fuel pump relay hotwire????
03-27-2006, 08:33 PM
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Car: 93 firebird,89 camaro,tuneport 91 chevy pickup
Engine: 350,350,350
Transmission: 350,700R4,700R4
fuel pump relay hotwire????
I have an 89 camaro that I bought less engine. I'm pretty sure that the previous owner had converted to a carb already. I am cleaning up the wiring and find that the tan and white wire from the FPR has been cut and tied into the hot wire for the ignition ( distributor). He rewired with those high tech scotch locks 
and the new "hot" leads back through the fire wall. I wonder if he did this to run the fuel pump without the fuel pump relay? Thanks in advance for your input!!! Got any ideas on the cure for this?
and the new "hot" leads back through the fire wall. I wonder if he did this to run the fuel pump without the fuel pump relay? Thanks in advance for your input!!! Got any ideas on the cure for this? 
03-28-2006, 09:43 AM
#2
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Hmmmmmm....... the big question would be WHY he would do that. Wondering if he ripped all the computer stuff out and/or the oil pressure sender above the oil filter and found that the factory relay would no longer turn on when the engine was cranking/running. Probably something like that.
I beleive that the ECM turns on the relay to "prime" the fuel system when you first turn the key for a few seconds. Then the ECM keeps it turned on any time it sees the engine is cranking on the starter or running on it's own, with the oil pressure switch serving as a "backup" to keep it going if the ECM fails for some reason. I THINK that's how it works, but you might want to get a second opinion before you take that as fact.
I would guess that he tapped into the ignition power to drive the fuel pump becuase the factory FPR only sends power to the pump when the trigger wire for the relay is GROUNDED (not when it is supplied power). It's tough to find a convenient source that grounds only when the engine is cranking/running. Plenty of places to find power when running, tough to find a ground-while-run source.
Please check this out with other board members who are better with electrical than myself. I'm sure I got a few points wrong here.
I beleive that the ECM turns on the relay to "prime" the fuel system when you first turn the key for a few seconds. Then the ECM keeps it turned on any time it sees the engine is cranking on the starter or running on it's own, with the oil pressure switch serving as a "backup" to keep it going if the ECM fails for some reason. I THINK that's how it works, but you might want to get a second opinion before you take that as fact.
I would guess that he tapped into the ignition power to drive the fuel pump becuase the factory FPR only sends power to the pump when the trigger wire for the relay is GROUNDED (not when it is supplied power). It's tough to find a convenient source that grounds only when the engine is cranking/running. Plenty of places to find power when running, tough to find a ground-while-run source.
Please check this out with other board members who are better with electrical than myself. I'm sure I got a few points wrong here.
03-28-2006, 07:40 PM
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Car: 93 firebird,89 camaro,tuneport 91 chevy pickup
Engine: 350,350,350
Transmission: 350,700R4,700R4
Your right that the ECM is gone. If the correct engine oil pressure switch is installed and wired back to the FPR I wonder if the fuel pump will work when oil pressure is established? The other wiring is landed correctly I think. I have installed a vortec 350 with a carb. If I prefill the carb bowls the sender will see oil pressure on light off and the fuel pump should pick up even without the ECM. Am I correct in this assumption? Thanks for responding to my post!
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