Fuel pump wont turn on any ideas/ecu controlled?
 

I also Posted this in the project section hoping for a look today. Well today was to be the first fire up of the ls7, unfortunately the fuel pump(ricks gs340) doesn't want to turn on. The computor is an e38 and when the key goes to the ignition I get 12volts at the pump for 3 seconds then the voltage goes to zero. The problem is while the voltage is present I dont here the pump running. The strange thing is when I bought the battery a week ago, I hooked it up with a dry gas tank, and turned the ignition one click to far and heard the pump growl for a second or two and immediatly shut it off and pulled the pump fuse to check the rest of the electrical system. Now the tank has 12 gallons in it and it dont want to turn on, I cant believe I could have damaged the pump with a momentaty turn on dry. If you guys have any ideas what to check I would appreciate it.

you could run 12 volts to it directly (unplug the voltage wire from the computer and see if it turns on. Running it dry that briefly should not have hurt it at all.

Some pumps are very quiet, and they're all quieter with fuel in them than when empty. Maybe disconnect the fuel line out of the pump, at the rail, etc. and put in a can and see if it's pumping fuel.

If it's not pumping but works with 12 volts bypassing the computer then you'll need to check the relay and wiring. Most computers control the pump by controlling the ground for the fuel pump relay.

Thanks Jody- I need to dig in, the speartech harness has a relay for the fuel pump built in to it and he provides a long grey wire coming out of it. The paper work says to connect the grey wire to the positive terminal on the fuel pump. I did run the ground from the neg side of the pump back up to the second bulk head fitting I installed in the firewall, where the neg battery cable is terminated.

I guess I will cut into my wiring to run 12v to the pump.

Thanks Agian Rich

yeah, they'll send a +12 volts wire for the pump, but that comes off the relay; the ground of the relay is wired directly into the computer and it turns the pump on/off by grounding the relay. Most computers control the ground side instead of the hot side.

Isn't there a way to just run a 12 volt wire from another battery or ? to a plug on the pump or directly to the pump without chopping into the harness? How does the gray wire attach to the pump and is it outside the tank?

Also check the relay itself to make sure it has 12 volts battery (all the time) at terminal #30, 12 volt switched (key on only) at terminal #86, ground at terminal #85 (this will be wired into the computer itself on most systems) and terminal #87 should be the 12 volts out to the pump (gray wire on your harness). This is if it's a standard 4 lead relay. Of course if you've already checked and confirmed that the gray pump wire has 12 volts for three seconds when you first turn it on then the relay wiring and relay itself should be fine.

I agree with Jody on all points. Run a hotwire to the pump + and see if that does it. Also confirm that the ground is good as well.

The ECM will turn off the fuel trigger after approx. three seconds unless it senses that the engine is running.

The 12v positive jumper wire fired the pump up immediatly running through the existing ground wire , I let it run off the battery long enough to completely fill the system. The pressure is 61 psi and its leaking at the stainless steel flare fitting comming out of the tank where Ricks has the #6 nut. Im not to worried about the fuel leak, the fact that the pump doesnt fire when Its got 12v on it for the 2 to 3 seconds has me very confused. Thoughts on the next step?

Thanks Rich

A -6 conical seal is often needed on stainless hardlines.

Use a test light and find out where there is, and is not, power. Use a test lead to extend the test light so you can see it when turning on the key since it should only be on for a few seconds.

Don't forget that the relay is triggered by the negative signal from the ECM.

Carl --

Hate to ever disagree with my buddy -- but NEVER use a test light on an ECU... Use a volt ohm meter....



Rag --- Stainless steel is often hard to get to seat.... so I use just a little dab of anti seize on the threads -- and then I SNEAK UP on the seat - I tighten just a bit - loosen - tighten it just a bit more - loosen -- and then tighten it to final. This helps FORM a seat between the two surfaces.

If that doesn't work -- PURE CHOICE MOTORSPORTS sells the conical copper "flare savers" that Carl mentions. So far -- I've never had to use them.

Good call Greg. I was thinking downstream of the relay.

I know you know that -- but I try to post so that someone that isn't as familiar with all of this kind of stuff doesn't make a big mistake....

Many of the 'circuits' in an ECU use only 5volts.... and we don't want to be putting 12 volts to them! So I don't use a test light in electronic circuits -- I save that for checking a light bulb circuit... :D