Car stumbles and recovers, transmission light on then off, now stalls getting worse
 

OK, So, my 97 vdp did a strange thing last week, the transmission stumbled,bucked, jerked, and then recovered to smoothness,in blink, all so fast I thought is was just one of those random events. In the next week or so it did it again only a little longer, but now concerning
Few days later in a parking lot same thing only this time it stalled dead with transmission light. I restarted, and tyranny fault light was off. I shifted the automatic like a manual, keeping it out of 4th and at higher rpm, and got home during which time It shifted very smoothly as always . Now I'm afraid to drive it. The transmission light is still off, and my ODB code reader shows no stored faults,fluid looks clean and full.
How do I trouble shoot this, it seems something is going bad, or getting dirty, or whatever. For what its worth not that i matters (but it might with a jag} my parking break has never really worked very well, now its to the point I can not pull the hand brake tight enough to keep it car from rolling. (Glad Florida is flat !} I Don't want to drive it in traffic, Has anybody got ideas how do I track down this problem?

car stumbles and recovers, transmission light on then off, Now i stalls getting worse
 

OK, So, my 97 vdp did a strange thing last week, the transmission stumbled,bucked, jerked, and then recovered to smoothness,in blink, all so fast I thought is was just one of those random events. In the next week or so it did it again only a little longer, but now concerning,

I suspect you are having an engine related problem rather than transmission. The Transmission light comes on if the engine stalls so is likely a red herring.

There are many things that could cause this and if it's intermittent it will be hard to diagnose. It could be Fuel Pump or Fuel Filter (less likely as you saw issue in parking lot at low engine load). It could be bad coil(s). It could be bad CKPS. It could be faulty wiring to coils or injectors.

I don't normally suggest changing parts without proper diagnosis but a failing CKPS is almost impossible to diagnose without specialist equipment (scope) and it has so many failure modes. The CKPS will eventually fail so if it isn't the culprit right now then you haven't lost anything as you can keep it for a spare for when it does fail.

I'm going to say its a failing coil. How old are they? Are they original Jag coils? Mine will do that with a failing cheapo chinese coil, RPM will go up and down super quick like the whole car switches off for a split second, then recovers, eventually car becomes rather undriveable until coil is replaced.
Might be crankshaft position sensor too and you should have a spare in the boot at all times.

+1 probably engine

Might be an air leak - check fuel trims using OBD. Very cheap and easy to do.

A direct relationship between the engine and transmission acting up near idle to gear shift range is the communication link between the engine ECU and the Transmission ECU and is caused by a dirty connector on the transmission body signaling the transmission ECU . The end result is the engine doesn't know what to do and goes just nuts

The connector is on the left side aft , no jacking required

Never got mine off but it may be a bayonet connector that disconnects like a air hose , so don;t try too hard twisting it apart

https://cimg0.ibsrv.net/gimg/www.jag...99caace6af.jpg

You've owned the car for a while so you should know when the spark plugs were last changed. Has it been more than 20,000 miles? If so, it is definitely time for a new set. Old spark plugs in this engine can cause stalling and stumbling exactly like you describe. It happens at random, and gradually becomes more frequent. It is nearly impossible to actually diagnose "bad spark plugs" for an intermittent stall, so just replace the plugs if it is time. It's easy and cheap. Champion RC12YC.

That same intermittent stall was showing up again on my son's 96 XJ6 a few months ago. We replaced the plugs - problem solved!! Those Champions had about 18,000 miles on them. The old plugs looked fine and the gap was not much larger than spec, but they were worn out. Maybe it has something to do with the old original coils needing a "sharper" plug to provide adequate spark energy. Anyway, I'm happy to replace the plugs once in a while, rather than messing with the coils.

As Brendan suggests, definitely get a new Crankshaft Position Sensor (CKPS). That is also a major cause of stalling and strange behaviour that is difficult to diagnose.

Ok, WOW, all these great suggestions.

When I first got this 97 VDP, I never owned a Jag before, so I had a Jag mechanic go over it. He replaced all coils and plugs (not with RC12YC either turns out) and kinda pricey too. Then 8-12 months later one coil bad, then another coil would go bad, so I learned how buy and replace those, and always keep 2 coil packs and tools in trunk, one time had to do quick roadside change when it did that exact thing noted “RPM up and down super quick like whole car switches off for split second, then recovers”. So; (1.) will replace plugs, Champion RC12YC, (2.) replace all coils, (3.) order a new (CKPS) Crankshaft Position Sensor (and go to YouTube school to see how to replace it), (4.) Check for an air leak – using fuel trims using OBD (5.) Check for dirty bayonet connector on the transmission body, and (6.) I won’t rule out Fuel Pump or Fuel Filter as they seem to appear in a lot of posts for all sorts of things.
Thanks to you all [SleekJag12], [b1mcp], [JagV8], [JagV8], [katar83], [Lady P.]

Ok... Yes. I agree with coils... Also with the transmission plug. I've had the identical problem with my 97.
The electrical system is VERY persnickity. If one thing happens it reflects the problem all over the place.
COILS:
If you have a coil going bad you'll spark through to your magnesium valve cover and it will eventually be destroyed. Do not delay. change the coil.
If you get good coils (NOT FROM EBAY) they are expensive. But the good coils last for 100K miles or so. If you get cheap or bad ones good luck getting 10k out of them. Be careful... They will sell you cheap bad coils for high price to fool you on ebay. Go yo Welsh or Jagbits. Real lucas coils if you can find them or the Japan made ones are they only good ones. There are several threads on coils here. Typically they will make the entire dash flash but they can cause all kinds of crazy problems. When you replace the coils do the following: Make sure the coil wells are clean, not burned, re-painted and smooth. Otherwise the walls of the valve cover will be too close to the coil causing sparking, pitting and oil leaks when they burn through. Make sure you put dielectric grease on the contact/plug and the inside of the coil springs and contacts (requires taking off the rubber boot (be careful they tear)) Make sure you have a really good gap/plug and great contact. Even a slight bad connection can cause problems and wear out the coil quicker. I also add a few layers of KAPON tape around the coil to prevent sparking. It's what they use inside transformers.

Transmission: clean the connector with contact cleaner and dielectric grease before putting it back on or it will do it again. This was my first fix... only lasted about a month then: ..... it came back....

This time, it was Battery/charging system. If your charging system is weak or the battery is old or the ground is bad at the body then many weird things can start happening including transmission lights. For instance. I had an idle problem that caused the car to start slowing to about 600rpm. That caused the alternator to only put out 11 volts... bam transmission hickup and car dies. Sometimes it's difficult to start again but sometimes it starts right up and all is well... After I fixed the idle problem about a week later It started again... very very frustrating... thought I had it but no.... wow then found a slightly loose belt for the alternator.... slipping belt causing same problem... tightened belt... went away for a while... came back.... bad voltage regulator... probably from pulling too many amps when slipping... Replaced alternator. tightened belt, fixed idle... all well for a while... back to tranny lights etc in about a month. Weak battery. Replaced battery with larger version. (more amp hours)... no more tranny problems for about a year now.

I actually think it was multiple problems mixed up at the same time... Took about 6 months to get to the bottom of it all.

Other suggestions are good as well. Have solved a multitude of small issues on my 96... ckps, air leaks, MAF dirty, Fuelpressure regulator, EGR valve. Keeping an old car running after 150k is always fun :)

I have 3 of them and looking for another :) nothing drives like a Jaguar!!!

How many mile accumulated of your Jaguar? What is full and clean mean? Is the transmission oil still has a red color? Oil pan/filter and new oil should be change out on these ZF4 transmission as a maintenance procedure. Oil pan and oil is super cheap now a day. Its a half a day job for DIY.

Oil is red color, no burnt smell, and is at or a little above the hot mark at warm idle in park. Never the less, won't hurt to change Oil pan/filter out. SO, what is proper trans fluid if I want to change it? I'm guessing it was LUCAS trans oil from factory, is there a US alternative like Dexron III or something?

Thanks Steve for that extra follow up. Now I will be so much less frustrated when facing repeated recurrences, I know now to expect them, and, have an ever growing road map of various causes and how to fix. So, I'm feeling much better about this car, my wife loves it, she's not a car person, but when she saw that white VDP for sale, she really fell for it, its her daily driver, and we have driven all aver the country in it in the past 7 years. Joy to drive, and strangers still give her compliments on the car and ask about it ! That's my motivation to keep it going !!

Yes the Transmission Fluid is Dexron III. There is some very useful information from @Don B and others in this thread

https://www.jaguarforums.com/forum/x...-fluid-177345/


But Transmission Fluid will not be a factor in to your current stall issue.

As mentioned earlier in this thread and I've read elsewhere that fuel filter and / or fuel pressure regulator can be a factor contributing to a launch "stumble" . Replacing these has helped me in the past.

There is a ground often mentioned that is missed as the large engine block strap from the lower starter mounting bolt to car frame

Hard to get a ratchet on it from the top but easy from the bottom

13 mm on the starter bolt and 8 or 10 mm on the car frame bolt

The surface on the car frame needs to be cleaned and rust free and some light bulb grease applied

The rest of the grounds in the engine bay also have to be cleaned for the engine regulation devices to work properly

I personally see the grounds as a regular scheduled maintenance item like a fuel filter

There is a vacuum line on the fuel pressure regulator going to the intake manifold

As an air leak at the intake manifold can cause the engine regulation to be out of trim and not able to correct itself in the lower RPM ranges

The FPR vacuum line makes the fuel pressure incress around !0 % ( 4 psi ) in the higher RPMs

Thee is one vacuum line under the manifold that goes to the EVAP system and is a thing that can go into detail to address that

Another vacuum line comes from the top ( # 3 cylinder ) with a tricky sealing fitting to the brake boost diaphragm which can leak itself

https://cimg4.ibsrv.net/gimg/www.jag...26984b9736.jpg
97 vdp, could this be a cover over the connector on the transmission body (for the wire that does the signaling to the transmission ECU)?

OK, I can't find the connector on the transmission body (that does the signaling to the transmission ECU), I know the connector is supposed to be on the left side aft (drivers side USA)? and no jacking required, but, I can't seem to find it. Coud it be the in '97 they put a metal protector around it I have to remove 1st? see picture. I did go to jag-lovers forum and find pics of the cable and connectors, but they were close-up and could not tell location.

Check the coils, It's always the coils :)

The shape of the box looks right to be a cover for the connector

I can't remember if the wire bundle goes straight up to the shift gate area above the large floor pan sheet metal

The transmission ECU is located fwd of the front right seat on LHD US models

It's on the very bottom very fwd under the glove box and is made by TRW or Bosch with a long ribbon connector

Remember it is a push / pull connector and not a twist off. But I can be wrong as mine is stuck on some penetrate spray helps remove it

https://cimg3.ibsrv.net/gimg/www.jag...7099068e55.jpg

sorry for these giant pictures, but On further inspection, when I got the car up on ramps, I now think the black cover goes over the moving selector assembly, because I now found the connector visible, aft of that box. I can;t tell if I should pull the black rubber part, or the black plastic collar in front of it, ot twist that collar by the white line. Your picture shows those pins sticking out to the side, like they are where a twist-lock would secure to.

https://cimg1.ibsrv.net/gimg/www.jag...2ef7a92545.jpg
https://cimg4.ibsrv.net/gimg/www.jag...6d3745f342.jpg

The 3 / 120 degree apart pins would indicate a twist off

The pins would indicate a quarter turn quick release and the white stripe painted barrel is what twist and not the rubber protective boot on the what's called the connector backshell

The later ZF 5 speed is a push pull

I never got mine off being stuck and too cautious knowing about the 5 speed and not wanting to break the connector

The device you see under the black cover is the rotary switch which is used in the starter circuit