XJ6 & XJ12 Series I, II & III 1968-1992

86 XJ6 - Throttle Cable/Transmission Issue

 
  #1  
Old 06-12-2016, 07:15 PM
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Default 86 XJ6 - Throttle Cable/Transmission Issue

Hey all,

I recently had a shop replace my throttle cable as the old one had gotten stuck in the accelerated position and the cable wouldn't retract.

After the replacement, the accelerator physically moves more smoothly but the car waits to shift from 1st to 2nd slightly too long and seemingly will not shift into 3rd whatsoever.

This makes my acceleration from 30-50mph VERY VERY slow and acceleration beyond 50mph impossible!

I did not have any problem shifting gears or getting up to speed prior to the installation of the throttle cable.

I'm not certain but I think there is a mistake in how the cable was connected to the throttle valve. There is a cable attached to each of the throttles and one of them is pulling in the direction of the cabin.

Unfortunately though, I don't have photos of how it was before when it operated correctly and can't remember.

I have attached a photo showing how the cables attached to the throttle. I have attempted to shorten the cable as much as possible but that didn't really help.



The shiny new metal cable is the new throttle cable.




As you can see, the new cable is attached to the lower point of attachment and the upper point of attachment is connected to a different cable which pulls back toward the cabin of the vehicle.


Thanks for any help or insight ya'll might have.

John Cook
86 Jaguar XJ6 Vanden Plas
 

Last edited by john_cook12; 06-12-2016 at 07:49 PM. Reason: clarity
  #2  
Old 06-12-2016, 08:21 PM
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From memory...others will chime in....the installation looks fundamentally correct.

The 'other' cable is the transmission throttle valve cable. Movement of this cable as the throttle is opened directly influences shifting.

I suspect the throttle cable is simply not properly adjusted.

Or......

In doing the job they also disconnected the transmission throttle valve cable and disturbed the adjustment slightly....and slightly is all it would take to change shifting.

Adjustment of both cables is described in the ROM/service manual. If you don't have one, post back

Cheers
DD
 
  #3  
Old 06-12-2016, 08:22 PM
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Where's your battery hold down?


Cheers
DD
 
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Old 06-13-2016, 12:09 PM
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Removed battery hold down to fiddle with the throttle - its just the traditional bracket style with screwtop hold-down.

The ROM/manual materials I read only suggested adjustment of the threaded exterior cable by adjustment of the nuts. I am curious about how to tighten/slacken the interior cable of each of these cables as I imagine this is what is causing the problem by being too loose. I am currently able to adjust the nuts thereby loosening or slackening the exterior cable but it doesn't seem to make a significant difference to the interior cable.

As I was working to adjust the cable I moved the throttle manually and noticed another problem:
when the throttle is manually raised, the bellows of the air duct form the AFM to the valve (the part in the first photo just before the curved piece directing air into the throttle body) sucks in like a blocked straw.
The portions which usually bellow out are sucked in when I activate the throttle and there is a strong sucking noise and the entire set of air hoses running up to the throttle moves a fair amount as if there is something blocking the hoses. I have checked the air filter canister for blockage and found none.
 
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Old 06-14-2016, 02:05 PM
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Not to revive my own threat but the only ROM manual instructions I could find concern the positioning of the outercable - adjust of my outercable however is not providing sufficient adjustment for the actual interior cable to resolve the problem

I have been setting the throttle exterior cable progressively further away from the throttle and even with the back nut as far down as possible on the bolt while still gripping, there is not sufficient (or at least, not correct tension) so as to permit acceleration above a very sluggish 50mph.

 
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Old 06-14-2016, 03:32 PM
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John, adjusting these cables is like adjusting bicycle cables; if you move the adjusting nuts farther away from the end of the sheath (as pictured above) you effectively make the inner cable longer, because the sheath is not forcing it into such a tight arc. The illustration above is at the loosest extreme of adjustment.

When you turn the adjusting nuts closer to the end of the sheath you are effectively lengthening the sheath and functionally shortening the cable inside, even though everything is the same true measured length as before.

Chalk it up to one of the great mysteries of the Universe.
(';')
 
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Old 06-14-2016, 09:17 PM
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Did you compare the new cable to the old? Are they the same?

Cheers
DD
 
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Old 06-14-2016, 09:17 PM
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Originally Posted by LnrB View Post
Chalk it up to one of the great mysteries of the Universe.
(';')




I love that !

Cheers
DD
 
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  #9  
Old 06-15-2016, 12:36 PM
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Thanks to everyone for the help so far.

Those adjustment instructions are somewhat counter-intuitive but I understand now. I'll make the opposite adjustment of what I had previously made to see if that can make any significant difference to acceleration speed or shifting up into a driveable 3rd gear.

I can't determine if the new and the old cable are the same cable because the shop I took it to discarded the old cable unfortunately. The new one does look longer than the former cable (by about 3-6" on the engine bay side) but having never straightened out the old one or laid them side-by-side its really impossible for me to be sure.

Thanks again for all the help so far. I'll fiddle with the throttle cable and the transmission cable tensions to see if that resolves the problem I'm having or if it is caused instead by the seeming failure of the air intake system causing this 'pressurized straw' effect I mentioned above or perhaps this was just mere circumstance and now there is a systemic transmission failure preventing shifting up into the 3rd gear. I'm not sure but will post results after fiddling with the throttle cables.
 

Last edited by john_cook12; 06-15-2016 at 06:05 PM.
  #10  
Old 06-15-2016, 01:18 PM
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Only a bit to offer here.


1. I don't think the overall length of the cable matters, so long as it reaches the attachment points. That is the housing and the cable inside it that moves and transfers motion. The housing must be secure at both ends or the results will be as Elinor's comments as to life's mysteries.


2. As a kid, my bicycles were far simpler than those using cable to breaks or select gear ratios. Peddle forward, bike goes forward.
Back pedal and it brakes!!


3. So, one Christmas, we got our a "5 speed "!! Some assembly required!! Wheels, bars and pedals, easy!!! Three cables, oh h....
Got it together ands it worked!!!


4. On lumping the Jaguar, I dealt with the throttle and transmission cable. Throttle unit, far to long. I managed to cut it down. First design at the capstan end failed early on. Improved version continues to serve. Transmission cable flunked in the drive way!!! New install fiddly but quite doable. The "improved" version continues to serve as intended.


Carl
 
  #11  
Old 06-19-2016, 06:09 PM
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All,

I went out, torn apart everything from throttle body down to the air intake by the radiator.

Found pieces of a rag blocking airflow at the intake and some more down in the cannister.

I also noticed the AFM flap was sticking and it seems the flap had physically warped such that the metal was contacting the housing and preventing free movement. I had an old perfectly operational AFM in my spare parts tub. Swapped them out, leaned everything up and down before reconnecting and now it's driving better than ever.

It seems this truely was a rare instance of pure circumstance and having had the throttle cable recently replaced had no bearing on the acceleration difficulty I was having which were a result of air flow obstructions (the debris and the faulty AFM flap in combination).

Now with clean airflow it REALLLY takes off on acceleration. Maybe its just the drastic change from heavy hesitation to free movement but the car's never driven better.

Again, thanks all for the throttle cable help - now if it comes to it, I feel I could probably just swap it out myself now that I know more about the adjustments and can really get things fine tuned.
 
  #12  
Old 06-19-2016, 06:40 PM
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Well let's just stick a rag in the air horn!
Wow!
Who would Ever have thought of such a freak occurrence!! No wonder it wouldn't run properly! Reckon how that got there?

Now that you're Intimately familiar with the workings of those components you'll be an Expert. The next thing will be a Snap!

Feels good to conquer it, doesn't it. Good Job!
>Clink<
(';')
 
  #13  
Old 06-20-2016, 08:13 AM
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Yahoo, beat the thing. The engine is a really big compressor. Strong suction at the air horn. Lotsa stuff can get in. but, that is why the filter is there!!! You suppose your mechanic was running it sans filter while fiddling with the cable change??


No matter, it's fixed and you are the better for it.


After my kids left, I watched a DIY show based in Waco. Chip and
Joanna Gaines rehabbing houses Woweee, some neat houses for a heck of a good price. Naah, my kids would go over the edge if I even mentioned. "Back to Texas"!!!


Carl
 
 
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