As the title states, does anyone know where to get a vacuum switch for an aux fuel pump?

is your switch broken?

and wont it be better to run the pump w/o vacuum switch and have it on all the time?

I dont know would it? I am not sure if my switch is broken, but for some reason i am getting power to the ground wire on the pump, and the pump is not working.(its a bn pump) I changed the relay, still nothing, so i am asuming the switch could be bad.

You can either remove the vacuum line (plug the source!) to the Hobb switch or provide constant ground from the Hobb switch to the relay... (latter if your Hobb switch is broken).

the latter i would have to ground hobb switch, and ground relay?

Ok i just rewired the relay, like stated in the link you sent me, i got the pump to go on with ignition using the 1st diagram. One problem.

The old relay was not grounded, and now i have an extra power wire to the batt. Before I had one ignition wire, one straight to battery, one to hobb switch, and one to fuel pump.
I succesfully got the pump to come on during ignition by connecting the ignition power wire to the post on relay marked Battery. and removing the constant source. Do I need an inline fuse in the ignition wire? Before the constand batt wire had one but i am not sure if i should switch it over.

it would. people had reported hesitation when they have the pump off. the car will respond better to boost when you do the hobb switch mod. you base fuel pressure will be a bit higher and you might lose some fuel economy.



Chunger: I powered the pump by tapping it to the MAF power wire. is this a good idea? will this affect the pump performance? it is on all the time and off when the engine is turned off. thx

You're powering the T-Rex with the MAF 12V?... I WOULD NOT because the MAF 12V is probably not built to power 8A+ and the ECM reads the difference in V to determine airflow... The latter may not be a problem if the T-REX is on full time but I would still worry about the current draw. If you just tapped the MAF for the relay (#85 or #86) then it may be "OK".

ah ha! good info here. thx!

I dunno if you have had a chance to read my recent fuel problem. But I was running lean from mid range to redline on my last dyno run. So far, I have been to two dyno session:

1.first session – found the inline pump was off and car is at 20:1 AFR. Did a quick fix by tapping the power wire to the MAF power. Problem solved and car’s running rich.

2.second session – the pump is buzzing loud and fuel pressure is there. But the AFR is lean, 14:1 from 3800 and dropped to 13:1 near redline.


Please tell me more about the MAF voltage change when more air is measured. Will the MAF voltage dropped when more air is measured and will this affect pump performance?

Should I try to wire it straight off the battery and see if things get better.



thanks for your help.

Dunno re: MAF signal changes w/o the FSM in front of me but the "modified" signal gets it's 12V from that wire you've apparently tapped in.

Maybe someone else here knows that answer.

And yes, I would power the T-Rex off the battery (using a relay and fuse of course).

thx again! appreciate it!


maximagtr420 : sorry for jacking your thread.

Ok guys, i have everything wired correctly, and i am considering the hobb switch mod, will I be ok to do this with the walbro 255lph aux pump? do you know if its able to be on 100% cylcle? Let me know what you think, thanks, i have a safc and a fmu 8:1 disk. thanks