Fuel pump relay

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: GRNSHRK, ron, bfons

User avatar
Brucey
6 Series Guru
6 Series Guru
Posts: 10077
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Fuel pump relay

Post by Brucey »

some common things that might cause some of the symptoms you see;

- failing main relay

- injectors mechanically seized

- failed 'start signal' to main ECU

- bad crank sensors

A failing main relay (i.e. one that closes but makes a high resistance contact inside, or that has manky connections to its terminals) can have a bad contact such that you see about 12V at the injector rail and at the coil when there is no load but when the ECU fires either (which is a very short duration pulse in either case) then the voltage droops enough that the injectors won't actually fire, and (if it is really bad) you won't get a spark either.

To test for a dodgy main relay, it can be replaced or temporarily jumpered (with some wires). Dodgy connections will have to be tested separately. Another simple test is to use a ~20W test bulb to load up the 12V feed to the coil and injectors. There should be virtually no voltage drop when you do this, if the feed is good with a low resistance connection.

Injectors that are actually firing (i.e. seeing current and moving) will make an audible clicking sound. You can easily hear this during cranking if you use a mechanic's stethoscope. IIRC on that vintage of car the injectors are low impedance type; they can be tested by briefly putting 12V across them, but if this is maintained for more than a fraction of a second without a ballast resistor in series, the injector coil may burn out.

There is a wire that connects to the starter motor solenoid and runs to a pin on the diagnostic connector and to (pin 4 from memory, but do check) on the ECU. This circuit often goes wrong by the connection to the starter itself going bad. If the ECU does not see the correct 'start signal' voltage during cranking then you won't get spark or injector function. It is easiest to check the voltage at the diagnostic connector but this does not 100% guarantee that the ECU sees the same signal; there could be a fault in the wiring loom.

Bad crank sensors will obviously stop the engine from running; these measure 1000ohms resistance and create a particular voltage pulse (use a scope or a DVM) on cranking. Best to test at the ECU plug rather than the connector at the manifold steady.

Regarding the fuel pump this is switched by the fuel pump relay. To run (fuel pump relay closed) it needs a feed from the main relay and a relay coil signal from the ECU (that routes through the OBC relay IIRC). To test, just put jumper wires into the fuel pump relay socket; with the ignition on and the main relay closed, the fuel pump should run.

BTW if the tachometer does not move during cranking then this usually means there is no signal from the ECU; bad crank sensors or no start signal are the common culprits here.

There could indeed be multiple faults on a car that has been standing this long... good luck!

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
User avatar
randall977
Posts: 264
Joined: Sun Jan 21, 2018 9:52 am
Location: Oxford, UK
Contact:

Re: Fuel pump relay

Post by randall977 »

I am trying to work through the tests as logically as I can. I have replaced items I've found to be faulty or to rule them out (to a limited degree) - it still helps things along.
Last edited by randall977 on Thu Feb 15, 2018 5:43 pm, edited 1 time in total.
baders
Platinum Member
Platinum Member
Posts: 1084
Joined: Sun Nov 23, 2014 7:38 am
Location: Perth Australia

Re: Fuel pump relay

Post by baders »

Sorry, but the approach you've taken is not methodical at all. You need to concentrate on one fault, and work your way through it. I cannot even fathom what you have actually done from your writings.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
User avatar
randall977
Posts: 264
Joined: Sun Jan 21, 2018 9:52 am
Location: Oxford, UK
Contact:

Re: Fuel pump relay

Post by randall977 »

Sorry, my previous response wasn't to you Brucey - thanks for your advice!

I have tested everything many times and gone through all of the tests methodically - apologies I probably haven't made this clear in what I've written in this thread. I've read almost everything I can find that's currently available on this subject including the Bentley book. I tested the sensors with a scope and they are fine. Relays, fuses all fine.

Anyhow, major breakthrough today - the car started when I swapped over the thermo-time and temp sensor connections which I had somehow mixed up when restoring the thermostat housing :oops: ! I was only able to run it for about 5 seconds due to weather, dark etc - so tomorrow I will more fully test.

It's possible it was just running on the cold start - anyhow it's a very positive move forward - onwards and upwards :D
User avatar
randall977
Posts: 264
Joined: Sun Jan 21, 2018 9:52 am
Location: Oxford, UK
Contact:

Re: Fuel pump relay

Post by randall977 »

The car starts and runs very well, however, you can't disengage the clutch without some pretty nasty noises. Starter motor is partly the problem but I think there's still a gearbox issue so up on the ramps and gearbox out - this weekend all going well.

Thanks again for the helpful advice - would've struggled even more to start the car without it!
User avatar
spartaans
Posts: 20
Joined: Mon Feb 13, 2017 8:50 pm
Location: Falkirk - Scotland

Re: Fuel pump relay

Post by spartaans »

randall977 wrote: Thu Feb 15, 2018 2:31 pm The car starts and runs very well, however, you can't disengage the clutch without some pretty nasty noises. Starter motor is partly the problem but I think there's still a gearbox issue so up on the ramps and gearbox out - this weekend all going well.

Thanks again for the helpful advice - would've struggled even more to start the car without it!
I'm not an expert at all - I would like to ask you something Randall: could be a problem also the crankshaft pulse (code 0 261 210 002) ??

Many thanks
2004 Ford Mondeo Ghia 2.0 TDci {Silver Machine}
2002 Opel Astra G Coupe 2.2 16v {Carbon Schwarz}
1985 BMW E24 635Csi {Dolphin grey | Delphin | #184}
User avatar
randall977
Posts: 264
Joined: Sun Jan 21, 2018 9:52 am
Location: Oxford, UK
Contact:

Re: Fuel pump relay

Post by randall977 »

I probably should have updated this thread... The car started perfectly, however, I can't be certain why. I suspect it was the flywheel position sensor all along. As I understand it, the crank position sensor is only connected to the diagnostic plug.

Christian
User avatar
spartaans
Posts: 20
Joined: Mon Feb 13, 2017 8:50 pm
Location: Falkirk - Scotland

Re: Fuel pump relay

Post by spartaans »

randall977 wrote: Sun Apr 22, 2018 5:26 pm I probably should have updated this thread... The car started perfectly, however, I can't be certain why. I suspect it was the flywheel position sensor all along. As I understand it, the crank position sensor is only connected to the diagnostic plug.

Christian
Do you have a link or a code for the flywheel position sensor? I could have the same issue! ](*,)

Thank you

Flo
2004 Ford Mondeo Ghia 2.0 TDci {Silver Machine}
2002 Opel Astra G Coupe 2.2 16v {Carbon Schwarz}
1985 BMW E24 635Csi {Dolphin grey | Delphin | #184}
User avatar
randall977
Posts: 264
Joined: Sun Jan 21, 2018 9:52 am
Location: Oxford, UK
Contact:

Re: Fuel pump relay

Post by randall977 »

I bought one of these; https://www.ebay.co.uk/itm/Bosch-Cranks ... SwVgtZ2Sg9

Before I got the car started I replaced the cold start valve (which wasn't working) and corrected the temperature sender and sensors, which were the wrong way round on the thermostat housing. I don't think these would stop the car starting...but it did start immediately after correcting these. Probably just coincidence.
User avatar
Brucey
6 Series Guru
6 Series Guru
Posts: 10077
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Fuel pump relay

Post by Brucey »

if the CSV isn't working for whatever reason most M30 engines do not start well.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
User avatar
randall977
Posts: 264
Joined: Sun Jan 21, 2018 9:52 am
Location: Oxford, UK
Contact:

Re: Fuel pump relay

Post by randall977 »

I don't think it had been working for a very long time, the pipe to it had been capped off...
Post Reply