EFI low voltage at relay issue

[casadejohnson]

I just finished organizing the ECM wires and relays behind the dash for my EFI and I seem to have created a problem. Tried to fire it up after my little project and the fuel pump did not cycle when I turned the key nor does it run when you ground the wire at the self test connector that would normally cause the pump to run. Tested the power to the relay and I'm only getting about 5 volts same result at the EEC power relay. The power for the relays should be from pin 37 and should be 12 volts if I'm reading my old notes correctly ( Is that correct ? ). So where should I be looking to find my voltage drop?

A few other things to consider,

I drove it about 10 miles Saturday with no issues prior to starting my wiring organization project.

A few weeks ago I was driving it and it shut down on the highway because the fuel pump quit working. At the time I thought it was a loose ground at the fuel pump because cleaning and tightening up the ground wire seemed to fix it but perhaps there was an underlying issue at that time that is the same problem I'm having now?

I'm an idiot and I forgot to disconnect the battery before I started pulling out relays and disconnecting things for my organization project so there is a possibility that I fried something. I did eventually remember to disconnect the battery and I never shorted anything that I am aware of ( No sparks or anything along that line ) so I think frying something is not the likely culprit.

I have not tried to pull codes yet mostly because I'm too tired to accurately count flashes on my check engine light.

Any suggestions on what to test would be appreciated.

 

[DirtDonk]

I would normally point at the safety switch (if you have one) first, but since you said it happened before haphazardly, it sounds like something different.
Not sure about the low-voltage issue. Someone with more knowledge about that will though, I'm sure.

Don't think you hurt anything by pulling relays with power to the sockets. I do it all the time on modern vehicles. Not sure if there is any inherent danger to it based on how the harness is made, but it hasn't cause any trouble on other cars and trucks.
You could try swapping a few around too (which might happen automatically if you pulled them all) in case one of them is intermittently bad.

Good luck.

Paul

 

[Viperwolf1]

Check the ECM grounds and power connections.

 

[casadejohnson]

I just checked again and found my 12 volts to the relay (I didn't test every wire apparently) that comes from pin 1 i think. I have one ground to the engine and one that grounds to the dash. I added a third from the EEC case to the kick panel previously. All seem to have good contact. I'm testing at the back of the relay plug and have 12 v in all of the time and 5 volts from pin 37 if the key is on. I thought the relay might be bad because I never here it "click" so I tried a few ( 5 ) spares I had with no luck. Not likely that all of the relays are bad. In the diagram I have it looks like the EEC relay and fuel pump relay share the same ground wire. The EEC relay seems to function correctly and I can here the " click " from that relay.

Is it safe to pull the relay out and run a temporary jumper wire across to see if the direct power will turn on the pump? That would at least eliminate any issues from the relay to the pump.

 

[ransil]

The dash is the worst place to find a ground, it relies on 3 plus bolts a bracket and other sheet metal to find it way to the negative side of the battery.

I like a nice welded stud with a direct wire to the battery.

sheet metal screws make for shitty grounds.


edited bad info out.

 

[Viperwolf1]

I'm testing at the back of the relay plug and have 12 v in all of the time and 5 volts from pin 37 if the key is on. I thought the relay might be bad because I never here it "click" so I tried a few ( 5 ) spares I had with no luck. Not likely that all of the relays are bad. In the diagram I have it looks like the EEC relay and fuel pump relay share the same ground wire. The EEC relay seems to function correctly and I can here the " click " from that relay.

Is it safe to pull the relay out and run a temporary jumper wire across to see if the direct power will turn on the pump? That would at least eliminate any issues from the relay to the pump.

The fuel pump relay cannot share a ground with any others. The ground for that relay is controlled by ECM pin #22. Fix that, then see if pin #37 comes back up to 12V.

 

[casadejohnson]

The fuel pump relay cannot share a ground with any others. The ground for that relay is controlled by ECM pin #22. Fix that, then see if pin #37 comes back up to 12V.

I see that now. I was not reading the diagram correctly. Currently I have a 12 volt power source at the relay and 5 volts at pin 37 when the key is on, nothing at 37 with key off. Should the power at 37 cycle on then shut off when I turn the key to on but not start (the way the fuel pump cycles with key on )

The 5 volts I get at 37 is constant with the key on.

 

[Viperwolf1]

Pins 37 and 57 power the ECM from the EEC relay. The EEC relay is triggered by the ignition switch. Any time the switch is on, those pins should have 12V. You can disconnect the ECM and test the voltage to 37 and 57. If the problem is in the relay section of the harness you'll still see it.

 

[casadejohnson]

I'm picking up some heavy wire today to run a more reliable ground. I have a hole in the fire wall that I will ground to with a bolt then another ground wire from the other side of the firewall to the (-) battery post. Ill pull the computer after work and test the voltage at the 37 pin out on the harness.

 

[casadejohnson]

I checked the voltage at 37 & 57 both only give me 5 volts. Phil, you mentioned that the power is pulled from the EEC relay so I checked that as well. I have my 12 volt power source and I get 12 volts at the red green wire from the ignition when I turn the key on but when the relay triggers it only puts out the 5 volts I was seeing at 37 & 57. I can't swap that relay out because its not a standard Bosch type relay like the fuel pump relay and I don't have a spare for that one. Am I thinking correctly that the problem should be the EEC relay?

 

[casadejohnson]

One more thing, that relay was pretty warm to the touch after having the key on for a few minutes

 

[Viperwolf1]

Yep sounds like a bad relay. Ford dealer will have one or you can pick one up in a wrecking yard.

 

[casadejohnson]

Thanks for walking me down the path Phil. I ran to the parts store and they actually had one in stock! Plugged it in and my problems were solved. I also ran a 10 gauge ground wire from the battery to the kick panel and then up to the dash for good measure.

Here is my new glove box layout. It's not perfect but nothing is flopping around in there anymore.

 

[EFI Guy]

Interesting.

I've never encountered one that built up resistance like that. I usually end up replacing them for intermittently not working. I've seen low voltage cause some crazy issues with EFI, I'll be filing that one in the back of my mind for later use.

 

[casadejohnson]

Yea, I thought it was strange as well. I have had a couple recent situations where the fuel pump stopped working. Previously, I chalked it up to a bad ground at the pump. In hindsight, I bet it was that damn relay all along. The relay was $18 which seems a little pricey until you weigh that against the $120 tow bill I had the last time it quit on me (Not to mention the shame associated with having your Bronco come home on a tow truck ). At least it was 1AM last time so there were not many witnesses!

 

[Viperwolf1]

Glove box looks good.