Wierd A/f Ratios

[Suspense]

I have noticed that sometimes whilst driving my Apexi Turbo Timer, shows the A/F ratio to be above 20:1, hoever it sorts itself out after a while.

Also sometimes whilst on idle, the A/F ratio would be shwoing as 14.6:1 or similar, i thought on idle it should be sitting at above 20:1????

Is it just my turbo timer, or something else?

Car seems to drive fine, however i dont really give it a hit when the A/f is showing 20:1 + whilst cruising

any help appreciatec

[Tommyk]

at idle, it should be ideally 14.7, which is stoich

While on boost, it should be around 12:1. Bear in mind, the a/f meter you have isnt very accurate, because it probably feeds off the factory o2 sensors ?

[Suspense]

at idle, it should be ideally 14.7, which is stoich

While on boost, it should be around 12:1. Bear in mind, the a/f meter you have isnt very accurate, because it probably feeds off the factory o2 sensors ?

<{POST_SNAPBACK}>

Dont know how the tubro timer is hooked up, but i have Stock AFM on a R33

how come it normally goes to 20 and above @ idle half the time :S?

On boost it is fine... its just sumtin the readings f*k up showing it to be 20+ if this was the case i would have stuffed my engine which i havent :S?

[Sydneykid]

It is a total waste of time looking at A/F ratios produced by a slow and narrow lambda sensor, especially if you don't understand what is going on.

Some things you need to be aware of;

1. the standard ECU turns the fuel off when you are coasting, that is not LEAN running. In fact the engine isn't really RUNNING at all.

2. the closed loop (cruise and idle) target is around 14.7 to 1 (stoich)

3. the standard (slow and narrow) lambda sensor does not react to changes in A/F ratios very fast. For example if you floor it, by the time the lambda sensor catches up you have moved 100 metres down the road and are going 40 kph faster.

4. the standard lambda sensor has no heater (a fast and wide lambda sensor does). This means it has no temperature compensation, so the readings are not very accurate outside normal exhaust gas temperature (that's both hotter or colder).

5. the sensor circuitry in the Apexi turbo timer is very simplistic, nowhere near as accurate or fast as those found in a proper wide band A/F meter, as used for tuning on a dyno.

6. the standard ECU is several thousand times faster at recognising changes (load, throttle position, rpm etc) than the standard lambda sensor is at recognising changes in A/F ratios. So by the time the lambda sensor sees an A/F ratio change the ECU will have moved on many many times.

7. Nissan knows all of these shortfalls in the lambda sensor, that's why the ECU only runs closed loop at cruise and idle. Where the changes in inputs are very small and slow. That way the lambda sensor can keep up.

My advice, turn off the A/F ratio display and get on with driving.

cheers

Edited November 26, 2005 by Sydneykid

[Suspense]

Cheers man... appreciate it..?

However is there any point in upgrading the lambda sensor? or is it just a waste of money, the only outcome i will get is being able to view an accurate A/F ratio?

[T04GTR]

what car is it?

[Suspense]

r33 gtst s1

[paulr33]

Cheers man... appreciate it..?

However is there any point in upgrading the lambda sensor? or is it just a waste of money, the only outcome i will get is being able to view an accurate A/F ratio?

<{POST_SNAPBACK}>

The only time you would change it is if you wanted to tune the car yourself. Dyno shops when they do a remap or tune an aftermarket ECU will use a wideband 02 sensor to tune the car accuratlely. You would not benefit from switching to wideband 02 sensor, infact the stock ecu won't support. It's really if you are going to tune your own car (or others) and you can install an additional wideband sensor (and keep the stock one) and hook up a guage to the wideband. Again this would be useless with the stock ecu, without remapping skills/tools.

[Suspense]

Cheers ppl