North American Turbocoupe Organization



VAM voltage questions...
Kuch Offline
Senior Member
#1
I had a strange issue where my 88 would start running very rich at idle and cruising, found some great old posts on here and I started checking some items. First one I checked was my VAM voltage. According to the write up on here, the voltage should be about .85, idling, norm temps. I checked mine and it was only at .69. I though that was odd so I pulled the small metal plug out and tried a few small adjustments. The adjuster eventually bottomed out, full closed and I still only had .73 volts reading. My question is, does the addition of the K&N in the fenderwell change the flow enough to effect the idle air flow in the VAM? I eventually found the problem with my rich at idle issue, it was a bad diaphragm in the BBK AFPR, put a stocker back on it and it runs great now. Any ideas on the VAM voltage? Thanks
1988 Turbo Coupe, Black/Black, 5 Speed, Moonroof,  T3/T4 50 trim, ported E6, 255LPH, Kirban, 3" DP dual 2.5" w Hooker Maxflows, MGW shifter, K&N, Gillis valve, RR cam, Koni's
1964 Ford Galaxie 500XL, 390 6V, 4 Speed, Vast and fast
1960 Ford Starliner, 292 Y Block, 3 Speed, slow and low
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Jeff K Offline
Administrator
#2
I dont think the mechanical VAM cares that much about changes in air flow with custom intakes, unlike hot wire MAF sensors that are very sensitive to intake changes due to the sampling taking place in a very small portion of the total air flow.

Years ago, I had to set the idle VAM volts to around .4 V via adjusting the air bleed so I didnt get a 42 rich code at idle after replacing my VAM due to a worn out slider resistance element. I have never messed with the flapper door spring tension.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Kuch Offline
Senior Member
#3
Thanks Jeff, I used the VAM voltage info from the tech pages on here and it had a voltage of .85. How did you get yours adjusted to .4 at idle? I guess I'm not sure what the setting should be then, is it .85 or .4? Is there a factory setting that it should be? I too do not mess with the spring tension, leave that be.
https://turbotbird.com/thread-vam-idle-adjustment
1988 Turbo Coupe, Black/Black, 5 Speed, Moonroof,  T3/T4 50 trim, ported E6, 255LPH, Kirban, 3" DP dual 2.5" w Hooker Maxflows, MGW shifter, K&N, Gillis valve, RR cam, Koni's
1964 Ford Galaxie 500XL, 390 6V, 4 Speed, Vast and fast
1960 Ford Starliner, 292 Y Block, 3 Speed, slow and low
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Jeff K Offline
Administrator
#4
If .85 V works for you and doesn't generate any rich or lean codes I would say set it at .85 V. No real clue why I had to set mine so low, but the car idles perfectly, runs great and no A/F rich or lean codes for many years. I do have a home made intake with a large K&N cone filter in the pass side fender connected to the VAM with 3" ID PVC pipe elbows and short straight sections. No clue if that has anything to do with why I had to set my VAM idle voltage where I did.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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