RJM fuel injection harness question

[Stevenb]

Hello! I’m having a couple of issues. 68 Bronco, 351w with 5.0 fuel injection. Run harness. C4, 37’s, etc.
so last year my fuel accumulator filter went tu. It’s about ten years old. So I replaced it. Drove a bit. Had to replace brake lines due to them swelling shut. Fun stuff like that. Didn’t drive it much this winter. Just started it the other day. Starts. Runs. Drives about 8 blocks. Dies. Like it’s out of gas. I check the filter. The rubber bladder ish thing inside looks s sucked into the holes of the filter. No fuel is getting through. I look for the obvious issues. Sparks good. But no fuel from the low pressure pump. I can use a power probe and it runs fine.
Now the issue(s). I test voltage. At the high pressure pump it starts at 12, then drops to 6.5. The low pressure pump only gets 2.9. The wires look fine. Relays I replaced. Is it the computer? I’m just not sure where to look from here. Thanks for the help!

 

[DirtDonk]

If the relays are new then I think it has to be the wires. You should check the outputs at the relay sockets though. Just to make sure they’re not corroded inside or something that might be reducing voltage.
Why it starts higher and gets lower I’m not sure, other than resistance building up heat, then more resistance.
Something getting old.

Check, refresh, renew, replace, or just add new grounds. I believe the computer simply switches the ground side of the relay, therefore should not really have anything to do with the voltages dropping at the load.

Hopefully somebody else has some more and better ideas. But with the long-term deterioration of your other items just from sitting, corrosion on electrical connectors becomes a high possibility.

 

[DirtDonk]

Of course I always like to fall back on the “new isn’t always good“ assumption. So the relays should not be ruled out completely. Just lower on the list.

 

[Stevenb]

I did switch several just double check them. I’ll keep looking. I’m hoping it’s not the computer. I have a spare, but not a modded A9L like the one I run. Thanks for the help!

 

[Jdgephar]

Computer just grounds the fuel pump relay's coil. It had nothing to do with the low voltage at the pumps. Check the grounds, inspect all connectors for any corrosion or overheating. After 10 years, its most likely a bad connection has developed somewhere in the circuit. It takes some current flow to overheat and then drop the voltage to the pumps.

Sent from my SM-G981U using Tapatalk

 

[904Bronco]

Do you have an inertia switch? Check it it to see if it is partial popped, Reset if needed. And/or ... Then take it out of the circuit (bypass it with a jumper) and see if the voltage goes up.

 

[Stevenb]

Do you have an inertia switch? Check it it to see if it is partial popped, Reset if needed. And/or ... Then take it out of the circuit (bypass it with a jumper) and see if the voltage goes up.

I pulled it off the kick panel, smacked it to trip it and reset it. No change. I’ll try to bypass tomorrow.

 

[Rustytruck]

The low voltage concerns me. check battery voltage check voltage getting to the relay and check voltage going to the pump. if you have a fuse for the relays check it. you may have rodent issues? if the relays are working you should get full battery voltage to the pumps I suspect the ground side of the relay if you have full power going in. hooking the oxygen sensor wrong can burn a trace on the computer main board the infamous computer swap problem between manual and automatic. or an exploded capacitor on the computer main board. Have the caps been replaced on you computer?

 

[Stevenb]

Thank you! No rodent issues. I have to check the voltage after I figure out which is the “out” from the relay.

 

[DirtDonk]

Luckily these are (usually anyway) the standard "Bosch type" relays that have an industry standard pin layout.
One of the sockets in the, well, socket(!) will have battery power all the time. With any luck you can find an imprinted diagram right there on one of the relay's surfaces. Sometimes silk screened on top or a side, sometimes molded into the plastic on the bottom. But usually there if you look

The location with constant power is pin #30. Measure voltage and make sure it's within .25v of battery voltage. For stuff like this, always know what the battery charge is, so you can tell if there is a big loss or not. With this short run on large gauge wire, your pin #30 locations should literally have full battery voltage. If it's more than .5v less, there might be a problem with a connection.

When you turn the key to the ON position, another location will test positive voltage. This is your pin #86 (but can be #85 without causing trouble).
Same test here, but if you lose a volt or two it will still switch. Still, any loss of voltage is something to investigate.

The pin #85 is ground and that can be tested with an ohm-meter, but I'm not sure how it's supposed to act because that ground is usually controlled by the computer. So you may not see a simple ground connection when testing. Maybe someone knows how to do that.

The pin #87 is where the power goes out to the devices (pump, ECM, O2 sensor, etc) and you can check those with an ohm-meter too, but it's awkward due to the locations of the ends. However, with the relay installed and the key ON you should be seeing full voltage. Which you're not currently from your previous tests.

If you have a pin #87a this is not used in our situation. It's an "on with the key OFF" circuit that sometimes is needed. Not in our case though.
You can view the diagram on the side of the relay to see the pin orientation. They are "keyed" so to speak so that not only will the relay go into the socket only one way, but you can see what pin is what by the direction it's facing, even if it does not have a number by it.

Paul

 

[Stevenb]

Luckily these are (usually anyway) the standard "Bosch type" relays that have an industry standard pin layout.
One of the sockets in the, well, socket(!) will have battery power all the time. With any luck you can find an imprinted diagram right there on one of the relay's surfaces. Sometimes silk screened on top or a side, sometimes molded into the plastic on the bottom. But usually there if you look

The location with constant power is pin #30. Measure voltage and make sure it's within .25v of battery voltage. For stuff like this, always know what the battery charge is, so you can tell if there is a big loss or not. With this short run on large gauge wire, your pin #30 locations should literally have full battery voltage. If it's more than .5v less, there might be a problem with a connection.

When you turn the key to the ON position, another location will test positive voltage. This is your pin #86 (but can be #85 without causing trouble).
Same test here, but if you lose a volt or two it will still switch. Still, any loss of voltage is something to investigate.

The pin #85 is ground and that can be tested with an ohm-meter, but I'm not sure how it's supposed to act because that ground is usually controlled by the computer. So you may not see a simple ground connection when testing. Maybe someone knows how to do that.

The pin #87 is where the power goes out to the devices (pump, ECM, O2 sensor, etc) and you can check those with an ohm-meter too, but it's awkward due to the locations of the ends. However, with the relay installed and the key ON you should be seeing full voltage. Which you're not currently from your previous tests.

If you have a pin #87a this is not used in our situation. It's an "on with the key OFF" circuit that sometimes is needed. Not in our case though.
You can view the diagram on the side of the relay to see the pin orientation. They are "keyed" so to speak so that not only will the relay go into the socket only one way, but you can see what pin is what by the direction it's facing, even if it does not have a number by it.

Paul

Thank you! I greatly appreciate the help. Just working through that now. At the high pressure pump it still just jumps to battery voltage and back down after a couple of relay clicks but I’ll check voltages and ohms now. I appreciate the help.

 

[Stevenb]

Luckily these are (usually anyway) the standard "Bosch type" relays that have an industry standard pin layout.
One of the sockets in the, well, socket(!) will have battery power all the time. With any luck you can find an imprinted diagram right there on one of the relay's surfaces. Sometimes silk screened on top or a side, sometimes molded into the plastic on the bottom. But usually there if you look

The location with constant power is pin #30. Measure voltage and make sure it's within .25v of battery voltage. For stuff like this, always know what the battery charge is, so you can tell if there is a big loss or not. With this short run on large gauge wire, your pin #30 locations should literally have full battery voltage. If it's more than .5v less, there might be a problem with a connection.

When you turn the key to the ON position, another location will test positive voltage. This is your pin #86 (but can be #85 without causing trouble).
Same test here, but if you lose a volt or two it will still switch. Still, any loss of voltage is something to investigate.

The pin #85 is ground and that can be tested with an ohm-meter, but I'm not sure how it's supposed to act because that ground is usually controlled by the computer. So you may not see a simple ground connection when testing. Maybe someone knows how to do that.

The pin #87 is where the power goes out to the devices (pump, ECM, O2 sensor, etc) and you can check those with an ohm-meter too, but it's awkward due to the locations of the ends. However, with the relay installed and the key ON you should be seeing full voltage. Which you're not currently from your previous tests.

If you have a pin #87a this is not used in our situation. It's an "on with the key OFF" circuit that sometimes is needed. Not in our case though.
You can view the diagram on the side of the relay to see the pin orientation. They are "keyed" so to speak so that not only will the relay go into the socket only one way, but you can see what pin is what by the direction it's facing, even if it does not have a number by it.

Paul

Ok. So the relay with the pink wire read 6.33on the output terminal. I can hear all of the relays clicking when I turn the key on. At first it’s 12 volt then drops to 6.33. Any ideas? I checked grounds and I seem to be good all over. I swapped all of the relays too. I’ll work on it more tomorrow. Thank you for the help.

 

[DirtDonk]

Just off the top of my head the Pink wire sounds like fuel pump, which is consistent with this discussion. But whether the Pink wire goes out to the fuel pump, or comes in from the Inertia Cut-off Switch, I don't know.
If it's the output to the pump, then there's your problem. It's not supposed to drop voltage. Where are you measuring though? If it's after the relay, then the relay may be bad. But you said you swapped relays, correct? In that case there would seem to be something amiss with either the connectors inside the relay socket, or the wires leading up to it.
Perhaps it's the main power feed and all the others are suffering the same fate but don't show it as much as the more needy fuel pump.

So let us know where exactly you were measuring output voltage on the Pink wire. That might help us narrow it down some.

Paul

 

[jamesroney]

Just off the top of my head the Pink wire sounds like fuel pump, which is consistent with this discussion. But whether the Pink wire goes out to the fuel pump, or comes in from the Inertia Cut-off Switch, I don't know.

The pink wire that goes from the fuel pump to the inertia switch is labeled “fp - inertia”.
The other pink wire that is labeled “Relay 2, terminal 87 to Inertia switch” goes from the fuel pump relay (R2,) terminal 87 to…the inertia switch!

I just happen to have my dash out, so enjoy the pics.

 

[DirtDonk]

Good timing James!

So the switch is between the relay and the pump then, and not the switching source and relay? Makes sense, but I was thinking it was cutting off power to the relay rather than cutting off power to the pump directly.
Still, if the OP is measuring voltage output after the switch, it would follow that something could be amiss inside the inertia switch itself. Looks like an easy thing to check both before and after power levels.

Unless I missed something in the previous descriptions, we need to find out where the testing is being done and where the power is being reduced.

Paul

 

[jamesroney]

Good timing James!

So the switch is between the relay and the pump then, and not the switching source and relay? Makes sense, but I was thinking it was cutting off power to the relay rather than cutting off power to the pump directly.
Still, if the OP is measuring voltage output after the switch, it would follow that something could be amiss inside the inertia switch itself. Looks like an easy thing to check both before and after power levels.

Unless I missed something in the previous descriptions, we need to find out where the testing is being done and where the power is being reduced.

Paul

Yep, I could see where you were headed in your thought process. But remember that all of those Ford inertia switches were mounted in the trunk tail light panel, (near the tank) and the relays are mounted up front. So they do indeed sit on the load side of the relay and carry all of the fuel pump current.

The OP was asked to measure the voltage on the relay (line and load side) back in post #8 in the thread. Until he does that, I can’t help.

 

[Stevenb]

Just off the top of my head the Pink wire sounds like fuel pump, which is consistent with this discussion. But whether the Pink wire goes out to the fuel pump, or comes in from the Inertia Cut-off Switch, I don't know.
If it's the output to the pump, then there's your problem. It's not supposed to drop voltage. Where are you measuring though? If it's after the relay, then the relay may be bad. But you said you swapped relays, correct? In that case there would seem to be something amiss with either the connectors inside the relay socket, or the wires leading up to it.
Perhaps it's the main power feed and all the others are suffering the same fate but don't show it as much as the more needy fuel pump.

So let us know where exactly you were measuring output voltage on the Pink wire. That might help us narrow it down some.

Paul

I was measuring on the bottom of the relay socket. I did switch to several different relays. On all of them. It’s got full voltage in on all relays. Just that one on output is low. But like I said it started at 12 and the. Drops fast to 6.3.

 

[Broncobowsher]

6.3 on the output only, or input and output?

 

[Stevenb]

Only on output.

 

[Broncobowsher]

Toss a relay in. Cheap enough and looks to be an issue.