Porsche 928 GTS emissions fail lambda high.

Ded_Zebra

My dads 928 failed the emissions on its NCT The readings were.

Lambda 1.24 (not between 0.97 and 1.03)

CO 0.00% _Pass

HC 15ppm _Pass

It has failed on high lambda for its last 2 NCTs (2010,2011) and was rectified both times by tightening exhaust fittings (they were leaking).

This year no leaks could be found in the exhaust and it failed its retest yesterday (same readings).

So my question is what else could cause high lambda and how car it be confirmed and rectified?

Thanks in advance.

Nissan doctor

A high lambda reading with perfect HC and CO readings is always a sign of a leaking exhaust. What way has the exhaust been checked?

Ded_Zebra

It has been visually inspected on a ramp by fast fit or one of those places. How else can you find a leak?

Nissan doctor

Ded_Zebra wrote: »

It has been visually inspected on a ramp by fast fit or one of those places. How else can you find a leak?

Block the end of the exhaust and listen along the system for leaks. It may even be up around the manifold.

Ded_Zebra

I have been trying that all morning and can't hear anything. I think it might be because the car is loud. It also makes no difference to the engine note when I cover either the right or the left tail pipe. It's not helping that I've got man flu .

Thanks for your help, I hope you have one more trick up your sleeve

mathepac

If the car has > 50k miles or has an oiled air filter (K&N or similar) it might be the MAF, usually the heated titanium sensor wires give up the ghost first. They normally run at 200C but will sometimes spike to 1,000C to burn off contaminents.

or it might be as simple as a poor electrical connection to the MAF which can be corrected by applying a conductive grease to the pins in the externally attached plug. The leads from the MAF go to the LH ECU to govern fuel / air mixture.

Any other symptoms like rough running, high fuel consumption, poor starting, etc?

Ded_Zebra

mathepac wrote: »

If the car has > 50k miles or has an oiled air filter (K&N or similar) it might be the MAF, usually the heated titanium sensor wires give up the ghost first. They normally run at 200C but will sometimes spike to 1,000C to burn off contaminents.

or it might be as simple as a poor electrical connection to the MAF which can be corrected by applying a conductive grease to the pins in the externally attached plug. The leads from the MAF go to the LH ECU to govern fuel / air mixture.

Any other symptoms like rough running, high fuel consumption, poor starting, etc?

The car has a standard paper element air filter. I think it has 76000 miles on it or there about. The car is running very well, starting sometimes isn't fantastic but that is due to a weak battery. Fuel consumption is the same old 22 to the gallon.

Ronnie Beck

A small piece of newspaper might help you find the leak

Ded_Zebra

Ronnie Beck wrote: »

A small piece of newspaper might help you find the leak

Thats idea is actually brilliant thanks

mickdw

Ded_Zebra wrote: »

Thats idea is actually brilliant thanks

I dont get it?

Ded_Zebra

mickdw wrote: »

I dont get it?

If the exhaust gas is escaping from a joint etc it'll make the piece of paper flutter.

Nissan doctor

IMO if there was a MAF issue then the HC's would be off.

I think if the exhaust leak was bad enough to make paper move then it would easily be felt by anyone checking the exhaust.

Ded_Zebra

OK so still no sucess. Is there such a thing as an exhaust gas detector?

Like the thing that you use to find AC leaks but for exhausts?

If it has twin exhaust could it be that it's drawing fresh air in from the second pipe when fitted with exhaust hose?

Ded_Zebra

samih wrote: »

If it has twin exhaust could it be that it's drawing fresh air in from the second pipe when fitted with exhaust hose?

Do you mean that there is no fault with the exhaust system and that the test equipment is causing the problem?

I think that this is unlikely as it passed before.....

nct tester

i've never seen a lambda reading that high that was caused by a leak in the exhaust that was hard to find. generally it should be fairly obvious to hear a blow in the exhaust when the reading goes above 1.07 or 1.08. the emissions are practically zero so it is running extremely lean. possibly oxygen sensor??

Ded_Zebra

nct tester wrote: »

i've never seen a lambda reading that high that was caused by a leak in the exhaust that was hard to find. generally it should be fairly obvious to hear a blow in the exhaust when the reading goes above 1.07 or 1.08. the emissions are practically zero so it is running extremely lean. possibly oxygen sensor??

Well I'm not an expert on fuel injection (the different systems how they work exactly etc) but I believe that the car uses an earlier system without O2 sensors but I am open to correction on that...

It definitely isn't preforming as if it is running lean (running smooth with good power and throttle response).

barneygumble99

what year is the car?

Ded_Zebra

1994

Nissan doctor

If its that late a GTS then it will have a cat and at least pre cat lambda's.

It is possible that there is a non exhaust related issue but it would almost impossible for this to be the case without certain running issues.

Looking again at your CO reading at 0.00 so you may well be running very lean as a reading of no CO whatsoever would be very difficult, even for a brand new modern engine.

If you rev the engine hard(when hot of course) is there any black/brown smoke at all?

Ded_Zebra

Ded_Zebra wrote: »

Do you mean that there is no fault with the exhaust system and that the test equipment is causing the problem?

I think that this is unlikely as it passed before.....

Maybe in the previous years they didn't use a suction hose and they did now?

To rule out the the other branch being the problem you'd need to fully block the second tip before taking reading from the first one.

You said previously that blocking one of the branches didn't affect idle at any way which makes it sound like the two branches are interconnected and therefore suction could draw fresh air in the unused branch. That would also help with the 0.00 CO value.

Ded_Zebra

Nissan doctor wrote: »

If its that late a GTS then it will have a cat and at least pre cat lambda's.

It is possible that there is a non exhaust related issue but it would almost impossible for this to be the case without certain running issues.

Looking again at your CO reading at 0.00 so you may well be running very lean as a reading of no CO whatsoever would be very difficult, even for a brand new modern engine.

If you rev the engine hard(when hot of course) is there any black/brown smoke at all?

I really don't think its runnig lean from how it runs and the colour of the plugs etc.
Never noticed any smoke at all....

samih wrote: »

Maybe in the previous years they didn't use a suction hose and they did now?

To rule out the the other branch being the problem you'd need to fully block the second tip before taking reading from the first one.

You said previously that blocking one of the branches didn't affect idle at any way which makes it sound like the two branches are interconnected and therefore suction could draw fresh air in the unused branch. That would also help with the 0.00 CO value.

Does the NCT use suction Things? this is interesting because the two pipes are connected. So should they block one pipe and test the other?

Thaks everyone for their help so far it's really appriciated.

nct tester

only exhaust fume extractors are held the back of the car, and ive never come across a car with twin exhausts that are connected, either having different readings or for the readings of one exhaust to be affected by the other. hope this makes sense.

Nissan doctor

nct tester wrote: »

only exhaust fume extractors are held the back of the car, and ive never come across a car with twin exhausts that are connected, either having different readings or for the readings of one exhaust to be affected by the other. hope this makes sense.

Almost all factory fitted twin exhaust systems are connected for reasons of ease of mapping an pressure equalisation.

Ded_Zebra

well these are definitely connected. do you think the tester just didn't block one of them off?

nct tester

Nissan doctor wrote: »

Almost all factory fitted twin exhaust systems are connected for reasons of ease of mapping an pressure equalisation.

i didnt really explain myself properly. what i meant was that when a car comes in with dual exhausts that are connected , then the readings out of both pipes are generally the same. one pipe does not affect the other one.

OP, did you ever get this sorted out?

Ded_Zebra

samih wrote: »

OP, did you ever get this sorted out?

Not yet unfortunately as far as I know but it was in with some Porsche specialists who's name escapes me now on Monday. I haven't talked to my dad since but I assume he has it back now fixed or not. I'll find out and post back tomorrow.

Ded_Zebra

ok so the story it's still with oph (the Porsche garage) they put in some magic potion stuff in the fuel and are going to run it through the NCT re-test. They are fairly optimistic that it

will sort it but i'm not too sure myself.

They should get a test slot next week so we'll find out then.

enumbers

Ded_Zebra wrote: »

ok so the story it's still with oph (the Porsche garage) they put in some magic potion stuff in the fuel and are going to run it through the NCT re-test. They are fairly optimistic that it

will sort it but i'm not too sure myself.

They should get a test slot next week so we'll find out then.

I would love to know what snake oil they put in that will fix a lean indication. I have never seen a reading of this far with out a leak or faulty testing