Can Overfueling Cause Detonation?

[Abo Bob]

Just trying to confirm something.

I got my car tuned with a z32 AFM that up until that day had been sitting in my garage for about 18 months and I've just found out had been unused but presumed to work for quite some time before then.

Anyway, the tune was good, it ran well but over a few days it seemed to deteriorate and I put it on a dyno where the air/fuel ratios went under 10 and it pinged.

I have since been steadily dropping the boost to now 7psi to stop it pinging.

The z32 AFM I believe maxes out at 4.5 volts.

I have seen it at 4.4 volts at 5000rpm with as little 10psi so it has been suggested that the AFM is dying or at least has something wrong with it.

My question is:

If we are right about the AFM showing far too much voltage for the actual air flow, it makes sense that it would be overfueling but can overfueling cause it to ping? Or is something else up?

[sh@un]

Fuel loses it's octane over time. But, too much fuel definately shouldn't cause pre-ignition/pinging. Has the car battery been flat? The ECU may not be running right now too (?)

[Cubes]

Mine was running in to the 9's (flat lines at 10 on the dyno as thats as low as the wideband reads) and there were no signs of detonation.

Sounds strange.

I gather you are running new fuel? Its quite possible the old stuff went off as it is 18months old.

Z32 at 4.5v. What sort of power are/were you making?

Mine hits 4.3v on the standard turbo running 10-11psi.

[Links]

I think adam was referring to his Z32 Airflow meter had been sitting around for 18months..

What ECU are you running adam?

[T04GTR]

well. it must of been making some power to reach the limit of the z32 afm.

to much fuel can cause pinging. not directly, but by carbon buildup in the cylinders. this glows and causes pinging. not detonation.

this is a pretty obviouse question but there isnt any air leaks is there?

also worth checking is the timing. if the cas hasnt been done up tightly it can move and the timing can change.

[T04GTR]

this is why i prefer map sensor equipped ecu's. coz your not relying on a sensor that gets blasted with dust and shit all its life

[T04GTR]

in throey. if its dirty it will take more voltave to keep the element hot. given the same volume of air.

coz the dirt will be insulating the film.

give it a clean(if its dirty) this will restore it to the factory parameters. if that makes any sense.

also oiled type air flow meters are no good for longevity on any hotwire or thick film afm (z32) it oils up the element and the dust sticks to it.

[Adriano]

Wouldn't that mean less voltage?

If you had an air leak in the intercooler piping, or a venting bov opening, the afm voltage will go high, as will turbo speed.

in throey. if its dirty it will take more voltave to keep the element hot. given the same volume of air.

coz the dirt will be insulating the film.

[Abo Bob]

Well with the old ECU, auto and stock AFM I was making around 255rwkw.

Then I did a manual conversion and put a pfc and Z32 AFM in. Tuned on a dyno that seems quite happy it made 300rwkw. This was at 11.8 A/F ratios I'm told.

Tried to run it on a dyno I knew and it ran 225rwkw, pinging and rich as feck. Didn't get too close to redline cos of the pinging.

Cubes - is that standard turbo but RB30?

Fuel is new and fine. 3 types tried.

I don't think there are any air leaks but I will check tonight.

The pinging doesn't seem to happen with heavy boost low to mid rpm, more like any boost high rpm, like over 5000.

My theory at this stage is, AFM tells PFC there is much more air than there really is, PFC puts lots of timing and lots of fuel in.

The only other thing I can think of is that the lambda sensor used to tune it was out and something is wrong with the tune although that wouldn't account for the pinging since it wasn't pinging at all when it was being tuned and on my test drive (and I gave it a good quality test drive).

[Cubes]

Abo bob,

Yer standardish turbo.. Its a VG30 Item, which is essentially an R34 turbo with the smaller RB20 compressor. So I would tend to rate it power/flow wise slightly less than a R33 RB25DET turbo.

[MattSR]

can overfueling cause it to ping?

In short, Yes - according to the Bosch Automotive handbook AFR's richer than 10.5:1 increases detonation.

Cheers,

Matt

PS - I shall try to find a reference.