75 450SLC TO RICH

450 slc 75' will not pass the co test. I do have a air fuel mixture meter however I do not know how to adjust or correct the air fuel mixture to get the co content down.
help!!!!!!!!!

[stevebfl]

Two adjustments on that guy (fuel that is). Before these adjustments the ignition should be right. Mainly the timing.

The timing was 5deg ATDC with the vacuum lines connected and more importantly WITH vacuum in the retard vacuum chamber. I usually advanced that spec to zero with vac on the retard. After testing this way pull the vac line off the retard and verify that the timing is at least 10deg BTDC with no vacuum.

Once you have done that remove the aircleaner. First remove and replug the air temp sensor (it must be in the system for adjustments.) Locate the manifold pressure sensor and verify that the large rubber hose to it is tight (not leaking vacuum). Remove the end cap (black plastic). You will uncover a 4mm allen adjustment. Remove the connection from the throttle switch (this disengages the idle compensation circuit). Run the motor and slowly turn the 4mm adjustment until you get a tad less than 1% CO. Reattach the throttle switch and make the final adjustment with the knob on the side of the computer. I usually make this to 2-3% CO but you might need it leaner for your test.

One other caution if you are using an exhaust analyzer. You must deactivate the AIR pump before making your adjustments. Removing the belt works or originally we removed one of the vacuum lines from the switch-over valve controlling the divertor valve (diverts the air from the exhaust to the atmosphere).

One other caution. The natural way for the manifold pressure sensor to fail is to go rich. The device has a signal range that is interpreted by the control unit. It looses its rane to the rich end. What this means is that if its range is narrowed then the adjustment just done will make the car too lean for heavy throttle loading. We can test it on the dyno but you have to go by the seat of your pants otherwise.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician