Throttle Body Cable Adjustment = Original Power Restored ?
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From: North Carolina
It might not be intended, but my OBD tool shows that I have 100% throttle when I floor the pedal. I'm not sure if it's possible to show 101%, probably not, but since the 2003+ vehicles have a "fly-by-wire" throttle, the car knows to open the throttle all the way when I floor the pedal. That's what matters.
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From: Southern New Jersey
I adjusted the cable on my 1998 XK8 and it made a big difference. No longer had to push pedal to the floor to get a down shift and the car really wants to launch now. Glade I saw this post.
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From: Los Angeles
It might not be intended, but my OBD tool shows that I have 100% throttle when I floor the pedal. I'm not sure if it's possible to show 101%, probably not, but since the 2003+ vehicles have a "fly-by-wire" throttle, the car knows to open the throttle all the way when I floor the pedal. That's what matters.
Doug
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From: Southern New Jersey
Well I never thought there could be any more to say on the subject but I was still bugged about not being able to completely understand what was going on when following the JTIS procedure for adjusting the cable. I was taking another look at mine today to check for slack and played around with removing the clip, moving the notched thing around, etc. Then it suddenly occurred to me (as a structural engineer) that the cable adjusting system is most like the strand anchoring system that is used for post-tension construction.
I am attaching the best illustration I can find as to how a post-tension cable is stressed and anchored. The lowest illustration shows a cable that has been stressed already. There is tension on the strand and what is identified as the wedge keeps the cable from slipping to the right in the illustration. The upper illustration shows how to re-tension the strand (assuming it somehow slackens over time). You pull at the exposed end of the cable which unseats the wedge and frees up the strand so that you can add more tension. When you release the exposed end the cable with wedge slides back into the wedge plate thus locking the strand with the increased tension.
I think the mechanism shown in Sam's video works analogous to this. The thingie with the ridges somehow grabs the cable inside so that you can tension it and the metal clip acts as the wedge once you are all finished.
It would be great if someone could do a dissection of the system to verify what is going on.
Doug
I am attaching the best illustration I can find as to how a post-tension cable is stressed and anchored. The lowest illustration shows a cable that has been stressed already. There is tension on the strand and what is identified as the wedge keeps the cable from slipping to the right in the illustration. The upper illustration shows how to re-tension the strand (assuming it somehow slackens over time). You pull at the exposed end of the cable which unseats the wedge and frees up the strand so that you can add more tension. When you release the exposed end the cable with wedge slides back into the wedge plate thus locking the strand with the increased tension.
I think the mechanism shown in Sam's video works analogous to this. The thingie with the ridges somehow grabs the cable inside so that you can tension it and the metal clip acts as the wedge once you are all finished.
It would be great if someone could do a dissection of the system to verify what is going on.
Doug
Last edited by Bigvettefreak; Nov 28, 2011 at 01:02 PM.
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From: Chicago
I am Convinced....
Have a 1997 xk8 coronada blue with 20'inch portfolio rims... Looks like a 94' Special edition 1994' Portfolio....Like you I love my car...Followed the instructions to clean my TB, clean my MAFS, my PLBT and tightened the tension on my throttle along with twisting my under the pedal adjustment to access 100% full throat body.
I must say....I AM SO HAPPY WITH THE RESULTS....Increased, restored, what have you...My mint 143k 1997 xk8 sprints, darts, wants to fly above and beyond the mature slowing beast of yesterday....
It is an indoubatible fact that adjusting the throttle body to no slack and other maintenance quick fixes made my old star aging star a new *****....
Not kidding, clean what needs to be cleaned in the air element section of your ride and adjust the throttle to no slack and your jaguar xk will bitch slap you to wake up on your next and following rides...haha....Amazing...
Phil
I must say....I AM SO HAPPY WITH THE RESULTS....Increased, restored, what have you...My mint 143k 1997 xk8 sprints, darts, wants to fly above and beyond the mature slowing beast of yesterday....
It is an indoubatible fact that adjusting the throttle body to no slack and other maintenance quick fixes made my old star aging star a new *****....
Not kidding, clean what needs to be cleaned in the air element section of your ride and adjust the throttle to no slack and your jaguar xk will bitch slap you to wake up on your next and following rides...haha....Amazing...
Phil
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From: Chicago
Dear H20boy,
It is amazing how the post 2006 xk is a forgettable car...Yet, the 97 to 2006 xk8 is a true classic that all drivers and especially kids just know it to be true....Like you I hope and suspect our xk8 is an all of the above type driving experience...
Must say when she started hesitating and balking and prior to learning of Dan's cleaning fix - I was beside myself.... It would take a serious exotic automobile to match the totality of good feeling that a well kept classic xk8 brings....
My two cents...Will post a picture soon...
Thanks again, Phil
It is amazing how the post 2006 xk is a forgettable car...Yet, the 97 to 2006 xk8 is a true classic that all drivers and especially kids just know it to be true....Like you I hope and suspect our xk8 is an all of the above type driving experience...
Must say when she started hesitating and balking and prior to learning of Dan's cleaning fix - I was beside myself.... It would take a serious exotic automobile to match the totality of good feeling that a well kept classic xk8 brings....
My two cents...Will post a picture soon...
Thanks again, Phil
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From: Los Angeles
Dear H20boy,
It is amazing how the post 2006 xk is a forgettable car...Yet, the 97 to 2006 xk8 is a true classic that all drivers and especially kids just know it to be true....Like you I hope and suspect our xk8 is an all of the above type driving experience...
Must say when she started hesitating and balking and prior to learning of Dan's cleaning fix - I was beside myself.... It would take a serious exotic automobile to match the totality of good feeling that a well kept classic xk8 brings....
My two cents...Will post a picture soon...
Thanks again, Phil
It is amazing how the post 2006 xk is a forgettable car...Yet, the 97 to 2006 xk8 is a true classic that all drivers and especially kids just know it to be true....Like you I hope and suspect our xk8 is an all of the above type driving experience...
Must say when she started hesitating and balking and prior to learning of Dan's cleaning fix - I was beside myself.... It would take a serious exotic automobile to match the totality of good feeling that a well kept classic xk8 brings....
My two cents...Will post a picture soon...
Thanks again, Phil
That's an interesting observation but probably a bit overstated. I did not like the new body style all that much when it first came out (compared to the first generation) but it has kind of grown on me. The new XK still looks very distinctive compared with most other cars on the road (of course still not as distinctive as 97-06).
Doug
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From: Florida
I just got done reading all 11 pages of this thread -- very entertaining indeed!
One question -- did anyone ever get their hands on the "special tool?" Or has anyone made one or improvised in any way?
One question -- did anyone ever get their hands on the "special tool?" Or has anyone made one or improvised in any way?
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From: Limousin, France
I am intrigued by the tool. I can't understand what the bent wire lever does.
It's too damn cold to have a look at the APP today but isn't it just a stop that comes into action before the APP bottoms out to prevent damage?
(as per Doug's post 432838)
The mechanics are a bit arcane because if you imagine the throttle cable ran dead straight from pedal to APP the outer would have no function at all. Because it goes round a bend the outer will experience a force when the inner is tensioned and that must be what makes it ratchet through the adjuster.
Presumably the tool thickness was arrived at by trial and error so the amount of spring in the outer cable gave full throttle movement with a tiny amount of slack at closed throttle.
Doesn't explain the bent wire though.
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From: Los Angeles
I think the purpose of the "tool" is to build in some predefined slack in the system. You probably do NOT want the cable to be totally taut but, without the tool, you can probably do trial and error to establish the appropriate slack.
Doug
Doug
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From: Dallas Texas
I would bet the factory original setting kept the throttles from going WOT. I wonder if anybody here has an ultra low mile car that can confirm this.
I also wonder what the difference in RWHP is. For mine I wold say the before oand after are a good 30-45+hp
I also wonder what the difference in RWHP is. For mine I wold say the before oand after are a good 30-45+hp
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From: Baton Rouge, LA
After I was aware of this situation, it helped explain why the several cars that I test drove before I bought the one that I have seemed very sluggish.
Another interesting thing that happened to me is that after I bought it and was on the 500 mile trip home, I got some gas and came back onto the interstate in a rural area, and decided to open it up to see what it could do. It went pretty well, but I was a bit disappointed.
It wasn't until a few weeks later when I was doing a detail job on the car (it was immaculate when I bought it) that I noticed that the very thick floormat that the previous owner had put in it was between the accelerator pedal and the button underneath, and was preventing it from going to WOT by almost an inch. When I corrected that, it was like a different car.
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From: Florida
When I first got my 2003 XJ8 I thought I might have a transmission slippage problem and was kicking myself for not having it checked out better before buying it. However, tightening the throttle cable has given my car the response that I expected and I no longer feel like I have a transmission issue. Sometimes I wonder if the previous owner got rid of this wonderful car because he/she thought there were pending major issues and didn't want the expense of fixing them -- I have resolved a couple of them, and hope to finish off the list soon without spending an arm and a leg (thanks to JaguarForums.com!)
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From: Dallas Texas
When I first got my 2003 XJ8 I thought I might have a transmission slippage problem and was kicking myself for not having it checked out better before buying it. However, tightening the throttle cable has given my car the response that I expected and I no longer feel like I have a transmission issue. Sometimes I wonder if the previous owner got rid of this wonderful car because he/she thought there were pending major issues and didn't want the expense of fixing them -- I have resolved a couple of them, and hope to finish off the list soon without spending an arm and a leg (thanks to JaguarForums.com!)
SHHHHHH! I am looking at an XJR for the wife.....
ud
Joined: Feb 2010
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From: USA
Simply amazing that after 11 pages and 218 replies there is a complete lack of understanding how a drive by wire system and this TB work. And since so many have seen remarkable improvements in prformance by tightening up the limp home cable, shows the absolute power of the imagination.
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From: Dallas Texas
Simply amazing that after 11 pages and 218 replies there is a complete lack of understanding how a drive by wire system and this TB work. And since so many have seen remarkable improvements in prformance by tightening up the limp home cable, shows the absolute power of the imagination.
This statement seems broad by design and assumptive.