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Old 09-02-2008, 10:34 PM   #1
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Tweaking Bosch FI

The search still continues for a car, I have been leaning towards Cavaliers and Saturns due to their ability to go into lean mode by either an HAI or resistor in the IAT circuit. The cars I have looked at have been in bad shape, so looking to alternative cars, I have found a 90's BMW that has the classic Bosch FI that uses the air box barn door MAF. Now my question is; Is there a way I can tweak it to get it into lean mode? Is there an IAT in the system that I can fool to lean the a/f ratio? I have read that the BOSCH system is harder to fool, can I reset the MAF barn door? Or EFIE the O2 sensor.

I know Ford and Mazda use a type of barn door MAF, as well as many other imports. Any ideas?

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Old 09-03-2008, 07:12 AM   #2
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Usually the clock spring in those AFMs can be adjusted to have the ecu read more or less air. I don't see why that in conjunction with an EFIE wouldn't get that engine to lean out a bit.

- Kyle
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Old 09-03-2008, 03:13 PM   #3
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On the ford 2.3L turbo's they were called VAM (Vane Air Meter) i believe. Many people try to tweak to gain power, I think results varied a lot. Here is some info on Thunderbird Turbo Coupe VAM mods:

We would want the opposite of course, for less fuel...

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Old 09-03-2008, 04:11 PM   #4
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I'd think of trying a plumbing valve in parallel with it for an adjustable bleed.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
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Old 09-03-2008, 04:32 PM   #5
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One way is to tighten the spring, and add a variable resistor in the coolant temp circuit. That way you can make it too lean and use the variable resistor to tweak it.

Whatever you do mark you present tension setting so you can go back to it if things get funky.

On the older Nissans (83 and earlier) there was bypass circuit for adjusting the idle mixture.

We used a vacuum guage to set the mixture, running at about 2500 RPM. Then we would set the idle, with the bypass.

You could play with the variable resistor then measure the resistance under different loads and maybe rig a set of individual resistors for different vacuum readings or throttle switch positions.

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