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Need help with fuel pump problem


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11 replies to this topic

#1 jimbo747

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Posted 22 January 2005 - 03:00 PM

I know this is going to seem rather lengthy, but I want to give you all the available information.

1993 Loyale, 1.8 SPFI, AC, 5-speed.

I am having an intermittent starting problem. Occasionally, when I go to start the engine, it will fire, run for about 1/2 second, then stop. Once that happens, I can crank it forever and it will not start. However, sometimes if I wait an hour or two and try it again, it fires right up and runs like it never had any problem.

While trying to diagnose this last week (when it happened to me miles from home), I pulled the fuel lines off of the fuel filter, and cranked it. No fuel squirted out. I rapped on the fuel pump, jiggled some wires, still nothing. Reconnected the fuel lines, waited 30 minutes, tried it again, and the SOB fired right up. :banghead:

Took it to my mechanic, who played with it for two days, started and stopped it 50+ times, without a single problem.

So, I'm thinking I either have an intermittantly failing fuel pump, or something is preventing power to get to the fuel pump.

From what I understand, (and please correct me if I'm wrong), the fuel pump relay is triggered by the ECU during three events:
1) When the ignition is first turned on 2-3 seconds to prime the system,
2) During cranking, and
3) While the engine is running.

I've looked at the wiring diagram, and see that the relay gets its signal from the ECU. I have heard that bad signals from various sensors can cause the ECU to shut down the fuel pump. I have heard coolant temp sensor, oil pressure sensor, TPS, MAF, etc.

My big question to the Subaru gurus out there, is which, if any, of these sensors will cause the ECU to not send a signal to the relay? :confused:

Thanks for your help, guys. Sorry this message was so long.

#2 85Sub4WD

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Posted 22 January 2005 - 05:05 PM

When was the last time you replaced your fuel filter? I think the interval is every 30,000 miles, but if you use cheap gas it will clog up quicker.
Other than that -
My guess (and I do mean guess) is that your fuel pump relay is bad. I think that there is some relationship between it and the automatic seatbelts, but I am not sure. Otherwise I would use a multimeter to check for resistance, specifically a bad ground. A bad connector could also cause the problem.

#3 MilesFox

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Posted 22 January 2005 - 05:11 PM

under the hood there are a pair of connectors along the driver side firewall, one green and one white or black. connect the green connectors and turn the key on.

this will cycle the fuel pump on and off. you can listen for the pump to come on, and listen for the relay to click. the relay is on the steering column bracket above the ecu. if you are going that far, you may as well pull the ecu codes, the procedure is described in http://www.ultimates...article.php?c=1 in the miscellaneous section

#4 naru

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Posted 22 January 2005 - 06:44 PM

I have heard that bad signals from various sensors can cause the ECU to shut down the fuel pump. I have heard coolant temp sensor, oil pressure sensor, TPS, MAF, etc.

My big question to the Subaru gurus out there, is which, if any, of these sensors will cause the ECU to not send a signal to the relay? :confused:

Thanks for your help, guys. Sorry this message was so long.[/QUOTE]


None of them.

#5 Snowman

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Posted 22 January 2005 - 07:33 PM

If the fuel pump relay doesn't click and turn on the pump, check to see if the ECM if providing ground. The small blue/black wire that connects to the fuel pump goes to the ECM. Hook up a digital ohm-meter to this wire and to a good ground and turn the key on. If you have continuity, the problem is either the relay, it's power supply, or its ground.

#6 UP2DSNO

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Posted 23 January 2005 - 01:12 AM

I believe you'll find he fuel pump relay to be at fault. Good luck.

#7 85Sub4WD

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Posted 23 January 2005 - 01:54 AM

There are NO sensors that will tell the ecu to NOT send a signal to the relay to get fuel, but if the CAS and the starter switch are BOTH bad, then it would not send fuel, and it would not give an error code. It would still run on/off in test mode (green connectors connected). I have run my car with each sensor unplugged one-by one while troubleshooting an elusive problem (which I found). So I know this to be the case. Disconnecting the water temp sensor makes the engine REALLY difficult to start though.

#8 Cougar

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Posted 23 January 2005 - 02:17 AM

If the firing pulses for the ignition are not seen by the ECU it will turn off the pump. You should be able to listen for the pump by turning the key to the run position. You should hear it turn on for a short time. You may have to crank the engine first and switch it to off, then turn it to run, if the system is pressurized.

The ECU may control the return lead to the battery for the pump. My '88 turbo was done that way.

#9 Snowman

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Posted 23 January 2005 - 06:11 PM

If the firing pulses for the ignition are not seen by the ECU it will turn off the pump. You should be able to listen for the pump by turning the key to the run position. You should hear it turn on for a short time. You may have to crank the engine first and switch it to off, then turn it to run, if the system is pressurized.

The ECU may control the return lead to the battery for the pump. My '88 turbo was done that way.


As far as I can tell, the ECM controls the pump by grounding the relay on ALL EA-series FI systems. It was that way on all the schematics I could find for SPFI, MPFI, and Turbo cars.

#10 MilesFox

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Posted 23 January 2005 - 06:17 PM

try groundint the fuel pump to the body itself, its on a trainagle shape mount in front of the passenger tire, it looks like an aquarium pump

#11 jimbo747

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Posted 24 January 2005 - 06:33 PM

Thanks for all the advice, guys. You are the greatest. The system failed on me again yesterday, and I determined that it was the fuel pump. However, while diagnosing that problem, I did a bone-head thing -- I inadvertently sent 12 volts "backwards" through the system and fried the fuel pump control unit.

"The what?", you ask. After I posted my original thread on this board, I was looking at some of the "similar" threads, and discovered that (lucky me) 1990 - 1994 Loyales with automatic seat belts have a special fuel pump control unit. It doesn't show up on most wiring diagrams. There's a TSB out on it.

Anyway, after I confirmed that my old pump was dead and installed my new pump, I had my car towed to my mechanic, and showed him the TSB. He was greatful, since none of the mechanics in his shop had ever seen it. I didn't tell him that I stupidly sent voltage backward through the system -- I wanted them to diagnose the problem, not immediately focus on that. After a few minutes of probing around, he came back with the news that the pump control unit was fried. "Some kind of voltage surge may have done it -- are you sure you installed the new pump correctly?" At that point, I confessed to my stupidity.

Anyway:
New fuel pump -- $196.00
New fuel pump control unit -- $319.00
Labor -- $75.00
Learning to be more F*cking careful when trying to bypass electrical systems -- PRICELESS!

Cheers! :drunk:

Jimbo!

#12 85Sub4WD

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Posted 24 January 2005 - 06:39 PM

Oh, all of us have done bone-headed things at one time or another ;) Honestly, I would have bypassed the control unit and saved the $$$, most other FI soobs don't have them and they are safe. I thought I saw a TSB on the Fuel Pump control unit for those cars, but I was not sure.




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