89 Jag xjs convt v12 engine vibrates

(LesOlinger) #1

89 Jag engine vibrates over 2500 rpm seems to run ok. I removed the belts and made no difference. exhaust is hot out both sides, starts right up, doesnt get hot, idle is good. I replaced the plugs 1000 miles ago the old ones look ok. Any ideas?

(Doug Dwyer) #2

“Vibrates” in the sense that it is running roughly, like a misfire or dead cylinder?


“Vibrates” in the sense that something that rotates is out of balance?


(LesOlinger) #3

well I took it to a trans shop and had the trans rebuilt. Then when i picked it up and hit the freeway it vibrated so i took it back thought maybe the driveshaft was in wrong. They had it for two weeks told me they pull the trans back and the engine still
vibrated and it the engine probably a valve or something. So I brought it home doesnt back fire or anything just vibrates doesnt get hot, oil pressure good. I removed all the fan belts to see if that was it but still vibrates. The exhaust is hot out both
sides sounds ok. I was starting to think one of the coils went out. But now Im thinking the torque converter they put in may be bad but they say no.

Car has 200000 miles on it Ive had it since new never had an engine problem… Replaced the plugs about 1000 miles ago just because. The originals looked fine.


(Doug Dwyer) #4

Take a good look at the trans mount and how it was re-installed.

I had my trans rebuilt by a shop I know and have been happy with. I told them to pay attention to the trans mount, owing to it being a bit convoluted.


The trans was fine but I felt a vibration. Returned car to shop and, sure enough, it was a problem with the mount. They didn’t elaborate but admitted that they got something bollixed up on reassembly


(Ptipon) #5

Don’t mean to sound belittling but Is the vibration with the car in 3rd and rolling with the engine above 2500 and is the vibration consistant at all speeds above 2500 prm? Is there any vibration when the engine is rev’d with the tranny in P or D?

Just thinking that it could be a tire balance situation.

(LesOlinger) #6

Its vibrates just sitting in the garage and running at 2500 rpm. Doesnt seem to miss idles fine . Im considering one of the coils messing up.

When I took it back to the trans shop they pulled the trans back and said the vibration was still there so it must be the engine.

(LesOlinger) #7

I took out the old mess of a trans mount jag made years ago put in a chev trans mount. Thats what still in there but funny thing is the trans shop said it vibrated even after they disconnected the trans from the engine and just ran it sitting
there. So Im wondering if it the torque converter they put in or something wrong with the engine like maybe one of the coils messing up.


(Paul M. Novak) #8

Does your 1989 XJ-S convertible have the Lucas or Marelli ignition?


(Ptipon) #9

Well that definitely rules out a rolling problem. If it’s possible to get an oscilloscope I’d also check the plugs and injectors, looking for any anomaly there too with high rpm.

(LesOlinger) #10

It’s the later v12 engine with martinelli dual coils. I know they will still run on one coil

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #11

They won’t vibrate, though. They run perfectly smoothly on one coil.


Check your crank damper. I had one with a cracked collar that would vibrate at similar RPMs. While I couldn’t see the damaged collar, a close look at the damper while someone revved it and I could see the damper oscillating.

(Steve) #13

This is NOT correct. When the Marelli v12 loses one bank, it continues to run, but POORLY and with no power.
I doubt you can rev it to 2500 rpm on a single bank.

Exhaust on the the side where the ignition is dead is silent. This is not the observation made by the OP.

(Steve) #14

Was the vibration there before the transmission rebuilt? If not, I think it is safe to conclude they they did something wrong. Perhaps not with the transmission per se, but with the matting to the engine.
Can you verify that they attached properly the ground strap and they have not crushed the fuel/vacuum lines that run on one side of the trans. tunnel?

(Carl Hutchins, Jr. ) #15

I’ve read of a “rough and ready” possible fix of a vibration. Easy on GM’s. Remove the converter “dust cover” down under. remove the three bolts that fasten the converter to the flex plate. "clock the converter one bolt over. Try again.

It may or may not work. Objective. A better match of the converter to the flex plate as to balance.

As to the dampener. Mark the inner and outter parts with a chalk or “white out”, Run the engine, up and down throttle a few times. Inspect. Is the line still straight across.

Is there a chunk of rubber or steel missing from the dampener ?

And, basic, is the big nut at the end of the crank tight?

Wild card. A V12 on 11 can offer a challenge as to finding which hole is "coasting.


(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #16

Still smooth, though, no vibration.

(LesOlinger) #17

where about do the lines run right or left top or bottom. You might have something there it does seem a bit stronger exhaust on the right side than the left but both have plenty of hot exhaust coming out it will rev up as high 5000 easy has good response just vibrates in the seat just sitting there not violent though put your hand on the motor not so much but sit in the seat and vibrates alot.

(Greg) #18

Vibration issues I’ve always had were usually mounts.

Did they put in a new trans mount? If they did, that could have put additional strain on old motor mounts, causing them to go bad.

(Ed Sowell) #19

My tranny was rebuilt many years ago at a tranny shop. Afterwards had a bad vibration problem. Had to take it to my Jag guy who immediately spotted the mount not installed correctly.

(Paul M. Novak) #20

In a previous post LesOlinger said that he removed the original Jaguar transmission mount and replaced it with a Chevy one.

My money is on a problem with the transmission mount, possibly due to confusion, missing, or wrong parts related to the non-Jaguar mount.