Fuel Pump - Updated

[KarlH]

I went to start the car(2001 K series) this morning and don’t get the usual fuel pump whirring when you turn the ignition on and the car won’t fire up.

I’ve checked the fuse, inertia switch, and the Immobiliser isn’t on.

What can I check next?

Typical, was fine yesterday!

Cheers,

Karl

[KarlH]

Sorted - the relay bypass fuse had blown.

[KarlH]

Just went to use the car again, it fired up and cut out a few times and then the fuse blew again (assume that’s what the pop was followed by the fuel pump not starting again).

Any ideas what may be causing this and what I can check out tomorrow?

[SM25T]

Might be a bit of corrosion in a connector or earth causing a high resistance. Do you have the right rating of fuse fitted ?

[KarlH]

I’ll check connections tomorrow, was fine the day before!

fuel pump fuse is 15A 

[Jonathan Kay]

Have you checked that the fuses are blown as well as that it worked for a bit after changing them? 

Have you got a multimeter and the appropriate wiring diagram?

High resistance will cause loss of function but it won't normally blow fuses.

If it is blowing fuses I'd start by:

1. Looking for damage to wiring or connectors.
2. Disconnecting wires at the fuel pump and seeing if it still blows the fuse. That should distinguish between faults in the pump and faults elsewhere.

Jonathan

[Toby S]

Karl

Relay by-pass fuse ? I've got a 92 1400 supersport and haven't come across that - where is it ?

[KarlH]

I’m not convinced the fuses have blown - it’s certainly no different with a new set of fuses and they don’t look blown on closer inspection 

I have managed to get the boot floor up and tested the supply to the pump (I’m guessing the pump is on the top of the tank) and it has just over 4v getting to it. 

I know there was a previous thread about a similar 4v reading but it has no conclusion so I don’t know what the fix is and can’t get into the connectors fo test where the voltage drop might be! I did try a direct connection to the pump with a fly lead but it still didn’t make any noise.

I’ve checked earths, cleaned up connections etc and it’s non different. 

What else can I test?

@Toby S - the relay I referred to was put in for the K click you can get with the starter, it’s a mod to the MFRU.

[Jonathan Kay]

... it has just over 4v getting to it. 

Where was that measuring between and was the pump still connected?

Jonathan

[PROBE2]

Karl, the pump is on the side normally not on top, top is Sender.

[KarlH]

Ah! Thanks. I thought being able to get to it fairly simply once I’d got the boot floor up was too good to be true. 

Looks like I’ll have to disconnect the fuel filler to get the floor out fully to get to it.

[PROBE2]

Karl, you should have enough room to access pump without any further removal

[Toby S]

 Hi Karl

Thanks for the note re the relay by pass - mine has this too, although this would only affect power to the starter motor and shouldn't affect the fuel pump.

I too have been having problems with fuel pump initially cutting out intermittently at first and them completely - Finally, I think, traced it to the live connection on the fuse box which directly powers the pump - self inflicted in my case - when I put the brookland screens on a year or so ago, being a lazy/smart arse (wanting the option to fit the windscreen back for winter) I merely pushed the wiper mechanism through the scuttle and held it in place with cable ties - the wiper mechanism passes behind the fuse box to the wiper motor located behind the passengers left knee trim, and during the intervening time, or so it seems, has fouled the fuel pump connections on the left hand side of the fuses box (found the fuel pump wire unconnected at back of fuse box).

Probe 2 is right on location of fuel pump, although a word of caution (from experience) before you start pulling wires around the pump

See above - The fat black connector is what you will see, which passes through the hole in the round plate bolted to the fuel tank (the other hole is where the fuel line screws in) - The black connector is a sealed 2 pin connector which connects to the white connector inside the tank which is wired to the fuel pump. Various problems to be wary of here (which I found to my cost)

• There isn't that much room to work with at the side of the tank
•  The white connector doesn't fit through the hole in the tank - pull the black connector out (and it's very tough to do so) and you may have difficulty re-connecting to the white connector as the white connector may disappear into the tank
• Once the black connector is removed from the hole, there's nothing to stop fuel peeing out through the hole it came out of if you have anything more than 1/8 - 1/4 tank of fuel. (mine had 3/4 of a tank when I tried levering mine off)
• If you break either the white or black connector in the process, they are no longer available - I had to do a bit of "dremel and silicone" engineering to fix my black connector after my attempts.

I would suggest if you want to check current getting through to the pump to determine whether the pump is knackered or not you cut the wires leading to the black connector and test and then reconnect with sealable connectors - Wish I had (may have saved me having to take the tank out to get the connection back in place and getting a gob full of fuel in my attempt to pull the connector off in the first place), albeit in the end decided to replace the pump at the same time given it was 27 years old.

Other things I checked during the whole process were:-

•  MFRU, situated under the ECU to ensure that was working OK and the relays were kicking in - you can open this with care and clean up the 4 relays inside
•  All engine loom, MFRU, ECU connections and wires
•  All earths - mine was by the air filter
•  the fuel inertia switch (had problems previously with that)

Hope the above helps - I'll be interested to know what you finally find the problem is - using a multi meter will certainly assist in the diagnosis.

One thing I didn't check and I'd be interrested if anybody out there know what it does, it the small rectangular flatish box to the left of the inertia switch - seems to have 2 push on rubber pipes, one leading from the engine and the other to the ECU - I understand this is also something to do with the fuel system, although as none electrical didn't investigate further

 

[Jonathan Kay]

One thing I didn't check and I'd be interrested if anybody out there know what it does, it the small rectangular flatish box to the left of the inertia switch - seems to have 2 push on rubber pipes, one leading from the engine and the other to the ECU - I understand this is also something to do with the fuel system, although as none electrical didn't investigate further

What engine and model is that? There's a fuel trap on the K.

Jonathan

[Toby S]

P.S. This is on a 1992 1400 supersport - obviously the connections may be different on yours given its a few years younger

[Jonathan Kay]

Crossed posts.

Jonathan

[Toby S]

Hi Jonathan

Yep - the fuel trap box  -  couldn't see it stopping the fuel pump working so didn't investigate further - what does it do  ?

[Jonathan Kay]

AFAIK it stops liquid getting into the pressure sensor in the ECU...

Jonathan

[Toby S]

Hi Jonathan

Thanks - I must admit ECU's are a bit of a misnomer to me, but if they are monitoring fuel pressure that would make sense - not quite sure what it's going to make the engine do if the pressure is abnormal (low or high) as the the fuel pump only has an on and off position and the air intake (throttle body) is hard wired (non electrical), but I guess it must control what the fuel injectors are doing (how long they stay open for working in tandem with the crank sensor) - carburetors seem much more understandable to me !

[Jonathan Kay]

I think that it's measuring the pressure in the gas phase in the manifold, not in the liquid fuel...

Jonathan 

[KarlH]

Thanks for the additional pointers. I may and try getting the MFRU apart again - I couldn’t figure out how it separated earlier!

Will the pump always prime - regardless of fuel level? Just wondering if the gauge wasn’t reading correctly and it was empty would it still make the priming noise? The gauge was reading 1/4 and I’m sure it does have fuel in it but you never know!

[SM25T]

From reading BlatChat for over 12 years, you wouldn't be the first to be trying to troubleshoot a starting problem, only to find there is no fuel in the tank.

[Jonathan Kay]

Will the pump always prime - regardless of fuel level? Just wondering if the gauge wasn’t reading correctly and it was empty would it still make the priming noise?

The pump will run with no fuel, but it might depend on the fuel to cool it.

Jonathan

[KarlH]

Thanks to my brother in-law being down I've finally managed to look at my fuel pump problem.

Starting at the econoseal plug which the black plug on the side of the tank joins we tested the voltage which was measuring 3v. We also tested the pump operation by supplying it 12v and it worked.

So, following it up the chain we tested the same things at each point we could and pretty much got the same reading and success of the pump working with a supply to it.

We then started seeing 12v at the MFRU, (only thing we did before that was move the fuse box and plug everything back in again) and the fuel pump started priming again. 

Put the battery on charge overnight, next morning - nothing, pump not priming. Then it started working again of its own accord. Tried again today, it worked, fired up and ran for 3 minutes before cutting out and now I'm back to where I was. 

Anyone got an idea what is going on here because I'm now even more confused and out of ideas!

[SM25T]

Can you gun a temporary jumper cable from the pump to the MFRU. Does it then run consistently ? If not, maybe test the pump on the bench ?