Help !!!! Came home, 45 min later the xk8 would not start. 137000 miles. Car is new to me. Did the remove the ground strap thing for 30 min, no help. Noticed a gearbox fault on dash and the j gate stuck in park. Preformed the key in hole to release from park, went to neutral still no start. Ran and shifted good before i got home. I'm going to check fuel pressure today, Thanks for any help.

 

Check the voltage of the battery. Do you have a code reader?

 

Thanks RJ237. New battery, 12.45 volts, cranks good, don't have a code reader. System check on Dash went from the gearbox fault only, to now showing traction control fault, incorrect part installed, engine fault, gearbox fault. 137,000 miles. I bought it 30 days ago. No new parts needed yet. The previous owner, i think sold me his troubles. Oh well, their mine now. I took console apart today can't feel or hear park solenoid working. Its got to be a connector or something simple because one min. everything worked, the next min. it would not start. I owned a Jag. shop in the late 60s. I am 75 now and thought i could have one last thrill in life. These modern cars may be too much for me. Thanks

 

I'm 78, share your problem. That's a classic low batt. set of symptoms, may be just poor connections. Trouble is, there's a lot to check. Also 12.45 V is a little low, charge it. There is a ground at the back right of engine, bellhousing to frame, may need cleaning. Also the batt to ground and to the two big fuses in front of the spare tire. Even the batt cables themselves have been found suspect.

 

If you keep trying to start, especially with cold engine, you may have bore wash. Excess fuel in starting cycle washes oil from cylinder walls, especially with early engine. Try turning over for a few bursts with pedal to the floor, which shuts off injectors, then back to part throttle.

 

Problem solved, (almost). The fuses i checked looked good, but on a recheck the underbonnet passenger fuse box, #10 did not blow in the hump where it usually blows. It blew low on one side where it connects to the main blade where i missed it. The fuse sends power to the EMS ECU, MECH GUARD, VAC VALVES. The Jag starts on the 5 amp stock fuse when cold, but when hot blows the 5, then 10, and a 15 amp fuse. I stopped there and will try to isolate these circuits. Can anyone tell me what the MECH GUARD is and where located . It may have to do with temperature because of the cold start but not hot.

 

Thanks for your help, its good to talk with someone older than me. You are not to far from me, i live in Anderson S.C. If we live long enough maybe we can meet someday. Thanks Richard (hobo)

 

although the throttle looks as if it is operated mechanically, it isn't. The cable from the pedal operates a potentiometer which sends a signal to the ECU which tells the motor in the throttle body to open and close the "butterfly" valve. But - there's also what Jaguar calls "a mechanical guard" in the throttle body which I guess is mainly for safety reasons and is also the reason that the butterfly valve still opens when the ignition is off and/or the battery disconnected. This has a couple of sensors which 'report back' if there is a fault.

Have you got a wiring schematic ? They are available from Gus Glikas' brilliant site - JagRepair.com - Jaguar Repair Information Resource. Look at figures 01.5 for the fuse layout in the engine management fuse box and the bottom left corner of figure 04.1 for the mechanical guard, vac valves etc. That should help you get started with the detective work. Best of luck !

 

As I recall, my 97 had a mechanical throttle link and the guard circuit was for cruise control and maybe some other function.

 

Thanks DevonDavid Subject: Re: Reply to thread '1997 xk8 Won't start'
WOW !! Thats very good info. I will get the schematic and post on my progress. I had no idea where the mech guard was located. That is a a likely place to start.

 

Under normal driving conditions, the loud pedal operates an input shaft which sends a signal to the ECU. The ECU sends a signal back to a DC motor which operates the throttle valve. The mechanical guard sort-of "mimics" this movement and takes over when the ECU decides that "computer knows better than driver" !! As you say, the mechanical guard takes over control when the cruise control is engaged.

The design of the input shaft and the mechanical guard, and the bias of their respective springs, means that, except in cruise control, they always rotate together. The throttle cable turns them in the open direction; the springs keep their
adjacent levers locked together and turn them in the closed direction. The ECM monitors the position of the input shaft and mechanical guard using the inputs from the accelerator pedal and mechanical guard position sensors. During normal operation, when the ECM detects any movement it signals the dc motor to turn the throttle valve and follow the input shaft and mechanical guard, maintaining a constant gap between the adjacent levers of the throttle valve and mechanical guard. The dc motor drive gears turn the throttle valve in the closed direction; the throttle valve spring turns the throttle valve in the open direction and keeps the throttle valve in contact with the drive gear. Inputs from the throttle valve position sensor enable the ECM to exercise closed loop control. The arrangement of the throttle valve drive prevents the ECM from exceeding driver demand, since if the motor is driven fully open the throttle valve engages the mechanical guard and disengages from the dc motor drive gears. The arrangement of the mechanical guard to throttle valve interface allows the ECM to reduce throttle opening to less than driver demand, eg. during stability/traction control or engine power limiting

Very interesting publication here which explains all in more detail. (see page 28)

http://www.jagrepair.com/images/Auto...ansmission.pdf

 

That's great David. Sort of falls into the category of 'all you want to know about something you didn't want to have to know'.

My 97 had a problem for years where the cruise control was intermittent when the engine was up to operating temp. I finally determined that the wiper springs on the end of the shaft needed to be bent a little because they were not making good contact with the tracks.

 

DeonDavid, the link you sent me is GREAT. ( http://www.jagrepair.com/images/Auto...ansmission.pdf ) Very detailed. It will take me 3 days to look every page. Thanks

 

Can you tell us what OBDII codes you have?

Gus
jagrepair.com

 

Gus, Thanks for the reply but i don't have a code reader. This problem started 2 days ago. So far with the help of a few guys on this forum i'm down to fuse #5, under the bonnet on the passenger side that blows when ing. switch is turned to "on" . I unpluged the BLACK harness below fuse and found a dead short in pin #10. I'm in the process of finding where that pin gos. It's hot in Anderson S.C. and at my age i take many, many breaks.

 

If I am correct fuse #5 is for the injectors. I have not looked at the one line yet. I do understand old at 71..

Gus
www.jagrepair.com

 

You need to look at the injector relay and the leads to it. If all look good swap or replace the relay and give it a try.

Gus
www.jagrepair.com

 

Thanks Gus. Its a white wire with a blue dot about every inch. Tomorrow i will look for the fuel ing. relay. Your web-site is very good, lots of info. Thanks

 

To all who tried to help, I stand corrected. Late nights and tired eyes and mind made me say it was fuse # 5. It is NOT fuse #5 but fuse #10 a 5 amp fuse. I unpluged the computer harness with a white wire with a red stripe and the "pin" on the harness from the computer is #01, a WHITE wire with a narrow RED stripe. I think i said "pin" #10 in a previous post on the "pin on the back of the fuse panel, it also is pin # 01. If that makes any sense. I must get lasik eye surgery. Thanks guys for putting up with me.