AFR Question

The other day i noticed a light amount of black smoke during idle and the car kinda felt a little umsteady at idle. This would normally indicate to much fuel.

And my AFR avagrage it around 12. It should be about 14.4ish for a good ratio

This must be a slight overfueling issue.

I changed the coil packs as they were cracked and still the same

Could it be my wideband lambder sensor?

Thanks

i would thought not, as you say black smoke is indicative of a rich mixture and your wide band is also saying rich for idle.

was engine at normal temp? if so it should be in closed loop. and the stock ecu and o2 tries to keep the afr at about 14.7 to 1.

my first port of call would be the stock O2 sensor, then possibly too higher a fuel pressure but thats unlikely.

have a check on the vac/ pressure pipe on the fuel pressure regulator, if split it will raise fuel pressure at idle/ tick over, but the ecu can normally keep afr under control in that condition.

have you pulled the trouble codes to see if the ecu is not happy with something?

lets us know what the fault was/ is.

regards chris.

12's is about right for first start / fast idle

But if warm them its not right, this is all mapping stuff mate unless your syvecs uses the wideband for afr mapping witch it soundnt really,

Cant really diagnose that without knowing full set up, and circumstances of when it occurs.

12's is about right for first start / fast idle

But if warm them its not right, this is all mapping stuff mate unless your syvecs uses the wideband for afr mapping witch it soundnt really,

just a quick question, why not use a wideband instead of a narrow one?

regards chris

just a quick question, why not use a wideband instead of a narrow one?

 

regards chris

when i say for mapping i ment in the open loop state , being that it will try to make it richer in rev ranges in stead of the closed loop 14.7 , i know thats a poor description but i hope you understand my point

Yer even warm and been driving for a while its below 14 It always used to run 14. I'm on syvecs and single turbo.

I am not a tuner but does the syvecs use a o2 sensor for idle/tickover? (closed loop for idle) if not, then it could be a map sensor fault? what does the afr gauge read for over load/rev ranges, like when boosting or light to medium load, is it showing something different than before this problem. or is the problem just at idle/tickerover

regards chris

when i say for mapping i ment in the open loop state , being that it will try to make it richer in rev ranges in stead of the closed loop 14.7 , i know thats a poor description but i hope you understand my point

Not quite. maybe this is for another day, not on this thread.

thanks for trying to explain anyway.

regards chris.

Yer even warm and been driving for a while its below 14 It always used to run 14. I'm on syvecs and single turbo.

could be water temp sensor.

what water temp sensor does the syvecs use, if a toyota then you could check resistance to temp to the manual. if another type you could still get a rough idea as most neg temp thermistors follow the same gradient. they are normally rated at 25 C for there nominal resistance, and there are sites online to see temp/ resistance graphs.

i used the above info for my blitz sbc i colour temp sensor. cost me 60p for a sensor that blitz would sell for £80. And it works fine, but thats for another day.

regards chris

No the syvecs uses the wideband lambda. No stock co2 sensor on the car anymore. I have literally just fitted a new map sensor. Could it be faulty maybe? Didnt notice the issue before.

I am not a tuner but does the syvecs use a o2 sensor for idle/tickover? (closed loop for idle) if not, then it could be a map sensor fault? what does the afr gauge read for over load/rev ranges, like when boosting or light to medium load, is it showing something different than before this problem. or is the problem just at idle/tickerover

 

regards chris

Sorry was way to early for me with a hang over lol.

I believe the syvec would use the wide band for the closed loop idle your right, but not maybe for first start up which i thought he was say as he said 12's so just assumed , but 12's when warm is way to rich ,so could be the sensor going , or like you say a map sensor thinking its got boost

if the syvecs uses the wideband for closed loop idle (when the engine is warm) then i would have thought that a new map sensor if it's close the the original that the car was mapped on should be ok at idle.

what i was thinking that if the new map sensor is the same as the old map in size (3 bar etc) there could be slight differences with it's output that could upset idle mixture if not in closed loop, example old map sensor at idle say 1.3v and new 1.33v this could upset upset mixture at idle. but if in closed loop ecu should take care of that. if syvecs use's open loop when boosting etc the new map sensor could upset mixtures then.

but to me if you have got a wideband sensor fitted and a ecu like the syvecs i would have thought that it could be used to dial in a target afr for all load areas on the mapping.

what i am saying is that the syvecs stays in closed loop all the time and changes the closed loop target value according to the load and conditions.

example cold start possible open loop until sensor warms up then maintains a afr of say 12 going to 14 as the engine warms up then when boosting say maybe trying to maintain a afr of 11.5 or what ever the mapper has set for closed loop in that condition.

enough waffle from me. sounds like the problem has started from the changing of the map sensor, so could be map sensor or as said before the map needs tweaking for the new map sensor?

regards chris

I agree, it could be down to slightly different MAP voltage output, however 2AFR richer is a bit much,

Cold start is handled by a separate map and uses a temperature gradient to scale the extra fuel and air from the stepper valve, until switchover temp is reached, so like you say if the ECU coolant temp sensor fails it will be at a low temp output and the result will be a slightly richer mixture, but as the 2jz uses the stepper to control cold start and idle I would expect the idle rpm to also be high because of this if the sensor failed, but I maybe wrong about that.

It doesn't sound like the lambda, I would presume that because the syvecs uses a wide-band it have its own control circuitry, and therefore is self calibrating, and would flag a fault should the sensor go bad.

Ok thanks guys.

I think I will order a different one from another seller and return this one.

I will let you know on the results

i am not into wideband circuitry but could the sensor have shifted its base figure by 2 AFR, so the sensor goes up and down ( so it keeps the syvecs happy) but be out by 2 AFR at idle.

personally i don't think so as most reset in air as a base.

also i don't know what has to be wrong with the wideband for syvecs to show a fault.

i know older cars did not throw a fault if a temperature sensor was in range, but could be reading normal temp when the engine is cold, but i thick later ecu's are more intelligent and apply some logic, in this case the ecu would expect the temp sensor to read cold as it's been standing for say 8 hrs.

i maybe talking crap, but just trying to give ideas as to what the problem is. but i now think it's the map sensor.

what if you take a voltage measurement of the map sensor with a warm engine ( when it's got black smoke) and replace with a pot but set at a slightly lower voltage, and then watch for smoke and afr gauge reading. this may confirm the map sensor is outputting higher than the original one the car was mapped with?

regards chris

do not drive the car like this.

i too late.

typing with a poxy tablet in the bath.

Thanks for the time to reply in this thread. Ive contacted Ryan and hes said it will be down to the voltage coming from the new map sensor. Hes gunna have a look at my loggin and map to make any adjustments.

I will keep this thread updated :-)