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Fuel Pump or Relay??? 95 Legacy


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11 replies to this topic

#1 BigBS

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Posted 26 July 2006 - 09:48 PM

I never had any problems with starting until the other day. Drove to work without a problem. Went to leave, and the car turns over, has spark, but won't start.

I pulled the cover in the cargo area, and have tested the voltage to the pump as the key is put into the run position. I get about 12 volts for a second, then I hear a click (relay I guess), and the voltage drops to zero. I pulled the relay out of it's holder, and popped it off. Took another relay from some other circuit, and put it in place of the original. Does the same as with the original relay.

I thought I read somewhere that the ECU might need to be reset in order to get power to the relay again. Is this the case? If so, what is the process?

Otherwise, any help would be appreciated.

BS

#2 nipper

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Posted 26 July 2006 - 11:50 PM

I never had any problems with starting until the other day. Drove to work without a problem. Went to leave, and the car turns over, has spark, but won't start.

I pulled the cover in the cargo area, and have tested the voltage to the pump as the key is put into the run position. I get about 12 volts for a second, then I hear a click (relay I guess), and the voltage drops to zero. I pulled the relay out of it's holder, and popped it off. Took another relay from some other circuit, and put it in place of the original. Does the same as with the original relay.

I thought I read somewhere that the ECU might need to be reset in order to get power to the relay again. Is this the case? If so, what is the process?


Otherwise, any help would be appreciated.

BS


the fuel pump relayis controled by the ecu, and the fuel pump hot comes from the main fuse box to the relay load side to the pump. The wiring diagram shows the coil side of the realy getting power from the ig switch, to the relay, then grounds through the ecu. The same wire before the relay goes to the ignition coil. Unplug the ignition coil connector and try it again.

nipper

#3 BigBS

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Posted 30 October 2006 - 11:52 PM

the fuel pump relayis controled by the ecu, and the fuel pump hot comes from the main fuse box to the relay load side to the pump. The wiring diagram shows the coil side of the realy getting power from the ig switch, to the relay, then grounds through the ecu. The same wire before the relay goes to the ignition coil. Unplug the ignition coil connector and try it again.

nipper

Took forever for me to get off my @ss and look at the car again. Seems like the issue is the ground signal from the ECU. I have good power to the relay, but the ECU ground is only present for less than a second after the key is switched to run. After pulling the positive from the battery for a while, I sometimes get the fuel pump to run for several seconds. The first time I thought it was fixed, as it started, and I let it run for several minutes. After shutting it down, it was back to the same issue (no power to the fuel pump).

Any ideas what could cause the ECU to not send the ground signal?

Thanks
BS

#4 porcupine73

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Posted 31 October 2006 - 12:39 PM

I'm probably missing something, but the fuel pump runs for maybe a second when the key is switched to run, which is normal isn't it? Then it runs again when key is in start or is in run and the engine is actually running? I mean there isn't going to be power to the fuel pump simply because the key is in run (without engine running)?

Do the Suby's have that sensor where if it thinks the car is flipped over it shuts off the fuel pump?

#5 BigBS

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Posted 31 October 2006 - 12:50 PM

My pump won't even start in the moment that it has ground. After power cycling the ECU, it will usually run for at least a few seconds. I believe this is to achieve a certain pressure in the injection system. i'm not sure on the roll over sensor. As far as my wife knows, I've never rolled it.

#6 uniberp

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Posted 31 October 2006 - 03:18 PM

Correct, the 1 second signal is to bring the system up to pressure for starting.


My pump won't even start in the moment that it has ground. After power cycling the ECU, it will usually run for at least a few seconds. I believe this is to achieve a certain pressure in the injection system. i'm not sure on the roll over sensor. As far as my wife knows, I've never rolled it.



#7 BigBS

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Posted 31 October 2006 - 04:12 PM

Just to be clear, the pump isn't even starting. The pump runs just fine when it gets power. The issue is that the ECM does not provide ground for more than the blink of an eye.

#8 mjreilly

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Posted 31 October 2006 - 06:14 PM

Couldn't this be an issue with the cam/crank position sensors? If the ECU doesn't think the engine is turning over, it's not going to supply fuel? Correct or way off base?

Anyway, good luck,

matt

#9 BigBS

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Posted 31 October 2006 - 08:15 PM

I would expect that if the car would start, then die from lack of fuel, but my ECU will not provide ground to the fuel pump relay long enough for the pump to start.

#10 Cougar

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Posted 31 October 2006 - 08:22 PM

The ECU needs to see ignition pulses before it will complete the ground to the pump. The short inital turn on is normal to get pressure up to start the engine. If you still think the pump is not working correctly then try running power directly to the pump and see what happens.

The problem of not starting may be due to the injector(s) not opening. Try squirting some starter fluid into the intake to see if that makes the engine fire up for a short burst at least. Then you will know this is a fuel problem for sure.

#11 porcupine73

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Posted 01 November 2006 - 07:53 AM

There was a post on here before where someone was not getting any output from the ECU for the pump relay, so s/he opened up the ECU and replaced the driving transistor I think it was and that fixed the problem.

#12 Cougar

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Posted 01 November 2006 - 12:21 PM

There was a post on here before where someone was not getting any output from the ECU for the pump relay, so s/he opened up the ECU and replaced the driving transistor I think it was and that fixed the problem.


I think that was me that wrote that. It was a driver transistor that tied to the output switching transistor for the pump ground and I found that same problem in two different ECUs.

I think BigBs problem is different since the ground to the pump comes on for a brief time least, as it should. From his posts it sounds to me that the injector(s) may not be turning on. That is why I suggested using starter fluid to what happens with that.




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