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bpu699 bpu699 is offline
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Join Date: Apr 2007
Location: wisconsin
Posts: 2,539
Originally Posted by T77911S View Post
if the AFR is too far off it cant correct it.
this can be due to an air leak
wrong control pressure
bad ignition
mixture set incorrectly
or just a bad O2 sensor.

in the end the mixture is controlled be a frequency valve (FV). it is on the back side of the AFM. you should feel it vibrate when the key is turned on.
i dont know how often these fail.

another place to look is under the drivers seat.
there is a computer that conrtols the FV. there is also a speed relay that controls the O2 sensor. this device is known to have solder joint problems. this can also cut off the fuel pumps.

the CD unit gets its power from a delayed action relay. this is the relay that keeps the ignition on after you turn the car off to burn off fuel. i would image it is prone to bad solder joints too.

did you connect the decel valve correctly? personally i would remove this device.

i would check the fuel pressures.
with the O2 not connected, set the mixture to spec.
connect O2 sensor and check AFR's

i would also check the throttle switch to make sure it is adjusted properly.
Thanks. Very helpful. I will buy the fuel pressure gauges next, just to check this.

It makes sense to me that if the afr is too far off, the o2 sensor cant fix it. But connecting the o2 sensor makes it worse! That's the part I don't understand.

If the afr is 12, connecting the 02 sensor should drive it towards 14.7. But it does the opposite. Connecting it drives the afr to 10.

I will check to speed relay. I didn't know that effected the 02 sensor? I thought it just shut off the fuel pumps?

I will also check the fuel pump output this weekend, to make sure the flow is correct...

Old 11-03-2014, 10:50 AM
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