Greetings All,

So I've acquired this (pic attached), which I'm told came off an XJR Supercharged V8, and I'm attempting to reverse engineer it, to a degree. So... Throttle position and pedal position seem straight forward, however:

How does the throttle motor function? Seems to be a DC motor, rather than a stepper or a servo, and works to close the throttle, rather than open it... Or am I missing something?

There's a coolant connection, presumably to open/close a thermostat/valve at a given temp and bypass the butterfly somewhat. Cold start enrichment perhaps? Or something else?

And the vacuum connection, what's that doing? Idle control? How does that work?

I may have more, as I dig into it...

Thanks.

 

Andy,

That is the early V8 type of TB. Despite being sourced from an XJR, you are likely to get more information from XKR owing members in X100 forum simply because of the numbers.
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/

If you want, I can move it for you.

Graham

 

Thanks Graham, That'd be really helpful.

 

A little more research suggests the vacuum device is cruise control, so that answers that. Still confused about the motor and the coolant circuit. Digging continues.

 

The coolant keeps the throttle from 'ICING'

bob

 

Thanks for that Bob. That makes sense, but... There's a spring loaded err, thing, in a bypass channel that looks to be if not in then very close to the coolant circuit. Presumably to bypass the butterfly based on coolant temp?

 

Isn't the coolant to the throttle body for emissions? To change the air intake as the engine warms up?

 

So... The vacuum actuator engages something called "the mechanical guard", the position of which is reported along with the APP sensor (I was wondering why it had so many pins... This, it seems, is a function of the cruise control. I'm still keen to find out what the bypass passage does; it clearly has a spring-loaded something in there, yet idle control, cold start, acceleration enrichment etc. all the fuelling requirements, appear to be done by the ECM (which makes sense), so what's that for? And I'm still confused as to how the throttle motor functions, but that might just be me being dense...

 

This:
http://www.thejagwrangler.com/upload...c_throttle.pdf
goes a long way towards explaining the E-throttle and cruise control side of things.

 

The vacuum actuator is definitely part of the cruise control. Mine doesn’t have cruise control and the vacuum actuator is NOT connected to anything.

 

I'm with Bob on this!

 

Some progress...

Looking at the APP sensor on the left hand side. If you give pin 4 vcc and pin 2 ground you'll get an increasing voltage on pin 1 when vacuum opens the mechanical guard, and an increasing voltage on pins 3 and 5 as the throttle pedal spindle turns. I'm assuming vcc will be 5v as standard, I used 12, 'cos it's what I had on the bench (it's a mechanical wiper type potentiometer, so it's not going to be fussy about what voltage it gets, within reason), and the range was around 2-12v in all cases.

Also worthy of note is the butterfly seems to be spring loaded open, as vac increases and the mechanical guard is released, the butterfly opens. So that's a step towards figuring out the throttle motor control I guess...

TPS is a bit different. Looks to be a hall effect arrangement masquerading as a pot. Appears to output two signals, but is going to need a supply, and this one may well be fussy about voltage, so more playing to do there.

 

The TPS is indeed a Hall-effect device in the early TBs.
It's a real shame that Jaguar didn't use these devices for all the TB position sensors as they don't suffer the same track wear problems that pots do.

That also becomes a dual-track pot on the later TBs where, for some reason, Jaguar chose to offset the tracking so the two outputs aren't identical:- perhaps that is also the case with the Hall-effect?

Ian Kendall's paper was very informative, although it took me a while to get my head round the mechanical guard function

 

Have you? 'cos I'm pretty sure I'm only half way there...

 

It was a while ago, but it did make sense then... See my rambling from 2015:
https://www.jaguarforums.com/forum/x...2/#post1244418

The post contains a link to another relevant document by Jaguar's Mark Gallagher. See section 2, which also shows the thermostatic valve

 

Brill. Thank you. I'll dig in to that.

 

TPS doesn't seem to be too fussy about supply voltage, which is nice. Outer two pins power the thing up and it outputs variable voltage on both inner pins. Testing was very rudimentary because it's not actually reporting the position of the throttle butterfly, it's the position of the throttle motor. So if the throttle isn't under control of the motor, cruise control for example, you get nowt from the TPS.

So that's what I'll be digging into next. It's a DC motor, rather than a stepper or a servo, I guess I'm leaning about H bridges now... The fun continues.