So did a nice 15 minute drive around town yesterday. With all that V12 power, one thing the car definitely is missing is that pickup. And I can tell it’s because I’m cruising around at 30mph in 3rd gear, and it won’t downshift unless you floor it. And I can’t see any way to adjust that to come on sooner.
So I was thinking of splicing the kickdown wires into the fuel enrichment switch, that would make it downshift at half throttle, which I think will be better.
Anybody else try this? I know I can simply downshift manually, but…
Always keen on “improving” things, I rigged up a microswitch that would give me an earlier kickdown. Wound up going back to the non-improved OE setup. Following K’s advice, I reinforced the accel. pedal hardware, which gives a much more positive response. Finally, I installed a Police/Taxi adjustable modulator which will really improve the shift points. (Later, firmer.)
If your kickdown comes on at half-throttle, I don’t think you’ll like it! Not sure how you plan to wire everything, but hitting your freshly repaired ECU with the 12v signal meant for the trans.solenoid might spoil your day.
How well does your transmission modulator work? Mine was shot. It has a rubber diaphragm in it that perishes with time. After replacing mine my car started shifting smoother and more promptly. Aside from kick down which occurs when you properly floor it, the transmission should down shift to accommodate more moderate acceleration too if the conditions are right.
The part is cheap and an easy fix so might be worth a try.
Also check/replace the vacuum line from modulator to manifold of course.
Transmission actually up shifts really nice, but I’ll check that vacuum line anyway. May as well replace modulator preventatively since it’s so cheap. I may try Dave’s adjustable one. The trans does seem to like to upshift quickly, maybe to save gas?
I think I’m used to driving my Volvo T5 turbos. They seem to have way more pickup with less HP and only 5 cylinders. I’m used to 1/2-2/3 throttle and vroom!
I actually started leaving the XJS in 2nd while cruising around town, so that I always had some pickup.
I have. It’s pretty aggressive. Didn’t bother me years ago on my XJS but in a sedan…well, I tried it again and didn’t like it. Kickdown when you don’t really want it. Not too bad on a 3-2 shift but pretty obnoxious on a 2-1 shift
However…
I abandoned the original kickdown set-up entirely (long story) and went with an adjustable electro-vacuum switch. It closes at about 1"-2" vacuum. I’m happy with it. I also wired-in a compressor cut-out. If kickdown is activated the compressor disengages.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
7
Whether it works or not, you might want to replace it. The diameter of the diaphragm section of that modulator varies among GM cars, with the smaller modulators holding low gears longer before upshifting. The Jaguar item, of course, is a great big thing in order to upshift as soon as possible for that cloud ride.
Even better, though, there’s an adjustable version available from GM. You disconnect the vacuum line and insert an allen wrench in the port and twist an adjuster one way or another until it upshifts the way you want it to.
I put a B&M shift kit in my car and was pleased with the results. I never did anything with the modulator, no idea what condition it might be in. I was simply seeking firmer shifts and earlier kick down. The result is that under “normal” driving, things are much as they were stock. Post shift-kit, things work better above about 2/3 throttle. If you “snap” the throttle open (not flooring it, but say going from half to 3/4) it will kick down. Under hard acceleration it will chirp the tires on the 1-2 shift. Neither of those was true pre-shift kit. Given the PITA that is involved removing the trans pan, I’d go modulator first, then if you are still not happy try the shift kit.
Regards
Bob
FYI, I finally installed a B&M vacuum adjustable modulator for the trans. I adjusted it all the way clockwise and then backed off 1/2 turn.
Wow! The car is alive! It is a true sporty trans now, like night and day. If I’m feathering gas, it shifts smoothly, but if I want pick up it shifts nice and late, but not too late to create a thump. Downshifting is there at half throttle when I want it.
Not sure how you plan to wire everything, but hitting your freshly repaired ECU with the 12v signal meant for the trans.solenoid might spoil your day.
