Ran car without S-AFC.

[JimX]

I accidentally ripped the wires out of my S-AFC last night (long story). Anyway I had to run the car without the AFM sensor wire for around an hour. It sputtered and choked all this while but I didn't really have much of a choice except call for a tow (at 3am).

Anyway I'm wondering if this has done anything harmful to my engine. I'm guess I only have to worry about it leaning out the mixture too much, but it didn't seem to ping at all. I just couldn't go over 2500rpm or so

Fortunately the wiring loom just plugged back in again when I took the unit apart today and it was all good. Oh yeah, one more question - I want to reset the ECU after last night's episode, but I don't know if I should disable the S-AFC after doing so while the ECU "learns" its new map again.

If I don't, won't the S-AFC settings interfere and it will think that they're all zero when they're not? (hope that makes sense). Ok, example - If I reset the ECU as-is, will it then run as if I'd set everything on the S-AFC to zero, and then revert to the complete OPPOSITE of what it's set to now if I disconnect the S-AFC and re-attach the AFM wire? Argh, that looks so confusing. I hope someone knows what I'm on about here

[inark]

i knwo its a long story... but jimx... u have to tell how this happend!

[predator]

I've done the same before, but only drove it for a few hundred metres before I pulled over and pulled it apart and stuck everything back together properly. Kinda weird bouncing of 2500rpm... Doesn't seem to have done any damage, but the engine wouldn't have a clue how much air was going in so it just guesses - in other words, not a good idea to drive for any distance.

Tape the wire where it goes into the board on with some heavy tape...that will stop it happening again.

[JimX]

Ok, storytime

I had duct-taped the S-AFC under my dash because the double-sided tape that comes with it is shithouse. This only lasted a few weeks though before coming off, and I never got around to putting it back on. So I just took up some of the slack from behind the dash and threw the whole unit across the centre console and had it rest sort of where the passenger seat meets the console.

This was ok for a few days, but then one time last night I slid the seat forwards to let the rear seat passengers out and it pulled the S-AFC forwards with it because it was trapped between seat and console, resulting in no more wire connection

If I had the right sized screwdriver with me I could have fixed it before we left. So now some tools are going into my car permanently, including the right sized screwdriver for that thing

[Doctor]

The bouncing is the lack of a signal from the AFM and it doesnt cuase any issues as it runs rich on purpose and stops revs at 2.5 ao you cant damage anything.

[macka]

Also your oxygen sensor acts below a certain RPM to recalculate A/Fs as well as your afm.

Not good running your car for ANY amount of time with the afm disconnected..Your car would be going lean rich lean rich, probably why it wouldnt go past 2500 is because your mixtures were that far out it couldnt run your car!

You can reset your ecu with safc still connected it shouldnt make any difference at all

[JimX]

Hmm, I'm more inclined to believe Doctor's theory over macka's. If there is no signal coming from the sensor, it would have no idea of whether to run lean or rich. I don't think it would just swap arbitrarily between the 2 mappings, I'm sure it would try to do one instead of the other. Since Nissan err on the side of caution with the default rich mappings, I'm inclined to believe that it would just run constantly rich with no AFM signal.

What I did was the equivalent of the AFM dying, and I think the ECU would be designed with a possible AFM failure in mind in the general scheme of things. Anyway that's just my theory, I've got no intentions of testing it again!

[Guest Nismo_Freak]

It would go into safe mode and over fuel like a mofo. The 2500 limit is to prevent boosting. Welcome to limp home mode!

[predator]

yup..it runs rich.. when it happened to mine all i could smell was unburnt petrol out the back exhaust.

[poyz]

JimX, you wouldn't have to worry about any damage to the engine. You've just experience your car in "limp-home" mode. The ECU detected a fault in the AFM. Limp-home mode doesn't allow you to rev past a certain rev range (it's about 3000rpm on mine - not a 'line tho). It retards timing way back and dumps in a shit load of petrol.

Originally posted by JimX

Anyway I'm wondering if this has done anything harmful to my engine. I'm guess I only have to worry about it leaning out the mixture too much, but it didn't seem to ping at all. I just couldn't go over 2500rpm or so

[PSIKO]

the 02 sensor is a back up for the afm signal, to allow higher end adjustments after teh afm signal (you can see this on a dyno afr ratio graph where up the top end it will fluctuate, since this is the 02 sensor altering the fuelling) - not sure if the 02 sensor can adjust when the afm isn't connected, but seems fairly reasonable to suggest it still would

[poyz]

Are you saying the O2 sensor adjusts fueling?

All it does is "sense". The ECU adjusts the fueling accordingly via the injectors.

Originally posted by PSIKO

the 02 sensor is a back up for the afm signal, to allow higher end adjustments after teh afm signal (you can see this on a dyno afr ratio graph where up the top end it will fluctuate, since this is the 02 sensor altering the fuelling) - not sure if the 02 sensor can adjust when the afm isn't connected, but seems fairly reasonable to suggest it still would

[PSIKO]

yeah it senses, and provides secondary fuel adjustments (mainly in higher rev range) ... however isn't the primary measurement device (the afm is) since it is located in the dump, and when the mixtures have reach it, it alters accordingly, therefore leaning and enriching as macka said

[keca18]

the o2 sensor sends signals back to the computer either rich or lean via voltage reading. if the o2 sensor reads rich, the computer compensates by leaning off mixture. if o2 sensor reads lean, computer richens mixture. an o2 sensor is a TRIMMING device, nothing more.