'93 chevy has this code DTC 54 PCM fuel circuit error

[hrc200x]

93 chevy 4x4 1/2 ton 350 motor. Get this code as of recently: DTC 54 PCM fuel circuit error

Its hard starting when cold, seems like it helps to give it some throttle when trying to start it. Where do I start looking for a problem?

[rokitdude]

Replace your fuel pump relay. It's on the top of the firewall on the engine side - very easy job.

Your relay is probably dead, and your fuel pump won't come on until there's enough oil pressure to activate the oil pressure switch. Both the relay and the switch provide juice to the pump.

The Code 54 means low/no voltage is getting to your fuel pump for at least 5 milliseconds while the ECM is on.

[ChevyTech]

I second what rokitdude said. It sounds like your fuel pump relay is not working.

The PCM controls the fuel pump relay.
A code 54 happens when the computer does not see power on the circuit from the fuel relay to the fuel pump, when the computer is sending power to the relay to apply the relay.

Sometimes when the fuel pump is failing the currant flow through the pump goes up considerably. This tends to damage many of the parts of both of the fuel pumps redundant circuits melting and damaging the connection at the fuel pump, fuel tank sender and wire harness.

[catch-22]

This is a perfect example of how this board can be so helpful. Getting an answer like saves so many people time and $$ - that's pretty cool!

[rokitdude]

ChevyTech,
Would you happen to know if there's a reference anywhere listing the amperage pull range of healthy GM fuel pumps?

I am a bit suspect of my pump lately (long story), and it seems like an ammeter check of the hot lead would be a good check. I've got a Delco EP381 pump.

[hrc200x]

Took off the black cover held on by 3 plastic nuts. I'm assuming the relay is the black thing with about 6 wires going to it and its held on by 2 bolts?

I was looking more for the type of relays that the Boss snowplows use for the headlights, small little square boxes with 4 to 6 metal tabs sticking out on one side.

Got one set aside at NAPA for $17.

[ChevyTech]

Originally Posted by rokitdude

ChevyTech,
Would you happen to know if there's a reference anywhere listing the amperage pull range of healthy GM fuel pumps?

I am a bit suspect of my pump lately (long story), and it seems like an ammeter check of the hot lead would be a good check. I've got a Delco EP381 pump.

If this is for your 1994 big block, at the information area of your posts, I think in 1994 and 1995 the big-blocks had the smaller injector with much higher fuel pressures of around 26-32psi. I have not tested these pumps to know a baseline current draw them. For the lower pressure TBI trucks, my guide-line for the current draw of a good pump is it should be under 3.75 amps.


If the fuel pump current draw is high, it could cause the contacts inside the relay to get hot, and or ark, damaging the relay which could cause a code 54.

If current draw is high it can also damage connections in the circuit and pull the voltage low causing a code 54 to get set.

When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through an oil pressure sensor/sender/switch.

Any time a fuel pump relay fails it is a good idea to test the redundant circuit which goes through the oil pressure sender.

If you pull the fuel pump relay while the engine is running it should keep running. If it dies the oil sender or its wiring is bad or the engine lacks oil pressure.

Originally Posted by hrc200x

Took off the black cover held on by 3 plastic nuts. I'm assuming the relay is the black thing with about 6 wires going to it and its held on by 2 bolts?

A 1993 should have five wires to the fuel pump relay.

Wire colors:
Red
Dark Green with white tracer
Gray
Black with white tracer
Orange

[rokitdude]

Yeah, it's for the '94 454. The fuel pump is not stock however - I believe they came with a EP376 (?), and the Whipple blower requires an EP381.

My fuel pump voltage stays pretty constant at 13.8V on the road (according to Datamaster via ALDL).

[hrc200x]

Put in the new relay today. Truck hasn't been started in over a week, installed relay without starting truck, try starting truck and it turns over for 5-10 seconds with no start, give the starter a break and try again, probably another 5 seconds no start but a fire, try it again and it starts, so it seems like it might still have the same problem. Left motor running tried unplugging wires from relay and it stayed running, turned motor off, plugged back into old relay, started motor and unplugged, stayed running.

When I first plugged in the new relay I didn't have it bolted to the firewall, does it need to be grounded through the mount? From what I could tell the mount was touching nothing but plastic around the relay.

It did get down to 6 degrees lastnight, and probably was up to 10-14 when tried starting it, hopfully it was just cold as to why it didn't start right away.

Should codes be cleared before hooking up new parts (relay)?

Is there a way to clear codes with out unhooking battery?

[ChevyTech]

When I first plugged in the new relay I didn't have it bolted to the firewall, does it need to be grounded through the mount? From what I could tell the mount was touching nothing but plastic around the relay.

It does NOT need to be bolted down to work.

Should codes be cleared before hooking up new parts (relay)?

The code will clear itself after 50 key start cycles if you don’t clear it.

You don’t need to clear the code, but if you have more trouble with it not starting you may be wondering if the code 54 problem still exists, or if it is the old code you are seeing. I always clear the codes.

Is there a way to clear codes with out unhooking battery?

Yes, by pulling the fuses that power the PCM for 10 seconds.

I would be a good idea the replace the fuel filter, but I have a feeling you may be replacing your fuel pump soon.

[hrc200x]

"I would be a good idea the replace the fuel filter, but I have a feeling you may be replacing your fuel pump soon."

Such a shame, truck only has around 70,000 original miles on it. Stuff breaks whether you drive it or let it sit.

[rokitdude]

One thing to try...

Turn off the stereo and heater blower (just for noise purposes).
When the truck has been off for at least 10 seconds, turn the key to the "Run" position (without cranking). Listen for the fuel pump whine (it'll last 2 seconds). If you hear it, your relay is kicking on. Additionally, you could unplug the oil pressure switch while engine is running (if it's accessible) - if it keeps running your relay is on during run mode.

I had a GM troubleshooting flowchart that should work for that engine/chassis. I'll try and find it and post up.

[hrc200x]

Truck started today in 30 degree weather no problem, will have to wait for mother nature and try it on a colder day. Can you hear the fuel pump run right after the ignition has been turned off?

rokit: how do you like your 6.2 with a banks? What are some pros/cons? Had any motor problems? Help power a ton? Fuel milage increase?

I have a '92 6.5 TD and I can't belive it will only get 16mpg. 6.2's get low to mid 20s and I've heard putting a banks on a 6.2 increases fuel milage by 10% or somthing.