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Discussion Starter #22
TMT, you are correct. My reading at inertia was KOEO. Started chasing plugs and seeing 5.4V at pump now KOEO. I checked/cleaned the plugs you referenced. About to clean the 2 grounds you pointed out in an earlier post. Are there any other known connection points to check? Really don’t want to fry yet another pump. Thanks.
 

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Discussion Starter #23
Up to 7v now KOEO at pump after cleaning grounds. What should this pump be seeing KOEO?
 

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Did you clean the ground at the firewall by the master cylinder? Among other things, it's the ground for the fuel pump.


It should be whatever the battery is at, initial Key-On that may be 11.5v before engine start.

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You were at 11.37 at the inertia switch,that's what should be at the pump at that time.

Again, this is a 2003 layout. Edit - you can see all the connections.


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If with the new HFCM you got a new short harness for by the fuel pump, I'd be using that.
 

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Discussion Starter #27
Up to 10.4V not after cleaning grounds and remaining plugs. Still a 1v avg drop from inertia switch. No plug came with this HFCM. Cleaned everything I can find this far and no loose connections.
 

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Def whatever voltage is at the inertia switch, should be available at the pump connector
are you testing this circuit with a load on it?

you can connect a light bulb like a headlight to the connector so you dont fry the new pump while looking for the bad connection
 

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Discussion Starter #29
Ok, figured I would go ahead and fire it up to verify voltage under load. KOEO I am seeing 12.3v at pump connector. Fired right up and idles very smooth. Hopefully I have this locked once and for all.
 

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When I got an HFCM, it came with this harness.

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You should not have a 1.0-volt drop across the inertia switch ... nothing close to that.

Hydro's suggestion for another load source is a good one. I'd rather have a load close to the pumps.
 

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Discussion Starter #33
My truck already has that harness installed, so likely the pump had been changed prior to my dilemma. Ran truck for about 10min w/out issues and saw 12.3V at pump plug. Going to button it all back up and road test in neighborhood to make sure everything is correct.
 

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FYI - The late build 2005 trucks should have had that harness with the heater disabled.
 
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