Vafc acting strange, displays higher RPM than actual.

[Dct5289]

Ive got a 93 civic CX with a b18c1 in it with a Vafc2. Recently i noticed that the RPM display on my vafc is acting a bit strange. the way it goes is at about 750 RPM, at idle, it displays correctly. But at about 2500RPM the vafc displays 3200. However, when the car hits vtec at about 4400 (i changed it on the vafc) the two RPMs match up. as well as when the car hits the rev limiter.
I just thought that it may be possible that this could be affecting the RPM reading my ECU is getting and may be messing with my air fuel ratio which according to a friend who was driving behind me it is really rich and gives off the richness smoke when it is given gas.
Also what is strange, i posted this before, but once the engine warms up it cannot hold a steady RPM, it fluctuates plus or minus 100RPM. It runs smooth as butter when it is cold, but progressively gets worse as it warms up. Could my oxygen sensor be bad?

P.S. I have not touched the fuel map with the VAFC, i was waiting to get a wide band for that.

Thanks, Daniel

 

[Dct5289]

could the vafc be bad? Im thinking my O2 sensor needs replacing. think thats worth a try? as far as i know it has the stock O2 sensor in it.

 

[TurboMirage]

make sure your VAFC is SOLDERED IN.

check to make sure nothing is loose.

 

[xj0hnx]

Well, are you basing the "wrong" RPM on a tach in you car? If so, it's possible the VAFC is correct, and the tach is wrong, OEM tachs can be lazy. Also this can account for the fluctuation you are seeing, the VAFC is reading an signal and displaying it in real time, while your tach may not register it, fluctuations that small aren't abnormal, I don't remember ever seeing a steady RPM on my VAFC, kind of like a A/F meter reading straight off the o2 sensor.

As far as you car running rich, well, you did set vtec pretty low, did you also adjust fuel curves to match? Did you do it with a wideband so it is correct? Well, I just reread you post..that would probably be the cause.

 

[Dct5289]

Ok, since then i have driven it, and i think you are right, i get about 3000 rpms at 60 and the tach is only showing 2200.
As for the vafc, ill check the connections. I soldered them myself, but one may have come loose.

 

[amadeuscr]

tacho

It happens to me too, and I have a safc Neo, and it's be cause the tacho is old , it losses strenght or somethng , be cause I installed an external and is the same thing !

 

[Dct5289]

this thread is ultra old, I dont even have a VAFC any more. My tach was the problem, let it die.