I have just had the terrifying experience of my local MOT Station offering to "adjust"(!) my CO2 as it had just failed the MOT for being way to high...

 

The thought of someone not familiar with the ZX tweaking things at random to get the CO down makes me shudder!

 

BUT the question is who can I turn to and whats the best course of action for me to take?!

 

I have an imported 92 Auto which is pretty standard (has a mild aftermarket exhaust), but (and heres the interesting part) the ceramic of the Cats has been removed. Judging by the evidence of dents and scraps I can only presume that they have been smashed and departed the exhaust out the back over time.

 

Can this have any effect on my problem? I thought the O2 sensors were directly in the down pipe (hence before the cats) and, whilst the no cats will obviously have some effect on the CO2, mine is like 7.5%!

 

Both banks of the engine are the similar in the CO2.

 

When fitting a new exhaust that removes the cats be design, does this have this sort of effect?

 

Is there anything I should try before handing over a mountain of cash to my local Nissan dealer?!

 

Any suggestions greatfully recieved!

 

M

There is a tube you can pull out in the engine bay that solves all your problems. Remember to plug it back in when you finished though.

 

Forget which tube it is, but I am sure some one will tell you.

 

Stuart

tadaaa

 

http://300zx-twinturbo.com/tech/co/co.html

I doubt if the cats just broke up and exited the back.

It's common for people to have the car de-catted by taking the section of pipe out and gutting it to give more power.

Cheaper than buying a cat replacement section.

Probably the previous owner.

Has it got the standard air filter fitted or an aftermarket unit?

Thanks guys!

 

Ill pull the tube and see what happens!

 

In response to ChrisC the rest of the car is, to my knowledge, standard. Unfortuneately I cant seem to find any insurance company that will allow me to do anything to the car as it is an import....GRRR...! Dont start me off on insurance companies...!

 

Do you think that a better air filter will flow more air and therefore weaken out the mixture? Can you recomend one?!

 

I also think it is probably due a service...which of course will help...

 

Cheers again!

Mark, with Co2 so high it is fairly likely that both O2 sensors have gone bad, do a mode II test to see if they are switching or static, my guess is they are stuffed failing that a very blocked filter?? even after market types if you have them can be a worry, these cars been typically Japanese should be lean on tickover, if you need any help with how to do a mode II test ring me an can talk you through it as you do it, some kind soul here my have a link to it somewhere.

 

Jeff TT

 

07974 051196

My import is insured with A-Plan (0845 0711234) and I have loads of mods declared.

They were also very cheap.

My full body kit and new wheels have only added £80, also got ECU, exhaust, intake, brakes declared and I'm paying about £750 I think fully comp with 6 points on my licence.

 

Fitting a new intake might not help the CO2 problem but with a de-caff exhaust it will give you a bit more power :D

couple of points:

 

1, CO2 (carbon dioxide) is not part of any mot test - its CO (carbon monoxide) - picky bit out of the way.

 

2, the 300zx is not in the database of my gas analyzer at work, nor is it in the emissions book provided by the ministry, meaning that you do a NON cat test.

 

what have they tested the car as?? cos unless its a 95 car onwards (default cat test) you must have an EXACT match in the database to test it against.

 

you can check the o2 sensors are working by going into mode 2 of the ecu diagnostic mode.

 

hth

shit - scrap that just seen its 7.5% you posted - too high to pass a non cat test anyway :o sorry!!

 

it IS CO the're looking at & NOT CO2, isnt it??????????????

ht. The data sheet in front of me from the MOT station says CO 3.97%, C02 7.19%, HC 277ppm, O2 7.05%.

 

I only have one set of results (they had one for each exhaust but claimed that both sides were high.

 

When he was explaining it had failed he DEFINATELY pointed at the C02 being high...I trust this garage (been going years blah blah - so they wouldnt try to stich me up on purpose)..but they might be idiots!

 

He also said he was testing it as Non Cat - its 92 so pre dates the Req.

 

But no matter!

 

If its the CO thats high do all the comments about the O2 sensors being bad still stand? Ill do a diag test and see what is says....

 

And ChrisC - thats a lot of car for not a lot of insurance premium! Damn! Every insurer I contact seems to laugh at me then the phone goes dead...! Especially as its an import.... Im 29, clean licence had the car for 3 years...etc etc etc I might just give them a call!

 

We really should have a section on the site for decent insurers, and tell them that they are being posted as good companies to do business with...might get a good group rate etc etc.

ok, co must be below 3.5% - it is poss its been decatted.

 

anyway, an avarage must be taken, so both sides must be tested then the results added together then halved.

 

CO2 is NOT part of the MOT!!

Vijay is trying to sort out club insurance for us so we're already on with that.

 

A-Plan are really helpfull and that number is for their import only division so you won't get messed about - they don't do UK spec at that office! :D

 

They seem very flexible and actually know about cars and mods and don't seem too fussed - obviously the price goes up but I've called them each time before doing anything major and they have not queried any of it.

 

When I was moving house they covered me at both addresses while all the other companies I called said they would have to re-quote after I moved and they couldn't tell me how much it might be until afterwards. Sounded to me like they would just put the price up even though it was a better area.

 

A-Plan reduced it by £300 2 months before I moved to the better area!

Got my past 3 emmission test results to hand so here goes :-

 

 

-------Limit -- 2000 --- 2001 --- 2002

CO ---- 3.5 --- 0.4 ---- 0.02 --- 0.79 --------- %age

HC --- 1200 --- 148 ---- 104 ---- 127 ---------- ppm = parts per million

 

Each of these are non-cat tests (as they should be) done at the same garage on the same machine and for the 2002 test the car had actually been de-catted. Also, I have no precats, never have, but I some cars will have them. So the conclusions that can be drawn are :-

1) I lost the piece of paper for 1999 test

2) Removing the cats does appear to increase the amount of carbon monoxide

3) Removing the cats makes naff all difference to the HC reading

4) I've forgotton what HC stands for (Doh!) - Paul C ???

Originally posted by AndyP

4) I've forgotton what HC stands for (Doh!) - Paul C ???

 

No that would be PC, surely? :)

Hydrocarbons, maybe?

Originally posted by Gio

No that would be PC, surely? :)

Hydrocarbons, maybe?

 

Ho hum !

 

 

Well I thought about that but it didn't seem right ..... could be through ...

After the car was warmed up and hadn't been sitting cold before the test for too long.

 

Although 7.5 is very very high, I dunno what you should get on warm up.... I would also suggest the o2 test... remeber to stay at the correct revs on a warm o2 sensor (like the tests suggest) or it will show a failure

Oooh looky here http://www.motuk.co.uk/manual_730.htm

 

This claims to be a site which has the MOT structure / pass / fail etc.

 

Can any MOT tester confirm whether this is correct? If so it would be useful for us to check on MOT stuff.

 

If its right it looks as if HC is Hydrocarbons.

yup, HC = hydrocarbons (unburnt fuel)

 

everyone ignore the 7.5% co2!!! its the 3.97% co which its failed on!! which is still high but not quite so crazy as 7.5% !:rolleyes:

 

the first thing to check is the o2 sensors are working still & no faults in ecu. poss temp sensor if it thinks its too cold still.

gio - that site looks like its directly out of the testers guide, so yes it seems to be accurate.

 

btw, im a mot tester. :D

That'll be a handy one for the reference links page when it arrives.

Right. The plot thickens!

 

I did the ECU test and the first time it passed fine - 55. I then did the O2 test as well for both sides and this was satis as well..

 

I then (stupdily) did another test and it told me the Det sensor was faulty! Doh! The o2 test passed again - so I did yet another test and the Det sensor failed again....

 

Soo....should I see the orange Engine warning light if the det sensor has gone tits, or does it just go into safety mode (wouldnt this put up the orange warning light anyway?) and does safety mode pump in gallons of fuel per second(!) to get the car home...

 

Too many questions! My head hurts...

 

Anyway back to more traditional car mechanics, I took out the air filters and they were pretty black. I will fit new ones, and carb clean the throttle bodies etc to see if this helps. Retest tomorrow - will let you know the out come!

 

My fuels consumption is pretty does seem pretty high - or is that just because I have been driving around in a desiel van for 3 weeks......?!

 

The mission continues.... !

The O2 sensor test only 'fails' if they are completely Donald Ducked or if the wiring to them is broken. What tends to happen is that they fail slowely and become 'sticky' in that they report a lean figure more than they should, the ECU then compensates by chucking more fuel in, still reports lean etc .... you get the idea.

A more reliable way to tell is by using a Consult/ConZult/Techtom and monitoring the voltage. I had exactly the same happen to one of mine and the only give away was that fuel consumption dropped from about 21 to 17mpg.

Yeah my fuel is seeming to dissapear a bit more rapidly than Id like!

 

I have just cleaned out the throttle bodies and (so far anyway!) the car drives MUCH better. no hesitation like there was.

 

There was loads of gunge in there as well - so well worth doing!

 

I guess I need a proper consult test done then.

 

Who can I turn to in S E Essex way who is reputable? My local dealer is a complete rip off and would have me change parts one at a time (usually starting with the most expensive!) until either everything had been changed(!) or they got lucky...

Mark,

 

If/when the detonation sensor 'fails' (which can also be a break in the wiring to it), the car will retard the ignition timing, and reduce the boost to the natural boost pressure of the actuator & wastegate system.

 

As far as I know, it does nothing to alter the fuel mixture.

 

SE are in Essex aren't they? But then, they are usually well booked up aren't they?

Originally posted by mark lupton

Yeah my fuel is seeming to dissapear a bit more rapidly than Id like!

 

I have just cleaned out the throttle bodies and (so far anyway!) the car drives MUCH better. no hesitation like there was.

 

There was loads of gunge in there as well - so well worth doing!

 

I guess I need a proper consult test done then.

 

Who can I turn to in S E Essex way who is reputable? My local dealer is a complete rip off and would have me change parts one at a time (usually starting with the most expensive!) until either everything had been changed(!) or they got lucky...

 

Mark,

I'm not that far away from you, near Great Dunmow, so if you drop in then we might be able to work out the cause of your problem.