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would this work (lambda sensoe related)

theconrodkid - 19/10/15 at 04:45 PM

My trusty mobile hair dressing salon "nearly" failed his MOT last year due to emmisions.
i have checked all the usual stuff,new temp and lambda sensors,plugs look ok but he do like a drink .
i was thinking,as the lambda sends out a voltage around 0.5 v for normal mixture and if richer a higher v to tell the ecu to cut the injector duration down,could i install a rheostat in the lambda sensor wire (single wire),feeding it with 12v or even a 1.5 v battery to fool the ecu and hence the MOT testing machine ?.

adithorp - 19/10/15 at 05:28 PM

Short answer... No.

britishtrident - 19/10/15 at 05:38 PM

No , no and thrice no! they don't work that way, when everything is working properly the voltage ouput on standard lambda sensor should "switch" between about 0.2 and 0.8 volts about 3 times per second, the PCM continuously monitors this and will flag up a code within a mile or so if it doesn't see the output voltage change through the 0.5v mid point enough times per second.

Fitting new parts at random is like pouring money down the drain.

If the car is obdII connect a scan tool check the IM Readiness Monitors, scan for codes and look at the live data to give you a hint what might be wrong.

CC Cyclone - 19/10/15 at 05:43 PM

No, but you might get a job in VW R&D department with thinking like that

britishtrident - 19/10/15 at 05:55 PM

If you have an Android phone those very cheap bluetooth OBDII dongles off ebay are hit or miss but they usually work buy one and load the Torque or the OBD Car Doctor Pro-app or get a hand held scanner such as a cheap Autel AL319 off ebay.

With these devices apart from showing and clearing fault codes show live date and the results of the I/M monitor readiness tests.
Any engine that has a green all the applicable I/M readiness checks is very unlikely to fail on emmissions.

theconrodkid - 19/10/15 at 06:08 PM

oh well car is too old for OBD (1991) so no warning lights to worry about,it is just for the 5 mins or so that the emmisions test takes.....as for working for VW...

big_wasa - 19/10/15 at 07:06 PM

ive seen a product called cataclean work well for mot's I don't know if its because it burns hotter or something else but I have used it on my dads car a couple of times at mot time.

britishtrident - 19/10/15 at 07:12 PM

The moment you interfere with any of the sensor signals the PCM will go into open loop on the default fueling map.
Whatever you do to the signal from the lambda senors it can only make emissions worse, the cat only works switching high and low

[Edited on 19/10/15 by britishtrident]

britishtrident - 19/10/15 at 07:16 PM

quote:
Originally posted by big_wasa
ive seen a product called cataclean work well for mot's I don't know if its because it burns hotter or something else but I have used it on my dads car a couple of times at mot time.

You can actually physically wash cats and get a considerable improvement in effectiveness but life is too short.

Oddified - 19/10/15 at 07:24 PM

What vehicle is it?, most ecu's from 1991 weren't all that smart and some can be 'fudged' a bit

Ian

theconrodkid - 19/10/15 at 07:33 PM

oddified, It,s a 1991 mazda eunos,as an import it dont need a cat (3.5%co) but the measurment was well above that according to the tester.i dont have a cat at the mo,just an empty shell and dont want to splash out on one as i would prob die as it,s running rich.
tried all the usual stuff but as i dont have a co meter now i have no way of checking the emmisions.

Irony - 19/10/15 at 08:14 PM

I have a co meter. Where are you?

theconrodkid - 19/10/15 at 08:47 PM

Irony...sunny Somerset i am afraid

britishtrident - 19/10/15 at 09:04 PM

quote:
Originally posted by theconrodkid
oddified, It,s a 1991 mazda eunos,as an import it dont need a cat (3.5%co) but the measurment was well above that according to the tester.i dont have a cat at the mo,just an empty shell and dont want to splash out on one as i would prob die as it,s running rich.
tried all the usual stuff but as i dont have a co meter now i have no way of checking the emmisions.

Mazda at 1991 should be OBD1 in which case it likely produce blink codes by jumping pins on the diagnostic connector.
The MIL not illuminating (unless the bulb has been pulled) suggest engine is not going closed loop . I would also spend a bit of time check the wiring between the sensors and the PCM.

You should also check the Lambda sensor heater circuit and read the lambda sensor output with a DMM.

It could be down to ther things like MAP or Throttle Position Sensor that can can be found with a bit of time with a multimeter,

theconrodkid - 19/10/15 at 09:19 PM

yup,blink codes is mentioned in the book of lies,ill have a look at that,it,s a single wire sensor so no heater.
looks like ill be bust with my ohm,s meter morra

cliftyhanger - 20/10/15 at 05:42 AM

Has anybody mentioned temp sender? Not sure if there are 2 on the car, but if the dedicated ECU one is giving a duff reading you may be getting cold start enrichment (choke to people with old cars)? could be a simple fix. In fact WHEN you find the fault, whatever it is, it will be simple. Always is!

theconrodkid - 20/10/15 at 07:40 AM

temp sensor was duff and replaced about 12 months ago,car went better afterwards so i could check that again but it,s a pain to get to

ianm67 - 20/10/15 at 10:52 AM

quote:
Originally posted by theconrodkid
oddified, It,s a 1991 mazda eunos,as an import it dont need a cat (3.5%co) but the measurment was well above that according to the tester.i dont have a cat at the mo,just an empty shell and dont want to splash out on one as i would prob die as it,s running rich.
tried all the usual stuff but as i dont have a co meter now i have no way of checking the emmisions.

Cheap cat for sale on eBay at the moment (NTDWM)...... Item number 231724704085
HTH,
IanM

theconrodkid - 20/10/15 at 11:38 AM

Thanks Ian,ill keep an eye on it

Mr Whippy - 20/10/15 at 12:08 PM

quote:
Originally posted by big_wasa
ive seen a product called cataclean work well for mot's I don't know if its because it burns hotter or something else but I have used it on my dads car a couple of times at mot time.

Used this and does work but if your cat is completely stuffed it can't perform magic. Given the age and emission requirements you shouldn't need one tbh and there must be an underlining issue with the engine, perhaps worn valve seats or valve stem seals. I'm running a 1989 jap carb engine and the emissions are excellent.

907 - 20/10/15 at 12:12 PM

My D in L's has no cat and has flown through emissions tests for the last 6 years.

Sedately driven to work through the week and thrashed round tracks at the weekend.

Paul G

MX5 at Snetty

theconrodkid - 20/10/15 at 02:40 PM

hc,s are low and he dont burn any oil so assume the engine is good ,it,s just the emmisions.
short of a lot of messing about in the dark to get the numbers down all i want is him to pass another MOT.