Help me diagnose: fuel pump or...?

[6speeds]

I picked up a parts car this weekend, a 2001 brilliant black - It dosen’t run, but I think we have narrowed it down to the fuel pump. First off, there are no codes, the battery was dead, and I believe the PO might have cleared them, and I don’t have VAGCOM. The car turns over well, there is oil, eveything is connected, etc.

We tested the fuel pump fuse, there were 12 volts in the socket and the fuse was good, that was not the issue. The relay seems to be working fine, I actually took it out of the car and put it in my 2000 and the car started up, so that was not the issue. I did not check the relay socket itself for power though. Next I checked the wiring that leads directly into the fuel pump, the most power I could get was ~.7 volts or so, even when trying to crank the car over. I was going to pull the pump and bench test it, but I need to make a tool to get it out, because it’s a pain otherwise. When you turn the key into the the ON position, there is no noise from the pump at all. I’m assuming there should be some sort of priming sound? I pulled the fuel pump door and everything looks to be in order, connected, etc.

So my questions are:

1.) What kind of voltage is normal coming out of the wiring harness that leads directly into the fuel pump? Again, I saw ~.7 volts or so.
2.) Does anyone have a fuel pump wiring diagram?
3.) What are the next steps? Bench test the fuel pump?


I know I need to test to see if there is power to the relay, but other then that I’m not sure. I don’t want to throw money at this car, but I’d like to get it up and running. I was able to get it to run for about 2 seconds by spraying starter fluid direclty into the Y pipe and then cranking it over, so to me this confirms it’s fuel related and not a cam sensor or other nonsense. Any input, ideas, or suggestions would be appreciated.

Thanks!

[aysix]

Maybe check to see if you are getting fuel to the rail before anything. Un hook the line to the rail and check if its pumping gas.

[1gcrazy]

First off, how much?
Second. If the battery was dead, the codes are already cleared. PO could have left a light on but seems unlikely imho.

If you have someone turn the key on and someone else listening at the back of the car(ear against the sheetmetal) and you don't hear anything, then it's likely your pump or it's connection. If you're only getting 0.7 volts at the fuel pump plug it's probably your ECU or the wiring leading to the pump. I've never heard of the ECU's dieing and limiting power to the pump so i'm guessing theres corrosion somewhere to act as a resistor.

Aysix had a good idea but it seems as though you've ruled out fuel at the rail since it ran on ether.

[ilyafil]

Check fuel press. That will tell you a lot. You can rent a gauge at Auto Zone or the like.

[6speeds]

First off, how much?

How much what?

If you have someone turn the key on and someone else listening at the back of the car(ear against the sheetmetal) and you don't hear anything, then it's likely your pump or it's connection.

I did this, there is no sound of any sort.

If you're only getting 0.7 volts at the fuel pump plug it's probably your ECU or the wiring leading to the pump. I've never heard of the ECU's dieing and limiting power to the pump so i'm guessing theres corrosion somewhere to act as a resistor.

I've heard of less then 12 volts at a fuel pump before, i'm not sure what should be expected in this car. Any idea where the ground for this leads?

Maybe check to see if you are getting fuel to the rail before anything. Un hook the line to the rail and check if its pumping gas.

I will check this out, but if the pump is not running, i'm not sure if there would be much residual left in the line after trying to crank it 1000X.

[6speeds]

Check fuel press. That will tell you a lot. You can rent a gauge at Auto Zone or the like.

This is a good idea, but if the pump is not running, wouldn't the pressure be 0?

[ilyafil]

You should see pressure rise almost immediately when you turn the key to ON. If it's slow or non existent, you have a pump/blockage issues.

[airjawed]

The pump only primes for a little bit when ignition first turned on... seeing less than 12v may just mean it is past its priming.

Not hearing the pump...pump is very quiet...doesn't mean much.

I would see if fuel is reaching fuel rail as mentioned by aysix... crack the line and fuel should spray out a little. If not then investigate electrical.

[tambat]

What ecu in the car? can you connect through obd2 port?

[tambat]

when you turn key to ON position, does check engine light display on cluster?

[6speeds]

What ecu in the car? can you connect through obd2 port?

It's a stock box, not sure what letter off the top of my head. I connected my scanner and did not pull codes. If the ECU was fried, would the car even try to crank?

when you turn key to ON position, does check engine light display on cluster?

Yes, that and all the normal lights display when the key is ON.

[tambat]

yeah, with fried ecu car still cranks over but wont fire up. i have a walbro 255 pump w basket in my garage i can sell you cheap if you need to replace your pump. i replaced it thinking my pump was bad, ended up being my ecu.

[aysix]

Try starting the car with the ECU from your 2000, just unplug the MAF. The car will start no matter what tranny.

This will rule out ECU issues.

[airjawed]

Also...to rule out ECU you should have the EPC light on... no light means ECU trouble.

[6speeds]

Try starting the car with the ECU from your 2000, just unplug the MAF. The car will start no matter what tranny.

This will rule out ECU issues.

OK. I will try this tomorrow after work. That's an interesting fact, didn't know you could start a manual with an auto tranny ECU or vice versa.

Also...to rule out ECU you should have the EPC light on... no light means ECU trouble.

My EPC light IS on, so that's a good sign anyways.


On a side note, I put my ear to the pump on my 2000. When you switch the car ON, you can CLEARLY hear the pump prime.

[airjawed]

Put some power directly to the fuel pump... I forget which ones are the pump power ones and which are the fuel level sender ones. Maybe someone can chime in on it.

[6speeds]

Yes that would be great. A wiring diagram would be tremendous. Does anyone have one????

[airjawed]

Yes that would be great. A wiring diagram would be tremendous. Does anyone have one????

Bentley manual says to check voltage at terminal 1 (green/yellow) and terminal 4 (brown).... at the fuel pump connector...they are next to each other(not opposite). Should be battery voltage when pump is priming.

Download the bentley manual socals4.com.

[ilyafil]

If you were able to get it started with starting fluid, your ECU is good. You need to test the actual fuel press. It doesn't mean you get fuel press. just because the pump runs. You could have a bad fuel press. reg. Testing for voltage on the plug will tell you if the pump is getting power. Good idea, but doesn't tell you if you have fuel press.

[6speeds]

Bentley manual says to check voltage at terminal 1 (green/yellow) and terminal 4 (brown).... at the fuel pump connector...they are next to each other(not opposite). Should be battery voltage when pump is priming.

Download the bentley manual socals4.com.

I will try to verify (again) if the pump is getting power at the connection. I might test my 2000 to see what kind of voltage should be expected.

If you were able to get it started with starting fluid, your ECU is good. You need to test the actual fuel press. It doesn't mean you get fuel press. just because the pump runs. You could have a bad fuel press. reg. Testing for voltage on the plug will tell you if the pump is getting power. Good idea, but doesn't tell you if you have fuel press.

Good to know. I will confirm there is/is not power again, then look at pressure.


I will keep you guys updated, I should hopefully get to play around with it more after work tonight. Until then, stuck in the office

[6speeds]

Ok, so I tested the plug going into the fuel pump on both cars. Zero volts across all wires while the key was off, which is what I expected. When I turned the key ON or tried to crank it over I found the following:

2000 Car (starts/drives):
Green/yellow wire: .96 volts
purple wire: 1.5
Other wires: 0

2001 Car (does not start):
Green/yellow wire: .76 volts
purple wire: 1.5
Other wires: 0

Would a variation of .2 volts in the green/yellow wire between the two cars cause the pump not to run? If not then I would say I have narrowed the situation down to a bad pump.

Thoughts? Thanks again everyone.

[airjawed]

Ok, so I tested the plug going into the fuel pump on both cars. Zero volts across all wires while the key was off, which is what I expected. When I turned the key ON or tried to crank it over I found the following:

2000 Car (starts/drives):
Green/yellow wire: .96 volts
purple wire: 1.5
Other wires: 0

2001 Car (does not start):
Green/yellow wire: .76 volts
purple wire: 1.5
Other wires: 0

Would a variation of .2 volts in the green/yellow wire between the two cars cause the pump not to run? If not then I would say I have narrowed the situation down to a bad pump.

Thoughts? Thanks again everyone.

Fuel pump operates on battery voltage...reread my post on what the bentley says on which 2 wires to check voltage. You should be seeing something like 12 volts.

[6speeds]

Fuel pump operates on battery voltage...reread my post on what the bentley says on which 2 wires to check voltage. You should be seeing something like 12 volts.

I did. The wires I mentioned were the only two I got power from on either car. As far as not seeing 12v I'm not sure. Maybe my multimeter is defective. I will have to retest with my friends multimeter.

[aysix]

was this resolved?

[ilyafil]

x2