help please

[Silver Fox 43]

Hi Guys, the race car has an intermittent fault. Sometimes when I go to start it, it fires and then dies straight away.

Fuel pump works fine, has it's own circuit.

Spark seems good and consistent.

It's as if the injectors are being shut off after firing once?

It doesn't happen all the time and has just started doing this.

Any ideas please?

Thanks, David.

ps, this is the new ti, M54B30 running M50B25 electrics, vanos delete.

Edited January 4, 2015 by Silver Fox

[BM WORLD 1283]

intermitant crank sensor ?? front hub moving around??

dry joints in the ecu , (coil driver circuit area)

[Silver Fox 43]

changed crank sensor and hub, and ECU, still same?

[BM WORLD 1283]

hhhmmmm , bad ecu main relay??

[Silver Fox 43]

Ok, got home and it started, seems to play up when it's been sitting in the sun, any ideas?

[Nobimmer 694]

Rub more sun lotion on it

[Silver Fox 43]

piss off

[Allanw 1071]

Dodgy ignition switch?

[will 169]

Process of elimination..

Use an indicator bulb (21W) to test the circuits as it will confirm that amperage is present, not just voltage. A multimeter will only show that voltage is present, it will not show up the presence of a dry joint which will allow voltage through but will fail with amperage demand. I have a bulb socket from an e30 with suitable interchangeable leads I use for this.

1. Connect the bulb between pin 87 (with red/white wire coming off it) and ground on the main relay, switch on ignition. The bulb should glow brightly. Try to start. The bulb should stay brightly lit all the time. If it dims/fails, you have an issue with the main relay and/or the power supply to the main relay.

2. If bulb dims/fails, remove the main relay from its socket and bridge pins 30-87, then try again. If bulb still dims/fails, the supply to the socket is faulty. Take a direct supply from the battery to the 30 terminal, then try again. This should sort the supply issue. You will need to figure out where the supply is being interrupted.

3. If bridging 30-87 sorts out the dimming/failing of the bulb, the main relay is faulty and should be replaced.

I have not considered issues with the fuel pump or with the crank sensor to be high on the list due to your info given above.

If the above does not sort the problem, you may have a wiring issue between the ECU and the crank sensor, the best way to test it is to use a multimeter between pins 16-43 on the ecu plug. you should read approx 550 ohms. If not, try shaking the wiring loom about and see if the reading changes. If it does, there is an issue with the loom somewhere between the ecu and the crank sensor.

If you still have problems after this, just shout.

[Haitoman 110]

Heat related misfire = cracked solder joints

[Nobimmer 694]

Dave I have a whole m52 loom with all sensors injectors etc. Holler if any use to you.

[will 169]

Heat related misfire = cracked solder joints

Dave has a total shutdown, not a misfire. Misfire when hot can also be caused by corroded male/female socket joints, faulty CPS etc...

Dave I have a whole m52 loom with all sensors injectors etc. Holler if any use to you.

Where were you when I needed one a few days ago???

[Silver Fox 43]

Thanks Ash, pretty sure the loom isn't the problem though.

Thanks Will, i'll have a look at that, main relay was my next port of call, hope you're right.

[Silver Fox 43]

Hi Guys, sorted thanks. Went thru almost everything, changed cam and crank sensors, coils, throttle body and TPS, Ecu, checked wiring.

Ended up being Ecu, I have 2 duds, 3rd one I tried fixed it.

Off for a remap on Monday and Hampton next weekend all going well.