My Baby won't run

[90 XJ-S]

OK, here’s the story as best I can remember it all.

I got my ’90 XJS Convertible about a month ago and have been driving it around enjoying the ride and the southern California sun. No real problems except that the transmission would not kickdown, the cruise control didn’t work and it never showed a “Fast idle” (always right on 750)
Last Sunday, after reading a post by Doug Dwyer about how easy it was to fix the kickdown problem
(“So, I did some exploring and discovered that the little round plastic throttle stop below the throttle pedal was adjustable. I screwed it inwards several turns. Now the kickdown *really* works.” DD)
I decided I would go fix that problem. I adjusted the little plastic thingy. Then I went exploring around under the bonnet and found the three-conductor plug going into the cruise bellows was partially disconnected. I seated it properly. Then while looking around some more I found one vacuum hose off the Vacuum Solenoid Valve. After hooking that back up I closed the hood and headed for the highway. (About a mile and a half, or so) After getting on the freeway and up to about 55 I went to WOT. The kickdown worked!! (I was suitably impressed. I instantly understood why I bought this black beauty. Then almost as instantly (I was up to about 80) the engine stumbled and coughed…twice. I grabbed the next exit…she seemed to be doing all right…so I turned her around and headed back. I tried setting the cruise at about 60MPH and it worked also!! But, once again, just as I was getting that “High” from something working right… she coughed again. From there on it ran fine, as long as I didn’t move the gas pedal. TPS pot my rookie brain said. So I took it home and checked the Pot ~.2 Volts. So I said Aha and adjusted it. Seemed touchy to me, but what do I know? Took it for a 100-foot cruise…still hesitates. So, after buying a new one of those (must be golden) pots… I installed it adjusted it (much easier this time…Set to exactly .320 Volts) No real change to the symptoms if anything, they got worse…didn’t really want to idle, considerably more sensitive to gas pedal movement. After fooling with re-breaking some of the things I fixed. With no improvements…it now doesn’t want to run at all. It will start and idle for around 1 – 2 seconds then die.

Does anyone have any words of wisdom for this bewildered Jaguar Novitiate?

TIA

Mike Smith

 

[John S Farrington]

Mike, The 90 XJS V12 is a very complex computer system. It has many sensors that tell the computer what to do. It sounds like you have done a lot of adjusting of things and now you have serious trouble. I would start with the basics. Check that you have proper spark ignition. Measure what your fuel rail pressure is. It should be about 40 PSI. Ascertain that your fuel injectors are being pulsed. (a simple test device is available for plug in to do this) My guess is that you should run up the idle speed to about 900 RPM. The only authorized control of the idle speed that is manual should be on the left intake mnifold on the rear. It is a 13mm hex screw. Other adjustments to the idle can send signals to the ECU that might have serious consequences. Unless you have professional advice, dont tamper with things. You probably need a V12 mechanic to straighten this out. It is going to be very hard to diagnose this over the internet after so many small adjustments. Best regards, Jack

 

[90 XJ-S]

[ QUOTE ]
It sounds like you have done a lot of adjusting of things...

[/ QUOTE ]

Jack,

Thanks for answering. Truly, I understand that I shouldn't mess with things that talk to the computer. However, I have only adjusted the TPS Pot. And that, to set it to .320 Volts between red and yellow as virtually everyone has said is proper. The old pot was definitely bad although it was, obviously, not the problem.
Another expert, on another board, suggested I check out the Distributor Cap. Nothing wrong there. I have good spark at both coils and my timing light says every plug is getting fire. My current belief is that I don't have fuel or at least not proper fuel. My next plan is to check fuel pressure at the fuel rail as that will support my theory (or disprove it)My current quandry is whether or not there is a simple way to hook a pressure gauge to the fuel rail, as I don't see any maintenance port on this rail. do people tee into one of the rubber hoses or is there a better plan?

BTW Jack,
I am by vocation an Electrics Engineer and by avocation an automotive mechanic. This is my first foray into jaguardom but not my first trip with british cars and certainly not my first trip with ECU's and EFI equiped cars. The Jaguar <font color="red"> IS</font> complex and fortunately, I try not to mess with anything that I am not <font color="red">SURE</font> I understand. I have the greatest of regard for your analysis of Jaguar problems and the advice you have offered on this board. Any advice or education you can provide to me will be greatly appreciated.

Mike

 

[90 XJ-S]

[ QUOTE ]
My next plan is to check fuel pressure at the fuel rail as that will support my theory (or disprove it)

[/ QUOTE ]

After spending way too much time rigging a connection for Fuel pressure monitoring... I have determined that I have <font color="red">NO</font> pressure. After turning the ignition on and off multiple times the needle did not even move. I would assume that my pump is not working at all. Tomorrow I try to figure out why.
I would guess the options are:
1 the relay is never being commanded on... is this even likely?
2 The Relay is broke.
3 The Pump is Broke.
4 There is a broke wire/connector somewhere.
5. A fuse? (are there any specifically for the fuel pump?)

Anyway, at least now it appears it is once again Lord Lucas' fault... and he and I are old friends. /ubbthreads/images/graemlins/rolleyes.gif
Thanks for the help, so far, and if anyone wants to chime in with more suggestions, I am still listening.

Mike

 

[Mark Beiser]

Did you check your fuel filter? /ubbthreads/images/graemlins/wink.gif

 

[90 XJ-S]

[ QUOTE ]
Did you check your fuel filter? /ubbthreads/images/graemlins/wink.gif

[/ QUOTE ]

Thank you, Mark,

Yes, yes I did. Fortunately, while I was back there I checked my fuel pump also. I had a bad pump. Whir.........whir.........whir etc with the relay jumpered. Would kind of pump the rail up but didn't have a chance of keeping up with a running V-12.

A NAPA store in the area actually had one!!!
So, on sunday morning on the fourth of july in the USA /ubbthreads/images/graemlins/patriot.gif /ubbthreads/images/graemlins/patriot.gifI was able to buy a XJ-S fuel pump!!!

Well, at least they thought they had one. I now know why they had it. Someone bought it, found the fittings to be wrong (the electrical connections are wrong also) and gave it back.

I did buy it and I managed to change the fittings so that it fits and my fuel rail pressure maintains 45PSI under all conditions. (I rigged it so that I could drive with the pressure gauge connected. The pump is NAPA Brand part number P60423. but, if you use it, remember you are going to have to get some hose barbs of the correct size to fit it.
/ubbthreads/images/graemlins/smile.gifMy Black Beauty does go down the road like a fine Jag should. /ubbthreads/images/graemlins/driving.gif /ubbthreads/images/graemlins/driving.gif /ubbthreads/images/graemlins/driving.gif
Unfortunately Basil doesn't have a Smiley for car washing, 'cause that's next on my agenda. /ubbthreads/images/graemlins/savewave.gif

Mike

 

[John S Farrington]

Congratulations and glad you found the fault. I have been on a long weekend trip and out of the loop. If you need any technical advice on V12 service or problems I will be glad to offer you what I know. The best way to tee a fuel pressure gage is to get a used inlet fuel line and use the connector ends to rig a test adapter tee for the gage.

 

[mdallaire]

Glad every thing work out Ok. I am still chasing a intermittent no start problem and a very very slight rouch idle. New tune up, new fuel pump. Some day I will find the problem.