Hi all

Does anyone happen to know where the line to the ECU connects to? Which manifold?

Incidentally I am getting about 16 in Hg at both manifolds and only 7 in Hg at the ECU... Are there any other possible causes for this besides a leak?

Many thanks

 

It connects to the balance tube at the rear of the engine.

Cheers
DD

 

check out the 'reservoir' canister in the illustration of the ECU vacuum supply

Pressure Sensor Pipe-5.3 Litre - Parts For Series III Saloon | Jaguar Heritage Parts UK


Is your 7" of vacuum upstream or downstream of it?


Cheers
DD

 

Assuming that the "reservoir" is located between the the ECU and the balance pipe in the engine bay, my 7 in Hg is downstream of it, I measured the vacuum right at the ECU.

Many thanks for all the help Doug, your knowledge is incredible, you are a great help, thanks again!

Cheers
Nathan

 

The reservoir should be just a few inches from the ECU......about 2.5" diameter and 3.5" long......about the size of a small fuel filter

As you might've guessed I was thinking about readings upstream vs downstream

Cheers
DD

 

Thanks Doug, I'll look for it today, I'm guessing it is accessible from under the car? I don't see a way of getting to it from the luggage compartment.

I'll see if I can get some vacuum readings and report back.

Cheers
Nathan

 

It is just a couple inches from the ECU......at least in the case of the V12 ECU I have sitting on my parts shelf. If you can see where the vacuum hose connects to the ECU then you have to see the reservoir.

A bit smaller than I mentioned earlier, though

Maybe it wasn't used on all cars?

Cheers
DD

 

I got under the car today, I managed to locate the vacuum line but no reservoir... I can't see it in the luggage compartment either... Perhaps this reservoir was omitted on my model... So I assume the fault must be elsewhere... I can only think of a leak.

Many thanks though Doug, I'll post any progress.

Cheers
Nathan

 

Sorry for sending on a wild goose chase!

Cheers
DD

 

Not a problem at least we can eliminate that one, next I'll check the vacuum from the balance pipe.

Cheers
Nathan

 

I've done some checks and it doesn't seem to be the vacuum lines or the balance pipe, neither are leaking at all.

The fact that she burns pretty clean, doesn't smoke and runs very smoothly makes me wonder if this isn't the correct reading (7 in Hg) to get at the ECU?

 

Another question relating to vacuum lines...

I understand that for a cold idle the vacuum applied to the vacuum capsule is taken from a throttle edge tapping (upstream of the butterfly), once warm, manifold vacuum is applied to the vacuum capsule. This switching as I understand it is controlled by solenoids, which are controlled by the oil temperature sensor. Where is the oil temperature sensor located?

Reason I ask is because I'm getting manifold vacuum applied to the vacuum capsule at all times.

Many thanks.

 

I've not heard of an oil temp sensor on a V12.

What *might* have happened is a previous owner bypassed all the controls and ran a vacuum hose from the vacuum advance capsule directly to manifold vacuum.

Many V12 bypass the control system....but it's incorrect to go to *direct manifold vacuum*. The vacuum hose should go from throttle edge (as you describe....we call it 'ported vacuum' over here) to the capsule.

Cheers
DD

 

The vacuum lines are all in place and connected correctly, with no leaks, thankfully. I hadn't heard of it either but was informed by a helper that it was controlled by an oil temp sensor, no wonder I couldn't find it. How are the solenoids controlled? And where is the "controller" located? I have heard of a 15 minute delay controlling the solenoids, might this be correct?

Many thanks

 

There were a half dozen or more different schemes with different delay valves, thermo-vac switches, timers, etc. all dependent on which market the car was originally sold in. You'd really need the Jaguar manuals, IMHO, to figure out what you have and how it works. It's all very Rube Goldberg-ish


Cheers
DD

 

Nothing straight forward about the vacuum lines, I'll see what I can find, the solenoids are controlled by another coolant temperature sensor that is located towards the rear of the engine, it sits under the right-hand manifold on the coolant rail. The delay mechanisms I am still to locate.

 

Hi all

I'm attempting to solve the problem I have of low manifold vacuum. There are a couple things that I thought I'd run past everyone before I get stuck in.

The brakes, as I understand are vacuum operated. Do these ever cause vacuum problems? Is it quite safe to disconnect the line at the manifold, block the spigot and check for a variation? The booster appears to be working, the brakes are almost useless unless the engine is running.

I'm getting 15 in Hg everywhere I check. I've closed the throttles off (on second thoughts the rods may be out of adjustment) and blanked the AAV off. And a correction to earlier, I am getting manifold vacuum at the ECU (I rechecked, this time with a T-piece).

The symptoms she shows are: if I slowly take her off idle her revs drop off, about 150 rpm down, if I continue to slowly open up she catches up and runs smoothly. Her manifold vacuum also increases to 16 in Hg if I take her up to about 2000 rpm

The TPS and ignition timing have been checked and set, and the distributor centrifugal advance is free.

Any advice on common problems or areas to check is greatly appreciated.