hello all. my dad and I are greatly confused by my civic not priming the fuel pump. A couple months ago I bought an eg hatch with a bad rod bearing, so we rebuilt the whole engine, ran awesome until a couple days ago where it just wouldn't start, would turn over but wouldn't start. I found this odd because every single time before that it would start up really strong, and then just all of a sudden wont start. I know it is not spark related because I have type R spark plugs with less than 500 miles on them and new spark plug wires. Figured it is fuel related, I replaced the fuel pump with a new one, still wouldnt start. My thermostat ground cable is fine. Checked all the fuses and they're fine. When I turned the ignition to II the fuel pump wouldnt prime.. so my dad decided to used his multimeter to try to narrow down where the problem was. We tested the voltage at the connector going to the fuel pump and when I turned the ignition to II, the connector got power. We tested the new fuel pump using the battery to see if it works, and it works. Sooooo we are both kind of baffled at why this is happening, if anyone could help that would be awesome. Thanks

 

This is a common problem with 93/95 civics.
Not sure what year your car is.

The bundle of wires that ground at the thermostat housing should be cleaned and tightened. ECU grounds there.

Also the problem could be the ECU if it is a P28. The capacitor 14 on the circuit board goes bad with moisture and the ECU will fail to prime the fuel pump. Borrow a known good ECU and try it.

 

thanks for the reply. My civic is a 94. I will go check/clean the thermostat ground in a bit. I have a chipped p72 ECU (B18C swap) so is that ecu still susceptible to that problem?

 

Could be the main relay

 

is there a way to fix the main relay or do I have to get one from a junkyard

 

I would get a junkyard one. A new one costs bout $50...

 

i just pulled out the main relay and all the solder points are all fine and not cracked. I don't really think it's the main relay. The wires going to the fuel pump are getting voltage when I turn the ignition to II, so if the main relay was bad wouldn't that not happen?

 

So your getting 12volts on the yellow/green wire from the main relay to the pump when the key is turned on,but the pump is not priming?

 

yes that is correct

 

If your getting power all the way to the pump plug then the only thing left would be the ground wire from the pump to the pump housing not making a connection.

 

well I checked that and it's connected :/

 

i used power from the battery to test the fuel pump and it works. I used the plug on top of the fuel pump housing, so that proves that the ground is connected (i think). the old pump worked too when I tested it using the battery.

 

There is two power wires at the main relay.

Yellow/white hot at all time

Black/yellow ignition power.

Black ground from thermostat housing.

Green/yellow trigger from ecu

Yellow/green power out to pump.

Are you getting power to both the yellow/white and black/yellow wires?

Try taking a piece of wire and jam one end in the green/yellow wire at the main relay plug and ground the other end to chassis,with the key in the on position the pump should turn on.

Make sure the main relay is getting ground. You can take a piece of wire and jam it in the black wire of the main relay plug and ground te other end to the chassis

 

I just tested connections again. I tested the other plug (the one that plugs into the connector with the 2 light blue circle things) and it's getting constant power when I turn the ignition to II. I grounded the main relay and the fuel pump didn't work. I put wire in the end of the green/yellow wire at the main relay plug and grounded it and the fuel pump still didn't work. I'm going to talk to this honda specialist mechanic tomorrow and see if he knows what's wrong.

 

okay i feel stupid now. I am not getting enough voltage to the fuel pump. I didn't know how to read the meter before and just assumed it was getting 12 volts because it had a reading but I compared it to readings off the battery and it's not getting enough voltage. Does this mean I have a bad main relay?

 

Just replaced the main relay with a new one from Honda.... Not surprisingly the fuel pump still doesn't prime. If anybody has any other ideas before I get it towed tomorrow that would be great. Thanks

 

Confirm that your getting 12 volts to the yellow/white and black/yellow wire at the main relay,the black/yellow is a switched 12 volt source do the key need to be turned to position 2.

Take a piece of wire and stick one end of it into the green/yellow wire of the main relay plug, the other end you can either touch it to the black wire of the main relay plug or to the chassis. You should hear the relay click.

 

Have you tried pulling the pump assembly out to make sure all the plumbing is intact?

 

Borrow a known good ecu just to see if it will prime the pump and start the car. Probably a P28 if you cant find a P72. If that works than phearable.net could chip a ECU for you.

 

there are those odd cases where it actually IS the pump. mine was weak and dying when I caught it(fuel pressure was 1t 25 psi on prime) thanks to B&M fuel pressure gauge. try a new/known good pump and or ECU