Re: L-Jet fuel pump and throttle switch

[ethan schartman <eschartman@domain.elided>]

> Date: Tue, 19 Mar 2002 07:30:24 -0800
> From: "Kurt Incledon" <kurt6507@domain.elided>
> Subject: GTV L-jet System/Fuel Pump shut-off
> 
> Group and especially Curtis,
> you will find that at idle with the throttle body 
> closed this switch will shut off the
> fuel pump.

kurt,
i have to disagree. according to the schematic in the
shop manual (for 2.5L V6 anyway), the throttle switch
contacts are wired straight into the ECU, not the fuel
pump relay circuit. 

furthermore, i do not know if the ECU can shut off the
fuel pump (i don't believe so, the ECU and main relay
coils only share a ground trace). 

over the summer i traced out the main relay wiring,
and learned this (IIRC): there are two relays in the
"main relay" block, one coil is wired to the ignition
relay - it powers the injectors and the ecu. as long
as the key is in "on" this is powered. i believe
shutting the engine down from the switch just
de-powers the injectors. the other relay coil has two
inputs (and a diode to isolate them from each other):
one from the "crank" position of the ignition switch,
and one from the AFM flap switch. this is the only
relay that controls the fuel pump. putting the
ignition switch in "crank" bypasses the AFM sensor to
pressurize the system before enough vacuum is created
to operate the AFM switch. when the key is released,
the AFM switch takes over the job of powering this
relay. 

according to the "how to tune and modify bosch etc"
book, an L-jet engine should run at about 500rpm with
the idle adjustment set to minimum (i.e. dialed in all
the way on the 2.5L), so the stop position of the
throttle body set screw should be set to accomplish
this (there is also a spec in the shop manual given in
CFM if you have an airflow meter). it also states that
a malfunctioning throttle switch may/will cause
driveability and fuel economy problems, but not
start/run ones.

somewhere, though, there is an AROC tech advisor who
will set the record straight. 

regards,
ethan schartman
'87 milano gold
princeton, NJ
Yahoo! Sports - live college hoops coverage
http://sports.yahoo.com/

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