Fuel Pump Wiring
Turbo Mini Forums

Hi,

I have a few questions about the fuel pump wiring as I keep blowing fuses as the Ignition is switched to on. The first fuse was 10A and I used a 15A just to see if it would work, but it blew this too, so Im worried there is something up with the way Ive wired the system in. Its running through a Canems ECU, and there is an Inertia switch wired inline with the + feed to the pump.
The Pump is a Rover MPI pump and tank combo. Since the car is a 1991 I have dont really know how this is wired in.
I used the two outer Pins on the Inertia Switch, presuming the middle is switched to live when it trips. The Connector on the Pump has two pins, the pin nearest the boot door is 90 degrees to the one behind it, with the one behind being flat.

I wired the + into the one nearest the door and earth from the one behind, is this correct?

Also I cant seem to get a crank signal, there is a Red LED that comes on to indicate power is going to the ECU, it should then turn green when I crank the engine, however it just goes off and there is no LED showing?

One final question is oil pressure, I got it there the other day, to make sure everything was okay, but its not getting pressure when Im cranking it today. Any Ideas?

Thanks :)

First, is the fuel pump wiring original MPI (1991 sounds a bit too early) or are you just using an MPI tank/pump ???

And is the pump relay the original (ie, MPI) or another one you have added ???
Presumably the canems ECU operates a fuel pump relay like most other injection ECUs so are you attempting to operate an original (MPI) one or a new one ???

Ignore the inertia switch for the moment, if fuses are blowing, just bypass it to be sure it hasn't an internal earth fault but, basically, they are an on/off switch - the third contact is to operate a warning light showing you have crashed if you feel the need for such a light.....

Re the cranking signal, I'm not familiar with the canems one but on Megasquirt it will synch once cranking and the VR signal is picked up - this is shown in the tuning software (TunerStudio or MegaTunix) rather than LEDs.

Usual problems in Megasquirt are the VR sensor itself (often the polarity of its wiring), sensor gap, physical settings in the ECU (variable resistors to match the pickup), or settings within the software (wheel configuration).

Again, without knowing anything about canems, are your VR settings correct for the system ???

Schrödinger's cat - so which one am I ???

In reverse order, most ECUs work quite happily down to about 6.5V.

The actual processor and all the sensors work at 5V and the voltage regulator inside the box only needs about 6.5V to provide the stable 5V internal supply required.

The 12V injectors are usually compensated for by low voltage in the software (certainly in Megasquirt) so starting with a low voltage really shouldn't be a problem (unless canems leave out the voltage compensation).

I think you need to investigate why your "switched" live drops so much during cranking or ask Canaems what it's lowest operating voltage is.

For the fuel pump, disconnect your ECU and just put power the relay direct to operate the pump and see if the fuse still blows.

But be carefull, most ECUs have a (fused) 12V supply to the relay coil and the ECU grounds the other side of the relay coil.

So make sure from the wiring diagram which terminal needs 12V or ground to test it (post the Canems wiring diagram here if you are unsure).

Normally the pump would run for about 2-3 seconds and the stop when you turn the ignition on, you need to make sure it will run permenantly with the ECU bypassed without blowing the fuse.

Schrödinger's cat - so which one am I ???

You state that the ECU provides the power for the fuel pump.

Most ECUs just earth the relay driving the fuel pump.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Ill head out an try the approaches suggested and report back :). The switched live drops to zero when cranking, I put a Multimeter on it to check.
Just to clarify, the Power for the pump goes through a relay and a fusebox, Power comes from a switched live and a Permanent into the Relay, then a output from the relay goes to the Canems Fuse box. The power for the ECU , Pump is taken from 4 different points on the Fuse box :)

Green wires (auxilaries) will drop their power when the ignition switch is turned to 'crank' this is to turn off all other things reducing the load on the battery while the engine is being turned over.

white wires are an ignition live. That means they remain live when the ignition switch is turned to 'crank'. You need to wire the power supply for the ECU harness to an 'ignition live'

Brown wires are permenantly live wires.

Just in from the car, Fuel Pump works when I put 12V from the battery to it, however it was working without a earth too which I thought was strange.

Working from the front back, it seems the fuse only blows when I have it earthed to the battery. Id didnt blow when i had everything disconnected, then Inertia switch connected, nothing, +ve into pump, nothing, when i connected the earth it went pop.

Now, when I just connect the +ve from the Relay, nothing happens, no fuse blown, but no pump working.

I had it earthed to the battery earth, would this be an issue??

Thanks sprocket! I got the live off the top of the fuse box after some prodding with a Multimeter :)

Just to add another point, the relay takes about a second or two to "click" after i turn the ignition.

better to earth to the body ratehr than the battery

Ive tried earthing to the body with power through the relay and it doesnt work, nothing blows but nothing works.
Is it possible there is a short so to speak on the Earth side? This would explain it running with the 12V from the battery with no earth.

What Amp is the fuse in the MPI minis for the fuel pump does anybody know?

From memory the vertical pin is the ground and is connected direct to the tank shell. The horizontal pin is the live.

Obviously connecting live straight to the ground will pop the fuse quite violently.

Connecting the live only to the horizontal pin will, if there is a ground path through the tank some where, allow the pump to run.

There sould be no reason for the fuse to pop if you have had the pump running, only if there is a short on the connectors or wiring you are using. Obviously you should be using insulated terminals when ground and live are in such close proximity as they are on the fuel pump connector.

Just a thought, check the inertia switch wiring. I thought the wiring was on two pins next to each other. Easy to check with a multi meter with the switch tripped and set.

The fuse should be 10amp.

Edited by Sprocket on 3rd Jun, 2011.

Ive left it for the night as the lure of beer was too tempting haha. I measured the resistance on the Pump which was approx 1.5 Ohms(very hard to be accurate while being a contortionist ) Ill measure the resistance on the Intertia switch too. If the pump grouds to the tank that could explain alot, The rover Wiring diagram states it earths to the rear left corner so maybe this is what it means.

Thanks For all the help, hopefully Ill have her up and running next week, as im stuck in work all weekend :(

rear left corner will be one of the bolts on the rear light, same place as the number plate light etc

Schrödinger's cat - so which one am I ???

Went over the whole loom today and changed the Cannections to shrouded ones, Fuels pump is now working perfectly. Thanks everybody for all the help :) . Got good oil pressure too, but engine kept backfiring when turning over, so I think the static timing may be out, I have it at 8 degrees but i think starting at zero may help, then get the strobe on it.

Does anybody see a fault with this running in procedure:

1. Start engine with no coolant, turn off when head gets warm.

2.Fill with Coolant and start again, and run up to temperature.

3 first 500miles , only use art throttle and dont Labour the engine.