Fuel module replacement part for C3500

[Yamaben]

This thing is called fuel module or hot fuel module. It runs the fuel pump when the key is turned on. Mine smoked and quit working.

You must be registered for see images attach

I ordered a used one for $25 and it was bad too. My original is on the right the junkyard one is on the left. I couldn't find a new replacement part as ot seems like nobody makes it.

You must be registered for see images attach

I saw a member on this forum had the same problem, but he is apparently an actual wizard and is able to make little circuits and program them as a replacement part for this thing.

You must be registered for see images attach

You must be registered for see images attach

The little circuit board pushed right in. It works great! I wondered if this dude was gonna scam me, but nope...he sent it right out and it works!

The more I search about this module, the more I find people having the same problem. Buy one from 92landyacht and fix yours before it smokes.

 

[92Landyacht]

Wow, those old modules were sure toasted. Unfortunately that's what I've seen on others. Thanks for the honest assessment.

 

[Yamaben]

Would this module handle higher current from a walbro 255lph fuel pump?

 

[Schurkey]

Would this module handle higher current from a walbro 255lph fuel pump?

No. Because this module doesn't power the fuel pump directly, it powers the fuel pump relay which takes nearly no current. The relay powers the fuel pump.

 

[92Landyacht]

No. Because this module doesn't power the fuel pump directly, it powers the fuel pump relay which takes nearly no current. The relay powers the fuel pump.

Actually that's not correct. It parallels the fuel pump relay's output so it does power the fuel pump directly until the engine starts. Once that occurs the fuel pump relay will take over unless oil pressure fails or the ECM stops seeing distributor pulses. The hot fuel module only provides power for the programmed time (OEM=20 seconds, 12 or 20 seconds for the new module) and then stops providing power unless the ignition is cycled again.

To answer Yamaben's question, it can provide up to 20 amps but that only occurs for the maximum programmed time. After that it cuts off and all power to the fuel pump is through the OEM fuel pump relay circuit, so it really doesn't add any long term current increase to the pump.

 

[Schurkey]

Thanks for the correction.

 

[92Landyacht]

Thanks for the correction.

No problem. Here's a diagram of how the module interfaces with the fuel pump relay, ECU and oil pressure switch.:

You must be registered for see images attach

Note that the Tan/White wire is the output of the HFM but is also the output of the fuel pump relay, the oil pressure switch and the ECU fuel pump signal input. The Dk Grn/Wht wire from the ECU is the wire that actually turns on the fuel pump relay.

 

[92Landyacht]

Ben, as I stated in my PM, I will be sending you a newer board as soon as I get it in hand. The board I sent you was the revision 5.0 board that didn't have reverse voltage protection and I would really like you to have the latest version of the board.

 

[Schurkey]

No problem. Here's a diagram of how the module interfaces with the fuel pump relay, ECU and oil pressure switch.:

You must be registered for see images attach

Note that the Tan/White wire is the output of the HFM but is also the output of the fuel pump relay, the oil pressure switch and the ECU fuel pump signal input. The Dk Grn/Wht wire from the ECU is the wire that actually turns on the fuel pump relay.

What model year/vehicle is that diagram for?

I have a service manual on DVD (Bishko) for C/K for '97; and that section on fuel pump wiring is missing. It goes from section 8A-17 to section 8A-30, and the fuel pump stuff is supposedly in section 8A-20.

I'm curious as the diagram says "5.7 (over 8500 GVW) and all 7.4L" but I haven't noticed extended priming time on my '97 7.4L K2500.

I also have extended cranking time when warm. I've been suspecting the injectors, but
maybe I need one of those modules.

 

[454cid]

What model year/vehicle is that diagram for?

I have a service manual on DVD (Bishko) for C/K for '97; and that section on fuel pump wiring is missing. It goes from section 8A-17 to section 8A-30, and the fuel pump stuff is supposedly in section 8A-20.

I'm curious as the diagram says "5.7 (over 8500 GVW) and all 7.4L" but I haven't noticed extended priming time on my '97 7.4L K2500.

I also have extended cranking time when warm. I've been suspecting the injectors, but
maybe I need one of those modules.

I think this module is a TBI thing. Other than injectors, I'd check fuel pressure for your issue.