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Jim Grant's Tech Tips
'93
Chevy Blazer, Running Lean
Q:
My son has a '93 S-10 blazer Vin W, Runs lean after warming up. The
entire primary and secondary electrical system has been replaced, as
well as TPS and MAP sensors. I have cleaned all the grounds and
swapped in a different ECM. We also put in a new Spider assembly
because we thought the injectors were plugged after he replaced the
fuel pump. The problem started the day after he replaced the fuel pump
and filter. I am also an ASE master tech, but I work in a government
fleet operation, so I have expended my experience on this one.
A:
I would first suggest checking the fuel pressure cold, warm and while
being driven. The pressure should be between 55 & 61 PSI, if the
pressure starts to drop below 55 PSI there is a problem with the fuel
supply, pump, filter lines, etc.. If the fuel pressure stays within
the limits, under all of the conditions, then the engine should be
checked for vacuum leaks or incorrectly routed vacuum lines. If no
problem is found then you have to start looking closely at the
information the computer is reporting. If the fuel trim/adjustment
information reported shows enrichment yet the engine is still running
lean then go back to checking for vacuum leaks. Oh yes, don't forget
that the set timing connector has to be disconnected to correctly set
ignition timing on this vehicle. Also check the condition of the
distributor. A worn distributor shaft or bushings will cause the
tach signal to the vehicle's computer to be off. This can result in a
fuel control issue, due to the computer needing that information to
control the injector pulse.
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