Help fuel pump

[Tomk]

Hi I’m losing patience with my z3 2.8.
having replaced a lot of components including engine, water pump, thermo, injector service, clutch, slave cylinder one headlamp, one wing mirror……

I think the fuel pump is dying. It occasionally wouldn’t start and on those occasions I wouldn’t hear the fuel pump prime. So I bought a secondhand replacement under warranty and have fitted it. Now no priming at all!
Could the cause be something else? It’s had a new battery and has been running since I replaced the engine. I’ve also checked the fuses. It’s turning over but won’t fire.
Gutted as I missed my mot re-test today.
Any ideas greatly received - realise the replacement pump could be faulty too is there any way to test.

 

[t-tony]

Have you had a code reader connected up?

Tony.

 

[Rudyrov]

Fuel pressure tester to test pressure.
Don't forget to check the fuel pressure regulator.
How many KM's or Miles?

 

[Tomk]

Fuel pressure tester to test pressure.
Don't forget to check the fuel pressure regulator.
How many KM's or Miles?

117 000 miles, never been replaced as carpet hadn’t been cut.
where’s the fuel pressure regulator?

 

[Tomk]

Have you had a code reader connected up?

Tony.

Hi Tony
I normally borrow one, so don’t at the mo. Was working on old fashion detection

 

[Rudyrov]

117 000 miles, never been replaced as carpet hadn’t been cut.
where’s the fuel pressure regulator?

The regulator is down by the fuel filter, but you should test the system pressure at the fuel rail. There should be a Schrader valve on the rail where the tester is connected.
There are a variety of tests that are done to test the fuel system including pressure and volume, these are assessed to see the condition of the pump and by extension delivery system (regulator, filter etc).
There are cheap code readers that will do the basic job available, it's a good buy to have one in the garage for these kinds of basic tests.

 

[Tomk]

Sure

The regulator is down by the fuel filter, but you should test the system pressure at the fuel rail. There should be a Schrader valve on the rail where the tester is connected.
There are a variety of tests that are done to test the fuel system including pressure and volume, these are assessed to see the condition of the pump and by extension delivery system (regulator, filter etc).
There are cheap code readers that will do the basic job available, it's a good buy to have one in the garage for these kinds of basic tests.

Surely you should hear the fuel pump priming even if there’s a pressure issue?
cheers

 

[Rudyrov]

I don't ever hear my fuel pump priming in my Z3 (98 2.8L, 140,000 Miles)
I do hear the one in my motorcycle tank, perhaps because its not down in the pits of the bike.

If you want to do a quick test for pressure (not a measure of PSI but the visual existence of some) try locating the schrader valve on the fuel rail and giving it a very careful press with a soft dowel, or better yet here is a detailed fuel pump test procedure you can follow.

BMW Z3 Fuel Pump Testing | 1996-2002 | Pelican Parts DIY Maintenance Article

Suspect your fuel pump is failing? This tech article shows you how to test it mechanically and electrically.

www.pelicanparts.com

 

[Tomk]

Right fitted new filter, swapped relays and have followed the pelican diagnostics.
The only thing I am not sure about is, i have 12v on the smaller cables that attach to the pump but no reading from the larger cables?
My gut feeling is the second hand pump I've bought is faulty too...

 

[Rudyrov]

Hi Tom, Sounds like you are at step 11. The larger or thicker wires are to power the fuel pump, the thinner wires are for the fuel gauge.
You need to go on to the relay testing and test bypassing section. You can get a replacement relay from amazon for as little as $17 (In the US) if it is bad or you have doubts.
The section also shows you how to connect a jumper wire to the relay so you can reinstall it and bypass the relay temporarily. This will let you see if the fuel pump will power up, if it does the relay is defective or is not getting signal itself to trigger when needed.

 

[Tomk]

Hi Tom, Sounds like you are at step 11. The larger or thicker wires are to power the fuel pump, the thinner wires are for the fuel gauge.
You need to go on to the relay testing and test bypassing section. You can get a replacement relay from amazon for as little as $17 (In the US) if it is bad or you have doubts.
The section also shows you how to connect a jumper wire to the relay so you can reinstall it and bypass the relay temporarily. This will let you see if the fuel pump will power up, if it does the relay is defective or is not getting signal itself to trigger when needed.

The thing is I’m not sure how I would get my head in the footwell to do the cable bypass trick. I’ve swapped relays instead and still don’t have 12v on the bigger two cables.
so is one of the cable’s potential damaged between relay and pump?
cheers

 

[Rudyrov]

The bypass is done to the relay terminals, not to the vehicles wiring.

 

[Tomk]

The bypass is done to the relay terminals, not to the vehicles wiring.

I understand that, what I’m saying is if I’ve still not got 12v at the pump plug and I have swapped relays for ones that work, it would suggest the fault is between the relay and the plug.!?

 

[Rudyrov]

Have you checked fuses?

If so and the fuses are good then I would consider powering the fuel pump directly, perhaps you have a 12 volt drill battery or you could go directly to the battery with a fused wire..... very carefully offcourse.

Also, if you have a low power test light and can identify the wiring colors with a schematic you can probe the solenoid rack for power where needed, again carefully.

 

[t-tony]

What you need is a “Power Probe”. Have a look on You Tube for how to us3 one.

Tony.

 

[Tomk]

Have you checked fuses?

If so and the fuses are good then I would consider powering the fuel pump directly, perhaps you have a 12 volt drill battery or you could go directly to the battery with a fused wire..... very carefully offcourse.

Also, if you have a low power test light and can identify the wiring colors with a schematic you can probe the solenoid rack for power where needed, again carefully.

Yes all fuses good even swapped them (old Saab V4 trick)

like the volt battery idea.

 

[Tomk]

Right so I stuck two cables from a tool battery on to both fuel pumps and the motor wizzed away. So I guess that means the pumps are good?

waiting on a new 20 pin converter to plug the OBD in with.

 

[Tomk]

ok so now I'm stumped! the OBD doesn't seem to be working .

However I spotted the attached cable has broken off the starter motor (should be attached at the red connector), what's it for? could this be the issue? Anyway I'll re-attach it and see but any light on what its for would be appreciated.

Cheers

 

[t-tony]

Yes, that wire needs to be attached, securely.

Tony.

 

[Tomk]

Yes, that wire needs to be attached, securely.

Tony.

What’s it for?