I have posted the problem I am having with my '*% XJS HE and wondered if any of you had struck this problem before.

 

I am assuming the rough running, as in 6 cylinders etc you posted in the XJ-S section ???.

Some suggestions have been given.

My experience with this over many, many years with the V12, are as followed in NO particular order at the moment:

The CTS (coolant temp sensor) on the rear section of the LH thermostat housing is a known flaky item. Get a V6 Commodore Bosch unit, part # ending in ...........023, is what I use.

The EFI loom sitting in the bottom of the "V" is more than likely the MAIN issue. It will be sooooooo old now, and insulation of any integrity will be loooooong gone. This has the 4 banks of 3 injectors firing at irregular times, or not firing at all. I have replaced (made my own) looms over the years, and lifted that loom out of the "V".

While at it, the "shielded" wire that supplies the ignition pulse TO pin #18 of the ECU in the boot, also suffers from insulation degrading. The main issue with this wire breaking down is NO engine operation at all, as in dead in the water.

The spark plugs are critical here, and gapped at 0.025" is also critical.

The spark plug leads take a beating. I use Magnacore standard spec ONLY, and have never had issues.

Many other thing can and will cause grief, but these should get it running on 12, then the fine tuning will need sorting, and that also is quite time consuming.

I have many "Word" doco's on these engines and the operating systems, and if you want them PM me. Some are HUGE, so your "inbox" will need to suitable clear.

If I dont already have a doco, I will simply write one, as all this "stuff" is still retrievable from my brain.

 

Hi Grant and Chukij; and greetings from the Coffs Coast ...

Contratz Grant for a clear, well structured, problem solving structure for these magnificent engines. Our S3 V12 Daimler VDP suffered from weird non-firing issues eventually solved by replacing the central EFI loom which had several areas of cracked and "gappy" insulation.

I recall this clearly (even though many years ago) for two simple reasons. Our late 80s prop-rider "JAGGERED" with similar V12-HE engine but opened out to 6L, twin Toyota turbos, dual custom tuned extractors and water injected pipes - never once exhibited any such ignition or efi issues. Reason? From day1 we had fitted it with a custom engine wiring loom!

The second clear reason I recall getting down into the vee of the VDP to get at the loom, was that I found 2 small spanners down there also! Heaven knows who or when they were dropped down there ... but for dying insulation of the efi wiring, they might still be there!

Obviously, this is an arduous location for wiring and is increasingly pointing up failures as age wearies the insulation. You are right to highlight this as the most likely suspect once plugs are proven OK. Once replaced on the VDP, issues disappeared and never returned! Best wishes, Chukij - keep us posted.

Other chassis located circuits have shown intermittent faults ... and beggar the question ... are there mechanical, stress or environmental (ie fuel, oil) reasons that insulation fails more in certain circumstances ... or like us, is it purely a function of aging???
.

 

Greeting Ken,

Toolbox restocking when a V12 is extracted from its home is a regular event. If you drop a spanner and it falls out the bottom, it aint a V12.

That loom in the "V" is OK for the first 10 years or so, then oil weeping gets to pool in the edges of the valley plate, and the loom is getting the fried chips treatment.

Just changed the sparkers on the wifes 01 S Type V6 and that familiar "crackling" of the wiring insulation of the coil connectors is already audible.

I reckon we have to live with this as corners are cut in all areas.

My '85 XJ-S V12 got my rewire treatment in 1996, and still soft and pliable. One I am sorting at this very moment has all the signs of loom shorting, as it simply cuts out at random, and all my obvious items have failed to sort it.

Never a dull moment.

 

Amen Grant and many thanks for sharing your experience ...

Like you, I have moved on from the big beautiful V's, but I worry that a whole new generation of XJS owners are beset (and often frightened) by these erratic misfiring events ... and completely unaware of their most likely cause after testing/replacing plugs etc. The fix, if not simple, is well proven.

May I suggest that you might cut-and-paste this accumulated knowledge into a "how to" sticky on the XJS forum. Perhaps, our OP Chukij, can contribute relevant pics for such a thread, and I am sure one of the Mods would assist.

Well done mate.