Fuel delivery question

[TC535i]

So, we dyno'd Kim's car yesterday ('95 M3 engine, intake, exhaust, Conforti programming). The graph was very helpful, as it showed exactly what I'd suspected. The midrange A/F ratio was 14.2/14.4 for most of it, which is pretty fuel efficient, but not extremely conducive to power. Right up in the top end, it swaps over to about low 13/high 12 AFR, which is nice for power.

Basically, for most of the RPM range, it's getting good gas mileage, but could be seeing signifigantly more power... and that's what we'd rather see out of this car, especially at WOT.

Would a adjustable fuel pressure regulator solve this issue, or would that run it TOO rich at the higher RPM's? I'd like to drop the AFR into the low 13's for a majority of the powerband. I need to test the line pressure, if it's already pretty high (the stock FPR is 3.5 bar!), I'm thinking injectors might be a better decision. Would pushing more fuel to the engine be able to drop that AFR into the 13's, or would the DME compensate and cut it back? It's still OBD-I, so it's not overly controlling, but I don't know how much it can do in conjunction with the 02 sensor, as far as controlling that ratio.

What's the best way to achieve these types of results?

[TC535i]

Another interesting tidbit, there was a sharp dip in the graph around 6,000 rpm, probably the engine retarding the timing due to detonation. What bothers me is that the A/F ration was 13:1 at that point (plenty of gas), hood open, fan blowing on the intake (CAI/airbox), good Chevron 91 octane, and she's running Denso plugs 1 temp range colder than stock... why the hell would it be detonation? We've heard pinging on occasion too, can't figure out why it would do that. Any guesses?

[ryan roopnarine]

uniformly $hitty gas as a result of current fuel prices/supply,perhaps? I'm using reputable 93 here from a major brand and I just started to ping...I could barely ping this 10-1 engine on crappy 87 in the winter, now, with EAT and 93, i'm pinging all over the place. thinking about pulling the intake and washing it out, and running the induction style ventil sauber application that Bill R doesn't like, but winfred suggested. .I'm considering just using the citgo near the onramp if this persists, as on friday-sat, and sometimes sunday, they price their premium at 1 cent above 89, would be nice to pay 2.14 a gallon for premium.


Another interesting tidbit, there was a sharp dip in the graph around 6,000 rpm, probably the engine retarding the timing due to detonation. What bothers me is that the A/F ration was 13:1 at that point (plenty of gas), hood open, fan blowing on the intake (CAI/airbox), good Chevron 91 octane, and she's running Denso plugs 1 temp range colder than stock... why the hell would it be detonation? We've heard pinging on occasion too, can't figure out why it would do that. Any guesses?

[Jeff N.]

I think the easiest way to dial in the air/fuel ratio is an adjustable MAF. Not sure what options exist for the M3 - if any exist at all. I was impressed how easy it was for the dyno guys to dail in Martin's car using the controller that came with the pro-flow maf (www.pro-flow.com).

This isn't to say there isn't some sort of problem too. Pinging sure suggests somethings wrong, doesn't it? Does the M3 motor have adjustable cams/Vanos? Might check to make sure that mechanism is working correctly. Trust you've gone thru all the other usual suspects:

- fuel pressure and flow
- fuel quality
- tune up / quality ignition
- vacuum leaks
- blah blah blah...

Curious how it turns out...

Jeff





Another interesting tidbit, there was a sharp dip in the graph around 6,000 rpm, probably the engine retarding the timing due to detonation. What bothers me is that the A/F ration was 13:1 at that point (plenty of gas), hood open, fan blowing on the intake (CAI/airbox), good Chevron 91 octane, and she's running Denso plugs 1 temp range colder than stock... why the hell would it be detonation? We've heard pinging on occasion too, can't figure out why it would do that. Any guesses?