Purchased a v12 XJS a little while ago - had a few issues which I've worked through

Next on the list is 'cold starting' - bit of a process to get it started from cold which usually involves 3-4 attempts and lots of 'feathering' of the throttle

Car runs fine once its warmed up - although a slight idle issue when its hot which may (or may not be related)

Any thoughts on where to start with the cold start issue?

Thanks

 

Firstly, is a PreHE or a HE, as 1982 is at that vague area depending on thf market.

That will enable us to assist, as the fix is different for each engine.

 

Good point - 1982 v12 HE

 

Test the coolant thermistor and wiring. Read the resistance when cold. See if you can find a cross reference or a nice member to give you their cold resistance values.

 

IIRC pre HE had the cold start injector. If yours does not (which I'm going off the assumption it does not) then turn the key to "run" and push down the gas pedal twice then attempt to start. Pushing the pedal with the key in run will "pulse/spray" the injectors. Make sure your throttle plates are set correctly also .002" If they are full closed this will also make for harder starting. V12 JAGUAR THROTTLE LINKAGE ADJUSTMENT / AJ6 Engineering

 

The early HEs had the cold start injectors as well but were problematic and discontinued. Many, I think, have been disconnected for years.

The coolant temp sensor certainly plays the big role in cold fueling.

Here's the resistance specs on the CTS

Testing the Coolant Temp Sensor

This ^^^ is actually for the Series III XJ6 sensor but the specs are virtually identical.

Cheers
DD

 

good information - thanks

have tried the cold start technique described with no change

I'll try the coolant sensor resistance reading later today - also I saw on youtube that the coolant sensor plug can also fail - so i'll test that also

Thanks again

 

Cold start injectors won't be working unless very cold. Probably sub zero temperatures.
Can you check fuel pressure to see what's happening?

Might be worth checking throttle potentiometer setting and seeing that it's sweeping correctly.

Run a few bottles of injector cleaner through it.

We used to add the cleaner and drive the car get it nice and hot. Then leave the car to stand for a few hours.

Would improve idle. Lower hydrocarbons and increase Co. Due to poor injector spray pattern.

It's always hard. Lots of little thing to do to keep these v12's running properly. The throttle plate setting is good advice. Check and set mixture. Set idle speed correctly.

 

have checked the coolant temperature sensor - can't seem to get any reading at all from it. I might be doing something wrong - but i'll just replace it anyway to be sure as they are cheap enough

Interestingly - I started reading the manual last night and noted it referenced a cold start relay in the engine bay which sits under a protective cover alongside the fuel pump relay.

When - I took the cover off, the relay wasn't there! For some bizarre reason - the relay has been removed and not replaced. obviously - i'll replace this also.

Question - this looks like a generic relay setup, can this be sourced from a local parts store (not Jaguar)? If so - what should I be asking for?

 

As far as I remember the relay was used to operate the cold start injectors.

Do you still have the CS injectors? Are they hooked up?

Circa 1984 Jaguar stopped using them and I think many existing CS injectors were intentionally disabled

Cheers
DD

 

good point - doesn't look like I have separate cold start injectors, so no panic on the relay now

I'll go back today and check the butterfly gaps and if that doesn't work - we'll order that coolant temperature sensor

 

ok - I've got myself into a bit of pickle here, so please bear with me while I explain

Still sorting the cold start issue - and was following the links provided.

Firstly - the throttle pentameter was reading 1.3 - and should have read 0.32 at closed throttle according to the AJ6 information at closed throttle so I adjusted the pentameter accordingly

Also - the throttle plates were fully closed with no gap - so I adjusted (and rechecked) the gaps at 0.002"

Feeling very pleased with myself - I restarted the engine and still had the cold start issue, but more worrying was the idle had jumped to 1300rpm and I can't seem to adjust it down using the AAV idle bolt

I also seem to have introduced a slight miss on A bank - which I don't think was there before. Anyway - seem to have gone backwards at a rapid pace

Any help would be much appreciated

 

You have extra air coming in from 'somewhere'....most likely a stuck AAV. But it could be a hose, loose intake manifold bolts.....any number of things.

The fact that throttles were set to zero clearance suggests someone has been in there ahead of you trying to mask the problem.

But.....

Did you have the air filter housings completely removed? If so, make sure all the bolts are tight. The bolt holes are open to the manifold so an air leak past the bolts is effectively just the same as a partially open throttle

Cheers
DD

 

only removed the airfilters - not the housings, so that shouldn't be an issue

The thought of an airleak occurred to be me as well - but have triple checked and can't find any loose pipes or missing connections

Next step presumably will be to remove and check the AAV as per your response Doug?

 

Doug has answered my thiughts also.

ALSO, that idle adjust bolt is ONLY for when the engine at operating temperature, and the COLD idle speed is controlled by precut slots in the AAV piston.

Have a read below.

AAV rebuild procedure.doc

Adjusting the HE TPS.doc

HE Tune up.doc

 

excellent - those are great write-ups

That's my next week sorted working through those - will keep you updated.

Thanks again

 

Recheck the potentiometer and also have a look under the intake manifolds for any missing connectors. You should be able to block the intake to the AAV and see if the idle settles down.

 

What is your timing set at? In my experience timing seems to have an enormous effect on idle speed and quality.

 

quick update to the many of you who have helped in this search for a solution to my cold start issue

Have rechecked the setting on the pentometer - that checks out ok.

The AAV failed miserably on the suction test however - so have just removed and clearly its badly seized.

Looks like the next job is an AAV rebuild as per the instructions provided - then i'll also probably undertake a full tune including the spark plugs, timing etc

I thnk i'm making progress - thanks again for the help

 

Well done.

DO NOT forget the Amber Fluid, FOR YOU, not the car.

Have fun.