Hi all,

Its been awhile since I posted... I hpoe you are all well!

Can anyone please advise if the TH400 from a late model series 3 XJS is identical to a series 2 (HE) transmission?

My one needs either a complete overhaul or I was thinking about getting a wrecked tranny from a later model.

Any thoughts?

Thanks
Craig

 

Any TH400 transmission from a 5.3 car will work. The later cars ( is that what you mean by series3? That's not a recognized description of the XJS) with a 6.0 engine have the 4L80e and that isn't interchangable.

 

Thanks mate... Yes I tend to call the 6.0L a series 3 facelift I guess.

Ok so basicly I need to look for the latest year for an HE?

Thanks

 

I think the 400 started in the XJS in 1978, so anything from 78-92 should work. The V12 saloons are the same transmission too.

 

Ditch it and do a 5spd conversion

 

Craig,

As mentioned, XJSs are not referred to by "Series". The easiest way to describe the big change-points is:

- "Pre-HE" - the original cars up to introduction of the HE V12 at VIN105048 in 1981
- "HE" - V12 cars up until end of pre-facelift at 179734 in March 1991
- "Facelft" - from VIN 179735
-"Big-Bumper" - revised body trim and intro of 6 litre at VIN 188105 April 1993

The TH400 is stated as being introduced at engine number 8S 7017 in 1977
It was fitted on the V12 from there until the intro of the GM4L80E with the 6 litre from April 1993 as detailed above.

Hope that helps

Paul

 

As above. The bellhousing pattern was revised on the 6.0L block to take the 4L80e, but any 5.3L Th400 should work (XJS or Sedan) including the early 5.3L in the Facelift series. That said..... honestly it's probably worth doing the rebuild to the TH400. They are by far the cheapest transmission to get rebuilt (though that's still some $$$ out). The reason is all of the Jag Th400's were kind of a bit of slush boxes built for comfort (soft shifting etc). Despite the Th400 being a VERY tough box, it was kind of de-built for Jaguar. And the seals will be old in any box you get. A solid Th400 rebuild with upgraded parts will make it last a lot longer, and be a snappier shifter.

I understand if you're really on a budget, but if you can consider these options, do so.

Again, since you're in the position of needing a transmission, the two other options that are worth considering if you want to stick with an automatic is John's Cars Quarterbreed kit (which requires you to source a TH700R4 transmission). This is a great option IF you get that transmission built to take the V12's power. If not, the stock Th700R4 wasn't nearly as robust as the Th400 though it CAN be made to be. https://www.johnscars.com/qb/v12qb.html

There is a 6 speed autobox now for the XJS V12, but WUF! $$$$.

And as suggested above, a 5 speed manual transmission truly transforms the car, but it is certainly an "investment" (more in the size of your smile than in the car) if you go for a full "kit" like from The Driven Man or Simply Performance. They're good kits but not entirely straightforward, and patience is usually required with the Driven Man's delivery time line. Personally I think a V12 with a well done manual kit would be more desirable than one with an automatic, but... the market is fickle.

~Paul K.

 

Thanks all for your comments...

I am definitely going to look into the manual conversion as I know this will be some fun, especially since I have the AJ6 upgraded ECU and the throttle bodies! (What a massive difference that made)

 

Since you're from NZ, take a look at Dellows from AU as they offer quite a number of bellhousings for the V12 for various more easy to obtain transmissions down under.
https://dellowconversions.com.au/?s=...&submit=Search
I'm not aware of who if anyone is offering a full "kit" though around Oz.

~Paul K.

 

When l had my ECU enhanced l was specifically asked by Roger if the car was manual or auto so it obviously makes a difference, if you haven't already done so you may need to consider that.

 

I think that has specifically to do with whether the overrun fuel cut is enabled or not. There is a possibility of stalling in some circumstances (I think) without the "tweak" for the manual.

~Paul K.

 

This is a simple adaptor you can make in a morning if you have a drill press and a way to cut aluminum. then find a good used Chevy manual transmission. ( or if you want you can buy a brand new TKX for about $2800) But it will be a lot cheaper than buying a kit. Ask and I’ll walk you through the process step by step.

 

I've oft wondered if adjusting the TPS to a higher closed-throttle setting could accomplish the same thing--disabling fuel cut-off.

Cheers
DD

 

Hi Mguar:
Responding to a somewhat older post here. I'm looking at various XJSs and thinking about a transmission swap. Along with going to a manual, I've also contemplated a 6L90e; those ratios look like they might generate a lot of fun. but, regarding the manual swap, I'm wondering if you might have a print on this adapter you made? While I'm still only in the hunt, I do actually have a couple of CNC machines at my house, one of which is a three axis mill. So, just trying to lay a little groundwork in advance. I'd appreciate hearing back from you when you have some time. Thanks Much, Drew

 

Wouldn't that mean the engine was being constantly over-fueled, Doug?

 

It wouldn't by much, if at all, IMO.

Over the years there have been many discussions on the exact purpose and function of the TPS. It isn't entirely clear from Jaguar literature.

My own conclusion from those discussions is as follows:

-The TPS tells the ECU that the throttles are being opened and the rate of opening. The ECU responds by slightly richening the mixture while throttle movement is occurring. This is akin to the accelerator pump found in many carburetors.

-The TPS tells the ECU that the throttles are closed. If the ECU sees that the throttles are closed and simultaneously sees high vacuum (21" I think), the fuel cut-off is activated.

-The TPS tells the ECU the throttles are wide open for maximum enrichment. This occurs at about 4.5 volts at the TPS. On Lambda equipped cars this also forces open-loop operation. For backup, max enrichment is ensured by the vacuum and/or mechanical full load switches.

Other than those three scenarios the TPS really doesn't have any authority over mixture control.

Not everyone will agree with what I've said :-)

Cheers
DD

 

See below

 

Further to the above, I have consuted the factory publication "Jaguar XJ-S H.E. supplement to the repair operation manual".
This was published as an extra to the existing ROM when the HE was launched. It has a description of the fuel injection system spread out over three pages, but the relevant passages are:

"The electronic sensing and control system which monitors engine operating conditions of load, speed, temperature and throttle movement. The control system then produces electrical pulses of appropriate width to hold open the injector solenoid valves and allows the correct quantity of fuel to flow through the nozzle for each engine cyle"
and
"As fuel [pressure] is held constant, varying the pulse width increases or decreases the amount of fuel pased through the injector to comply with the engine requirements.
Pulse width and therefore fuel quantity is also modified to provide enrichment during starting and warming up, at closed throttle, full throttle and while the throttle is actually opening"
and
"[discussion of the control chip parameters and fuel map] so that for any combination of manifold pressure and speed the memory gives it a number proportional to the amount of fuel required by the engine... the injectors will be energised for a time proportional to the number computed [ie acording to the digital fuel map] plus the constant of the proportionality varied according to the secondary parameters"

What the "secondary parameters" are, I am not sure, maybe TPS signal is one of them? BUT what the manual description does NOT say is that the pulse width decision at steady load is controlled by the TPS position! As Doug said, the TPS does affect fueling on acceleration and at full throttle, but it does not say at a steady load the TPS affects pulse width.

However, if you disconnect your TPS the car engine will NOT rev at all, however gently the throttle is opened, so it's proper operation is for sure having some effect on pulse width!

 

Likely coolant and air temperature. The system is a MAP style system, which means manifold air pressure. That means instead of measuring the amount of air coming into the engine, it calculates it. The density of the air is very important to that, so temperature and barometric pressure are useful things to assist the calculation.

TPS is a leading indicator, as you open the throttle to start changes in engine state. Things like manifold pressure are lagging indicators, as they respond to the change in throttle after it has happened. So using TPS the ECU can enrich so the mixture doesn't go lean, rather than reacting after the mixture has already gone lean. Measuring the amount of throttle opening as well as the rate of change in throttle opening are both important.

 

I agree 100%. I feel sure that the throttle opening value (at a steady load) must be needed by the system as well as the rate of opening. It would be nice to have someone who was an Bosch expert tell us exactly how such a value is used though!