Acrid smoke and low vacuum

[lowact]

Pls can I have your sage advice?
Symptom #3 is insufficient manifold vacuum. I’ve tried everything to fix this: blanked off the carb bypasses, repaired the gulp valve, capped all other manifold tappings (for filter box hot air diverter valves and carb bypass valves) and capped the throttle edge tappings. All to no avail; vacuum vibrates around -7”Hg, should be steady around -20? Here is video of the vacuum valve, just started, still on choke …
https://1drv.ms/v/s!AiSPBKa26IcchJolgPRvVdkcJwNZCA
Symptom #2 is the clatter you can hear until it warms up. Just a bit of piston slap I tell myself, nothing to worry about …
Symptom #1 is the clouds of acrid smoke. Having to remove my (stinking) clothes before being allowed into the house is becoming tedious. And now even the neighbours are asking (very nicely) if car tuning could not coincide with their outdoor dinner parties?
I’m thinking, if there is no manifold/carb vacuum leak it must be valves, this would also explain the acrid smoke? Might there be anything else I could/should check before pulling the heads off?

[jagwit]

Colin

The clatter and low vacuum point to a slipped / loose timing chain (ie incorrect cam timing) - most likely from a broken timing chain tensioner.

I suggest you remove the tappet covers and check cam timing. This would also help you to check for excessive timing chain play on the RH side (where the timing chain tensioner is).

While the tappet covers are off, you might as well measure / correct tappet clearances.

What colour is the smoke? Blueish is oil, blackish is excessive fuel.

[johnetype]

Have you tried removing and capping off the vacuum feed to the brake servo and reservoir? A fault here could be the source of both your low vacuum and clouds of acrid smoke.

[chrisfell]

Am I the only one thinking, pistol slap and acrid (blue)smoke = pistol rings seized/worn/broken and bore damage? That’s the sort of result I’ve seen when an engine has seized due to overheating and lack of oil.

[abowie]

Low vacuum and "acrid" smoke could indicate a problem in your brake booster that is letting brake fluid get sucked into the inlet manifold. To understand how this could happen have a look at the schematic diagram of the brake system in the manual. If this is happening you should be noticing the level dropping in your brake fluid reservoirs.

A rattly engine is worn... somewhere. Sorry that's not very helpful, but you need a lot more info to diagnose engine noises and even then often you never work it out, even after you've stripped the engine and rebuilt it.

[MarkRado]

Acrid smell- reminds my of the Rover V8, where two plug leads were wrongly connected. Was completely down on power though; maybe not easily detected on a V12

[lowact]

Thanks gents.
The clatter turned out to be the air pump, cut/removed the drive belt solved this, gave me confidence to warm up the engine and sync the carbs (which I’d just reinstalled) whereupon the idle vacuum gauge mysteriously improved to a miserable -12”Hg (ish).
Disconnecting and plugging the brake vac., was good to check as I’d recently messed with this, fitted new master and slave cylinders, servomotor and hoses. However, disconnecting did not improve the vacuum.
Nothing improved the acrid fumes (exhaust is blue). Stings my eyes and makes me nauseous, the smell and fumes are embarrassing and is a major reason I am planning a HE upgrade.
Here is the vacuum gauge diagnostic chart I use (I believe they’re all the same?): https://1drv.ms/i/s!AiSPBKa26IcchJtjkIKugwPIYHUxkw
Here is video of the vacuum eventually achieved. It shows: At idle, fast vibration and 2ndry oscillation around -12”Hg (gauge); Rapid opening, closing throttle pulls the vacuum gauge needle down to zero; etc. https://1drv.ms/v/s!AiSPBKa26IcchJtkAxRxYdtAOYJGWQ
Comparison suggests: Poor rings or oil, loose valve guides, maybe late valve timing? Which is pretty much what yr telling me (dammit, engine’s only done 70k miles). I just needed the reassurance before starting the engine out thing, which I didn’t think I was quite ready for, incl. HE, EFI, RHD conversion, 5 speed and ….

[jagwit]

Nothing improved the acrid fumes (exhaust is blue). Stings my eyes and makes me nauseous, the smell and fumes are embarrassing and is a major reason I am planning a HE upgrade.

You say you synced the carbs, so they are now all pulling the same amount of air?

Did you also set the fuelling by adjusting the needles with the long Allen key that goes down the damper hole?

Colin, it "smells" to me like your engine is running excessively rich. Did you look into the carbs to see how much fuel is being drawn in?

The reason I ask this, is that I had a carb of which the needle and seat was sticky and this would flood the one carb but the engine ran - kinda. But then you get that serious foul smelling, eyes stinging effect.

[Whitact]

Hi Colin,
Before dismantling anything it might be worth doing a compression test. The blue smoke could just be worn valve guides rather than piston or bore wear. The compression test numbers should help to narrow down the possible causes.
Cheers,

[lowact]

Thx gents. Imo compressions are ok, 9.8 – 10.5 Bar (142 – 152 PSI). Does this suggest valve guides or rings?
Yes, with bypass valves removed carbs are now balanced to have same air flow (vacuum) and idle speed 600 rpm (yay!).
Carbs were refurb’d by “x-spurt” back to OEM spec about 4 years ago, however I recently found this was not to the standard I had assumed (e.g. 1 bypass valve was missing it’s spring tensioner!). I have never attempted to adjust the needles, lifting each piston a little or a lot has negligible impact, so nothing to be gained by adjusting needles? Here is video of one such test, other carbs are the same:
https://1drv.ms/v/s!AiSPBKa26IcchJtsNc_23csiSaSKqg

Also some (yesterday) test results, graph of vacuum versus 600 – 6000 stationary rpm.
https://1drv.ms/b/s!AiSPBKa26IcchJttvIeceYlJFvDoiw
One thing this shows is both manifold and ignition retard vacuum initially rising dramatically before falling away, suggesting that there is a leak when idling that gets choked by rising rpm. But I cannot find ANY leakage. Ok, valve guides may be leaking and are probably loose (vibrating vacuum signal) but is this enough for low vac and acrid fumes?
Do u think any value giving it to the dyno-tuners, letting them work their magic? I would need find one could function without an OBD2 connector…

[jagwit]

Colin

Your compression figures seem rather high to me, almost as if your car already has high compression pistons. Your figures compare with my Jensen with 10.9:1 CR !! My Etype figures were way lower than yours (and I'm rather confident my car is as good as it should be based on its performance). Now there is of course the altitude thing as well as possible measuring instrument calibration discrepancies.

Consider also that the lower your idle speed, the lower the vacuum she will pull at idle - as can be seen on your graph.

An instrument that is very handy to find manifold leaks with is a stethoscope with just a tube with which to probe around the various areas where manifold leaks could possibly exist. One can hear the hiss quite clearly and then zoom into it.

The vibrating signal could arise from the physical point where you measured as that point may see vacuum pulsing from nearby inlet tracts.

[christopher storey]

Jagwit : the Compression pressures don't strike me as too high. Your figures may be lower if you are at a significant altitude above sea level

What I do wonder is whether someone has inadvertently fuelled this car with either paraffin or diesel ( people do sometimes grab the wrong can , as well as the more obvious failures at a filling station ) . This would explain the acrid exhaust efflux

I would not be pulling the engine yet. Perhaps a quick check of the fuel in the tank would be useful ?

[lowact]

Only ever fuelled by me and only ever 98RON. Including yesterday, only time I've ever run out of petrol tuning a car. And it does turbine to 6k quite smoothly which I suspect it wouldn't if the fumes and smoke were due to diesel? Here is one video of the vacuum vs rpm tests:
https://1drv.ms/v/s!AiSPBKa26IcchJtl-2B4f-6ivQmiAg

However I do think Phil you are correct that somehow it is running way too rich, it is a very petrol smell and the plugs are very black. Maybe time to give up and take it to the professionals

[jagwit]

With the creosote poles removed, I got opportunity today to measure the compression ratio on the 10:1 XJS and - I believe - 12.5:1 DD6, in both cases cyls 1a and 1b:

XJS (pre-HE): 900kpa (130psi)
DD6 (HE): 1100kpa (160psi)

While measuring the DD6, I got readings around 950kpa, and realised she was really not cranking as good as she should be. The battery was really not well charged as it stands for months on end at times (battery disconnected). I let it charge for 10min with my 25A CTEK charger and the readings went up to 1100. Therefore, cranking speed can have a substantial influence on the compression test readings one gets - obvious I suppose.

Colin: The DD6 has engine no 7P58000SA

[malcolm]

Don't understand how cranking speed can change the pressures? You are concentrating a starting volume into a smaller one. Regardless of speed, the compression is surely the same? Unless it is so slow that pressure is being lost during the compression, but then you'd have to have very poor rings? Or to be loosing pressure somewhere else where you shouldn't?

[jagwit]

Don't understand how cranking speed can change the pressures?

The rings do not offer a 100% seal. Even when the engine is running they do not seal 100%. This is why all modern engines have a Positive Crankcase Ventilation (PCV) system. Its purpose is to draw the gases that escape past the rings into the crank case, back into the intake.

Jag V12 HE engines, are known for "distributor fires". Unburnt Air/fuel mixed gas escapes past the rings into the crank case. This eventually finds its way past the dissy shaft into the distributor where you have sparks flying between the rotor and the HT terminals. Eventually conditions arise where those sparks ignite the air fuel mix inside the dissy and it explodes sometimes starting a small fire. This is why HE engines also draws fresh air through the dissy in the same way a PCV system draws fresh air through the crank case.

At cranking speeds, a fairly significant amount of pressure loss is experienced past the rings and obviously the worse the condition of the engine, the more pressure loss occurs. The slower it cranks, the more time there is for pressure to be lost.

[malcolm]

OK, thanks Philip. It does sound like a big drop just via rings (unless as I said, they are very worn) but I know nothing about the V12 engines. In truth, I don't know much more about the straight 6 I have! But I try.

[MarekH]

So 900kPa implies 9x atmosspheric pressure and 1100kPa implies 11x atmospheric pressure, but Philip lives at altitude, so that's more than 9:1 and 11:1 respectively. What is ambient air pressure where you are Philip?

kind regards
Marek

[jagwit]

Marek, I live at about 1430m AMSL where barometric pressure is around 85kpa.

[MarekH]

I'm surprised nobody has bothered to look at the plugs or do the tests in the manual to check whether too rich or too lean. In the absence of a lambda sensor, a colourtune spark plug, or just looking at any spark plug might help with diagnosis.

Since you report no loss of brake fluid nor any loss of oil, I'd look to the fuelling and whether it is actually being burnt in the cylinders, rather than tipping out of the back of the car. A quick check with a timing light wouldn't go amiss.

If some of the plugs are consistently not firing, then you ought to be able to work that out by seeing whether you have spark at all twelve cylinders. With a nice vacuum leak, you could probably idle comfortably on less than all twelve.

After all of the basics check out, then you can start wondering about possible mechanical shortcommings.

kind regards
Marek