OK you MAF and ECU hackers - what do you make of this?

[Jeff N.]

My car is pulling about 15 to 18 more HP (repeatedly) when I disconnect the WOT wire from the ECU. This is with the MAF setup...

Measured with a G-tech Pro. Back to back tests, same road with no more than 30 minutes separation.

Interesting, huh?

Disclaimer: Mess with your own car at your own risk. I can't tell you what your AFM based car will do if you pull the wire. Yer on yer own.

[emw525E34]

Yeah, fascinating!. Maybe the Germans wanted to richen the mixture at WOT to preserve the reliability of the engine. Did you, by any chance measure the lean/stoic/rich mixture at WOT ?.
My M20 engine with modified APEXI SAFC maintains some richness at WOT. I could lean it out a bit but does not really help much.

Which pin on the ECU is wot ?.

[SRR2]

Do you have more information on your AFM-MAF conversion? I'm interested in doing something like that.

Concering the WOT wire, are you talking about the WOT signal from the throttle position switch? You don't happen to know your switch part number by any chance? It's easy to read the p/n on the front of the switch.

[Martin in Bellevue]

The split second o2 gauge will now show rich under full throttle. It didn't, with the WOT sensed from the tps. If fact, the 2 middle maf pots are right where this can be leaned back to dithering o2 readings with small adjustments. I guess this means it may be leaner than best for acceleration.

It did pass the WA state emissions test yesterday morning. In fact, the numbers were better than the test from 2003. This is with the cam, new valve seals, & maf. Oh yeah, and 21lb injectors.

[Jeff N.]

Martin - disconnecting the WOT wire with no other change and going richer makes sense (I think). The chip wizards tend to lean out the mixture to gain power.

Here's (again-I think), where this is going:

- when the ECU sees WOT, it ignores the voltage signal from the air meter
- the injector pulse, ignition advance is based only a value determined by engine RPM
- the MAF is essentially ignored at this point

Soooo...I thinking the "problem" is along these lines.

- the WOT tables in the JC chip really not very optomized for my engine setup and somehow the combination of the voltage signals from the MAF and the midrange tables do a better job
- Mark D would have to comment on how the ECU tables handle lookups of injector and advance settings when MAF voltage tends towards the upper limits (4.7 or 4.8 if I recall).

[JoeS]

MIRICLES never cease.

[Bellicose Right Winger]

Is it possible that you are already at an AF ratio that produces maximum torque and the additional fuel added by the DME at WOT is making mixture excessively rich, resulting in less power?

Paul Shovestul




Martin - disconnecting the WOT wire with no other change and going richer makes sense (I think). The chip wizards tend to lean out the mixture to gain power.

Here's (again-I think), where this is going:

- when the ECU sees WOT, it ignores the voltage signal from the air meter
- the injector pulse, ignition advance is based only a value determined by engine RPM
- the MAF is essentially ignored at this point

Soooo...I thinking the "problem" is along these lines.

- the WOT tables in the JC chip really not very optomized for my engine setup and somehow the combination of the voltage signals from the MAF and the midrange tables do a better job
- Mark D would have to comment on how the ECU tables handle lookups of injector and advance settings when MAF voltage tends towards the upper limits (4.7 or 4.8 if I recall).

[winfred]

that's something i may try on my 535 afm'd 325is, i still have a lean problem on the top end, and sometimes at lower rpms when i hammer it at around 3k rpm it goes lean for a second or three. dammit i need a ams conversion, i tweek and tune and a week later the sob has adjusted and leaned out, i had it running like a bat outta hell a couple weeks ago and now it's leaning out again

[Robin-535im]

I think you're probably right about the WOT map not being set up right. IIRC, the DME dumps in a bit more fuel (~10%) to give you an A/F ratio closer to 13 at WOT, as opposed to 14.7 everywhere else.

It would be most helpful to see that wideband O2 reading in the two different cases. You could also have an O2 sensor on it's way out and setting the mixture rich all the time, so that you're too rich once the WOT map kicks in.

How do you like the G-Tech meter? Does it record RPM too or just use accelerometers to estimate velocity?