phil.s

Hi all. I've been messing around with my techtom mdm100 and if I monitor the 'O2' it keeps flicking between lean and rich on tickover (spends more time on lean) but on boost stays on lean until I lift off then it reads rich. First of all I checked the spark plugs and they are brown - is this OK?

Also been monitoring the o2 sensor voltage and it flicks between 0.08 (techtom says rich) up to 0.58 volts (techtom says lean) at tickover (825rpm). On boost the voltage is anwhere between 0.90 and drops to about 0.66 higher up the rev range but techtom stays on lean.

Done a lot of reading up on this but thats just made me more confused. Does anybody know what voltages I should be seeing here and how the techtom works out if its lean or rich because based on those voltages is seems to me its working backwards?

'97 type ra btw standard bar air filter and FMIC

cheers
Phil

Geordie_Aaron

iTrader: (3)

dont you need a wideband to measure true AFR?
Maybe wrong

phil.s

Yes but ignoring the actual AFR, if you look at the lambda voltages I'm seeing then as far as I gather lower voltage = lean, my techtom says rich! Maybe I'm wrong just wondered if anyone else had one as a comparison.

marcevs72

iTrader: (5)

i have same techtom in my 93 wrx and good bit of kit.mine reads the same voltages as you but reads lean on tickover and as soon as i start coming on boost reads rich.
when i used fuel additive it turned my plugs brown but since last service just run on 99 momentum and plugs light brown colour after 2k.

JTinnovations

iTrader: (2)

Generally, narrow band lambda's produce a low voltage (100mV-ish) when lean, and a higher voltage (800mV-ish) when rich. The voltage swings rapidly between rich and lean - it's more-or-less binary, and any voltage in between is pretty much meaningless.

I think a wideband generally works the other way round - lower voltage is rich, and higher is lean. I wonder if either your techtom has been configured for a wideband rather than narrow band...or, indeed, you have a wideband sensor fitted and didn't realise?

I'm not familiar enough with classics to know what sort of lambda was fitted as standard, but I imagine it's easy enough to find out.

Are you monitoring the standard Lambda, or have you had a dedicated one fitted for the techtom?

phil.s

I'm pretty sure you cant configure the techtom, not 100% sure tho. Its the standard lambda and standard ECU, dont think it has a wideband fitted tbh.

marcevs72 your posts came up in my search and the voltages you had were pretty much what I had but like I say my techtom reads opposite. Thats why I got confused! So when yours is idling and drops to 0.1v does it say rich or lean? And what about 0.6v? Thought I'd check my plugs and they are a rusty brown because of the octane booster. Did you do anything to yours in the end to stop the odd readings?

marcevs72

iTrader: (5)

mine reads lean at tickover and rich as soon as i accelerate.mine gave funny readings a while back but put new lambda in and fine since

harvey

iTrader: (48)

It would be prudent to have your AFRs checked properly and you can can compare the readings your equipment gives.
Fitting an efficient FMIC without a remap can cause weak AFRs.
In closed loop lambda the ECU is always trying to achieve lambda 1 so the reading will alternate from rich to weak and back to weak again and so on as the ECU controls the fueling and cycles to a weak position then adds fuel at a point that is too weak and so on.