My 96 vdp 4.0 six will not shift below 4200 rpm s . It shifts fine when it shifts but 4200 rpms under slight acceleration seems wrong. I have changed the ecm , the o2 sensors [all 4] the throttle pos sensor, the ignition coils,the crank pos sensor, checked the tranny fluid level,i looked for but could not find a vacume hose going to a modulator valve....Im lost folks . please help

 

Assuming all those items were really needed, as few have anything to do with the transmission, in my opinion of course.

The mighty 4ltr has an "electronic" transmission, sooooooo, somewhere on the side of the transmission WILL BE an electrical plug, usually round and quite largish in diameter. ZF have many discussions on this "thing" on many cars, such as MB, Jag X308, etc, and that plug is the #1 cause of erratic shifting, and other oddities. It gets contaminated inside, and connectivity is challenged, so simply unplugging it, CLEANING inside it, and the mating transmission section can fix the hissy's.

I am no use as in "hands on" as my 3.2ltr also has a ZF trans, BUT, a cable controlled unit, as it is a non-electronic transmission.

Another little "fix" that works most times, is to disconnect the battery, leave it a while, such as overnight, and reconnect, and mostly the gremlins have gone AWOL.

 

Thanks for your help grant. And unfortunately yes all those parts were nessesary. This is my personal penance for something I must have done But for the life of me I can't remember doing anything that nasty I have a love hate relationship with this car. I'd sell it if I didn't love so much

 

HAHAHAHA, you only got 1 Jag, therin lies your problem.

Any self respecting Jag "person", MUST have a V12 lurking somewhere in the background.

That alone keeps you sane.

Maintaining a V12 brings you down to earth with a resounding THUD, and anything else life throws at you pales in comparison.

 

Hi Grant, I had the jag up in the air yesterday but wasn't sure what I was looking for. I found an item on the drivers side of the trany with wires going into it,so I took off the metal cover covering this round metal {thing} .But when I tried to remove the wires I found they were sealed with a white silecone inside the switch like thing. Is this the switch you spoke of? It is held in place by 3 10mm nuts and located near or even beside what appears to be the linkage. I tried your idea about disconnecting the battery as well but had no luck,she still wont shift below about 4500 rpm's. Any ideas would be greaty appreaciated thx...Jamie

 

OK, this is going to be from memory and some BMW ZF stuff I downloaded ages ago, for the sons 740 trans oil leaks.

I think that switch you have found is called the "rotary switch", and is more to do with the reverse lights, and LH side of the J Gate positions??.

All the info I have talks of a "valve body to case o/ring" and the nut to suit it. The drawings are terrible and show almost nothing, except that this nut appears to be at the LH rear corner of the trans casing, just above the gasket line. It also appears to be facing the rear of the car, and is a 7 pin or more round connector. That o/ring is what leaks and fills that connector with trans fluid, thus interrupting the signals, and eventually leaks on the ground.

I dont have this on mine, and the guy I know with a 4ltr is away on holidays in the car, so no use at the moment. The other guy with an XK8 says his plug is as I described, rear LH corner just above the gasket line, and his trans had all sorts of strange issues, and that connetor was full of oil, and once cleaned, all sweet, so maybe the 5 speed is the same basics as the 4 speed????.

 

Thx again grant. She's going back on the jack stands shortly.