No electrical feed to fuel pump - help!

[usrjd]

Hi Guys

After replacing the engine and gearbox into my 350i (new camshaft and 'box overhaul) the damn thing won't start...

I suspect that I've done something wrong / left something off, but can't find the fault.

She will try to run when cranked on the starter, but will not catch and I can't hear the petrol pump running with the ignition on. The fuel rail isn't pressurised and there seems to be no electrical feed to the pump fuse, hence no fuel pressure.

I'm wondering if it's related to the oil pressure switch wiring, as my engine has the two oil pressure switches, one with the 3 prongs, the other just the one connector.

Currently, the brown/white wire is on the front switch (single connector) and the white/brown is on pos.1 with an earth on pos. 3 (opposite) on the 3 prong switch.

The oil press. gauge reads OK, with pressure building off the starter etc. but still no power to the petrol pump fuse.

I've looked through the wiring diagram in Steve Heath's book, but still can't find the fault.

Can anyone shed some light on this please?

[rev-erend]

Check the impact switch is not in the up position .. if you have one.

[TVRleigh_BBWR]

could be a problem with the fuel pump relay, you could just wire the pump direct for now to the battery or another battery to see if will start, they mess about with the wiring after.

[wooly350i]

I'm no expert on this but doesn't the pump get a signal from around the airflow meter or throttle or somewhere in that area,would make sense if its all been out,or am I in cuckoo land again!

[usrjd]

Thanks for the responses, much appreciated but...

I'm not sure if I have an impact switch (never tested it- ) but I will have a look if you can let me know what it looks like / where it's normally located?

And I can't identify which relay controls the fuel pump - it doesn't seem to be marked in the wiring diagrams that I have - does it live on the relay panel above the passenger footwell?

All suggestions gratefully received!

[E Ponym]

The fuel pump does not receive any power UNLESS the engine is being cranked OR the flapper is partially open.

Turn on the ignition and remove the air filter, open the flapper a bit with your finger and you should hear the fuel pump start to run, if not there is a problem in the circuit.

Russ

[honestjohntoo]

usrjd said:

try to run when cranked on the starter, but will not catch and I can't hear the petrol pump running with the ignition on. The fuel rail isn't pressurised and there seems to be no electrical feed to the pump fuse, hence no fuel pressure.

I'm wondering if it's related to the oil pressure switch wiring,

When cranking, the pump is energised by the cranking circuits and when its cold the Cold Start injector is firing in some fuel to give you the initial firing reported.

When you stop cranking the Air Flow meter has a pair of contacts that holds on the pump relay a long as the engine is running.

I suspect that the AFM contacts are not working or connected and/or the pump relay is playing up, or its local connections. Or possibly pump steering module.

Everything you need to know about the pump, its relays and its operating circuit is here, it also include a full test procedure for checking out malfunction, and here for the steering module and relays.

The oil pressure circuits are not part of the fuel pump system on an Efi car, but there was an oil pressure switch inhibit function on some carb cars (at least for Rover SD1 carb V8).

Regarding the pump running with just ignition on, that does not normally happen so there is something weird going on there. Engine has to be either cranking or running for the pump to run.

If all this is making you moggydawed, search the adjacent archive for comprehensive material as to how the whole Efi system works and each of its components likewise.

This will help you no end with your ability to self diagnose.

Edited by honestjohntoo on Monday 25th July 14:35

[KelWedge]

After having tyres fitted, I had starting issues that the fuel pump sometimes would run and sometimes would not, Some nice person had half cut the wire to the pump with a trolley jack !

[TVRleigh_BBWR]

usrjd said:

Thanks for the responses, much appreciated but...

I'm not sure if I have an impact switch (never tested it- ) but I will have a look if you can let me know what it looks like / where it's normally located?

And I can't identify which relay controls the fuel pump - it doesn't seem to be marked in the wiring diagrams that I have - does it live on the relay panel above the passenger footwell?

All suggestions gratefully received!

As said try using a 2nd battery 1st, also some pump can stick if sitting around and the extra jolt can free them, and then they seem to work ok.

so try a 2nd battery or wired direct and when running try disconnecting and see if it still runs.

[rev-erend]

TVRleigh_BBWR said:

As said try using a 2nd battery 1st, also some pump can stick if sitting around and the extra jolt can free them, and then they seem to work ok.

so try a 2nd battery or wired direct and when running try disconnecting and see if it still runs.

The AA do exactly this trick to see if the problem is with the pump or with other switches / cabling etc..

[usrjd]

Thanks to all for the help and info so far - and for letting me know that the fuel pump shouldn't run with just the ign on.

I've now tried the quick check of; ignition on and pushing the A/F meter flapper valve open. Doing this, the fuel pump runs just fine, but she still won't start. I've also tried starting her with the flapper slightly open to ensure a good supply of fuel in the rails, without success.

I've checked that the petrol pipes are the right way around, the cold start injector is working and have reseated the A/F meter and ECU connections, but still luck.

To recap; on cranking, the motor fires, but will not pick up and run. I'm really hoping that the ECU hasn't gone bad (as one did on my old Range Rover one morning).

Any ideas on what I might check next...?

[mrzigazaga]

Hi mate..I had major issues with my 280 where it would take ages to start, A lot of the time it would flatten the battery and the booster pack..I had a problem with the fuel pressure dropping away which turned out to be the fuel accumulator which was leaking fuel from the air valve on the rear of it..The car would catch loads of times but not run as the only fuel it was getting was from the cold start injector..Eventually after coughing and spluttering it would catch..Is your systems fuel pressure ok..Its just an idea..Ziga

[honestjohntoo]

usrjd said:

I've now tried the quick check of; ignition on and pushing the A/F meter flapper valve open. Doing this, the fuel pump runs just fine, but she still won't start.

To recap; on cranking, the motor fires, but will not pick up and run. I'm really hoping that the ECU hasn't gone bad (as one did on my old Range Rover one morning)

OK, so the pump runs when the flap opens, therefor you should have fuel pressure? Assume you do because the CSI squirts, we know that!

We also know you have sparks because the engine fires (perhaps not very well??) at cranking.

If the system will not run after cranking ceases, then the engine running signal from Coil negative may not be getting to pin 1 of the ECU.



Its a WB wire going thro the 6800 resistor that is usually mounted inline with the wire adjacent to the AFM.

That signal is NOT required during cranking, because the engine gets it starting/cranking fuel from the CSI (sometimes too much due to repeated attempts to start and it gets seriously flooded - see later).

But it must be present as soon as cranking ceases to trigger the injectors to fire in harmony with the sparks.

If that is NOT the problem then you need to look at the connections to the power resistor pack, because that is where the injectors get their voltage from via the main relay. The ECU only grounds the injectors.

You can see all this from the above image.

Then there are the relays to check if they are properly seated, also the steering module.

Final suggestion, this system/engine does not like being flooded and will simply not fire and run, so check your spark plugs for being wet with petrol.

And Yes! the ECU may be toast, the only practical way to check is by substitution, but you do not go there yet, still loads to check before that.

Don't overlook my previous suggestion about getting all your Efi reading material together and studying it.

[usrjd]

Success!!

Thanks to all who helped - but especially to honestjohntoo.

He nailed it with the w/b wire between the dissy and the A/F meter being broken (The one that triggers the injectors to fire). The wealth of info he has provided on the Rover V8 fuel injection system is fantastic and is a great resource - well done mate!

So, a new bit of wire, a tweak on the dissy and away she went!

Happy Days...

[mrzigazaga]

..Smiles all round..Enjoy..Ziga

[grahamw48]

After engines have been out, you can almost guarantee that it's a wire off or broken somewhere.

Most unlikely that a previously working component is suddenly going to break.

[honestjohntoo]

usrjd said:

He nailed it with the w/b wire between the dissy and the A/F meter being broken (The one that triggers the injectors to fire). The wealth of info he has provided on the Rover V8 fuel injection system is fantastic and is a great resource - well done mate!

Cheers, but dont under-estimate your own input!

You gave a whole raft of signs and symptoms which enabled a disciplined evaluation of the possibilities, eliminating the unlikely and focussing only on the probable.

How many times - one wonders - do we see a query like this

"My engine stopped working, tried everything, no luck, please help!"

Whereas the same person might have mentioned

"3.5 Efi RV8 flapper, stopped working suddenly, there are sparks but the plugs are black/wet - also a smell of petrol"

Immediately, one is able to focus on the reasons why the engine is suddenly overfuelling. Seemples!



IF ONLY??

[dixiebabes]

usrjd said:

Success!!

Thanks to all who helped - but especially to honestjohntoo.

He nailed it with the w/b wire between the dissy and the A/F meter being broken (The one that triggers the injectors to fire). The wealth of info he has provided on the Rover V8 fuel injection system is fantastic and is a great resource - well done mate!

So, a new bit of wire, a tweak on the dissy and away she went!

Happy Days...

Exact same thing happened to me after the head gaskets refit.

Dix