ECU Fuel Pump Signal

SubieMad · Post by **SubieMad** » Mon Mar 22, 2010 11:13 am

What makes the ECU decide to turn off the fuel pump?

Given that the fuel pressure regulator is vacumm driven, it cant be fuel pressure.

After you switch the ignition on the fuel pump goes for a few seconds and then switches off, is this simply a timed thing? I presume that when you turn the ignition to start, the signal from the ignition switch then tells the ECU to start the fuel pump again, is this correct?

The reason i'm asking is that my ECU won't prime the fuel pump at all. If i provide direct power to the pump it works fine, the relay works as it should but the ECU won't turn it on.

Any help would be much appreciated.

Cheers

mattl200 · Post by **mattl200** » Mon Mar 22, 2010 4:23 pm

when the ecu gets power it primes the pump for 3-5 seconds

and the pump starts again when it receves a valid timing signal from the cam and crank angle sensor

the start signal dosent have anything to do with the fuel pump as far as i know it has to do with over injection when starting no signal makes the car hard to start

have you checked the error codes

and if you plug the brown connectors together under the dash near the steering coloum the ecu should cycle the pump on and off

how to on error codes
showthread.php?t=14372&highlight=error+codes

SubieMad · Post by **SubieMad** » Mon Mar 22, 2010 7:37 pm

Progress update........

Swapped ECUs and the fuel pump primed

Cranked it over but wont start

Sprayed stuff down the air intake - started straight off

Soon as the spray stopped so did the engine

The engine ran 3 weeks ago b4 i rewired the car (complete rewire not just engine loom) so the injectors would appear to be ok, i have fuel, spark etc.

What else could it be

I'm beginning to think its the ECU - thoughts anyone please.

I have spent most of the day searching this site for answers but it is really hard when the search function doesn't accept 3 letter words - ie ECU MAF etc

steptoe · Post by **steptoe** » Mon Mar 22, 2010 8:53 pm

Wot car, model, helps get more responses

Gannon · Post by **Gannon** » Mon Mar 22, 2010 9:09 pm

So if you bypass the fuel pump relay, will the engine start?

If it doesn't, you have a bigger issue, and i'd be looking at the cam and crank angle sensors

vincentvega · Post by **vincentvega** » Tue Mar 23, 2010 10:15 am

you do realise that the fuel pump is negatively switched?

ie put a fused positive supply on one side of your relay, and the ECU provides a ground to turn the pump on

spike · Post by **spike** » Tue Mar 23, 2010 10:47 am

somthing from the realms of racing
some ecus when the realise that the fuel pump is on its way out it will switch to the spare
it does this by determining how much power the pump is drawing when i begins to draw say 14 volts to over come friction cause the bearings are gone, maybe its trying to do this without a spare to switch too??

vincentvega · Post by **vincentvega** » Tue Mar 23, 2010 2:15 pm

its a stock ECU mate there is no spare fuel pump output

mattl200 · Post by **mattl200** » Wed Mar 24, 2010 2:30 pm

dose the pump come back on when you crank the engine over

if so do the injctors have a positive supply from the relay on the ecu loom
the injectors are constant positive supply and switched negative through the ecu

SubieMad · Post by **SubieMad** » Wed Mar 24, 2010 7:36 pm

Problem fixed

Got another ECU from the wreckers and it started straight away!!!

Thanks for your responses everybody.

The car is an 89 Touring wagon with an ej22. When i got the car the wiring was crap so i decided to do a complete rewire, not just engine loom. Main reason being that i wanted cruise control on the steering wheel, proper temp gauge (installed the lib dash as well) fans switching on when they're supposed to etc etc.

Well it has certainly been a learning curve lol.

My only remaining problem now is the temp gauge (the one i didn't want to have to play with

). As soon as i turn the ignition to on the gauge jumps to 1/3 (completely cold engine) and when the engine starts it jumps to half

I have tested the resistance of the temp gauge sender unit and it is correct.
The gauge was working fine in the donor car so i'm at a bit of a loss. Funds are in very short supply at the moment so i can't afford an after market gauge.

Any suggestions on where to look to try to solve this???

By the way i would have been lost without this website, it really is cool !

Cheers

Tony