Fuel Pump Switch Wiring Questions

[steve]

Do you know for sure that the MFI relay will still supply power to the ECU if the engine dies?

Yes. If it didn't you wouldn't be able to restart the car. Conversly if the ECU looses power the engine stops.

Steve

 

[SFRacingGST]

Regardless, something is causing your problem. I would first look into solving the fuel system problem before I would do any unnecessary modifications to the wiriing of you fuel system from the ECU. Unless you feel confident in your wiring skills. You could cause alot more damage and or make your car unsafe like steve said. A simple bad groud could very easily destroy your ecu.

 

[turbosax2]

Regardless, something is causing your problem. I would first look into solving the fuel system problem before I would do any unnecessary modifications to the wiriing of you fuel system from the ECU. Unless you feel confident in your wiring skills. You could cause alot more damage and or make your car unsafe like steve said. A simple bad groud could very easily destroy your ecu.

My brother currently has nothing installed but an intank fuel pump - therefore, the afpr is not giving him a problem currently because he does not have one.

I REPEAT, THERE IS CURRENTLY NO PROBLEM - WE ARE JUST PLANNING AHEAD.

And I do feel pretty confident in my wiring skills for something like this - just not sure which wire(s) to use yet.

 

[turbosax2]

We finally got around to wiring up the switch. Since my brother removed his cruise control, we used the cruise control switch on the steering wheel. We used this switch because it is not an on/off style switch, you have to hold the switch down for it to remain activated. So to turn the fuel pump on, the key must be in the accessory position and you pull the cruise switch toward you (the "cancel" function).

To wire the switch, I just traced back the wires from the switch that run along the steering column. Underneath the dash is a white connector that connects the switch wires to the harness. There are three wires on the connector. I cut the red wire and taped off the harness side of the wire. The switch side of the wire gets spliced into the power wire for the fuel pump relay (the wire is black with blue stripes). I spliced into this wire where it runs underneath the drivers side kick panel. There is a large bundle of wires down there, just cut the tape that holds them all together and pick out the fuel pump relay wire and splice the new wire into this one. Sorry, I don't have any pictures.

Although this switch would still work if the car stalled, I think it's pretty safe because it's not an on/off style switch. I'm still going to look for a better wire to power the switch from the ecu that loses power when the car stalls when I get time.

 

[luv2rallye]

Important note for others doing post 29 above: turbosax2 has already done the FP re-wire mod which means he is splicing into the stock 12V pump wire that goes to the FP relay that was added back at the FP (which is now that relay's control wire) so it draws little current and works.

If you have not done the FP re-wire mod, you should not do this as you will be splicing into the wire that goes to the real fuel pump which carries a lot of current and will burn out your switch. PM me for a different way to handle this situation.

 

[turbosax2]

luv2rallye, thanks for catching that.

 

[turboglenn]

I didn't read the whole thread, but why not wire it to the stock fuel pump relay. It kicks on and primes when the key is turned to on. The reason people have hard starting after a wally 255 or similar is that they turn the key directly from off to start.. you need to turn it to "on" for about 2 seconds to let the pumps cycle and teh injectors prime teh engine. Not waiting for this makes it to where you don't get the intial prime and it's harder to start. That would build the pressure in the lines. Then turn the key and it should start, and you won't have to worry about switches to the pump. Just wire the extra relay for the load of the 2nd pump to kick on with the FP relay. Problem solved!

 

[eclipsh]

I didn't read the whole thread, but why not wire it to the stock fuel pump relay. It kicks on and primes when the key is turned to on. The reason people have hard starting after a wally 255 or similar is that they turn the key directly from off to start.. you need to turn it to "on" for about 2 seconds to let the pumps cycle and teh injectors prime teh engine. Not waiting for this makes it to where you don't get the intial prime and it's harder to start. That would build the pressure in the lines. Then turn the key and it should start, and you won't have to worry about switches to the pump. Just wire the extra relay for the load of the 2nd pump to kick on with the FP relay. Problem solved!

Maybe there are some model differences but last I knew most DSM's out there do not prime the fuel system until switched to "Start" not "On." That is why various people came up with mods to prime the system before switching the car to "Start" to avoid excess cranking.

 

[turbosax2]

Maybe there are some model differences but last I knew most DSM's out there do not prime the fuel system until switched to "Start" not "On." That is why various people came up with mods to prime the system before switching the car to "Start" to avoid excess cranking.

That is what I have always read too, and is how my and my brother's cars are. However, I was hesitant to state this again because of this thread, where 2 guys insisted that their fuel pumps prime in the "On" position. I pm'ed steve to get verification on the subject.

 

[steve]

Not owning one of every type of DSM I can only state that the DSMs I've seen do not prime the fuel pump when you turn the ignition on. I've looked at the 1G code and don't see any code that would do so. My 2G EPROM doesn't but I can't say the all 2G ECUs don't.

Perhaps they are hearing the ISC get initialized or maybe their CAS glitches on power up causing the ECU to think the engine it turning which causes the pump to be turned on. Or maybe some years of 2G do.

You would think it would be well know at this point if any year DSM did prime the pump but instead we get people who report they think its happening but they don't know how to check.

 

[Mikael SS]

i'm not reading all of that, but i saw diodes, way over complicating it

have a relay powering the pumps. use the stock + wire as a hot to turn them on, as well as a switch that gets its power from a source thats on with ignition. that way the pump will act like normal, and all the switch will do is turn it on when it would not normally be on, of course only when the key is on. it won't turn them off.

 

[turbosax2]

i'm not reading all of that, but i saw diodes, way over complicating it

have a relay powering the pumps. use the stock + wire as a hot to turn them on, as well as a switch that gets its power from a source thats on with ignition. that way the pump will act like normal, and all the switch will do is turn it on when it would not normally be on, of course only when the key is on. it won't turn them off.

If I understand what you're saying correctly, that's exactly what I did

See post 29.

 

[luv2rallye]

Not owning one of every type of DSM I can only state that the DSMs I've seen do not prime the fuel pump when you turn the ignition on. I've looked at the 1G code and don't see any code that would do so. My 2G EPROM doesn't but I can't say the all 2G ECUs don't.

Perhaps they are hearing the ISC get initialized or maybe their CAS glitches on power up causing the ECU to think the engine it turning which causes the pump to be turned on. Or maybe some years of 2G do.

You would think it would be well know at this point if any year DSM did prime the pump but instead we get people who report they think its happening but they don't know how to check.

I agree many people think they hear the FP when it's actually something else that's being iniytialized when key is to ON. My understanding is the only DSM's that prime the FP are the 2g NT which of course have a chrysler engine/ECU and so can operate differently. I haven't worked on one but so many people here that have one insist that it primes (including a wiseman, Doug99RS I think said so), makes me believe that it must.