172 emissions failure

[Ev__]

Hi all,

Your help on this one would be greatly appreciated.

My mk1 172 failed its MOT on emissions today - high CO and high lambda at idle, apparently, with the suspicion being that its constantly using choke.

The dealer claims to be running out of options. Its had a new oxygen sensor and air filter, and the cambelt has been done (so the timing should be right).

Theyre now talking about possible internal engine damage (burnt valves, damaged cam) with *huge* bills for inspection. Needless to say, I have removed the car from their custody.

The car runs without any suggestion of a fault or damage, by the way.

Has anyone experienced anything similar or got any suggestions?

The values of the emissions report are as follows:

rpm Speed: 0790
degC oil temp: 21

%vol CO: 0.62 <<<<
%vol COcorr: 0.70
%vol CO2: 12.6
%vol O2: 3.51
ppm vol HC: 0498
Lambda: 1.140 <<<<<

(Anyone know what the limits are for a 2001 172?)

 

[davep24]

dont know the limits, but your oil temperature is very low, should be around 80ºC so i think they might have tested it with the engine cold, so its no wonder that its failed.



What mpg are u getting, because if its constantly on the "choke" then it will be crap

 

[Ev__]

I didnt want to prompt anyone, but I noticed that low temp too. Not sure if thats accurate or not, though.

mpg seems very reasonable: 25+ for my short, slow commute, 40+ for long, steady journeys.

 

[Mole]

take it elsewhere, and get another MOT garage to test it.

But before doing so, make sure you go for a thrash to warm the car and oil up properly.

high lambda is usually caused by the mixture being either too lean (i doubt) or the exhaust has a hole in it, or clamps arent done up tight enough

if CO fails, the Lambda reading is high and the O2 reading is high (0.5 to 1.5%) the catalytic converter could be faulty.

youd usually notice about the catalytic converter as it would smell eggy, and no doubt the material inside the converter wouldve broken up, so youd hear it

[Edited by Mole on 7/28/2005 10:18:45 PM]

I doubt your catalytic converter has gone as the 172 has dual lambda sensors (i do believe) which check the gasses before and after the cat, and youd get a light up on the dash saying that the emissions are too high

 

[Ev__]

Well waddayaknow? Took it to the garage at the end of my street and it passed first time. Absolutely borderline, admittedly, but a pass nevertheless, with CO emissions more than halved.

My suspicion, which I tried not to distract you with yesterday, may well have been correct. I think the MOT regs say you should allow the engine to run for at least three minutes before performing the idle test, yet the oil temp on the Renault dealers slip was a suspiciously low 21 deg C. It looks like they started the engine from cold (theyd had the car overnight) and stuffed the probe straight in. No time for the cat to warm up, and no time for the engine was to switch from its "just started" mapping to its "warmed up" one.

So thats another Renault dealer off my list. In fact, I think Ill stay away from them all from now on. Best to let them concentrate on changing pollen filters in six-month-old Scenics.

Cheers for the suggestions, guys.

 

[Chris&Amber]

report them to VOSA, its illegal to perform an emmisions test without the oil temp being 60 degrees.