The air leak MUST be in the balance pipe and its fittings, OR, as Doug mentions, the vac pipe to the balance pipe from the ECU. If your pipe tests as holding vac, then it might be that the ECU itself is feeding air into the engine.
I do not believe the ECU can make 2000 RPM by over fuelling, but in line with Doug's idea, I suggest:

1. remove vac pipe from balance pipe (do not lose it down the gap)
2. Block off the spigot for the vac pipe
3. Start the car and see what happens
4. If the revs drop, then either the vac pipe or he ECU vac gizmo is letting in the air
5. If the revs DO drop, next reconnect the vac pipe
6. Pull the pipe off the ECU and block it that end
7. Start the car and see what happens
8. If the revs ALSO drop as before, the ECU gizmo is the trouble. If they do not, the pipe is the trouble

Greg

 

Inside that ECU is a small rubber hose. This connects the spigot in the casing side TO the MAP sensor attached to the circuit board.

I have had one with that hose split.

High revs was NOT the fault, black smoke was.

If that hose/pipe assembly from the balance pipe to the ECU is split, leaking, etc, the ECU will overfuel, AND the ECU will sense a vac leak, but the size of that hose/pipe will only up the idle by a MAX of 500rpm.

To get 1000+ idle speed, there is a huge hole somewhere.

Have you plugged the overrun feed pipes at the aircleaner front spigots????, as they WILL give that rev rise easily.

This parts drawing shows those valves and the hose you need to cap off.



#22 is the hose to remove, then cap the spigot an #21. The item on the branch line of item #21 is the over run valve. You have one on each side.

Jaguar fitted them, removed them, fitted them again. I remove them at all times.

At the risk of sounding silly, has someone removed these valves before, coz the rev issues you have would 100% be spot on with those valves removed and the manifolds left open to the outside air??????? This would also answer why it was still running with the AAV blocked off, and T Shirts stuffed in the throttle bodies, AND answer your original ask of "hard to start".

 

I've followed the process above - and the problem certainly appears to lie with the ECU. Will try and source one of those (the lucus 16CU model)

This was an ex UK car with no Cats - if i source a lucus ECU from the US, will this work ok?

 

Hi Grant - i beleive the problem lies with the ECU as per my recent post, but i'll follow this procedure anyway and remove the valves - although they all look really well sealed to me and certainly haven't been tampered with or removed in recent times

It will give me something to do before my replacement ECU arrives

 

Might do! easier to source a 16 CU from the UK and probably cheaper.
Greg

 

If you just want to check the over run valves, its easiest to just plug the hole
In the air filter box. Gorilla duct tape will do. Nothing that can be sucked in. Don't run the car without the air filters in place.

 

I agree with Greg here.

The USA cars were 11.5:1 comp engines. The ROW were 12.5:1 engines. That comp ratio would need different fueling maps etc. It will work, but may create other issues, and I reckon you have enough of them already.

 

Interested in your comment about not running the car without the airfilters in place - i've done this the whole exercise. Could this be part of the high idle issue?

 

I don't think the filter themselves could do it.

But if the bolts the hold the air filter housing to the throttle body are loose, leaky, or absent....THAT could most certainly cause a high idle


Cheers
DD

 

As Doug has mentioned twice. The bolts in each throttle body are OPEN to the vac side of the manifold.

The covers and filters elements can be removed for diagnosis, and primary running etc.

The backing plates, and their bolts, 4 each side, MUST be installed and the bolts tight, or you will have a BIG vac leak.

Downside to trying to start a hard to start V12, is the habit of it BELCHING flames out the throttle bodies, hence the metal plate on the air element that "covers" the throttle body. NOT so much an issue with the HE but the PreHE is a regular belcher.

No harm, just your pacemaker will miss a beat, and the paint on the shocker towers will blister.

I got caught once, and that was enough for one lifetime, so now the air elements are ntsalled and the covers clipped in place, ALWAYS.

 

Ok - the filter housings are certainly on and the bolts in place (and tight) so just to confirm that won't be the issue

Trying to track down a new ECU

thanks again

 

Loads on UK Ebay.
Greg

 

Cold start issue and related high idle speed appears is resolved

Ended up pulling the inlet manifolds off and refitting all new gaskets when refitting. I suspect the problem was the inlet manifold gaskets as the manifold bolts were a little bit too easy to undo

thanks for all the great help on this thread

not quite finished yet however as I still have a significant miss on A bank - namely cylinders 1 and 4. Removed injector harness clips on all cylinders and 1&4 made no difference to the poor idle

Before i start ripping and replacing everything in relation to these cylinders, is there some simple tests I can do to test if it's an injector, harness, spark plug, lead or distributor problem?

Im used to dealing with carburettor fuelled engines - so this is all new to me

almost there - thanks again

 

Well done.

Simple cars these V12's. A tad trying at times, but still simple.

The injectors on the V12 are fired in 4 banls of 3:

1,3,5A
2,4,6A
1,3,5B
2,4,6B.

So, if you have 1 and 4 on the A bank, that would be 2 sections of the RFI loom. Not uncommon now with age.

The Injectors may no be "clicking", so run the engine, use a listening stick, stethoscope in fancy talk, and listen to the injectors. Start with the working ones, then you know the noise you are seeking, then the duds. If they be clicking, good, but they may NOT be passing fuel. Removal is the only way now.

If there is NO click, or even a click, pull #4 plug, easier than #1, and note if its dry, as in NO fuel.

Spark plugs are next, but not a common failure item.

Leads, they do suffer.

Distributor????, nah, its running, so the dizzy, and its upstream items are all doing what they should. Coils also, its running, they are working.

However, as with many, many posts over the last few years, that EFI loom is #1 in all cases.

 

ok - swapped the spark plug leads with good known leads from the other bank and that made no difference to the lack of firing on 1 & 4, so i think that eliminates the leads

I also checked the injector clicking as outlined above - and they all 'clicked' the same

Checked the spark plug(s) and they were dry - so it looks like a clogged injectors

Took the fuel rail off - but now can't workout how to remove the injectors from the hose clamps. Is there a trick to this? - looks like they are crimped on??

Hoping to get these off - and use some carb cleaner to unblock them> do you just leave them to soak??

Almost there......

 

The original 12 Injector hoses are a "push on" style, with tin "cups" at each end. Look like crimps, they are not.

Outside the box thinking will get them off WITHOUT damaging the sharp barbs that hold the hose in place. If those Barbs get damaged, plan B will be discussed IF required.

I soak them in carby cleaner, or paint thinners (care need here), or simply in a large coffee jar with a suitable amount of diesel fuel and a lid, come back in 2 days.

Alex, AKA Orangeblossom, has an excellent write up on how he cleaned his on his 16 year stored beast.

NEW EFI hoses are needed no matter what.

 

Hi Mobileman

I cleaned all my Injectors (Six of them were blocked) for the princely sum of £4-50

Without taking them off the Fuel Rail and since you've got the Rail off, it shouldn't take you long unless you want to go and replace all the hoses.

Which I did not but that's your call not mine.

You can see how I did that here, near the bottom of the page.

https://www.jaguarforums.com/forum/x...122634/page10/

 

Ok - taking the injectors off on A bank to look for clogged injector as the spark plugs and HT leads look ok

Was interested to note that there was very little fuel that came out of the rail when I took off the 1A hose

Could the problem with the misfire be poor fuel pressure?

I note that the B bank regulator has some minor fuel in the vacuum hose if that helps

This is a RHD car and I'm not sure which is the inlet vs outlet regulator

I'll keep checking the injectors - but I'm now starting to think low fuel pressure might be the issue

Am I on the right track?

 

Replace the B bank fuel pressure regulator. Fuel in the vac pipe indicates the internal diaphragm has failed. This may well be why the injectors are not flowing fuel, as the pressure may be too low. BUT clean them and replace the flexible hose from rail to injector anyway.
Additionally, removing the A bank FPR all together is a very god idea. If you decide to do this, post for the Grant Francis method!

 

Ok - seem to have resolved the situation. Car runs smoothly now - still not a great starter, but much better

To summarise - the inlet manifold gaskets had to be replaced, as well at the TPS and fuel pressure regulator. The last 'miss' problem i had on A bank - was a cracked spark plug!

No idea how it got cracked - i've certainly never removed it in the 3 years i've had the car. Took the opportunity to replace all the plugs - which is a mission in itself

Found eventually found the use of a spark plug wobble bar allowed just enough room for the removal of plugs on cyclinder 5 without the removal of the pedastal. I couldn't work out how to remove the pedastal anyway as i couldn't get a spanner with enough leverage anywhere near the bottom bolts

Anyway - excellant assistance from the a number of members here so thanks again for all your assistance

The next project is to check the vacuum advance