Help - MOT failure due to emissions

[Brian King]

My GTi 4x4 has just slunk away from the MOT registering 9 instead of 3 on the CO reading. My local Citroen expert says he cannot adjust the Bosch jetronic unit, and the vacuum advance & retard doesn't work. Has anyone got a Jetronic unit and distributor known to be working? If I get it this week I save another test fee, so money waiting !

[jeremy]

If I didn't know better I'd say the tester had left the choke out - which may be the clue as to what's wrong - its quite common for the temperature sensor to fail - which means that the thing continues to fuel for a cold engine.

If you search this and other similar forums you will find that strangely ECU's don't give problems unless they have been damaged by abuse or misfortune and that problems generally are due to external factors - the problem being finding which one.

I think if you search here or on the Frenchcarforum some time ago (like 3 years or so) there are the resistance figures for these sensors. What I do not know is if it increases or decreases as temperature rises and what the consequences of open circuit are. I do know that some people tinker with them or this circuit to increase the mixture strength by fooling the system into thinking it hasn't warmed up fully and so deliverer a richer mixture. I suppose this means that the resistance drops as the temperature rises.

The workshop manual (and other info) for at least the 16 valve is here:

http://www.rwbsmith.plus.com/citroen2

[Barnsley BXer]

If I didn't know better I'd say the tester had left the choke out -

Obviously you don't know any better,the 4x4 hasn't got a choke(or at least mine hasn't)

[MULLEY]

I thought all 4x4's were injection 1.9 petrols????

[jeremy]

I think some 4 x 4's were carb 1.9's and some were diesels.

I'm fully aware that a GTi won't have a choke control - the point I was making was that such a high reading would be consistent with a cold start device remaining on - which would be much the same as not pushing in a choke.

[docchevron]

As such there is no cold start device, the ECU takes into account several factors and works from it's own mapped memory.

As it goes Jetronic is very simple, the mixture is controlled by the injector duration.

Something is VERY wrong if it's reading 9 though. Even if the coolant temp sensor had given up the ECU would revert to program settings or "limp home", and the K light should be on. Have you got access to a fault code reader?? and does the K light work? If so, is it on? Cos running THAT rich, it bl**dy should be!

Are you about any morning this week? If so I could pop by and wham my fault code reader on it if you like, after all, if the ECU will tell you whats wrong, it's easier than chasing unknown possible faults.

[Barnsley BXer]

I think some 4 x 4's were carb 1.9's and some were diesels.

I'm fully aware that a GTi won't have a choke control - the point I was making was that such a high reading would be consistent with a cold start device remaining on - which would be much the same as not pushing in a choke.

All hatches were injection,estates were carbs.No diesels(at least,not in the UK)

[Brian King]

Thank you everybody. It is a 1.9 GTi XU9J2 D6A engine. Bosch jetronic fuel injection so no manual choke. I am checking the exact figure it gave for CO2 since your comments have made me doubt it ! The funny thing is it starts and runs fine.

Doc chevron - I can be at home every morning this week if you would like to visit with your stethoscope. Coffee, bacon rolls, whatever !

[jeremy]

Its not quite clear from Haynes which fuel injection system your car has. It seems D6A (XU9J2) engines were up to 1991 and LE3 Jetronic was fitted to July 1990, with Motronic MP3.1 from July 1990.

The LE system looks simple - with a water temperature sensor in the front of the block (square) and an idle supplementary air control which is adjustable and a flowmeter under the ECU in the air supply near the battery.

You mention the distributor. It can fail in 3 basic ways assuming its cap and rotor arm are sound - bearing (obvious if you shake it), centrifugal weights which are inactive at idle and could seize at either end of the travel (may respond to lubrication) and the vacuum unit which will function at idle and is dependent on sound piping and a sound diaphragm. The vacuum unit may be mounted with the coil - as used by Renault.

A dirty exhaust could confuse things (only likely if the car hasn't been warmed through recently) as could excessive oil consumption but I'd have thought both of these would have shown as hydrocarbons.

[Brian King]

I've just checked with the MOT station. He says my car was between 7 and 8 on the Richter scale.
Thanks for the advice, men. However the shortest cut seems to be for me to buy a distributor and jetronic box which are known to be working. Any out there?

[docchevron]

I really cant see ignition timing or advance causing the emissions to be THAT high..
Even if the ECU reverted to programed settings I cant see the emissions being above 5 or so.

PM me your address mate and I'll try and pop up tomorrow, although it's more likely to be Thursday.

[docchevron]

although he has another Motronic box to try, if the emissions are that high then I reckon that the valve stem oils seals are shot, and it's leaking oil into the combustion chambers to get a reading that high. Very typical of the XU petrol 16/19.

Agree or disagree?

Er, I thought it was jetronic??? Infact I would have thought it would be Jetronic??
However, yes I agree, it is VERY common for the valve stem seals to give up, but Brian hasn't mentioned clouds of blue smoke from the exhaust, and frankly a reading THAT high, I would expect there to be ALOT of blue smoke! Although it might make sense actually, since even on base settings it shouldn't be running that rich, but.... I would expect the plugs to be oily as fcuk really....

The vacuum advance issue on the dizzy, we used to see a few 19GTi's with this problem when I worked at Citroen during mid nineties, we used to replace the (Bosch) dizzy with a new one in those days, although now I admit a good s/hand one is probably the only option. The worn dizzy fault does not manifest itself in high emissions though, what you get with that fault is terrible holdback and hesitancy when accelerating hard.

Yep, I've seen this alot, and if the advance is FUBAR then yeah, a good secondhand one is the way forward, but it should still pass an MOT without vacuum advance without issue. I'm having a ganders on Thursday so I'll see what can be assertained.

[Brian King]

It's Jetronic. Appreciate the common-sense advice that the distributor advance/retard has nothing to do with the emissions - Doh - so I'll concentrate on the jetronic probs. US cavalry arriving Thursday in the shape of Docchevron. No smoke from the exhaust by the way.

However, I will still need to replace the distributor (or can I fit a good vacuum unit to my existing one?) and would be grateful for any offers.

[jeremy]

You can usually replace the vacuum unit on its own. You may be able to find a specialist supplier on the internet.

The unit on the GTi is an advance unit - providing 9 to 11 degrees advance at 395mmHg. The advance commences at 60/120mmHg and apparently is measured in distributor degrees rather than flywheel - so in terms of normal engine timing the figure should be doubled.

I think it may well operate at idle. With the throttle open (ie acceleration) the manifold depression is at its lowest, on the overrun its at its greatest - and I think its considerable at idle. (old Fords were fitted with vacuum powered wipers which would'nt work on acceleration but went berserk when stationary when the weren't needed)