not-so-good gas mileage (about 18.5 overall). Perhaps there are air leaks through the pump too, even when off.

I believe my stalls occurred when the air pump engaged and pumped a lot more air into the exhaust. Already running rich, the engine was then flooded with fuel as the ecu tried to equalize the mixture. I believe my stalls and stumbles were due to fuel flooding, not fuel starvation. There was one occasion when I noticed a very strong fuel odor outside the car as it was idling, although that was not a stall event. I looked for fuel leaks and found none. It must have pumped right out the exhaust pipes!

How are your O2 sensors, EZ? If they haven't been replaced, you should try pulling the plug on that air pump.

There is also the possibility that my air pump is defective too. I have not resolved that yet. I used to see the voltage drop too much as the air pump engaged, while stopped at a light. I think that voltage drop could cause the fuel pressure to drop momentarily, as the ecu simultaneously demanded more fuel.

One important clue to the unpredictable stall is that the ecu cycles the air pump on and off at seemingly unpredictable times. I would guess the ecu is programmed to test it now and then. One night after a warm restart, when I was outside of the idling car, I heard the air pump come on and the engine immediately stalled. That's when I pulled the plug!

So what good is the air pump, except to help warm up a cold engine quicker (by causing over-fueling)? Why would it need to pump at all when the engine is already warmed up? Is my theory bunk??

Best of luck EZDriver. We got this.

 

Im not gonna read every response, but yes a pdu orientation would never hurt. But seeing how ive had a 96 vdp for 13 yrs and have had this issue exactly twice, both times a crank sensor on its way out

 

Thanks guys for all your input. Over the period when this has been happening I have been checking all wiring. Found nothing amiss so far. Will keep looking. The O2 sensors replaced about three years ago. I would think they would throw a code. NO code from any stall ever. Have replaced the crank sensor about two months ago. No improvement from doing that.

Next step is monitoring the fuel pressure as close to the rail as I can, if I can figure out how. That will tell me a lot.

Thanks again guys. All the info is welcome.

 

Unfortunately we simply can't depend on trouble codes to help us along with X300 Jags.

I've had multiple coil problems, some outright failures with *massive* misfiring: no CEL and no trouble codes.

Faulty crank sensor: no CEL and no trouble codes

I have operated the engine with the MAF sensor, coolant temp sensor, and air injection pump *disconnected*: no CEL and no trouble codes.

Heh heh....but the OBD II *still* turns on my CEL for a code P0430 at totally random intervals :-).

Cheers
DD

 

To clarify, when this occurs, it's a "clean" stall?

Not announced by any roughness/misfire/chugging or such?


Cheers
DD

 

Yes Doug. It is a clean stall, all cylingers at once, and if you get off the throttle quick the engine will go to idle and you can continue. It somewhat is like turning off the ignition with the key for a second, or less. In the old days you would get a backfire doing that. No such thing with this. As I remember there are all instrument lights on for that second but go right off if you are quick off the throttle. Also, it has always done it after a drive of at least twenty miles or a completely warm engine. Never with a cold engine.

 

I have been thinking about the airpump idea. The only difference is that my car gets really good mileage. There doesn't seem to be any extra fuel flowing normally. But I have had a flooded engine during a cold start recently. Bu before and after that I have to let the pump prime the fuel for about five seconds to get a smooth start. If I hit the starter instantly with a cold start it stumbles a little then catches and smooths out. I'm sure that is due to a lack of prime not flooding.

But I will give the air pumt some thought and I wish some one would come on and explain the function of the airpump.

 

The air pump, Secondary Air Injection, is there to add air to the exhaust during the richness of a cold start. By doing so it serves to light off some of the unburned fuel that got through, and in doing so, more quickly bring the catalysts up to temp so they can start functioning sooner. Absolutely no detriment to the engine or performance, but certainly helps the catalysts work better and last longer, and make you a better citizen.....emission wise.

Ezdriver, your comment about all the lights coming on at the time of the hiccup fits right in with the 'Christmas Tree' I mentioned as related to ignition coil feedback!

Cheers,

 

Sounds like something upstream of individual cylinders then. Not a single-cylinder loss of fuel or ignition.

An ignition switch problem isn't out of the question IMHO, or anything else that might interrupt voltage supply (or ground) to the ECU or other control unit.

Might wanna try a little jiggle test on the ignition switch wires.

Failing only after a fair bit of heat has developed often suggests a problem with a solid state component. Not carved in granite, but typical-ish.

Fuel pump is probably OK. If it was cutting out I'd expect at least a moment or two of roughness or hesistation before the engine stalled.

Sorry I'm not much help

Cheers
DD

 

Thanks XJR. I'll have another go at checking the coils. Didn't make sense before but maybe it does now.

 

Hi XJR, I checked the coils again. I have done this several times in the past and found them all good. Had not used the paper towl roll technique before. Using that technique after a drive to town and back, about 20 miles they all looked good. After dark in a totally dark garage checked again and could find no light show. Had to feel for the coils to know where they were it was so dark.

Had only one very short stall and paid good attention to the warning lights. No lights came on. Just a short one second stall.

This stalling situation is not nearly as bad as it was when it first stared several months ago. Then it would stall for a longer time, all warning lights on with a complete shut down requiring going into park and restarting the engine which did start with no problem. Now the stall seems to be just a short blip with no warning lights. Don't know what I have done. Hope it goes away completely.