Continuing my quest for improved "off the line" performance, it's been mentioned that the problem(s) may be the torque converter, or possibly the transmission.

My reading leads me to think that a faulty torque converter may mask itself as a transmission problem, and vice versa.

Since it appears that the tranny needs to come out to examine the torque converter, it would seem to make sense to just replace the torque converter at that time, since the lion's share of the labor charge would be dropping/reinstalling the tranny.

Am I thinking along the right lines?

Thanks,

John
1987 XJ-S V12

 

Check the stall speed. Stall now doesn't mean engine dies out. It means the point at which the engine will not rev higher due to a frictional limit due to the hydraulic properties of the ATF in the TC and transmission.

Engine should be at temperature. Press your left foot onto the brake pedal. As far as possible. Now fully depress the throttle pedal. Not for long. The engine should go to a set rpm figure (IIRC it should be around 2000 rpm) and remain there. If it goes a lot higher, the convertor is toast. If it says below, the TC is fine.

 

Tach when up to about 21-2200.

Thanks!

John

 

2200 is tolerance. Means the TC is totally fine.

Give the TH400 a fresh filter and some new ATF.

 

Did that last year (tranny filter/new fluid).

The shop that did it didn't mention anything out-of-place with the transmission.

Continuing the search for an answer...

Thanks,

John

 

What are the problems you're having with the trans.

 

He's saying that the car seems sluggish. Off the line isn't how it should be. The TC was suspected to be a problem but as the stall speed is fine, there is no problem with that.

 

Well, I don't know that they are with the trans or not.

Virtually every report I've read indicates that a stock V12 should be able to at least "chirp" the tires when one puts the pedal to the floor. Mine does not. The list of work I've done on it is extensive...

new fuel pump, cleaned out the fuel sump, new injector hoses, spark plugs, installed a "cold air" inlet system, new fuel inlet regulator, serviced the mechanical advance, replaced the vacuum advance module, removed air injection system, rebuilt fuel injector wiring harness (and moved it out of the V), engine driven water pump and fan are gone, replace with dual electric fans and electric water pump, replaced half-moon seals, replaced tranny filter and fluid, replaced the dual coil system with a single coil, new spark plug cables...and that's just the list of things that might slightly affect performance.

So, now I'm redoing the engine set-up from scratch, and while I'm at it I'm replacing the old TPS with a Hall Effect TPS. The torque converter is within tolerance, and short of changing the differential ratio, I'm running out of options.

It's not an end-of-the-world thing, I love the car and love the way it drives and looks. It just seems it should move quicker off the line, and I can't figure out what I'm missing to make it do so.

Thanks!

John

 

Keep in mind, mate, that, depending on the tire compound, some tires will chip and others not. Less grippy tires - like the factory Pirelli P600s in 235/60R15 - will chirp. Grippy tires will - erm - grip and not spin...

It CAN well be, that your tranny and tires and engine are all fine, and that you are focusing too much on a described part rather than a fact.

Best way would be to use a proper accelerator to mesaure how your 0-60 mph time is off the line and then compare. If you are well behind, then obviously something isn't perfect. You could go on a dyno/rolling road, see what arrives at the wheels. Also do the mathes and see what the crank hp would be and then decide.

My car chirped it's tires quite well off the line BUT they were old, hard, not grippy. The older, the harder, the less grippier...