Symtom: car starts fine but as soon as i touch the throttle, it dies. Starts right back up and seems to idle fine. Then even the slightest rotation of the throtle plate, engine wants to die. If i am quick or only do it for a milisecond and retun it to idle, the engine will continue to run.

Car is new to me. Drained the tank. Replaced the fuel pump. Opened the lines under the hood and flushed a gallon+ fuel thru the lines. Replaced the fuel filter, flushed another quart or more. I had the injectors cleaned and hoses replaced. Checked plate clearance to .002 after cleaning, I replaced the spark plugs with ngk - gapped to .025, cleaned the butterflies, checked fuel pressure at rail (35 lbs), going to check o2 sensors next but want a longer list (I know it only takes one thing sometimes to fix a problem...).

Hoping for something simple - willing to try anything.

Thanks for any suggestions ( be gentile, this is my first fuel injected car)

 

You've done a lot of the right things.

At this point I'd be tempted to check the throttle position sensor. Do you have a voltmeter?

Post back

Cheers
DD


PS- hopefully a moderator will move this thread to the "XJS" section
Done, thanks Doug

 

I did not think the 86 had tps. I do see two micro switches on the throttle mechanics ( I cannot think this am what it is called ).

One activates just as the throttle cabe begins to move, the other when the thing is rotated about 15 degrees. I have checked both with a multimeter, for continuity, and for voltage thru it when each are activated.

Sorry, ment to put this in Xjs - must have accidentally started it from a window from one of my many search results. Thanks for pointing that out.

M.

 

I confess ignorance about your engine. There is an air flow meter, it would be worth checking that it moves.
Checking everything downstream of the meter for air leaks is also a good idea.
Hopefully Someone Who Knows will be along soon to help

 

You're still in the wrong section :-)

If this is a 1986 Jag V12, in either a sedan or XJS body, you have a throttle position sensor. It is underneath the throttle turntable.

Arrange your volt meter to *backprobe* (that is, probe the wires from the back of the connector while it is still connected) the yellow and green wires and, with the key "on", s-l-o-w-l-y turn the throttle. You are looking for a smooth voltage reading from about .32v-.35v at idle position to about 4.8v-5.0v at wide open throttle. If the reading "drops out" as the throttle is gradually opened, the TPS is fauly. Of course you're most interested in the reading just off idle.

Note that the wiring colors at the TPS change where it is connected to the main harness....don't get confused :-)

The switches you mentioned are the "kickdown switch" (on the throttle cable) and the "enrichment switch) at the throttle turntable

Cheers
DD

 

No air flow meter on this car :-)

Cheers
DD

 

Note to self - don't move threads and read the HOW-TO in the wrong section before having coffee.
Let's try again.......

 

I had a Ford Taurus that did that. I replaced the MAF Sensor.

Not sure if your car has one of those...

 

See post #6 :-)


Cheers
DD

 

Ahh yes, I apologize. I spent so much time trying to recall what I did with that Ford that I forgot the previous post.

EGR? Cheap to find out. Take the EGR off, give it a good cleaning and see if there's any change.

 

you need to get in there and hook up a vacuum gauge. report back your findings.

 

Sorry, but no EGR valve on this car, either. You probbaly think I'm trying to pick on you, but I'm not! :-) Just don't want the OP spending time looking for something that doesn't exist!


Cheers
DD

 

About the only thing that makes sense is the throttle position sensor. They are known to be troublesome. Doug has described how to check it. if you have access to a DSO that is the best way to check. But the DVOM will work.

BTW the replacements units are expensive. Some have played around trying to get some GM or Ford one to work. I would either buy AJ6 Engineer's replacement kit or a genuine unit.

 

This eve I discovered that my multimeter batt was dead. I am too tired to run to the store avd get a 9v. I think your logic is spot on Doug. Thanks for the clear explanation on testing. I do not think I can get a probe into the connector ( looks sealed cast plug ?) but I can take .0025 safety wire and carefully loop it and reconnect the terminals....

Will update tomorrow.

 

The AJ6 Engineering replacment looks pretty slick. Worth considering.

The original "Bournes" TPS was discontinued ages ago. Jaguar replaced it with a later design used on the "Marelli" cars. I think the TPS and required adapter kit will be in the ballpark of $300

Years ago I bought an aftermarket knock-off of the Bournes TPS. Direct fit, but quality was poor. I think it failed in less than a year....$150 down the tubes

I and others have had good luck with the $25 Mustang TPS but that success is not universally shared, as we've found out on these pages.

Cheers
DD

 

When my TPS finally goes I plan to go with the AJ6 setup.

I think the Mustang TPS will work if you find one with the correct resistance.

 

Sadly AJ6 do not actually do their TPS replacement any longer. The later, red in colour TPS will work perfectly in earlier cars (about 100US from Rockauto). But the throttle capstan centre shaft fitting that turns the TPS has to be fixed a bit. As Doug said, you can buy a Jaguar kit to do it, and pay about 250USD for a few bits of alloy, or make your own adjustments. This is basically what I did:

Take off the capstan.
Remove the old black TPS.
Remove the capstan shaft (two little screws on the top and out it comes).
Cut a small alloy plate about 5mm thick and 2 inches or so sqare, with a hole in the middle so the TPS spindle/capstan shaft can go though it. Mount this plate to the bottom of the capstan using the threaded holes in the capstan previously used by the old Bournes black TPS.
Mount the new TPS to this plate, being careful to place it so there is adjustment available at the closed throttle position. If you get this wrong, it is easy to re-site the TPS on the alloy.
Then offer up the capstan shaft as if you were refitting it (it will be too long for the new TPS and have the wrong 'key' to engage with it) and having measured carefully cut down the shaft to shorten it to the correct length to engage and overlap enough with the drive-flat on the new TPS.
Finally cut a slot on the shortened capstan shaft so it engages correctly with the flat on the TPS spindle. As I mentioned above, if the slot is in the wrong position at closed throttle, just re-site the TPS on the alloy plate
Reassemble, test and adjust the TPS position to get the correct signal.

Greg

 

I hope I do not have to go that route Greg - but thank you for a great write up! Was there a change after 83? I noticed rockauto sells a tps for the 84-92 as the same part number :
More Information for STANDARD MOTOR PRODUCTS TH418. There appears to be a different style after 93: More Information for STANDARD MOTOR PRODUCTS TH416 that does not look like what you were explaining. Is the first red one the one you had to make the stand off plate and machine to fit? Thank you, M.

 

The "TH416" type (DBC2626) was used on the 6.0 V12s and also the 4.0 six cylinder cars from around 94-onward or thereabouts

The "TH418" type (EAC9634) is what you're after. It's the replacement for the earlier (black) TPS that your car has (unless, of course, it has already been replaced)


This might be of interest:
http://www.jagrepair.com/images/Auto...TSB%20C-11.pdf

Cheers
DD

 

No, only when the original black Bournes type was changed to the newer type.

Yes, on my car (1985 V12) it is this red one, which I got sent fromm Rockauto.
More Information for STANDARD MOTOR PRODUCTS TH418

Greg