RomRaider

I noticed something interesting today about the failsafe mode adopted by the 32-bit ECUs when there's a MAF sensor problem (i.e. P0101, P0102, P0103). I've attached the description from the service manual.

It appears that the ECU begins to use input from the MAP sensor to calculate load (i.e. grams of air intake per engine revolution). That sounds very much like speed/density.

The form of "limp" mode adopted seems realatively benign. The only concerns are the changes to knock compensation and idle speed control. Perhaps knock compensation could be modified to ignore the MAF failsafe switch and perhaps the MAF could suddenly appear broken only when RPM is above 1500.

I wonder whether there's a VE table to support this failsafe mode. If so, it's even conceivable that the ECU copies it to RAM and "autotunes" it with feedback from the A/F sensor in order to be better support this failsafe mode.

There is no MAF failure failsafe mode for 16-bit ECUs.

Interesting find.

The 16bit ecus will run with the MAF disconnected and someone on this board mentioned that there is a MAP multiplier that is involved.

Nice find !! Can be intersting for 32 bits ECU to switch between the 2 modes, like idle and low RPM with MAF and track with MAP

think there is a VE table in here? what would I look for if I were to bust out a hex editor and start looking myself?

Its true, the 16 bit ecu will run with the MAF disconnected. Last winter I blew apart the intercooler Y pipe and it wouldnt run with the MAF connected because of the gross leak, it kept stalling. So I disconnected it and ran home (20 minutes on the highway) with no MAF. But then again, I had no boost either. I guess I'll have to see if it runs with no MAP and no MAF. That would mean its just running on failsafe values and still not being speed density. Also since the IAT is in the MAF, thats another big factor on correct speed density function so that wouldnt work unless there was a software function to ignore MAF signal while in SD mode but still leave it connected.

I just recently read something about this in one of the experimental aircraft forums. I didn't pay much attention at the time, but I'll try to dig it up for you.

-jjf

I don't think there is a VE map, but I do think some of the basics for calculating MAF flow from MAP instead of the MAF sensor are there.

There are a few maps that could be requisitioned for use as VE tables, or one could be created.

I think what you're seeing is really only fail-safe code. It isn't built to run the car in any sort of efficient way. I do think it could be made to.

The air temp sensor really needs to be moved to the intake manifold, but otherwise I think speed-density is completely within reason. There are other reflash solutions that do this, like HP Tuner. I'm amazed that the current commercial solutions for Subaru reflashing haven't done it yet. They're about to be passed up outright.

when ramtune for 02-05s hits, opensource will eclipse closed source on that platform.

Where did that GIF come from? Can you share the original document?

It is true. The experimental aircraft guys running Subie engines in their RVs (eggenfellner makes firewall forward kits) run without the MAF sensor connected so that it runs off of MAP. I have seen a few of them run this way.

They're probably not running the same Denso ECU's we are. At least, if I were doing it I'd be running a specialized standalone, not an OBD-2 car ECU.

A few are using replacement ECUs, but many are not. I didn't find the original thread I was looking for, but I did locate a Van's RV builder who is supposedly doing this and dropped him an email.

Personally, I like flying behind a big old honking Lycoming air cooled aircraft engine - with fixed timing, duel magnetos, and the 'ECU' being a big red mixture knob in the cockpit - but that is just me.

-jjf

Actually the eggenfellner kits use the factory Subaru/ Denso ECU. Some of the RV guys I was talking with were using th Denso with MAF unplugged defaulting to MAP. They even sell the subaru select monitor II as an option for their kits.

And I agree, The lycoming is much more simple and redundant. Ide feel alittle more comfortable in that. However I do not trust continental as much anymore after I had one throw a rod through the block

Thanks Jon!