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Old 03-03-2018, 02:53 AM   #1
Drives: Yaris yrs 2006
Join Date: Mar 2018
Location: Australia
Posts: 7
Unhappy Odd Fuel pump issue. Feeling at a loss.


After a few weeks of going at it on my own, I thought it was time to ask peoples advice :)
My "Toyota Yaris yrs 2006" was having starting problems a few weeks ago.

Long version of story :)

The engine turned over, but there was no fuel coming in. It sparks fine,
I checked the air flow sensor and cleaned it and it seemed to work for about 7 starts, and I drove it all over the place across Tasmania.

Then it stopped again, after I got out from the movies. (I thing the sensor cleaning didn't fix it but I just got a lucky start after the clean).
Bumping the fuel tank from underneath worked and got me home for a bit, but restarting was touch and go, bumping the fuel tank worked 3 times. (Clearly it wasn't the MAF sensor because that wouldn't stop initial fuel coming in, especially when it's disconnected. It should run for 2 seconds with fuel and then cut out, but there was no fuel pressure). So obviously I had to replace the fuel pump. I replaced the fuel pump, but there was still not a start.

I checked for relays, and realised there wasn't a fuel pump relay for the car, but while I was there I checked all the relays manually with a multi meter in both current flow directions and they all worked, under the bonnet and under the dash. I also checked every single fuse in the car.

I suspected that the new fuel pump may have been a dud, so I tested it with direct current 12 volts, and it pumps perfectly!!!, it simply doesn't turn when I start the car. (I'm guessing the old fuel pump was on it's way out but that it wasn't the real problem)

I pulled the electric plug off the fuel pump and stuck a multi meter on the fuel pump terminals, and indeed it gets over 10 volts when the engine starts, and 14 volts momentarily when the starter gives up, but it doesn't pump. (I tested this multiple times just to make sure, I also put low current through the fuel pump to see if it was getting current all the way through while installed, and yes it was) (I may have also attached a 12 volt battery directly to force it to pump while installed in the car, and it worked perfectly, I disconnected it and started the car, and it worked, and the car ran with what was pumped in the line for 15 seconds, meaning I could make a bypass from the battery straight to the pump and it would technically run the car, the fuel pump works, I forced fuel into the line twice like this and both times it was a go). And the car doesn't cut out until the fuel is depleted from the line
So I was like... well the fuel pump works, there's power going to the fuel pump, then why won't it pump?!!

I'm assuming it's not getting the Amps it needs!
So I started checking resistance in the wires from the fuel pump to the connectors under the dash, and the wires seem.. fine..... I think... No change in resistance, and the connectors look solid. (I don't have a meter to test the high amps directly, so I'm not sure if I did it right). I have yet to check the connectors of the ECU properly...

I'm at a loss. Maybe theres a safety sensor that cuts the amps but not the voltage to the fuel pump? I can't for the life of me work out what's going on!!

It's a problem that got worse over time, and was not always a problem.
I expect that the fuel pump has been running on low amperage for a time and eventually it just got too low to turn the pump. Anything that would do any of this?

Any wisdom and amazing help would be a god send.

I miss my car, it's a really nice car when it works

Edit- to the point abridged version
1. Engine is getting 0 fuel pressure under normal starting conditions
2. I can force the fuel pump to work with direct 12v battery connection, and the car will run fine ( installed new fuel pump after problem).
3. I have checked all the relays, fuses, and it's not the Mass airflow sensor
4. The car provides the Fuel pump with the correct voltage, but my guess is, that it's not providing the correct Amperage.
5. At a loss

Last edited by Marchalis; 03-03-2018 at 03:38 AM.
Marchalis is offline   Reply With Quote
Old 03-03-2018, 10:35 AM   #2
Drives: 2010 yaris 3 door hatch
Join Date: Jun 2013
Location: Sheboygan Falls, Wi.
Posts: 515
Is there a security system on the car? Do you have a good wiring diagram of the fuel pump?
ex-x-fire is offline   Reply With Quote
Old 03-03-2018, 09:19 PM   #3
Drives: 2009 5-door, 5-speed
Join Date: Sep 2011
Location: White Rock BC
Posts: 687
Haven't read too detailed, but try switching relay with another one. Poss burned contacts. After that, do a voltage drop test:
CoryM is offline   Reply With Quote
Old 03-03-2018, 11:31 PM   #4
Drives: Yaris yrs 2006
Join Date: Mar 2018
Location: Australia
Posts: 7
I can't find any good wiring diagrams for the whole system.

I tested the relays and they all work.
I did the voltage drop test and it was at 0.2 volts :)

I'm getting an OBDII to help solve the problem a bit easier on Tuesday.
Marchalis is offline   Reply With Quote
Old 03-06-2018, 08:55 PM   #5
Drives: Yaris yrs 2006
Join Date: Mar 2018
Location: Australia
Posts: 7

Lack of sleep over problem was the cause?

When I tested the fuel pump I tested the negative and positive as indicated on the pump.

It was a new pump that looked identical to the old. The plug that went into the pump only fit one way.

I can't say if I installed the pump with the plug somehow back to front or if the motor came in reverse, but changing the negative and positive on the top of the fuel pump unit in the car fixed the problem.

With direct connection with battery to the pump, it will make noise and run in reverse, but connected to the car it will not.
Marchalis is offline   Reply With Quote

electrical, fuel, fuelpump, problem., pump

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