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Old 08-01-2011, 03:50 PM
 
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If your car doesn't have fuel pressure, how can you tell if it's the main relay or fuel pump? Thanks.
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Old 08-01-2011, 03:53 PM
 
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Test them and see if each is working?
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Old 08-01-2011, 04:07 PM
 
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Quote:
Originally Posted by Sayantsi View Post
Test them and see if each is working?
Thanks. How do you test them?
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Old 08-02-2011, 11:34 AM
 
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You need to start working up the system, pull the fuel line after the relay and see if fuel spurts out of it when you try and start the car (be prepared to catch the fuel, its best a two person job to start the car and check the line). If nothing comes out of the relay, try pulling the line between the filter and relay and see if anything comes from there. Some relays prime the engine, so see if there is any fuel in the line at all.

If not, time to check the pump. Pull the tank and test it for operation. It could also be clogged so check the pump's filter and see if that was the problem.

Depending on age and how often the car is run, the fuel lines could need to be replaced as well. Did the car recently run out of gas completely and now it wont start or does it just have no fuel pressure?
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Old 08-02-2011, 09:15 PM
 
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I don't expect to get fuel pressure anywhere at all. The main relay is basically a switch that turns the fuel pump on. If the relay fails, the fuel pump won't turn on and there won't be any fuel pressure to check. If the relay is good and fuel pump is bad, then there will be no fuel pressure to check either.

Of the two, the relay is much easier to get to. So I will start there. I can pull it out and check for cracked solder joints. That's about the only thing I can do. Is there any electrical test/procedure I can do to test a main relay? If I know for sure the relay is good, then it's most likely the fuel pump is bad.
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Old 08-02-2011, 10:09 PM
Status: "SSRIs = school shootings = MKULTRA = Pol Pot America" (set 15 days ago)
 
Location: Meth capital of the world.
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Just manually close the relay after you have the cover off......if the pump starts.........well then, either the relay is bad or it is lacking a signal to turn it on. It could also be that one of the output pins for the relay is cracked and open, should be able to see that with a magnifying glass or use a Vmeter.
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Old 08-04-2011, 09:50 AM
 
Location: Suffolk County, NY
875 posts, read 1,534,555 times
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Quote:
Originally Posted by Sayantsi View Post
You need to start working up the system, pull the fuel line after the relay and see if fuel spurts out of it when you try and start the car (be prepared to catch the fuel, its best a two person job to start the car and check the line). If nothing comes out of the relay, try pulling the line between the filter and relay and see if anything comes from there. Some relays prime the engine, so see if there is any fuel in the line at all.

If not, time to check the pump. Pull the tank and test it for operation. It could also be clogged so check the pump's filter and see if that was the problem.

Depending on age and how often the car is run, the fuel lines could need to be replaced as well. Did the car recently run out of gas completely and now it wont start or does it just have no fuel pressure?
I believe a much easier, safer test would be to use a multi-meter to see if power is getting to the pump. If it is, the relay is good and the pump is bad, if it is not, you have to check further into the relay or a wiring issue.
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Old 08-04-2011, 02:59 PM
 
Location: Eastern Washington
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With most cars with a fuel pump relay you can pull the relay, and referring to the shop manual, use a *fused* jumper wire, preferably one with a switch in it, to run the fuel pump independent of the relay. Every car I have worked on, you can hear the fuel pump running, although if you want to test pressure, that gives more information. If you come up with a "clamp around" amp-meter you can check fuel pump amps.

You do need to get a proper shop manual so you can hook up the jumper correctly, you can cause damage if you don't know what you are doing.

Just a thought - if your fuel filter is more than 30K or so miles old, I'd change it. A fuel filter can get plugged enough to make the car not run at all - rare I have heard of it happening.

Final thought - a spare fuel pump relay ought to be in your glove box anyway, so this would be one of the rare times it makes sense to "Easter Egg" a bit - go ahead and get a new relay, change it out, if that fixes your problem put another one in the glove box. If not, keep it as a spare.

Egobop makes a good point that you can test for voltage at the + terminal of the fuel pump, if it's getting voltage and not running, very likely it's defective (I would check amps first though, it might be a bad (high resistance) connection somewhere in the circuit.)
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Old 09-20-2012, 08:50 AM
 
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If its not the relay or the fuel pump or a fuse or fuel filter what else could it be.
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Old 09-20-2012, 08:52 AM
 
Location: San Francisco
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What kind of car--early 90s Accord?
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