Thread: EFI/ECM Wiring ???

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My E-Z Wiring harness has a fusible link that is to be installed at the starter post/bulkhead and crimped to the #10 fuse block feed so that all feeds are fused. The Edelbrock ProFlo XT EFI is made as an add-on system for carburated engines, and the wiring has one power lead that they say is to connect to the starter hot post for a constant feed, and a second switched 12v lead to control the system. The fuel pump is controlled by the ECM, which is normal for an EFI system.
I am hooking the main feed from the + bulkhead connector to a four post terminal block using the supplied fusible link, then taking feeds to 1) fuse block, 2) SPAL Fan, 3) VA Heater/AC, and 4) ECU from that TB. The SPAL fan has an in-line fuse, and the VA has a breaker. My concern is the ECU feed, and especially the fuel pump - if the fuel pump shorts out the fusible link is the only circuit protection and that takes out everything. I'm thinking of replacing the fusible link with a Maxi-Fuse, and using a "Smart Fuse" that lights up when blown just to minimize the troubleshooting in a future problem, but I'm still questioning not having the fuel pump fused. Has anyone run into this, and how do you handle it?? In-line fuse in the pump wiring (not ideal, IMO, but may be the only way)?

isnt the wire going to the pump a kicker for a relay ? and i would never never feed the computer for a EFI off the starter post , go straight to the battery .

Kenny is right....the controller cannot source enough current for the fuel pump....it's a fuel pump relay wire.

mike in tucson

Originally Posted by kennyd

isnt the wire going to the pump a kicker for a relay ? and i would never never feed the computer for a EFI off the starter post , go straight to the battery .

Kenny,
You are 100% right - I should have gone into the schematic before posting. The under-dash wiring is my last piece to do today and I overlooked the two fuses that are in the support wiring for the Edelbrock system. The main power feed is into a 20a fuse and then to the fuel pump relay. I have this connection coming off of the bulkhead connector through the firewall (battery post and 18" cable to the bukhead). That is as close to a direct battery connection as I can get. The 12V switched feed also goes through a 3a fuse, then powers the ECU. That one comes from the ignition switch.

Tracing the circuit helped me know that Edelbrock took the main power feed into the engine harness (assumes under hood battery), through their bulkhead connector into the main harness, out to the fuse/relay and then back out via their bulkhead to the engine harness and the pump connector. Lots of trips through the firewall...

Thanks for getting my head straight.

i would still not connect it to anything except the battery , i have had efi from , FAST,BIGSTUFF3,HILBORN,STREETANDPERFORMANCE all tell me only direct to the battery because of interference with computer . i had a hilborn efi that would not run correct it was that connection at the starter that caused the poor run problem .

Originally Posted by kennyd

i would still not connect it to anything except the battery , i have had efi from , FAST,BIGSTUFF3,HILBORN,STREETANDPERFORMANCE all tell me only direct to the battery because of interference with computer . i had a hilborn efi that would not run correct it was that connection at the starter that caused the poor run problem .

Kenny,
You're talking about the main 14ga wire that goes to the fuel pump relay and out to the fuel pump and no where else, right? Everything else in the system is powered from the little 3A switched feed per the schematics, and that has to be switched. Not sure how the power feed to the fuel pump can pick up anything through 18" of 0 gage cable, but I will remember this comment. If there's a problem I can cut that relay power feed and jumper it to the battery post about 12" away.

no , i am talking about the constant feed for the computer only . the main power wire for it should be direct to the battery as should the ground for it .

Originally Posted by kennyd

no , i am talking about the constant feed for the computer only . the main power wire for it should be direct to the battery as should the ground for it .

You're getting me into the Edelbrock schematic up to my chin (which is good)!!

Edelbrock requires two feeds:
1. Switched feed, hot in both "start" and "run", which turns on the fuel pump relay; and then powers the calibration module plug, the ECU and the distributor.
2. Battery positive, which they say is to be "an uninterrupted +12v source such as the positive terminal on the starter solenoid" (quote from installation manual). This supplies the fuel pump relay ("30" contact), which is turned "on" from the switched feed above (not really uninterrupted ) and it powers the fuel pump; the map, O2, air temp, coolant temp sensors; the injectors; and the coil +.

There really is not a constant feed to the computer or any EFI component (other than the "30" contact on the fuel pump relay) the way this is wired and controlled. I am using the EZ Wire fuse block feed allocated for "Coil" for the switched feed to the EFI wiring which should be ideal - hot in start & run, fused. The second feed I now have from my bulkhead connector on the firewall, direct from the battery+. There is also a 12" long battery cable from that bulkhead connector to the starter feed.

If there is somehow some power interference to sensors or injector feeds my solution would be to disconnect the EFI power feed on the firewall bulkhead, abandon that conductor into the EFI harness, and run the wire powering the "30" contact on the fuel pump relay direct to the +battery post. I don't see how this can be a problem and there will be some discussions with Edelbrock before I do that, but I appreciate knowing that it might be a gremlin waiting to bite.

the one i am talking about is your #2 , battery positive wire .