A handy fuel pump relay tweak

[S2central.net]

I got to the bottom of why MAF, ISV and so on get 12V when the key is ON... they are not only activated when the engine is running. I couldn't see it at first, but one of the ECU pins is taken to 12V when it is powered up. The common connection is AFTER fuses 24 and 28 which is all a bit strange but it explains that weirdness we saw last week when I thought only the fuel pump relay triggered these. I need to dig more to see if the ECU always holds this pin high or whether its part of a start sequence which times out unless the ECU sees some flywheel teeth.

It might also be related to MAF burnoff, but this pin is also part of afterrun logic as well.

[S2central.net]

I got to the bottom of why MAF, ISV and so on get 12V when the key is ON... they are not only activated when the engine is running. I couldn't see it at first, but one of the ECU pins is taken to 12V when it is powered up. The common connection is AFTER fuses 24 and 28 which is all a bit strange but it explains that weirdness we saw last week when I thought only the fuel pump relay triggered these. I need to dig more to see if the ECU always holds this pin high or whether its part of a start sequence which times out unless the ECU sees some flywheel teeth.

It might also be related to MAF burnoff, but this pin is also part of afterrun logic as well.

[S2central.net]

Planning to bench test this particular bit of nonsense tonight if I can.

[BrianSmith_S2]

Ive been lent a spare MAF by a kind forum member .

In our many pm's on my S2 non starting issue i was confused how the voltage im seening at the MAF isnt always 12V.

Going to swap them over to see if this helps, just incase somethings failed internally in my MAF.

Cheers,

Brian

[BrianSmith_S2]

Ive been lent a spare MAF by a kind forum member .

In our many pm's on my S2 non starting issue i was confused how the voltage im seening at the MAF isnt always 12V.

Going to swap them over to see if this helps, just incase somethings failed internally in my MAF.

Cheers,

Brian

Nope, no change

[S2central.net]

The MAF is fed 12v by ecu when ignition is on. Pretty sure there is an internal relay that drives this output on pin 37. When engine is running this is bolstered up by the fuel pump relay. This reduces load thru ecu fuses 27 & 32.

Try unplugging maf, ISV, injectors, evap, wgfv and afterrun pump in case one of them is dragging voltage down on pin 37. With all unplugged see if you get 12v on the maf or injector plugs.

[Koplint]

It sounds like you've made some significant progress in tracing the power supply to components like the MAF, ISV, and others. The observation about one of the ECU pins being connected to 12V when powered up sheds light on why these components receive power even when the engine isn't running.

Your insight into the ECU's behavior regarding this pin is quite intriguing. Understanding whether the ECU consistently holds this pin high or if it's involved in a startup sequence that times out without certain inputs (like flywheel teeth) could provide valuable insights into the system's operations.

Moreover, the connection of this pin to MAF burnoff and afterrun logic suggests a broader function within the system. It seems like you're on the right track to uncovering more details about the system's intricacies and dependencies.

Keep up the meticulous investigation! It's fascinating how these small electrical connections play a significant role in the overall functioning of the engine management system. If you uncover more information or insights, it'd be great to hear about your discoveries.

[Fat Audi 80]

Holy thread resurrection Batman!

[K Simmonds]

Yes, 13 years takes some beating!

Not seen Paul on here for ages does he still have anything to do with us or even have an S2 for that matter?

Bloody FaceFart has ruined my favoriate forums.

[newsh]

Holy thread resurrection Batman!

It's a spammer. The bots are getting smarter.