2.3L ('83-'97) Fuel pump secondary circuit failure

[Alex_g]

I've got a 92 2.3 and its throwing a 542 Fuel pump secondary circuit failure
and a 452 insufficient input from vehicle speed sensor

I drove out to the garbage dump no problem started it up and drove it a couple hundred feet to drop off my recycling and it wouldn't start. Fuel pump will prime once if you disconnect and reconnect the battery but then the starter will just click once like it has a dead battery every time you try to crank it after the battery disconnect.
I did a little diging on the forums here and the only solution i found was a bad ground by the electronic brain/ CPU on the utside passenger side footwell wall. I cleaned paint off the grounds buy the CPU and checked the inertia switch and still nothing.
Once I'm home where should I start looking? I checked my Haynes manual and couldnt find anything about a fuel pump secondary circuit.

 

[scotts90ranger]

That sounds reasonable, they could be related but I don't know the circuit for the VSS very well, I think it uses the one on the end of the speedo cable for that. As for the fuel pump circuit, there's a feedback wire into the computer out of the fuel pump relay which is probably the code you are getting. The problem could be a connection in the power distribution box on the passenger inner fender which is where the fuel pump relay is. I would pull the fuses and relays in there to see if any are blown or corroded.

 

[Alex_g]

That sounds reasonable, they could be related but I don't know the circuit for the VSS very well, I think it uses the one on the end of the speedo cable for that. As for the fuel pump circuit, there's a feedback wire into the computer out of the fuel pump relay which is probably the code you are getting. The problem could be a connection in the power distribution box on the passenger inner fender which is where the fuel pump relay is. I would pull the fuses and relays in there to see if any are blown or corroded.

I checked the fuses in the fuse box. I'm assuming you were talking about the obvious one right up on top on the passenger side and there all good.
I was looking around the CPU a bit more and I saw a broken white wire connected to what looks like a small fuel filter under my glove box. Any idea what it is?

 

[sheep herder]

The white "wire" is a vacuum line. I believe it's for the blend door.

 

[Alex_g]

Jumped in the truck and put my foot on the break, key not in the ignition, and heard a click from up front under the hood, CEL and battery light came on, my oil pressure needle jerked to max and my engine temp needle slowly swung to max as well. Which is odd because the temp gauge hasn't worked since I bought the truck.

I'm guessing that the vacume line isn't playing into my current problems but good to know what it is. I'll add it to the list of things to fix.

 

[pjtoledo]

in OBD 1 the 542 secondary circuit failure is set anytime the engine stalls. or at least it does in a '92 Taurus.
it's not an issue.

 

[Alex_g]

Did some searching on youtube and found how to access the fuel relay. As I was lifting the fuse box out I heard something drop from underneath. Found a grounding strap laying down there broken off on one end and disconnected on the other.
I can't find where it used to be connected too. Anybody know where it should be attached too?

 

[RonD]

Fuel system Primary circuit is the fuel pump RELAY's coil, computer grounds this coil to activate this relay

Secondary circuit is the 12volts that goes THRU this relay to the inertia switch in the cab and then to the fuel pump
Computer pin 8 has a connection to the wire that from relay to inertia switch, dark green/yellow stripe wire
If Computer doesn't "see" 12volts on this wire when it Grounds the Relay, it will set 542
(just FYI, when computer is on pin 8 will have 5-8volts, no amps, so you might see 5-8v at inertia switch, its not fuel pump power, its just from the computers monitor circuit)

Battery----FP Fuse-------FP relay----/------inertia switch----------------------Fuel pump(FP)
Computer pin 8---------------------/


Computer pin 22 grounds the FP Relay, and you can manually ground the FP relay as well at the OBD1 connector

Look here: https://www.therangerstation.com/tech_library/OBD_I.shtml

In the second drawing the Fuel Pump slot in the OBD connector is labelled
The computers pin 22 wire runs to this slot and then another wire in same slot runs to FP relays coil to ground it
The FP Relays coil gets 12v from the EEC relay with key on

So you can use a volt meter, key on, and test that slot for 12volts, should be 12v with key on(if not then wiring issue at relays)
Then Ground that slot, key on, and you should hear FP Relay click closed, and it should stay closed until key off or you remove the Ground jumper in that slot

 

[Alex_g]

Fuel system Primary circuit is the fuel pump RELAY's coil, computer grounds this coil to activate this relay

Secondary circuit is the 12volts that goes THRU this relay to the inertia switch in the cab and then to the fuel pump
Computer pin 8 has a connection to the wire that from relay to inertia switch, dark green/yellow stripe wire
If Computer doesn't "see" 12volts on this wire when it Grounds the Relay, it will set 542
(just FYI, when computer is on pin 8 will have 5-8volts, no amps, so you might see 5-8v at inertia switch, its not fuel pump power, its just from the computers monitor circuit)

Battery----FP Fuse-------FP relay----/------inertia switch----------------------Fuel pump(FP)
Computer pin 8---------------------/


Computer pin 22 grounds the FP Relay, and you can manually ground the FP relay as well at the OBD1 connector

Look here: https://www.therangerstation.com/tech_library/OBD_I.shtml

In the second drawing the Fuel Pump slot in the OBD connector is labelled
The computers pin 22 wire runs to this slot and then another wire in same slot runs to FP relays coil to ground it
The FP Relays coil gets 12v from the EEC relay with key on

So you can use a volt meter, key on, and test that slot for 12volts, should be 12v with key on(if not then wiring issue at relays)
Then Ground that slot, key on, and you should hear FP Relay click closed, and it should stay closed until key off or you remove the Ground jumper in that slot

Ok so there is 12v at the FP slot and the fuel pump runs some of the time when the slot is grounded and the relay clicks most of the time, there is also a faint click from something right around the TPS or the back side of the throttle body when the fuel pump is grounded. Is that an indication of a bad relay or a bad fuel pump? I also tested the inertia switch and it is getting power and the switch is itself is good as well.

If I remove the ignition relay the check engin light turned off and only the oil pressure gauge moves to the top of their range when I step on the break pedal? It makes me think that something is shorted out with the break lights.

 

[RonD]

As for the brake pedal check the ground strap from the engine to the firewall, thats the main ground for all the cab electrics
Make sure its there(often gets left off after engine work) and if you can't find it add one, a ground wire from engine bolt to firewall bolt


Not clear on your FP relay adventure
If relay is clicking then replace it, its either on or off, should click at all while engine is running

 

[Alex_g]

Sorry for the late reply to this thread. But I think the problem has been found. My brother, who happens to be a mechanic, came over the other weekend he lives in Idaho or I would have had him look at it sooner. After maybe 5 minutes of testing things I had already tested he bumped the negative battery cable and a relay clicked. We opened up the negative battery terminal and sure enough the inside was coated in corrosion and the wires were corroded back into the wire insulation.
We stripped it back aways and re attached it. And re tested, everything but the starter seems to work now. Fingers crossed that this is the last thing I have to replace on the truck for a good long while

 

[RonD]

Good stuff, thanks for the update

 

[tomw]

There is/was a kinda hint that the gauges started moving when the brake pedal was pushed. Most times when that sort of thing happens, current is flowing and finding a ground(compared to infinite ohms of a broken circuit) via something that is just a bit closer to ground. More or less.
The 'starter will just click once' is another signal that a poor connection exists that forms and breaks when it tries to deliver a lot of amps. If everything goes 'dead' immediately after trying to start, first thing to look for seems to be a loose battery cable or terminal, or in this case, hidden corrosion.
tom