Intermittent no start issue...
 

Hey all,
I recently bought an 98 XJR and have recently got done servicing the car. I replaced the secondary tensioners and timing chains, plugs, all fluids changed etc. Car runs like a champ! The no start symptom was pretty consistent before I performed the work(ignition on, ENGINE FAILSAFE MODE then pops on, crank and that's it. The car won't completely fire, it just cranks) but upon doing some research I found that lubricating the brake switch could be the fix... and it worked! However, a couple of days ago I got the same problem but just once though. Anyone have any ideas?

Hello again, hopefully I get some replies this time... Like stated above I am having a continued intermittent no start (just cranks, doesn't fire completely over) issue. The good news is I have tracked down the area where I am having the issue.

When the vehicle just cranks I get the "ENGINE FAILSAFE MODE" warning but to fix the issue and get the car running, all I have to do is jiggle the shifter in the park position, turn the car off and it fires right up??? I did replace the J-Gate assembly recently due to my auto dim mirror leaking and destroying it but I had the exact same symptoms before I replaced it. Can anyone help me?

geez, that is odd. Sounds electrical based on your symptom and 'fix', but I have absolutely no clue what could be affected. I'd be curious to know how often this happens (like 4 out of 5 starts), and if the same jiggle fixes it every single time, no exceptions.

Sorry you didn't get an initial response on your first post, the engine failsafe mode warning is extremely vague and there are so many possibilties that would cause it. I do know that the dealer computer (WDS i think its called) can get more accurate codes than any reader we can purchase out there, as evidenced by my latest air bag message. I'd swing by the dealer, explain your symptom, get the codes read...and get some more direction as to the cause. You may, or may not, be charged for the diagnosis, so be prepared for a possible charger of $125 or so. I'd do that if I were you. good luck from this point, and keep the thread updated.

I 'd have to look for info, but I don't think the linear switch for the MB trans in your car would enable cranking and prevent the engine from starting...more likely it just wouldn't crank.

Trouble codes are the only route to guide you to the problem, jiggling and sqirting stuff can sometimes yield extremely fortunate and confusing consequences. The brake light switch is one example.

If the engine "won't completely fire", as in it sputters a bit when you initially try to start it, I'd be testing fuel pressure. The fuel pump/ pump link lead faults which result in this symptom can be very intermittant at their onset. I have not yet seen one that causes a trouble code to be logged, but Poboyblues has assured me that it can happen. Read the codes before you proceed.

Thanks for the replies guys, it doesn't fire up and sputter like it's getting a lack of fuel etc, it just cranks and cranks and cranks. I stop trying to start it, with the car in the on position, I jiggle the shifter, turn off the car and it will fire right up.... every time.

Food for thought, when I was replacing the J-Gate assembly I noticed there is this little metal tab that the shifter made contact with that let's you know if your trying to engage the transmission into another gear without your foot on the brake. If you move the shifter away from this metal tab it beeps. Could this be a culprit? What if the car thinks it is another gear when trying to start it?

If you have the car scaned for trouble codes , it is likely going to reveal a linear switch fault. That is on the right side of the gear selector housing (S/C only).

I just spent about an hour looking into this to try to learn myself something, and the best I can come up with is from the S/C starter circuit schematic. That circuit shows two outputs (both red/ blue wires) from the dual linear switch: one is a ground signal for the body processor module (BPM), the other is a ground input for the fuel pump control and ignition circuits of the Engine Control Module (ECM).

So the BPM gets a ground from the linear switch when the transmission is in park, it gets a signal from the key transponder module because you are using a good key, and it enables the starter relay to crank the engine. If that signal is not present (like when the shifter is not in park), the engine won't crank. A misadjusted or faulty linear switch would also cause this. But your car always cranks....

So the other red/ blue lead that is the ground signal to the ECM is where the problem is: you intermittantly are losing both the fuel pump and ignition circuits, even though the car still cranks. That's why you can jiggle the shifter to wake the car up, and it is something I have not encountered as it can only happen on an S/C car ( normally aspirated cars with a ZF trans don't have a dual linear switch) and I don't work on many of those. My bad luck.

The fact that the engine will always crank, even on the occasions it won't start, leads me to the GUESS that the dual linear switch is faulty and not just mis-adjusted: if it were mis-adjusted, I'm suspecting you would lose both ground signals at the same time and the engine wouldn't crank at times, either. I'm GUESSING that there is a microswitch inside the dual linear switch with two contacts that are depressed at the same time when in park, and you can guess which one is making intermittant contact. As you have found out, the magic juice that drips out of the rear view mirror is corrosive: perhaps that is the reason behind the failure.

First step would be to scan for fault codes, I think it was P1290 that was the likely culprit if I recall correctly, and try to adjust the switch to see if that will do the trick. The dual linear switch has a list of other responsibilities, if you just start moving it around to improve the contact in Park you can induce a whole range of other problems. I wouldn't be trying that if I were you. Jiggle on, or get it checked out and prepare yourself for the cost of a rather expensive dual linear switch.

By the way, Mr. Initial Man: Please do post back if you have the car diagnosed, reading accurate findings helps learn me things too and I'd like to know for sure that I have this figured out correctly. Thanks.

Someone once said 'I'd trust your guesses over other people's facts'. What do you know, another Star Trek reference. I'm on a roll.

Logic is sound JTO, can't wait to hear what the codes read.

Will do guys, will do... I appreciate you spending your free time in helping me diagnose my car. I will certainly get the car scanned as well as explore the other options you mentioned and let you know the results. Thanks again!

Thanks to you too, it's a mutually beneficial exercise when we're both learning something. And it helps the next guy the day he pulls into my shop with the same problem, since now I will at least have a better starting point that I didn't have yesterday.

2001 XJR Linear Switch Availability?
 

I have paid the $125 diagnostic fee with the Jag dealer I purchased my car from only to be told that the linear switch is not available to dealers at the present time as the company that manufactured them went belly up. This was at the beginning of 2010. I have checked back with the Service Manager on 2 different occasions and been told that the part is still not available. I questioned the Service Manager yesterday about the legality issues of Jaguar not supporting their product with the necessary parts and he told me that Jaguar has no responsibility to supply parts for their cars beyond initial purchase. He added that this was especially true for one as old as mine (XJR 2001). Does this sound shady??? I am really not pleased and continue to be challenged by the car intermittently not starting due to the faulty linear switch. Any insights would are appreciated. Thanks!

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Chad, please try using our Jaguar dealer vendors on site here. If it can be got chances are they'll get it for you:)
Do yourself a favour and check them out in the vendor directory!

I'm disappointed that USDM-STI-FTW never came back and reported the outcome.....Thats kinda shady after all the effort other people went to to try and help out!:icon_no:

Yep ... I got all the way to the bottom only to find out there was no firm answer on the dual linear switch.

I'm good at breaking arms you know !!!

... and spinning knobs :D

Went down and read the code using a *working* mongoose.

Got the right expected code, which would have narrowed the search instead of searching first and reading the code after ;)

P1517

PARK/NEUTRAL switch failure. Which is shift cable, rotary switch, circuits to ECM, or dual linear switch.