V12 white smoke and slight misfire?

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V12 white smoke and slight misfire?

Postby RayGardner » Mon Feb 11, 2019 11:17 pm

My 1986 v12 xjs has spent most of its life off the road (I think) and I am trying to see how far I can get before I have to resort to a proper mechanic finally has to hep....so far the fuel has been cleaned out, spark plugs, dizzy, leads , fuel pump changed etc done. After chasing the wiring and some fuses, relays etc it does start, so half way???

On start up (especially when cold ) the white smoke which almost goes after a few minutes, but a heavy bit of throttle and it does smoke (but not blue or black still white). Also does not seem 100 percent smooth , possible one cylinder (or more?) not firing? ...so starting with simple items and I did try small change on dizzy advance , putting in injector cleaner in the tank, the Italian tune up ( but bottled that after I think the neighbours think I,ve set fire to the garage). The air con is out so I can get to spark plugs...some were a bit oily ( not yet re-checked after running for a while.) Crank Breather cleaned...did look at fuel vacuum in boot but possible need to take things apart a bit to see behind it and if it's correctly connected. So next steps? Check all spark plugs, compression test, check injector (listen with screw driver to ear listening for clicks? Buy a noid tester, clean injectors (bit scary taking off fuel line off the top?...ummm what's simplest try try first ( or should I lie and get RAC home start and say it drove in OK last night!)

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Re: V12 white smoke and slight misfire?

Postby RichardSEL » Tue Feb 12, 2019 8:15 am

How many years off the road?

Had a Mk IX that'd been part of a collection for 12 or so years (53k miles only documented for a '59MY). It'd start but virtually immediately oil up the plugs. Change the plugs and it'd start, run and then oil them up again after a few mins. Eventually found out that engine oil seperates after a time of stagnation, and it'd carbon up the plugs.
So use a Meggar on them (a 600V one will do -- I had one left over from my ships' servicing days). If there's any sign of leakage then ditch them. And get that engine oil and filter changed. It's gotta be done anyway. Use a fully synthetic

How's your coolant level? Has that been changed, flushed thru? Any bubbles in the header tank when you leave engine running on tickover? Does the white smoke eventually lessen when engine fully up to temperature? What does the white smoke smell of?

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Re: V12 white smoke and slight misfire?

Postby davidr » Tue Feb 12, 2019 7:19 pm

White smoke could be brake fluid being drawn into the induction system from the servo? Or maybe transmission fluid from the gearbox vacuum modulator?
1996 XJS Celebration Conv. (shown on the JEC stand at NEC Nov 2015)
2001 XKR Convertible

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1989 XJ-S V12 Coupe. 2006 XJ TDVi Sovereign. 1995 XJ6 3.2. 2013 XF 2.2d. 2009 X Type 2.0d Sovereign estate

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Re: V12 white smoke and slight misfire?

Postby RayGardner » Sun Feb 17, 2019 9:11 pm

Thanks for the replies, oil change certainly on the to do list! It looked ok but best to play safe and change filter. Did check and can hear the injectors click when listening to the end of a screw driver placed onto each For it possibly being brake fluid , well I was party through putting on new front callipers so finished that off and bled the brakes, not sure if that could help ( the smoke did not smell like brake fluid and sweet). Will also probably check/ do the transmission vacuum too. Anyway read elsewhere that it can be condensation in the exhausts and maybe I was just not ruining it long enough to clear this, I was doing 6-8 mins.... Thus ran it again today (warmer day too) and It cleared quickly, also whilst a little smokey on heavy revs it was no where near the level of white smoke as before.

So looks better but now more jobs for the list.

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Re: V12 white smoke and slight misfire?

Postby BigCatXJS » Fri Mar 22, 2019 5:54 pm

White smoke could be over-fueling on one of the banks. The simple ECU can fail and flood one of the banks (you will know about this if you are driving at the time!). Tell-tail sign prior to failure is a very strong smell of petrol that may be smelt by the driver or passenger of car following behind with the white smoke! If the ECU is on its way out or fails then AJ6 Eng can troubleshoot and repair as they did mine.
1989 Jaguar XJ-S V12 HE 5-speed manual
1994 Jaguar XJ40 Sovereign
2007 Mercedes CLK350 AMG Convertible
2010 BMW E92 3 Series Coupe heavy oil burner

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2004 Volvo S60 D5 (RICA 210bhp)
1985 E28 BMW M535

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Re: V12 white smoke and slight misfire?

Postby steve_m » Fri Mar 22, 2019 10:47 pm

+1 with David on checking the brake servo.
Had a Porsche 911s many years ago (still wish I had it) and was stitched up royally by various experts.
I was informed that the engine was 'blown' and I considered it wasn't worth spending 4K on an engine rebuild on a 7k car.
Traded it in (with cash my way) for an XJR6.
Turned out, in later years, that the engine was pulling brake fluid in and burning in.
Mind you, we are talking battlefield levels of white smoke here; the entire village was blinded everytime I drove through.

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