924 Turbo emissions

tref · Jan 21, 2011

Ok... the infamous 924 Turbo Cab went in for MOT today - failed on hand brake performance, one of the brake hose securing grommets broken on the strut, one winker bulb decided to play up (which if it had just been that, then percussive maintenance would probably have got the certificate, and the awkward one, emissions...

So the question... where on earth do you start with a total unknown to get the emissions right? Given that the car has never had a clean bill of health in 6 years, and I don't really want to/can't afford to replace everything, where do I start?

For those to which the figures mean something, C.O. should be under 4.5%, it is 11.759% HC is ok at 436ppm (max permissable 1200ppm).

It runs quite evenly on tick-over, but doesn't seem to pull that well. That said, as the MOT station is literally across the road, it hasn't been out of first gear.

My best guess is that as its revs up and dies back as one would expect, that the metering head is working ok. On that basis, I am wondering if I should suspect the fuel pressure regulator, or warm up regulator - which-ever you like to call it. One other thought though is on my 944 Turbo, the engine temperature sensor wreaked havoc with the emissions - am I right in thinking there is no such control on the 924 Turbo?

It is a 1981 car, so assume S2 or 177, depending how you wish to refer to it!

TIA, Tref.

CarreraRSR · Jan 21, 2011

Can't fix your problem but at the last MOT in November mine had a CO of 0.24% and HC of 40ppm, so your figures are way up over mine. I drove mine for 6 miles to the tester plus warm up and idled before entering the station. It also had a dyno session last year so I know the ignition and fuelling is optimised. I would guess a cold engine would have higher results as yours did if just driven over the road. When did it last get a proper tune up/service?

tref · Jan 21, 2011

Never! The car was bought non-running, with a seized engine about six years ago... A donor engine and most of the injection system was fitted, and I did get it running - that engine came from an MOT failure, but th. reason unknown... That was about five years ago... since then it sat in a body-shop for two years, and following on from that has suffered a severely contaminated fuel system. I had all sorts of problems getting it running, including having to dismantle the fuel pressure relief valve in the metering head, etc.

It has had a new fuel pump, filter, air cleaner, plugs, a bottle of injector cleaner in a gallon of fuel in an empty tank, now had about three gallons of fresh fuel added. The underside of the bumper is black with soot, so I think it is a straightforward rich mixture problem... I am now thinking the first thing I should do is check the fuel system pressures... and hopefully that will give me some idea of what the problem might be.

Thanks for the figures - they are a useful guide of what I should expect.

geoff Ives · Jan 22, 2011

Am I missing something?
Is the MOT mmision test relevent to a 1981 car?

tref · Jan 22, 2011

'tis in Dorset Geoff... what's the name of your garage? I can feel an MOT coming on[

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CarreraRSR · Jan 22, 2011

All cars have MOT emission checks. We have to adhere to the non cat limits which are shown in trefs post.

vitesse · Jan 22, 2011

A Gunsen CO meter(actually reads CO2 & interpolates the CO) would be adequate to allow you to check the mixture settings-I used mine on a Rover SD1 Vitesse all the time & could set the mixture really quite accurately.It's only the current modern fuel systems which are too accurate & sensitive for it to be used.

vincematthews · Jan 22, 2011

ORIGINAL: tref
It has had a new fuel pump, filter, air cleaner, plugs, a bottle of injector cleaner in a gallon of fuel in an empty tank, now had about three gallons of fresh fuel added. The underside of the bumper is black with soot, so I think it is a straightforward rich mixture problem... I am now thinking the first thing I should do is check the fuel system pressures... and hopefully that will give me some idea of what the problem might be.

I don't know if it helps but CO (carbon monoxide) is produced when a fuel is burnt with insufficient O2 (oxygen) to form CO2 (carbon dioxide) . . .
So too much fuel for the correct oxygen amount or too little oxygen for the correct fuel amount.

My MOT results for a 2.0 NA were
0.16% CO with limit of 4.5%
97ppm HC with limit of 1200ppm (unburnt hydrocarbons)
us oldies have a different MOT to the modern cars [

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BTW you're a braver man than me dismantling the metering head - on re-assembly I wouldn't trust the relief valve to give the correct pressure without checking with an accurate gauge. I visited the local hydraulics supplier and got parts to make a fuel gauge tool similar to that in the workshop manual for about £50.

924nutter · Jan 23, 2011

Tref there is a mixture screw on the body of the m/u in betwen the steel head and the pressure duct outlet. 3mm allen key to adjust. Lean it out a bit but no too much as it will start to pink. The access orifice is often tamperproofed but not 'welded shut'. Go only about a sixteenth of a turn and try not to push down.
A 177 turbo has a single round entry into the throttle body, the 170 uses a throttle body similar (if not the same) to the unblown 924 with twin butterflies, and is secured by a jubilee clip. The engine would probably benefit from a bit of running too. Its going to be difficult with no MOT though. Just letting it idle won't really get the jodb done. On the road the 170 is more switch like. I could feel the boost bbuilding from 2500 in my 177. It is going to be great to see this wee beastie. Workers conference? If the worst comes to the worst I have another metering unit in the ebay special but that might not be much better as it hasn't run for two years. If all else fail it might be worth swapping them over and if it cures your ills you can have it for £75. Special offer JUST FOR YOU.

How do you reckon 220 would go in a 924. I have a camshaft for about 20 bhp, plus intercooling and a tiny rise in c/r.

If my maths are correct; 177 + intercooler= 196.(known fact)
+20 for the cam = 216, + 4 or more for the increase in compression ratio

924nutter · Jan 24, 2011

I have been clearing out some old 'Posts' and in a twist of fate, the first one I opened to check for content opened at a photo of Tref's pristine engine bay after restoration. It is difficult to tell by the picture but the red sealing ring on the throttle body leads me to conclude it to be a 177 engine. Actually the 170s were quicker in the bench march O-60, due to the higher torque, once on boost, but fell short on v max by a single mile per hour so don't be too disappointed Tref!

tref · Jan 26, 2011

Thanks Guys!

Agree re taking the metering head apart, although taking out the pressure relief valve is a little different to taking the fuel distributor apart... I had nothing to loose (and gained everything) - the car wasn't running before - it is now!

I wouldn't be at all surprised if the result is incorrect fuel pressure, which is why I am thinking I should check this first - hopefully I can get the requisit gauge and valve made up to test it out - assuming an M10 x 1mm tap and die get here in time, this weekend.

The other thing I am expecting is that if the metering head was gummed up, the Warm Up Regulator will be the same. Again, I am hoping this will be proven or disproven with a fuel pressure test.

As for performance... I'm not expcting it to set the world on fire! To start with, it is a cabrio - I don't think I'll want to test out the upper limits of it's capabilities - no roll hoop on this, and I'm not sure exactly how well the seatbelt would really hold you in! Then there is the fact that all the fibreglass has been replaced with metal - apart from the bootlid, and that has been supplemented with a substantial steel frame. It is now a lot heavier than the coupe, and aerodynamics? What aerodynamics?! I'll settle for running smoothly...

The good news... is that on the run to the MOT testing station the only concern was the running of the engine - when asked about how it felt, Claire said "cold", I said "running as rough as anything" - steering, suspension, brakes etc were conspicuous only in their absence of all concern.

Not sure about when it will be released on an unsuspecting public! At the moment, it is fitted out with the bare minimum to pass the MOT. As there is no centre console (still looking for a linen side carpet) it took me ages to find the foglight switch in the tangle of wires! The doors are bare baring the required internal door handle, and most important, no hood. nevertheless, it's good to feel it is progressing again.

vincematthews · Jan 27, 2011

This is the gauge arrangement I made up - should allow you to test most things including the fuel pressure retention time after switching off (for hot start issues).
The gauge is 100 psi and the other hoses rated accordingly.
Hope this helps . . .
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PaulHere · Jan 27, 2011

ORIGINAL: tref

Not sure about when it will be released on an unsuspecting public! At the moment, it is fitted out with the bare minimum to pass the MOT. As there is no centre console (still looking for a linen side carpet) it took me ages to find the foglight switch in the tangle of wires! The doors are bare baring the required internal door handle, and most important, no hood. nevertheless, it's good to feel it is progressing again.

Must be time for another installment from you for the 924 column in PP eh? [

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tref · Feb 28, 2011

Thanks for the mention in this months PP Paul! I have to hope this proves useful to some-one else now! I do indeed have plenty of material for another article or six, I just haven't had a chance to write them.
Currently progress with getting this beasty running right is hampered... hampered because I assumed(fool!) that the thread for the fuel distributor to WUR was M10 x 1... so a week away from home making an adapter was wasted... as I came back to the car to find it is actually M8 x 1... so another week away, hopefully when I get to have a look at it next I will have the copper washers that I forgot all about too!

One other point that has only just dawned on me really... the car stood in a field six years before we got hold of it... and this saga has been running for what? 4 years? So it must be ten years since it was last properly driven.

tref · Mar 5, 2011

News!

I have at last been able to get a pressure gauge on the car! Fuel pressure, running is 5.1 Bar... sounds a tad high to me. I couldn't run it for very long as it is in an unventilated garage. pressure remained the same irrespective of valve open/valve closed, but then I guess since it is cold it probably would.
On stopping the engine pressure drops to 2.1Bar. Haven't looked to see how long it maintains this pressure for, but I suspect that would just be to do with starting, which at the moment, isn't a problem.

Any comment welcomed! Hopefully tomorrow I can get it up to temperature and see if the pressure drops/warm up regulator is doing anything.

Regards,

Tref.

tref · Mar 6, 2011

OK, I have run it up to temperature now... and no change in the fuel presure... does kind of suggest the warm up regulator isn't doing anything doesn't it?

Anyone have one spare?

Regards,

Tref.

tref · Mar 18, 2011

I have measured the resistance of both the WUR on the car, and a spare one (of unknown quality) I have. Both read 45-46ohms,so I am assuming both are ok heater wise...
So, I assume from that, if it is a problem with the warm up regulator, it is a mechanical one?

tref · Mar 18, 2011

OK... I have found something!

Looking at the vacuum connection to the Warm Up Regulator - Now please correct me if I am wrong, but this goes from the Warm Up Regulator to the hard pipe from the throttle butterfly to the turbo. Since I believe it is used to enrich the mixture during accelation (low vacuum), it would seem logical - it would also seem logical that if this was leaking, it would enrich the mixture too - the problem I have.
That all seems as it should be. I guess I should be pleased!

However... whilst looking at this I discover I have another loose vacuum pipe, floating in the breeze around the Warm Up Regualtor, with no obvious place to connect it...
It is tee-ed off the vacuum line which runs from the front of the inlet manifold plenum, to a connection on that big black cylinder-like thing at the back of the inlet manifold. Anyone any idea what it should be connected to?

Afraid there is no chance of taking a photo to show it, it really is buried in the depths of the spagetti that is at the back of the inlet manfold.