CA18ET - ECU Fuel pump circuit help please!

alvin.l.ryan · Post by **alvin.l.ryan** » Mon Feb 12, 2018 9:04 pm

Hi all and thanks for letting me join up to the forum (even though i'm not a scimitar owner

) !

I was directed to here by Philip Andrew - he helped diagnose my broken fuel pump circuit on the ecu. The help was much appreciated as I'm still very much a beginner when it comes to car maintenance...

So I read this post

http://scimitarweb.co.uk/sgwrs/viewtopic.php?f=4&t=2013

Which was really useful - pulled my ecu apart and replaced the resistor. Then wired up a relay to power the fuel pump, controlled by the ecu's on/off fuel pump earth

However, it doesn't seem to be working - I'm guessing there is further damage to the ecu as it looks like the tracks have been very hot.

My question is, is there any harm having an ignition on controlled relay, to turn on the fuel pump... then it runs all the time (instead of toggling on and off like it used to when my ecu worked)? Will it overfuel? And if so would a good solution be an adjustable fuel pressure regulator?

Many thanks!

ps this is my car... bluebird turbo zx - few subtle mods (t25, huge fmic, piper cam, filter, etc etc)

Post by **scimjim** » Mon Feb 12, 2018 9:24 pm

No problem at all.

frase29 · Post by **frase29** » Mon Feb 12, 2018 9:39 pm

yep - no problem to solve it that way. If you've got a multimeter worth checking the continuity of the various tracks that look a bit toasted, if one (or many) have broken it may be simple to just bridge them with some small wire, and keep the ECU switching working!

alvin.l.ryan · Post by **alvin.l.ryan** » Mon Feb 12, 2018 10:01 pm

Brilliant - thanks very much for the replies!

And will I need to install an adjustable fpr? Or will the fuelling be ok?

Post by **scimjim** » Mon Feb 12, 2018 10:25 pm

There should be a pressure regulator on the fuel rail assuming it’s the same as the SS1?

Post by **CNHSS1** » Mon Feb 12, 2018 10:34 pm

Pump runs all the time and is modulated when engines rotating, only difference between a relay driven and ECU driven Pump, is that you'll lose the ecu 'prime ' circuit. This just ran the pump for 5 secs to ensure the fuel rail was full and ready for cranking. If you have ignition on relay driven pump, this will do the same thing. What a relay driven pump will give you, is a pump that runs when ignition on, irrespective of whether the engine is rotating or not. The std ecu would cut the pump if the engine stopped turning. If you crashed and the engine stalled the pump stops, but with relay driven the pump will push fuel out at high pressure until the battery goes flat!! Very dangerous in a crash! You need to fit a G switch, which will cut the power to the pump in the event of an impact. They can be reset easily if a dropped curb or bouncing off a trailer trips it. There's a few threads and pics in here somewhere showing fitment

Post by **CNHSS1** » Mon Feb 12, 2018 10:36 pm

Yeah fpr is built into the rail on bluebird, same as Silvia and ss1.
Altering the power source for the pump won't change the fuelling rate or pressure, so no aftermarket fpr required

alvin.l.ryan · Post by **alvin.l.ryan** » Mon Feb 12, 2018 11:35 pm

Ok great! Just bought a Mini Cooper crash switch off eBay... i assume it'll be easy to adapt

Thanks for the advice!

Post by **scimjim** » Tue Feb 13, 2018 6:25 am

Yep - same as they used in the mk2 K series Scimitar Sabre - I’ve fitted one to my K series SS1.