Jump to content
SAU Community

Recommended Posts

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 :D

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 :(

Link to comment
https://www.sau.com.au/forums/topic/10149-ran-car-without-s-afc/
Share on other sites

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.

Ok, storytime :D

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 :)

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

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!

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.

  Quote
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 :D

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

Are you saying the O2 sensor adjusts fueling?

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

  Quote
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

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

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • @Haggerty this is your red flag. In MAP based ECU's the Manifold pressure X RPM calculation is how the engine knows it is actually...running/going through ANY load. You are confusing the term 'base map' with your base VE/Fuel table. When most people say 'base map' they mean the stock entire tune shipped with the ECU, hopefully aimed at a specific car/setup to use as a base for beginning to tune your specific car. Haltech has a lot of documentation (or at least they used to, I expect it to be better now). Read it voraciously.
    • I saw you mention this earlier and it raised a red flag, but I couldn't believe it was real. Yes, the vacuum signal should vary. It is the one and only load signal from the engine to the ECU, and it MUST vary. It is either not connected or is badly f**ked up in some way.
    • @Haggerty you still haven't answered my question.  Many things you are saying do not make sense for someone who can tune, yet I would not expect someone who cannot tune to be playing with the things in the ECU that you are.  This process would be a lot quicker to figure out if we can remove user error from the equation. 
    • If as it's stalling, the fuel pressure rises, it's saying there's less vacuum in the intake manifold. This is pretty typical of an engine that is slowing down.   While typically is agree it sounds fuel related, it really sounds fuel/air mixture related. Since the whole system has been refurbished, including injectors, pump, etc, it's likely we've altered how well the system is delivering fuel. If someone before you has messed with the IACV because it needed fiddling with as the fuel system was dieing out, we need to readjust it back. Getting things back to factory spec everywhere, is what's going to help the entire system. So if it idles at 400rpm with no IACV, that needs raising. Getting factory air flow back to normal will help us get everything back in spec, and likely help chase down any other issues. Back on IACV, if the base idle (no IACV plugged in) is too far out, it's a lot harder for the ECU to control idle. The IACV duty cycle causes non linear variations in reality. When I've tuned the idle valves in the past, you need to keep it in a relatively narrow window on aftermarket ecus to stop them doing wild dances. It also means if your base idle is too low, the valve needs to open too much, and then the smallest % change ends up being a huge variation.
    • I guess one thing that might be wrong is the manifold pressure.  It is a constant -5.9 and never moves even under 100% throttle and load.  I would expect it to atleast go to 0 correct?  It's doing this with the OEM MAP as well as the ECU vacuum sensor. When trying to tune the base map under load the crosshairs only climb vertically with RPM, but always in the -5.9 column.
×
×
  • Create New...