If you've read any of my post on Jessie you know she has always had an uneven idle. I've replaced, repaired or removed and checked just about everything potentially involved. It remains. Sometimes it's an irregular miss, sometimes just a little stumble here and again, sometimes she shakes a bit when in gear at idle. She starts instantly, runs perfectly at start up and for a short time as she's warming up. then i'll hear, or more feel, a little stumble an irregular beat. Sometimes it will stay subtle, sometimes it will get a bit worse.

It's not my only remaining project on her, but it is my white whale, my nemesis!

I have never done a compression test on this V12. I don't know why exactly, perhaps it just held too much potential info I might not want to know. Well, I finally decided to look and see. I warmed her up with a good run and definitely remembered a story or two of some dog's last hunt. We both enjoyed blasting down the empty country roads.

I did not pull all the plugs out at once for my tests. I understand some people suggest this to allow for the engine to spin freely and generate as much compression as possible in the tested cylinder and also to save the battery. The supernatural forces that guide things when they are dropped so that they end up far away, under a carpet, in a crack are huge Jaguar fans and 11 open spark plug holes on a V12 would just be too much to resist. A nut on a satellite could be pulled from orbit straight into 6B.

Jessie battery is a beast. Didn't care about the test at all. I started at 1A and ended at 6B and took pics of the results and the corresponding plug for each cylinder. These plugs have about 1000 miles on them. Arranged here as viewed from above the engine.

I'm relieved that they are all pumping up! No zeroes! And fairly consistent across the board. No clear answer for my idle, but that's what I expected. It's my nemesis! I'm not sure whats doing on with the plug from A1. That sloped area of black does not look right. Anyone know what causes that? Anyone a wiz at reading plugs?

 

B5 is the only really scrappy looking plug.
B1 has that odd colour, but appears to be firing OK.

Have you trimmed the ECU fuel pot once its up to temp?. That took the hissy out of all mine.

 

I'm not a wiz at anything except talking

That A1 does seem a little odd, being blackened on just one side. Some sort of injector spray problem? I dunno. Just taking stab.

Cheers
DD

 

It is odd how certain things get to an owner, I have my own bete noirs. Grant's ECU fuel trim adjustment is highly likely to do it, but in case not, in no particular order, have you done/considered these things (obviously all the cheap ones first!), ?

• Distributor dismantle, clean and lube, vac capsule renew, test star wheel/pickup gap
• Ensure ECU vac line holds vac
• Renew pickup (if all else fails) and change starwheel for another
• New 8mm HT leads
• New cap and rotor
• New coils
• Carefully check the shielded wire connection between the amp and the engine loom
• New amplifier
• Remove, clean and spray pattern test injectors
• Test fuel pressure at tickover
• Renew B bank FPR and remove A bank FPR
• Very carefully check the entire intake system for vac leaks
• Check the TPS under the capstan
• Try disconnecting the crankcase vent system

Greg

 

Jigjag, your's was a Marelli, right?

If yes, how is the REST of the system? I mean, how old are the coils, the plugs, the rotor, the cap and the ihnition modules?

 

Sorry, this machine is quirky today. I could not open the picture of the spark plug read.

Tis somewhat of a lost art in some cases. The old tech classic was to run a "hot lap", cur clean and coast in for a read. Loupe's preferred.

But "modern fuel" burns are deceiving.

If any of the plugs are "suspicious" clean and replace or just go for broke and splurge for good quality new ones.

But, yup Doug's comment as to a quirky injector
sounds plausible.

I do have a replica sand clean device for plugs. My son flippped over it!! I do not use it on my cars. But, on my "lawn toys", definitely......

Carl

 

Trying to answer all in one post...

Here you've touched on a curiosity with Jessie. I have adjusted the ECU idle mix. In fact, I modded the ECU to have the mix pot mounted in the opening that you usually have to go through to adjust it. I can tweet it easily now.

Here's the curiosity. I run it lean as it can go and it runs pretty well. Plugs don't read as running lean, and temps stay quite reasonable. No indication that it is actually running lean.

If I adjust it richer ( say midpoint in the adjustment range ) it smells rich, runs worse and looses idle speed. All indications that it's running too rich.

I suspected one of the injectors may be over/under delivering, causing the a misfire that the ECU reads as a lean condition causing it to richen the mix. But this is at idle, no closed loop. SO I don't think thats the right direction if I understand the ECU correctly.


[*]Distributor dismantle, clean and lube, vac capsule renew, test star wheel/pickup gap
Yes
[*]Ensure ECU vac line holds vac
Yes
[*]Renew pickup (if all else fails) and change starwheel for another
No. Both tested good. Can runs fine at high RPMs.
[*]New 8mm HT leads
Yes. 10mm for good measure.
[*]New cap and rotor
Yes.
[*]New coils
Yes. The single Jag OEM replacement coil.
[*]Carefully check the shielded wire connection between the amp and the engine loom
Yes.
[*]New amplifier
No. New modules x3. Also removed the capacitor.
[*]Remove, clean and spray pattern test injectors
Yes. Most tested good, no leaks, decent patterns. 4 new injectors replaced questionable ones.
[*]Test fuel pressure at tickover
34 psi.
[*]Renew B bank FPR and remove A bank FPR
Yes. OEM Regulator in B position. None on A bank.
[*]Very carefully check the entire intake system for vac leaks
Yes. Very thoroughly.
[*]Check the TPS under the capstan
Yes. Regularly.
[*]Try disconnecting the crankcase vent system
Yes.

Nope. Lucas 16cu. All those items are new and in good condition. Except the Amp itself. Case and blobs inside are original. Module is new.


Plugs are fairly new ( 1000mi. ) NGK BPR6EF.

I swear it's like the idle is Moriarity to my Sherlock. Nothing quite gets it right. Many many things that I have don't to this engine have made it better, but always not quite there.

 

Damn, thats a long list, and well done methodically.

Straw grabbing this early.

When did you last check and tighten the inlet manifold nuts? Sometimes that 1/6th turn stops a misfire.

Does your engine have-the over-run valves in the snout of the Inlet manifolds??? Mine did, and I removed them, and that altered the whole playground.

More of an issue with the PreHE's, is the gunk inside the throttle bodies. Sir Arthur gets a hissy idle, wipe out the 2 bodies/discs, nothing else. all sweet. The Red HE does the same, and none of my cars have any engine venting into the aircleaners, so I dont know where this stuff comes from, but it does. Its a real misfire/stumble. and can be erratic, which really did have me scratching in the early days.

 

Thanks for the comprehensive answers. Grant's point about the inlet manifold nuts very important. FWIW, I had an amp start to go a bit (to quote Grant) female. Changed the gizmo inside twice, did the condenser, all fine and then the odd problems returned, all this over about three years. A new one cured it. Can you get another s/h one to try?


Finally, have you cleaned up the resistor pack plug? Also, are you 100% sure the injector loom is 100% OK?

 

This is just the highlights Greg called out. I've tested, repaired or replaced every item in the system that could influence this problem. Except for the ones that are still doing it apparently!

It's been about three months since I re-torqued the intake manifold. They're tight. Testing for leaks with spray shows no leaks at intake gasket or throttle body gaskets.

Mine overrun valves are still in place. I need to fabricate end caps to replace them. They are, however, sealed up in the air intake housing. No leaks.

Throttle bodies are clean as deep as I can clean. I do have the crankcase breather on B bank head still piped to the air cleaner box. Plan to swap this to a filter, but no direct connection to the intake manifold from that breather. Certainly could be a source of oily air for the B throttle.



Those AMPs aren't easy to come by, and I've confirmed the internal components ( blobs ) other than the module. That module has been swapped three times to alternates without any change in behavior. But I am more than willing to buy a new one to try just based on the fact that you had a similar behavior fixed by replacement.

My resistor pack is clean as can be, with a thin coat of dielectric grease on the pins. Same goes for the loom connector. All injectors are ticking very consistently according to my modified mech stethoscope with shooting ear-muffs.

My loom is not 100% perfect. I've removed the wrap from it to confirm the wires insulation. All appears intact and not degraded or inflexible. I've re-routed it out of the vee. It needs to be replaced now, for aesthetic reasons, but it's not shorting or broken anywhere. I've the bits to re-make it but haven't started that project just yet.

I was honestly anticipating a burned exhaust valve. I though that suited the symptoms. A small burnout at the seat could cause an erratic misfire. I'm glad its not, and I'm relieved but it resets my current suspicions to "I dunno!"

 

That same limb, damn thing will snap one day.

The CTS is a flaky thing at best.

The original is White topped, superceded by Jaguar many times, and then Bosch (the original maker/supplier) got into the mix via its aftermarket section.

The Bosch one I have used ends in 023, and is a Blue topped thing. It is the same part number for some Volvo, BMW, Holden Commodore (Aussie thing with a Buick V6 derived engine), and SAAB, etc etc, and NONE of them run the P Digital system.

This is 100% a rationalisation of part numbers, and the resistance is probably very close for all these cars/systems, but that could also be an issue with some. My money would be on Jag be the hissy system.

My fuel pot was very sensitive, and ONE clisk made a difference. My "sports type" exhaust system gave an audible change as the pot was clicked and easily heard as OFF the sweet spot. Mine also ran at the lean end of the pot, and if adjusted to anywhere near the other end, black smoke was visible, and the engine was seriously unhappy.

At the risk of flaming, and my care factor is in the minus zone here, I only ran our 98 RON fuel. I tried our 95 and 91, and that engine was a horror. Ethanol fuel here is hard to find, GOOD, and even harder back in those days, but also note our engines were 12.5:1 comp engines.

Next thing, and you really need this like a hole in the head.
The timing chains DO stretch, fact. I have had a few, mine was one, where the RH camshaft was up to 6deg late, and that was at 140K kms. I had the camcovers off for oil leaks HAHA, and just decided to check the 2 camshafts, and found that. Did it 4 times, SOBER, just to settle my head. Redialed the RH shaft, and buttoned it up. What a difference that made. Sharpened the whole thing up seriously.

 

Thanks so much for all the tips!

I always suspect the CTS! I have a brand new one but I'm not sure of the maker. Can you clarify if you found a brand of CTS that did run the p digital well? Should I look for an OEM Jag part?

I know that the adjustment I have made at the ECU is covering up a flaw somewhere.

I really do not need a stretched chain! Nor another hole in my head, but I do want to resolve this. How do I check the cam timing?

I have only ran Premium top tier fuel in Jessie. 98 us RON/???. I do have the lower 11.5:1 I assume, from market and compression figures. What psi does the 12.5 pump up to?

So, currently moving a new ignition amp, CTS, and ( shudder ) cam timing check to the top of my to-do list.

 

OK,

Searching the archives in boxes in the shed.

CTS I used is Bosch 0-280-130-026. The OE sensor is made by Bosch anyway.

Cam timing can only be checked with both cam covers off. Engine MUST be set at TRUE TDC, NOT the readings from the marks on the slotted plate under the front. I used #1A, plug out, and a dial indicator with a loooooong probe to get it spot on. Took ages, and many extra rotations coz I was not paying attention and went past the TDC. The setting plate is same as the XK 6 cyl plate.



The flat notched plate is what you need, the other tool is for the XK top chain adjuster.

 

Thanks Grant! I aleready have the plate in the XJ6. Purchased but never used.

I don't suppose you have one of those nifty write-ups on setting the cam timing would you?

 

Not yet, but will do so in the next few days.

 

At last, here ya go.

Thanks to Greg for proof reading and correting my "English".

Resetting the camshaft timing on a Jaguar V12 engine.doc

 

Thanks Grant! This is very clear and makes perfect sense now. Looks like a good Saturday project.