MAF Return to idle

[Tom]

Back in the day, MAF conversions for the 944 Turbo would often have a problem when returning to idle after full boost. If you floored it to redline, for example, and then completely let off the throttle, the RPMs would drop back to idle and often stumble or drop through idle and and let the motor die. People explained it as turbulence in the MAF tube, vacuum leaks, MAF-clocking problems, etc. It affected some MAFs way more than others. I'm curious how common that problem still is these days? Is that an issue for anyone here? I developed an electronics solution for that issue a long time ago for my own car and just stumbled across it recently -- so wondering if it's worth resurrecting....

[gruhsy]

Tom

You need to add the category idles but is erratic.
That’s what my Mtune did.

Hopefully I fixed that with all my checking over all related parts but won’t know until I get the engine together .

[Tom]

Tom

You need to add the category idles but is erratic.
That’s what my Mtune did.

Hopefully I fixed that with all my checking over all related parts but won’t know until I get the engine together .

I've seen m-tune cars do that. That's a different issue that my little electronics gizmo can't fix. Fingers crossed when you get the motor back together, but some m-tunes would do that on an otherwise fault-free motor. Joshua used to re-program chips to minimize that issue, but not sure that's an option these days. My gizmo addresses the original old-school MAF issue where the motor could not get back to idle after boosting without stumbling or dying. The root cause for that is the MAF signal voltage not returning to idle-levels fast enough. It will go up to 4 volts or more on boost, and then when you let off, the rpm's drop faster than the MAF signal, and the engine is flooded when the injectors turn back on. My solution monitors the signal and substitutes a suitable idle voltage for a few seconds after heavy boosting when the idle contact is closed. Works well for that particular issue.

[gruhsy]

Tom

You need to add the category idles but is erratic.
That’s what my Mtune did.

Hopefully I fixed that with all my checking over all related parts but won’t know until I get the engine together .

I've seen m-tune cars do that. That's a different issue that my little electronics gizmo can't fix. Fingers crossed when you get the motor back together, but some m-tunes would do that on an otherwise fault-free motor. Joshua used to re-program chips to minimize that issue, but not sure that's an option these days. My gizmo addresses the original old-school MAF issue where the motor could not get back to idle after boosting without stumbling or dying. The root cause for that is the MAF signal voltage not returning to idle-levels fast enough. It will go up to 4 volts or more on boost, and then when you let off, the rpm's drop faster than the MAF signal, and the engine is flooded when the injectors turn back on. My solution monitors the signal and substitutes a suitable idle voltage for a few seconds after heavy boosting when the idle contact is closed. Works well for that particular issue.

Ahh.

Nice function

[michael2e]

I'm currently running an older LR MAF that does have this problem. There are other running issues with the entire set up so I'm just about ready to call it and go with Johns V-MAF+ and enter the modern world. I had one of his older MAFs on my old 951 and it was flawless. I would be curious about your solution. Cheers!

[Tom]

I'm currently running an older LR MAF that does have this problem. There are other running issues with the entire set up so I'm just about ready to call it and go with Johns V-MAF+ and enter the modern world. I had one of his older MAFs on my old 951 and it was flawless. I would be curious about your solution. Cheers!

Yes, my solution works for that kind of MAF -- at least the return to idle issue. I may dust off the moth balls and make some up, but it will take me a little time. It doesn't do anything for the other drivability issues though. For that, I'm a long-time believer in the Vitesse MAF set up. On a standard 2.5L 951 motor, it's just dialed-in like no other off-the-shelf tune out there. That said, I honestly don't know if @Fast951 is still making them....?

[michael2e]

Tom it would be cool to try your solution out. And yes I agree about john's persistence and experience over the years at dialing in the 951. Maybe I better get on that order before it's too late!

[Fast951]

Some cars do experience this issue, others do not. Cars running on the rich side (via FQS or FP), a lightweight flywheel, a lightened crank, an aging gummed up ICV, a vacuum leak do not help.

Tom's idea is nice, as long as the idle voltage is user selectable (not all MAF sensors generate the same signal voltage at idle).

[Fast951]

.....
That said, I honestly don't know if @Fast951 is still making them....?

Still making them, but it's getting difficult due to components shortages. The supply chain for some items yet to recover.

[Tom]

Some cars do experience this issue, others do not. Cars running on the rich side (via FQS or FP), a lightweight flywheel, a lightened crank, an aging gummed up ICV, a vacuum leak do not help.

Tom's idea is nice, as long as the idle voltage is user selectable (not all MAF sensors generate the same signal voltage at idle).

My approach had two buttons used to calibrate the idle voltage -- one for a cold engine and one for a fully warmed up engine. When you push the buttons, it stores the pin 7 voltage, and the software extrapolates between cold and hot voltages as the motor warms up.