Broken Fuel Module?

[adamj]

1,500 lb. 87 V20 Suburban, so I have the heavy duty fuel module that keeps the fuel pump running for 20 seconds instead of 2 by overriding the ecu/m.
I noticed today that my fuel pump only stayed on for 2 seconds, and I had a longer, more difficult cranking time (~3-4 seconds to start up). Any correlation there? Do these modules ever go bad? Here is a picture of what should be the fuel module itself, I cleaned out the connector, but still only 2 seconds of fuel pump. Should I be concerned about my fuel pump going bad, or anything else?

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[adamj]

Update: I tested wires.
- black/white = ground: all good.
- tan/white = continuity to fuel pump (via relay): all good.
- pink/black power = only got 1.5 V (does it need the full 12V?)

 

[adamj]

One more thought:
Even if the module is faulty, I don't think it should be causing extended crank times, right? Engine should be able to start right up normally with 2 seconds of fuel pump prime, the extra 20 seconds that is applied to heavy duty models above 8600 GVWR is just for hot starts/extreme conditions, do I understand this correctly??

 

[chengny]

Update: I tested wires.
- black/white = ground: all good.
- tan/white = continuity to fuel pump (via relay): all good.
- pink/black power = only got 1.5 V (does it need the full 12V?)

The tan/white is the power output from the module to the pump - but it doesn't go through the relay, it just splices onto the normal power feed at the relay's harness connection.

You should see 12VDC at the pink/black lead. That is the auxiliary power supply into the module.

As you know:

1. If the ECM doesn't see a pulse from the distributor after two seconds, it gives up and kills power to the pump.

2. The oil pressure switch is supposed to provide a secondary power supply to the pump. But it won't close - and complete the secondary power supply circuit - until 4 psi is developed in the lube oil system. It is possible your oil pressure switch is not working (and you just haven't noticed due to the presence of the module which has been providing the fuel pump's power supply). Or maybe your engine is not as tight as it once was and it just takes a little while longer to build up that 4 psi in the lube oil system.

3. The third method (the module) of keeping the fuel pump running - until the engine fires - is only used on heavy trucks and those with 454 engines. It has a power feed from the fuse block (via the ECM/IGN fuse) that is independent of the power supply to the oil pressure switch and FPR. That is the pink/black lead that connects to the "C" terminal on the fuel module.

If there is only 1.5 VDC there, check the fuse and associated wiring.

Description of operation for the fuel pump circuit - including module applications:

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Diagnostic chart. Only for the standard fuel pump power circuit - does not include module troubleshooting:

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[adamj]

False alarm on the long cranking, it was just a weird coincidence that I noticed the fuel pump stopped and then it taking longer than usual for a few start ups back-to-back when I was out running errands. It starts up just fine now that I've taken it out a few times. But fuel module is still not kicking in. Engine is in good health, it is not worn out, oil pressure is great. I'll check again if I can get power to the fuel module, but if not, I might just leave it as is...

 

[adamj]

Problem solved, fuel module is working again.
I found a blown 20A fuse called: "Gage/Idle"
Replaced that and it works, I guess that's where the module gets its power from. I checked ECM/IGN fuse, that was fine.