Emissions Problem

[danhay]

My dad's car failed it's emission test in the MOT due to High Hydrocarbons (1400ppm) which I guess would suggest it was running rich? However the CO was within range (0.17%) which would suggest the fueling is OK?
Is the CAT knackered?

[deltaf]

What car? how old? mileage? etc etc?

Really the co% would be almost zero if the cat was ok.
Oil past the rings perhaps?

[danhay]

It's a dual fuel Cavlier V6 with 67k miles.

I thought about the oil, but it's not at all smoky?

[nighthawk]

whoooooooa

have the testing station tested this thing right?

what fuel was the car running on when it was presented for test?

also, propane Hc's are different from hexane, so the tester needs to perform a calculation to assertain the correct Hc reading.

the conversion factor should be on a label somewhere on the gas tester.

High Hc's on a petrol car indicate unburnt fuel, if the hc's were that high, and the Co% is within spec, i'd suspect an ignition fault and a very very effeceint cat.

[danhay]

nighthawk said:

whoooooooa have the testing station tested this thing right? what fuel was the car running on when it was presented for test? also, propane Hc's are different from hexane, so the tester needs to perform a calculation to assertain the correct Hc reading. the conversion factor should be on a label somewhere on the gas tester. High Hc's on a petrol car indicate unburnt fuel, if the hc's were that high, and the Co% is within spec, i'd suspect an ignition fault and a very very effeceint cat.

Thanks.
I think you may be right about the conversion factor? I wasn't aware there was one, though it doesn't surprise me. The original test was on LPG ,but they retested it on petrol and it passed. Although only because the engine wasn't in their book, so they used default (and fairly lax) allowances...so they said.

>> Edited by danhay on Wednesday 31st March 20:33

[nighthawk]

I've come across this before on mondeo and focus LPG variants.

you need to know the PEF (propane/hexane equivalancy factor for the gas analyser being used.
As I said, it's on the machine somewhere. iirc a few vosa approved machines have an automatic facility for doing the conversion.
But it won't be of any help if the vehicle is running on LPG and the tester tells the machine it's on petrol.

still, it looks like you have 12months before you lock horns again on the matter.

[kayble]

HI

realise this topic has been left for a very long time but I hope there's still someone watching it!

Basically I think I have the problem you have described above. Firstly a spec of the car and lpg conversion:

Engine:
Vauxhall Senator 3.0 12V, Bosch block injection feul management system, engine code: C30NE

LPG system:
OMVL open loop inductuion based system with single venturi mixer

Tank:
Stakko 80ltr torpedo tank mounted over back axle in boot

Injector emulator:
Pitagoria

The problem is that the emissions from the car are very bad on LPG versus petrol.

Gas emissions:
CO = 3.48%
Hc = 166 ppm

Petrol emissions:
CO = 0.69%
Hc = 100ppm


The exhaust gas analyser (Sun DGA 1800) was set to petrol on both runs. Having read the above post is it possilbe that having the EGA set to petrol will result in inacurrate readings for LPG? If so, why is this the case?

Thanks for any info,

John

EDIT: FYI, I have removed the cats.

>> Edited by kayble on Sunday 26th June 01:04

[Matthew-TMM]

My car had it's MOT recently, although it doesn't have a cat, and the CO was low and HC high, indicating a weak mixture. To the best of my knowledge, CO gives an indication as to how rich the mixture is as it is formed when combustion is incomplete (i.e not enough oxygen), although you'll always get a bit. More fuel=lower proportion of oxygen=more CO. However, the weaker it is, the higher the HC content (afraid I don't really have a good enough explanation for that). However, if the car originally had a cat. the mixture would be set up a bit weaker anyway, as the cat needs oxygen in the exhaust gases to be able to do it's job, so the mixture needs to be weak enough that not all of the oxygen is used.

Hope this helps.

[GreenV8S]

Matthew-TMM said:

To the best of my knowledge, CO gives an indication as to how rich the mixture is as it is formed when combustion is incomplete (i.e not enough oxygen), although you'll always get a bit. More fuel=lower proportion of oxygen=more CO. However, the weaker it is, the higher the HC content (afraid I don't really have a good enough explanation for that).

As I understand it, high CO indicates incomplete combustion i.e. the fuel has started to burn but the second phase of combustion (CO to CO2) hasn't occurred. High HC indicates that [some of] the fuel hasn't burnt at all. This could be because it is mega rich but could also be because of poor fuel/air distribution or an ignition fault.