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Re: Smokey from one exhaust pipe.

Posted: Wed Apr 24, 2019 7:37 am
by pimgmx
More good news for you, I guess...

I'm far from a V12 wizard myself, having owned 6.0s only for a relatively short period of time.
Thankfully others are... ;)

Below the thoughts from Starbuck's engineer sister, whose V12/6.0 knowledge goes light years beyond mine:

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There is no vacuum modulator on the GM4L80e transmission fitted to the 6.0 cars, so you don't need to be worried about cross-contamination of transmission fluid to the engine intake. The GM4L80e transmissions are electronically controlled and take an electrical load signal from a dual track throttle position sensor, not from engine vacuum. Only the 'old' three speed fitted to the 5.3 XJ/XJ-S has that vacuum modulator.

As for ‘smoke’ from one exhaust only - condensation is a likely culprit.
One side of the Marelli ignition might not firing correctly, and therefore only one side of the V12 exhaust is getting hot enough to turn the condensation to steam.
Something happening on only one side of a V12 with Marelli ignition should always make the ignition system the first point to check!

After checking the ignition: the 6.0 V12 has a different crankcase ventilation system to the 5.3.
It is possible for one of the small ventilation pipes that come up out of the engine 'Vee' to get clogged, then the other will pump quite a lot of oil vapour into one inlet manifold only. This is especially likely if the car has only seen short trips.
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Hope this helps!

Re: Smokey from one exhaust pipe.

Posted: Wed Apr 24, 2019 8:42 pm
by Walker
I can't see me being allowed to own a V12 for a great many years yet, but that right there is a gem of a reply! Invaluable information as usual, I'll be sure to note that down :D Cheers!

Re: Smokey from one exhaust pipe.

Posted: Thu Apr 25, 2019 9:38 am
by naki_k
Good reply.

Whenever recommissioning a car that’s been stood unused for an extended period, a full service of fluids and filters, plus all ignition parts would be the best place to start. Following by a good run out.

Does the engine sound like it actually runs ok? Or can you hear any misfire at idle?

Re: Smokey from one exhaust pipe.

Posted: Fri Jun 14, 2019 4:11 am
by brebner89
leo_denmark wrote:
brebner89 wrote:As its only one exhaust it means its only one bank of cylinders?
the car had been sitting about 4 years prior to my purchasing it so could be sticky valve.
The gearbox oil connected to exhaust?
I understand any work on the bowls of the engine will be a big job. Will need to be 100% sure on the fault.



The gearbox is connected via a vacuum line. If the diaphragm at the gearbox end cracks, the inlet manifold will suck in gearbox oil through this line. If it's anything like an XJ-S V12, it's on the A-bank, RH side.

BR Leo

I have been informed that my car wont have a vacuum modular system on gearbox which eliminates this as a possibility.

Re: Smokey from one exhaust pipe.

Posted: Fri Jun 14, 2019 4:18 am
by brebner89
pimgmx wrote:More good news for you, I guess...

I'm far from a V12 wizard myself, having owned 6.0s only for a relatively short period of time.
Thankfully others are... ;)

Below the thoughts from Starbuck's engineer sister, whose V12/6.0 knowledge goes light years beyond mine:

-------------------------------------------------------------------------
There is no vacuum modulator on the GM4L80e transmission fitted to the 6.0 cars, so you don't need to be worried about cross-contamination of transmission fluid to the engine intake. The GM4L80e transmissions are electronically controlled and take an electrical load signal from a dual track throttle position sensor, not from engine vacuum. Only the 'old' three speed fitted to the 5.3 XJ/XJ-S has that vacuum modulator.

As for ‘smoke’ from one exhaust only - condensation is a likely culprit.
One side of the Marelli ignition might not firing correctly, and therefore only one side of the V12 exhaust is getting hot enough to turn the condensation to steam.
Something happening on only one side of a V12 with Marelli ignition should always make the ignition system the first point to check!

After checking the ignition: the 6.0 V12 has a different crankcase ventilation system to the 5.3.
It is possible for one of the small ventilation pipes that come up out of the engine 'Vee' to get clogged, then the other will pump quite a lot of oil vapour into one inlet manifold only. This is especially likely if the car has only seen short trips.
-------------------------------------------------------------------------

Hope this helps!


This is a peach of a reply. People with knowledge like this is hard to come by.
It is definitely smoke rather than condensation from the exhaust so blocked ventilation pipe sounds like a good place to start.
So much great replies from everyone on here.

Re: Smokey from one exhaust pipe.

Posted: Fri Jun 14, 2019 4:50 am
by brebner89
naki_k wrote:Good reply.

Whenever recommissioning a car that’s been stood unused for an extended period, a full service of fluids and filters, plus all ignition parts would be the best place to start. Following by a good run out.

Does the engine sound like it actually runs ok? Or can you hear any misfire at idle?


Yes i when its running it sounds good and no misfiring when on idle either.
Could be difficult to hear a miss fire with it being a V12?