JTS running very rich

[josh18]

Hi all. I have a JTS that has run very rich since we have owned it. I mentioned this early on and also that it ran cold and was told about the dodgy thermostat issue. So I have changed that, could have sworn it was running closer to 90 degrees but a few months later it doesn't seem to get above 70 degrees or so and takes a long time to warm up. So I think the new stat is knackerd or the gauge is reading wrong. I wanted to buy a laser thermometer to get a proper read of the running temp but figured a new thermostat cost about the same so have just ordered a new one. If the old one is still ok I will have a spare at least. Also I noticed the rocker cover is leaking oil into at least one of the plug holes which I have read can be a problem so one of those is also on order. Also I haven't looked at the air filter yet (bad I know) so one is on order. Apart from a new thermostat I have read  the O2 sensors could be on the way out, dirty MAF or even leaky injectors. Air filter is easy and will be the next thing I do but failing that what do you guys reckon should be my next port of call? I don't really think it's leaky injectors as I reckon this would be more of an issue at low revs or on start up. Our issue seems to be from about 3000 rpm and up- drive it even semi hard and you see a huge black smoke plume behind, but no noticeable smoke below that. At the price injectors go for I don't want to touch them until last!
I have read about a fair few rich running JTS's but seemingly for a lot of different reasons. I want to keep the car so don't want to let it do any (more?) damage- I can't imagine its that good for it.
Another thing, I know these cars are OBD2 compatible- would a scan gauge tell me anything of use? It's not giving me engine lights ATM.
Cheers
Josh

[josh18]

I did a bit of investigating today. I found a hose from the rocker cover to behind the throttle body cracked. I replaced that but it didn't seem to make much difference- maybe a smoother idle. Next I pulled out the air filter- what a crap design to access something that should be easy! As i thought it might be it was filthy so I fitted the AFM back in without it. Then I let it warm up and then held it at 2000 rpm and watched the temp gauge to see what it got up to, if I could tell when the thermostat opened and at what gauge temp the fan cuts in. It took its time but slowly rose to 90 degrees where the fan cut in- so I can tell the gauge is right and the fan works. I then took it for a drive and it quickly settled back to about 70 and rose to maybe 80 at slower speeds. It is much less smokey than before, seemingly better the closer it gets to 90 degrees.
So my verdict is that seeing the thermostat is supposed to open at 82 degrees and I have worked out the gauge is correct that the thermostat is at least slightly open- crap because it's a new one. I think my smokey problem was a combination of a blocked filter and stuffed thermostat. So as in the previous post I have ordered a new thermostat, I went for an Aussie Tridon this time, rather than the european one I ordered last time. I was going to order a new filter but I decided to modify the airbox and fit a pod filter I already had. This basically involved cutting most of the box out but retained the top and bottom so it mounds as it should. I'm really happy with the results- it revs much more cleanly and sounds great, with a really throaty induction roar but not droney at cruising speed. Hopefully this new thermostat can make it run at the right temp and we'll be very happy.
Cheers

[poohbah]

Josh, check posts by our resident thermostat expert Colcol for a definitive account of the crapness of thermostats fitted to 156s, and their tendency to pack up anytime from new.

[josh18]

Thanks mate, Colin is the one who first let me know of the thermostat issue. Im pretty sure he told me that about them too.
Cheers

[josh18]

Hey again guys. I finally got around to fitting the new thermostat and yes, the old (new) one was buggered. It now rises quickly up to and holds 90 degrees and does seem to run a little better but still smokes like a chimney. Give it a boot full and watch the black smoke plume in the mirror from about 4000 rpm and up. Looking at the plugs though, they don't seem too bad- light brown colour with small black deposits around the base of the thread. So it seems it is running the right mixture most of the time, just not when I have described. So what's next, O2 sensors? Also is the ECU one of the learning type, ie might it take a while to reconfigure to the new running temp or something?
Also our car uses a LOT of oil, which I know is a JTS thing. Could this be the smoke plume? I always thought oil smoke to be blue in colour, where this looks very black.
Cheers
Josh

[bazzbazz]

You need to get a compression test done to see if the rings have gone. JTS cars are known for having fragile rings and they crack with age.

[johnl]

Black smoke is a rich AFR, i.e. unburnt carbon.

To the best of my understanding;

When running on a light throttle the ECU should be trimming the AFR according to the signal it gets from the O2 sensors (i.e. 'closed loop' running). When you floor it the ECU will ignore the 02 sensors and run the engine according to unchanging pre-programmed maps (i.e. 'open loop'). The ECU also operates in a (different) open loop mode when the 02 sensors are still too cold to work properly, i.e. for the first minute or so of driving (a bit longer if the engine is left to idle from cold). This is why the sensors have an electrically driven 'self heating' function, i.e. to get them up to working temperature more quickly than the exhaust heat alone can do.

Open loop AFRs are fairly rich (i.e. cold temperature and wide throttle opening). When the engine is cold this is because the ECU assumes a rich AFR is needed for the engine to run acceptably (even when the 02 sensors start to work and the ECU goes into open loop mode but the coolant temp is still below X°, the open loop AFR will still be fairly rich because the ECU assumes a rich AFR is needed due to the the still relatively cool cylinder temperature, i.e. it's harder to ignite and adequately burn a relatively lean mixture in a relatively cool cylinder). This is why you get poor fuel economy when the thermostat sticks open and the coolant fails to reach X°, the AFR is still in open loop cold mode.

At throttle openings approaching WOT (wide open throttle) the open loop AFR mode will be quite rich because the engine requires a fairly rich AFR both to produce the power needed for acceleration (or maintaining a high speed), and because a rich AFR burns cooler than a leaner AFR. This cooler burn helps prevent 'detonation' (which is damaging), but also means that the spark plugs, piston crowns and the exhaust valves are in less danger of overheating when the engine is approaching or at max power output.

So, if the engine black smokes with light throttle openings then it could be an issue with the 02 sensors, or one of them. If it smokes with heavy throttle then it might be something else, maybe injectors, or an injector. If say one injector is not flowing enough fuel (i.e. partially blocked) then the resulting lean condition can (counter intuitively) cause a rich AFR in other cylinders.

I'm not sure of the JTS set up, but for example the TS engine uses two O2 sensors (the pre-cat sensors, which are the ones the ECU pays attention to for controlling AFR), each serving to read O2 content from two cylinders. If one cylinder is running lean then the sensor will detect an overall lean AFR in the combined exhaust gasses from both cylinders, and will then increase pulse width for both injectors (i.e. open the injectors for a longer time) until it 'sees' the reading it 'wants' to see from that sensor. This will result in one injector over fueling and the other still probably under-fueling, but the over fueled cylinder will still be producing black sooty smoke because it can't burn all the fuel injected into it (this will also have an adverse affect on power, so the driver will open the throttle more...).

This assumes that the ECU can control the pulse width of each injector individually (or at least the two associated with each sensor, independent of the two injectors associated with the other sensor), which I'm not certain of. If it can't then the result may be more or less the same, the ECU will increase injector pulse width for all cylinders until it sees an overall O2 content that it 'wants' to see. The result will be some cylinders over fueled and at least one under fueled, and even though overall O2 content in the exhaust gasses may be within parameters, there will be unburnt carbon blackening the exhaust gasses, loss of power, and worsened fuel economy.

I would expect that if the ECU 'sees' a significant disparity between the readings from both O2 sensors (as might happen if say one sensor is faulty) that it would 'know' something was wrong and at least throw a CEL warning. But it might not.

I've had two injectors totally fail on  my TS engine (not at the same time). They stuck completely open, and just hosed raw fuel into their cylinder. Of course this resulted in lots of black smoke and very poor running. I expect it also caused the ECU to substantially lean off at least one other injector (the other one associated with the sensor), and maybe all three other injectors. I doubt this has happened with your engine, the symptoms are quite severe, much worse than you describe.

It might be worthwhile to have your injectors checked and cleaned. It might be worthwhile to have the O2 sensor outputs checked. Accretions from burnt oil can affect the O2 sensors...

Regards,
John.

[Jekyll and Hyde]

The ECU will generally not adjust the mixture from the O2 readings beyond a certain amount, which should be nowhere near enough to cause 'plumes of smoke'.  Given the smoke starts appearing at around 3-4k rpm, and its a JTS I'd be wondering whether the camshaft variator is actually working, or whether the cams have any lobes left on them. 

Of course, it could also be that 3-4k is where there is enough volume and heat moving through the cylinder to clear the build up of fuel or oil.

How much oil is it actually using - a 'lot' doesn't really tell us much...

[bazzbazz]

Before doing anything, get a simple compression test done, it will tell you if you have problems with the rings/valves.

As the smoke seems to be coming on at above 4000 rpm the next two usual suspects are valve guide seals or a bad intake manifold seal around the Variator Oil Galleries. If you are leaking oil at the manifold gasket though you should notice #1 & #2 spark plugs suffering from more oil fouling than the others.

Also check all the vacuum hoses going to and from the main air intake hose and the PCV crankcase hose that is just behind the throttle body.
Baz

[johnl]

Yes, but Josh is saying that the smoke is quite black, not grey or bluish. Of course this doesn't preclude that there might not be oil smoke mixed up in the blackness of what sounds very much like smoke created by an overly rich AFR.

I agree that the ECU shouldn't normally enrich so much as to cause "plumes" of smoke. However, the ECU on our Saab was certainly able to massively over fuel the engine when the O2 sensor died, to the point that the spark plugs sooted up so much that the engine wouldn't start. Once I managed to get the engine going (after pulling and cleaning the plugs), it would run very badly and produced lots of black smoke. It would run fine if you planted the boot, but as soon as you backed off it was rough as guts with little poke (can't drive with WOT all the time...). I replaced the sensor, problem sorted...

This issue with the Saab O2 sensor was a bit of a learning curve for me, took me quite a while to diagnose the problem (after nearly all other possibilities had been investigated and ruled out). One thing I learned was that an O2 sensor can be utterly defunct and the ECU won't necessarily detect it, just continues to trust the signal it's getting and blithely dumps more and more fuel into the engine...

Regards,
John.

[josh18]

Thanks guys, definitely some food for thought. How would I tell if the variator is working or not? There has never been any rattle from it but that doesn't mean that it is working. It doesn't have a "V-Tec" style step in power delivery but I always assumed this was due to it being continuously variable and not intrusive. Can the variator be felt kicking in normally?
Oil use wise it will go from the full to the low mark on the dip stick within a week or two of driving, about 500km.
Cheers

[johnl]

How would I tell if the variator is working or not? There has never been any rattle from it but that doesn't mean that it is working.

At idle, disconnect the variator solenoid electrical plug. If the variator is operable then when you disconnect the solenoid it will stop working (i.e. oil pressure will stop being fed to the variator), and the idle will get rough. At least this is what happens with my TS engine, i.e. disconnecting the variator solenoid causes a very marked deterioration in idle quality, which makes me think that the variator must activated at lower rpm, so must be 'inactive' at higher rpm.

It doesn't have a "V-Tec" style step in power delivery but I always assumed this was due to it being continuously variable and not intrusive. Can the variator be felt kicking in normally?

My understanding is that the the variator is either 'on' or 'off', it doesn't have a progression in the way it works (at least with the TS engine, though I expect the JTS variator is similar).

I don't know about the JTS (never driven one), but the TS (at least mine) has a point at about 3500 rpm where the power picks up noticeably. I assume this is when the ECU cuts power to the variator solenoid and it stops working, which is when the inlet camshaft advances (this is just an assumption that may not be correct, the pick up in power could easily be explained by other engine parameters). When the inlet timing is advanced there is also a resulting increase in 'overlap' of the inlet and exhaust cam timing, which is a 'good thing' for high rpm power, but causes rough running and poor power at low rpm / idle.

Oddly, the variator purportedly stops advancing the inlet timing above about 5000 rpm, which seems exceedingly strange to me. I would have though this would impair power above 5000 rpm. It would also make the engine less rev happy (unlike a V-Tec where the change in timing is carried all the way to the red line). Maybe it's supposed to, perhaps to discourage revving the engine above this speed...

I have read somewhere (a few places I think) that the solenoid is not activated at idle / low rpm and becomes activated at higher rpm (at differing rpm depending on the particular version of the engine).  However my experience suggests that it is opposite to this, i.e. activated at lower rpm / idle, and becomes deactivated at higher rpm. If the variator was not electrically activated at low rpm, then why would disconnecting its solenoid cause the idle to become rough??

So, unless I'm missing something, discounting what it does over 5000 rpm, it seems to me that rather than the variator activating and advancing the inlet timing at higher rpm, it instead is activated at lower rpm and retards the inlet timing when it's activated. If so then the variator deactivates to allow the inlet timing to advance at higher rpm, as opposed to being activated to allow the timing to advance...

Oil use wise it will go from the full to the low mark on the dip stick within a week or two of driving, about 500km.
Cheers

That could be enough to coat the O2 senors in gunk. This could easily cause the sensor to work badly. If the gunk is thick enough to impair 02 from being detected in the exhaust gasses, then the sensor will generate a low voltage which the ECU will interpret as a lean AFR, and will then enrich until it 'sees' a signal voltage that it 'wants' to see. The problem is that the actual AFR may be already a lot richer than the ECU 'thinks' it is, so a very rich actual AFR will be the result.

Regards,
John.

[bazzbazz]

OPERATION IN CLOSED STAGE
When the closed stage is required (idle speed and maximum power zone), the solenoid is de-energized, so the slide valve in the base mount of the solenoid prevents the oil from reaching the variator.
In this case the timing of the inlet valves remains unchanged (closed).

OPERATION IN OPEN STAGE
When the open stage is required (medium rpm with high torque). The solenoid is energized, thus opening the slide valve allowing oil to enter the Variator and forcing it to rotate clockwise which transmits rotation to the camshaft, thus varying by 25° engine the timing of the inlet valves.


The Variator operation is disabled below 2500-3000rpm, the idea being to give better economy at more "conservative" driving styles. Hence the reason why 2.0 TS & JTS seem doughy and unresponsive below 3000rpm, drop a gear, put the boot in and it kicks in and "away we go!"

There is an old Alfa Romeo saying, "Fun starts at 3000!"   



From Wikipedia -

Alfa Romeo system

In 1970, Fiat patented a variable valve timing system, however it was Alfa Romeo who first applied VVT in 1980 to the long-established Twin Cam engine used in the Alfa Romeo Spider. The technique derives from work carried in the 1970s by Ing. Giampaolo Garcea and in Italian the device is termed variatore di fase. The Alfa Romeo Twin Spark engine, introduced in the 1987 Alfa Romeo 75, also uses variable valve timing.

The Alfa system varies the phase (not the duration) of the cam timing and operates on the inlet camshaft.

Alfa Romeo's variator is a cylindrical chamber that contains a pressure chamber and piston along with helical splines. Engine oil pressure, moves the internal piston which rotates slightly due to the helical splines and advances the inlet valve timing by 25 degrees. Oil flow to the variator is controlled by a solenoid valve. When engine speed reaches a certain speed, normally 1500-2000 rpm in the Twin Spark application, the solenoid energises, causing pressurised oil to be directed through the inlet camshaft into the variator. The inlet camshaft position is advanced 25 degrees, thus increasing valve overlap. It remains in this advanced state until about 5000 rpm when the solenoid switches off, and the variator piston returns the valve timing to its natural state. The variable timing increases the engine's mid-range flexibility and reduces emissions. Exact changeover points depend on version. It is notable that this relatively early system only has two settings: unchanged and fully advanced.

[josh18]

Thanks guys.
The car goes really well and revs freely so I reckon the variator is working. Gunked up O2 sensors seems to be a more logical path to me. I know one pair are active and one pair are just something to do with the cats, but don't know which. If I were to replace a pair which would it be, or should i do all? Even O2 sensors seems a bit fishy though as the rich running is only up higher in the revs, not all the time. Also I would have thought if the sensors were not working right it would throw some sort of code.
Honestly the car goes great, I just want to know what's causing all the smoke (and soot on the bumper!) and how much better it might go at the right mixture.
Cheers

[bazzbazz]

It's got nothing to do as to whether the variator is working or not, it has to do with is it leaking oil from galleries that run through the inlet manifold due to a poor sealing gasket.

And if you have soot all over your bumper it is NOT from faulty O2 sensors, true they probably are not working too well but they are not the cause of the problem, they are collateral damage.

As no smoke is emitting at less than 4000rpm (from your supplied information) it is most likely worn Valve Stem Seals, damaged rings or oil leaking from the Variator galleries due to a poor sealing inlet manifold.

The fact that your car uses oil like a Destroyer on D-Day doing Smoke Screen Duty is ALSO indicative of one of these errors.