97 impreza outback sport - no power to fuel pump

[wsjones]

I have a good fuel pump relay and fuel pump with good circuit in between. The ground side of the fuel pump relay control circuit (violet wire) goes into the MPFI control unit. Key 'on', the positive side of the relay control circuit reads 12.5 v; the negative side reads 11.5 v.  Therefore, my relay is not closing.  Does anybody know why it's not giving me a good ground?  What might hold it open?  I am assuming that is how the MPFI controls the pressure put out by the pump.  I possibly had a pack-rat chew wires in the engine compartment but cannot find any damaged wires there.

[lmdew]

If you provide a good ground does it work?

 

www.brighterideas.com

 

You meter can lie to you.

 

Larry

[wsjones]

yes does work with good ground.  Someone suggested that it might be the crank shaft sensor.  Haven't had time to check that one out yet.  Do you know how to tell a good crankshaft sensor?

[lmdew]

You have to hook up an O-scope to read the input to the ECU.  Just hit the Junk yard and grab a couple.

[wsjones]

How does the ECU sense the ignition pulses that control the rule pump relay?  Is it through the crankshaft sensor or by some other route?

[lmdew]

Crank and Cam Sensors go to the ECU to control the engine.

[wsjones]

Latest update:  I supplied the fuel relay control circuit with a hard ground.  The pump works fine, however, it continues to pump as long as key is on 'run' even if the engine is not running.  I checked all the pins to the ECU and could not find one that had continuity to the ground side of the fuel relay control circuit.  I have to assume that my ECU is most likely the problem.  I saw online that AES Modules , Jacksonville FL, offers to rebuild ECUs and gives a lifetime warranty.  For Subarus the quote between $200-$300.  Is anybody familiar with this company?

[kbrumley27]

I am having a similar issue with my 2001 Subaru outback. I cant get it to start and had to get it towed home on Christmas. Turned the key on and can not hear the gas pump starting up. This car is new to me. It has 195000 mi on it. Right after I first got it the check engine light came on so I hooked it up to scan it and it said the o2 sensor. Well the previous owner removed the catalyst and the o2 sensor along with it. Any how the reason I stated that was because I was able to get a read off the ecm. So now I tried to hook it up and it wont read anything. Tried multiple times. Disconnected the battery hoping to reset the ecm. Still nothing. Ive also had troubles with fuses blowing. My question is this, Is there a way to test the ecm to see if it is working properly and also where is the fuse for the ecm? It is not under the dash where the others are for audio and lights etc. Thank you in advance for all your advice.

[Fairtax4me]

Latest update: I supplied the fuel relay control circuit with a hard ground. The pump works fine, however, it continues to pump as long as key is on 'run' even if the engine is not running. I checked all the pins to the ECU and could not find one that had continuity to the ground side of the fuel relay control circuit. I have to assume that my ECU is most likely the problem. I saw online that AES Modules , Jacksonville FL, offers to rebuild ECUs and gives a lifetime warranty. For Subarus the quote between $200-$300. Is anybody familiar with this company?

Can't say I've heard of AES.

 

If you have no continuity from the relay to the ECU, the ECU isn't the problem. It's the wire from the relay to the ECU.

 

If you search around there is a website (I don know it offhand or I would post a link) with factory service manuals for many Subaru models. Find a wire diagram for your car so you know which pins are which on the ECU. Otherwise you're just poking around in the dark.