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Old 09-26-2006, 05:22 PM
will e's Avatar
will e will e is offline
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Holley Projection /fuel pump/ electric relay problem

Holly ProJection, 2bbl, analog unit. I have 2 fuel pumps (one high volume low pressure feeding into the standard high pressure pump).

I have wired the two pumps using a standard 30amp relay (with two aux post (87)). I followed the holly instructions and all was working great until this weekend when we went wheeling

The main power wire rubbed and grounded. This blew the fuse. Fixed wire, replaced fuse and no worky. Long story short we wired the pumps directly to the hot from the battery (left the fuse in place) . This worked great except I have to pull the fuse to stop the pumps.

I went back out to work on it today. Still doesn't work.
I noticed while trouble shooting that the voltage from the ECU, red hooked up to post 85 and green hooked up to post 86, only produced 6.xx volts. So I hooked post 86 directly to ground (removing the green wire from the ECU). I got 12 volts and the truck runs. While running I checked voltage between the red ECU wire and the Green wire (not connected to anything) and it was less than 1/2 volt. Is this normal? WOuldn't 6 volts still be enough to get the relay to flip??

Like I said, hooking the 86 post to ground and it works great. However, this causes the pumps to run whenever the ignition is on. This isn't correct (the unit normally turns off pressure if there is no rpm signal)

Thoughts?
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Last edited by will e : 09-26-2006 at 05:36 PM.
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Old 09-26-2006, 05:38 PM
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will e will e is offline
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Okay, I tested it during 'crank'. At this point the ECU ignores the TACH signal and should send some volts to what it believes is the fuel pump. I got less than 1/2 volt.
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Old 09-26-2006, 06:03 PM
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me again.

Put my spare ECU (from my mustang) in and it fired up and acted 'normal' I must have blown the ECU resistor.

Intresting to note, the holly instructions show the red wire from the fuel pump cable to post 85 on the relay (normally ground) and the green wire to post 86 (normally switched).

I tested the voltage with the truck running 12 volts from the ECU.

I will leave this set of posts here in case someone has a similar problem.

Anyone got a spare 2bbl analog ECU?
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Old 09-26-2006, 08:31 PM
Joe Guilbeau Joe Guilbeau is offline
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There is a transistor that is used inside the ECU to power up the fuel pumps, this will fail when stressed.
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Old 09-26-2006, 08:34 PM
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Kenall Kenall is offline
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do you have an oil press cut off switch for the pumps??..its recommended.
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Old 09-27-2006, 11:55 AM
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Kenall - The ECU has a RPM sensor. If the engine isn't turning it shuts off the fuel pump. (It also knows when you are cranking the engine and turns the pump on).

Yeah, with the 'work around' the pump is on when the ignition is in the ON position. Not GOOD. I won't drive it that way.

I am in the market for a replacement ECU.
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Old 09-27-2006, 12:16 PM
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Twinpinion Twinpinion is offline
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I had a similar problem. I ended up wiring the pump to a switch in the dash. Good theft deterrent too!
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