Hi, I'm afraid I need some help to solve a stalling problem that just won't go away. In attempts to solve this problem I've replaced the fuel filter and blown out the fuel line, checked the readings from the TPS, removed throttle body and cleaned throughly, cleaned and checked ISC, replaced air filter, replaced spark plugs etc.
The motor always starts well from cold and runs smoothly.

I've only had the car for a few weeks and so far have not ventured far from home, which is in a country area. One day I can take the car for a 30 mile run around the block and it goes like a dream. The next day I drive a couple of miles from home and when I slow down for a T junction the motor just dies. On several occasions the motor has cut out in almost the same place - give or take a hundred yards or so. Once this happens the motor will not start no matter what I do or don't do with the throttle pedal. This said, I do manage to get the motor running again and quite quickly if someone gets under the bonnet, grabs hold of the top of the throttle shaft and turns it open as far as it will go - to the stop in fact. Just why the motor should spring into action when the throttle is fully opened by hand and not at full throttle from the pedal seems strange. I guess the extra bit of movement must be doing something if only increasing the voltage from the TPS a small amount - maybe.

Just why the motor will run so well one day and not the next is a real mystery so if anyone has any ideas I'd be very pleased to hear from them.

Cheers, RogerB
1994 XJ300 - 4 litre

 

Roger:
The hand operated throttle twist is indeed puzzling. I have no hypothesis for that, unless it is a cold gust of air from opening the hood! These cars are known to have problems from intermittent CKPS sensors, the one at the front of the crankshaft and some folks have even changed them out on pure fear of time. I would suggest you give that a try- they are not expensive, and having a spare is not a bad plan anyway.

If the throttle plate fix is indeed significant, then you could adjust the throttle cable to assure you are getting full movement plus some and try the pedal when it acts up. There IS apparently a feature on the X-300 that kills the fueling when cranked at full throttle. I say apparently because siome folks have debated it being there on the X-300, but I am pretty sure I have read it in the literature. (My memory is not so good, though!).

Obviously, the ISSC, the idle control valve could be sticking. Be careful as you try and get it off, since the screws are loktited in and easy to break. And DO NOT operate the key while the valve is not mounted, unless you have something to catch the pintle and other parts it will eject! I assume you know about the TPS orientation procedure, run on dealer level software. Your symptoms by themselves would not seem to indicat TPS issues, but the ISSC, does not operate unless the TPS properly indicates throttle closed position.

Sorry I do not have any specific answer, but you aked for ideas...

Good luck.

Sorry, I do not havbe

 

Hi Ross, thanks for you input and suggestion re the CKPS. I have noticed the taco moves when I'm attempting to start the car so I reckoned it was ok but as I always carried a spare for my XJ40 I will see about following your suggestion.
When I replaced the plugs I noticed the wires to the coils were very hard and brittle with some even having been repaired (?) with insulation tape. From what I read this could also be a problem area. Unfortunately I've no way of getting the car to a Jag dealer who could do a diagnostic check so I'm really shooting in the dark. Think I'll talk to an auto electrician and see what it will cost to rewire the coils and check out the cost of replacing some of the sensors.
Time to make some hard decisions. Apart from a few marks to the paint the car is in very good condition both inside and out. This said, I do have to consider the age of the car and the high milage - 132,000 miles. So, I'll check out some prices then make a decision wether to fix or break up for parts. The car was owned by a friend for many years but had been in his garage for three years unused and he just wanted rid of it so it doesn't owe me a great deal.

Cheers, Roger B

1994 XJ300 - 4 litre

 

Adding to the above.

"....standing for a few years", worries me a tad.

The fuel pump at your mileage is always a concern, then add teh standing bit, and maybe it is just not happy.

No added ideas on the TPS bit, but fuel pump on/off is TPS signal related in part.

The pumps are in the tank, bugga, and it is a standard Nippon Denso pump, as in Toyota, Mazda, etc, and about $90, last I got one.

 

Hi Roger' is the car a Singapore import; The reason i ask is running a Jag dismantling yard here in Wellington i have found that the humidity in singapore played havoc with all alloy parts such as cam covers. It also made most of the wiring hard and brittle and hard to find any breaks in wiring. Iwould certanly start with the plug leads and coil leads to each plug.Ihave dismantled a few from there for that reason. Hope this will help.
Cheers Ray

 

Well, 132,000 miles is just getting started on most x-300s . I retired mine for appearances after 270,000 miles- original engine, using less than a qt of oil between 7000 mile changes and the original reanny was still smooth. You are right , of course, about the tach signal indicating the CKPS is still reading pulses. I should have thought about mentuoning that!

 

Thanks guys for input. I've decided to remove the tank and while I'm there replace the pump. I doubt it's ever been replaced anyway.

Your are right Ray the car did come in from Singapore and it's very interesting to hear about their humidity problems. Once the tank and pump have been done I will certainly see about getting the plug leads renewed. My only concern in this area is that along with the lead replacement I may need to replace the female coil plugs unless it's possible to fit new leads into them. Wonder if these plugs are still available?

I should have also mentioned with all the stalling problems I'm not getting any codes displayed. Don't know if this is a good thing or bad.

Thanks again for all suggestions.

Cheers, Roger B
1994 XJ300 - 4 litre