Fixing the "our fuel pumps don't prime" dilemma

[RealMcCoy]

While a non-issue for someone with a well sealed stock fuel system, it's a constant topic of conversation for people that have switched to aftermarket regulators that tend to leak down...

This fix is very easy to do, cheap, and works awesome... I originally came up with it trying to solve the same issue on an older carbureted vehicle that would have an empty carb after sitting for a week or more. Realized the same concept would be perfect in our cars.

If you have a hotwired pump, and some electronic imagination, you could do this with a little less complexity, but the method I'm outlining here can easily be copied, and it doesn't care if you are running a stock pump or hotwired, as long as you are using the stock system to turn it on... It is also pretty non-intrusive, as it pretty much leaves the stock system in place, and piggy backs onto it. Just make sure you use a relay and pigtail that is compatible with the load it will be carrying.

It all hinges around a five pin Bosch style relay, and this very cool little piece of modern electronics:
http://www.3rdbrakeflasher.com

They sell them on Amazon and ebay as well. So they shouldn't be hard to find.

First step is to set up your timer. I won't go into the instructions on how to do that, as the manufacturer has that covered, but you do want to configure it to turn on for a short time when powered up, then turn off. (I use 5 seconds, but you can set it up any way you like) Once the timer is configured, I snip the unused trigger wire back and wrap it to the ground wire, then snip the two configuration wires back at slightly different lengths, and wrap them to the output wire:



Once you have a neat little three wire device ready to install, you want to 'T' the power in (red wire) to pin 87 of your relay harness, 'T' the black ground wire into the pin 85 wire of your harness, and run the yellow output to pin 86 of your relay. (ignore the fact that 87/87a are reversed in the below pic, I moved it later)



Now you have a timed relay ready to install... I little electrical tape to tie everything together and you're ready to start putting it in the car:



You're going to install this in the harness at the MPFI. You are going to 'T' the power in wire (Pin 87 of your relay) into the black/white ignition source. You are going to snip the black/blue wire to the fuel pump, and run the MPFI side to pin 87a of your relay, and the fuel pump side to pin 30. You then ground pin 85 of your relay, and you're done...



The hardest part is finding a home to mount the relay... On a late model with the separated MPFI, I was able to just rotate them back and use the free mounting screw. On an early one with the large single MPFI relay you're on your own as I haven't done one yet:



Now you have a timed prime function for your fuel pump every time you turn on the key...

[fastbikes76]

Very handy info !! I know someone who will use this for sure .


Sent from my iPhone using Tapatalk

[stealthee]

Larry as always an electrical champion. I was thinking of doing this exact thing to my cousin's Talon. He kept talking about just running a switched hotwire and I have been trying to convince him this would be cleaner and he wouldn't have to turn his pump on every time he started the car.

[sublime_whatigo]

I can't say I've ever noticed anyone with a real complaint about the extra 2 seconds of cranking it takes to start the car, actually it is probably a bit better to get oil moving a little further before the engine starts cold. With that said you can also do this mod with a chrome ecu and 1 wire jumper to the clutch switch.

[stealthee]

It's not the extra 2 second that is the problem. As Larry said sometimes as the fuel systems get older they tend to lose their pressure while sitting and it takes much longer than the 2 seconds to start the car.

[sublime_whatigo]

My AEM fpr bleeds down the second I turn the key off, never had any issues besides it taking 2 seconds extra of cranking, and that's being generous I would probably say 1.5 seconds.

[Turbo Beast]

My AEM fpr bleeds down the second I turn the key off, never had any issues besides it taking 2 seconds extra of cranking, and that's being generous I would probably say 1.5 seconds.

How big are your fuel lines?

For me (different platform) I'm 10an all the way around. It fucking sucks without a priming pump.

[anyonebutme]

Stock lines here. Damn near instant starts from 0 pressure here, dunno. Everybody made so much of a fuss about this before that I made a startup video.

I would post it, but for the life of me I can't find it.

[anyonebutme]

http://vidmg.photobucket.com/albums/...ps2f60e900.mp4

Note, this is starting with a jump pack and not a battery so you can hear it struggle to turn over. Car is on jackstands and hasn't started in probably months in that vid. -6 AN fuel lines in bay, stock hardline from tank, AEM FPR. Gauge on left is fuel pressure at the fuel lab filter. "Supra" Denso pump.

[stealthee]

I would venture a guess that there are varying amounts of bleed off. Maybe on some the pressure bleeds off the rail, but there is still enough fuel in the line not to cause a problem, whereas other people have more severe bleed off that cause delayed start up.

I know on my Stealth it started without issue when it was still on the road. Once it was parked for awhile I started having delayed start up issues due to fuel pressure. I even started to think the fuel was bad and drained what I had and put 5 gallons of fresh in and still took awhile to get it started. Mine could actually be multiple things, but I won't know until I actually put the bitch back together.