Grim Reaper

This question has been addressed quite a bit, and it has been determined that for SD cars that the ecm does in fact use the MAT to calculate air flow and ultimately the injector pulse width.

But I have been reviewing the hac for MAF cars (as well as Greg Westphal) and no where in the hac can I see any code or tables similar to the SD's MAT Inverse Look Up Tables. The only check of the MAT appears to be as Grumpy has said earlier controls the enabling of the EGR.

I do not have a MAF car, so I cannot test this with a variety of resistors to see if there is affect to the Injector Pulse Widths, but it starting to look like the MAT has no effect in the calculation of air flow for MAF cars. Possibly as Greg has suggested to me in an e-mail, the cooler temp is already accounted for by the way the MAF reads the air flow.

If this is all true, then a relocated MAT is truly a useless mod for MAF cars and a complete waste of money.

GregWestphal

iTrader: (1)

About the only (main) benefit of the relocated MAT sensor is having a much-more accurate temperature of the air going into the engine. I sure thought it had some effect since when my engine would get heat-soaked (as opposed to the coolant getting too hot), the engine would feel like a dog. With my relocated MAT, I didn't get that "problem" any more. I might try the resistor trick and see if it changes the pulse-widths any. Hmmmm, I could temporarily wire in a switch inside the ****pit to switch back and forth while on the highway and see what happens.

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Greg Westphal
'87 IROC 305TPI/A4

Craig Moates

I'd like to use the MAT input to log a WBO2 sensor. Or maybe an EGT. That'd be cool. I'm pretty sure MAT is useless for the MAF cars. You could probably stick it just about anywhere, present company excluded, without significant effect.

mike89z

Glenn what hack are you looking at? If its the 6E could you post a link? I cant seem to find it anywhere.

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355 10:1 , AFR 190 heads, LT4 HOT cam w/ 1.6 roller rockers, complete Superram intake, 58mm BBK TB, 24# injectors, screens out of MAF, MAT relocated, March underdrive pulleys, Streetdampner, Crane HI-6 ignition, 160 thermostat, K&Ns, TES headers(Jet hot coated), Mufflex 4' cat back, B&M shift Kit, 2500 converter, and 3.27s. Chip is custom(doing it myself) Just got a 2 1/2 Harwood and soon to be painted.

Grumpy

couple things:
You have to remember the lastest of the all MAF code was 89 and that had to certified in 85 so we're talking almost 20 year old code.
Detroit has always done enough to get by, so there was no reason for them to get any more **** then necessay.
If you were to look at say a 95 S/C Pontiac hac you'd see where there are timing corrections just on IAT / MAT.
The older MAFs weren't all that accurate, or should I say had that great of resolution. On *some* MAFs they actually run better with the MAF disconneted, in just a Alpha N default mode.
IF the MAF was perfect then the fueling would be right as far as fueling goes. Trouble is you need a timing correction for IAT / MAT for best all weather performance.

On the 148 code there is a IAT timing table that they use in the N/A applications, and yet is 0'd out in the GNs. Figure the logic out in that one. Specially since so many guys tune during hot weather, and then are surprised when they detonate in the cold weather, oh well.

Grim Reaper

That's interesting about the timing change inside the newer cars' eprom for IAT/MAT changes. I'd love to see a hac for a newer car just to see how much more advanced the technology has gotten and possibly get some ideas for changes to make to my AUJP.