Fuel upgrade annoyance.

[Talesin]

I've installed a Walbro 255HP and an Aeromotive AFPR; the problem is, the stock FPR keeps 21psi in the fuel system when it's turned off, to make starting easier. At the moment, as soon as the key is off, the pressure drops to zero, forcing a longer cranking time. Is this supposed to happen? Is there any way I can alter the behaviour back to stock with the upgraded fuel parts?

I'm just worrying that I'm over-wearing my starter, cranking it for 5-10 seconds each time, instead of the 1-2 for a 'normal' car. I'm also concerned about air/vapor bubbles in the fuel lines possibly lingering, and making their way into an injector at a bad time, like under full boost.

Or would the question better be put... is this normal behaviour for the fuel upgrade parts, or should I get my mechanic to pressure-test the system? I haven't checked for a cocked o-ring yet, wanted to make sure it was still SUPPOSED to be holding pressure with an aftermarket FPR before I had to deal with that bastard of a line fitting bolt again.

 

[94Jettameowpsst]

Since i have the stock fpr still, idk FIRST HAND, but every car i've seen with an afpr takes a good while to start just because its supposed to empty out when you turn the car off.

 

[larsrya8]

If you turn the key to ON does the fuel pump turn on? If it does, maybe you can keep it on ON for a few seconds before you decide to start the car. I don't have an AFPR, so I can't try this for myself. Let me know if it works or not.

 

[4g63forlife]

And all this time i thought i was the only one that had that problem, any way you should allow the pump to run for its ten sec prime than start it ,mine cranks right over every time.

 

[gixrman]

Mine does the same thing, with the same setup. I've had it that way for 3yrs now with the stock starter with no ill effects. Maybe a one way check valve.....

 

[92awddsm]

I always spin the engine over once, let off of the key, then it starts right up. The 1g fuel pump doesnt energize untill it gets a signal from the cas. If you just bump the ignition switch once, the pump energizes and the fuel line will prime. Now when you hit the key again, it fires right up.

 

[rob_rousseau]

It might be best to just wire the fuel pump to turn on with the accessory stuff on the ignition. This way you can get everything up to pressure before you start cranking. If you used a relay for your 255 and re-wired it already this shouldnt be too hard

 

[90AWDTalon]

My car does the same thing with the fullspeed throttle afpr. Haven't been able to solve it yet. It appears to just be an annoyance though.

 

[steve]

The 1g fuel pump doesnt energize untill it gets a signal from the cas. If you just bump the ignition switch once, the pump energizes and the fuel line will prime. Now when you hit the key again, it fires right up.

On a 1G the fuel pump turns on when the starter is activated and kept on by the ECU seeing the engine running. The end result is what you describe but way it works is slightly different.

Aftermarket AFPR do bleed off pressure faster than the stock regulator but they don't seem to go to zero the second you turn the key off. The fuel pump should be able to pressurize the system in less than a second. If your having problems I'd check the regulator and make sure there isn't something holding the return port open.

Steve

 

[Talesin]

The odd part is, it was less noticable when something *was* blocking the aperture.. a bit of teflon tape found its way under the rod when first installed. It'd sink slowly (say over 3-5 seconds) to near-zero, holding just under the zero mark. After opening it up and clearing that out about three months back, it now drops immediately to the bottom gauge pin.

Good to know that I'm not the only one with this issue though. I wonder if a stock FPR could be plumbed in downstream of the Aeromotive, to try to hold that stock 21psi from falling through the return... adding a new potential point of failure, but it could be worth it. Wouldn't want to put it in before (as I already have a rail fitting and would worry about pressure leaks from the return side), but I'd be concerned about erratic behaviour downstream, if the stocker made for any appreciable backpressure on the return line (possibly giving me an unstable fuel pressure rise under boost).

I still need to do the rewire, been lazy about pulling up the carpet. Already planning to put in a fuel cutoff switch for antitheft purposes, maybe put in a second momentary switch to hand the pump battery power independent of the ECU? Would there be any danger of ECU brainfry if I just set up two toggle-switch lines, one from the standard and one direct to the battery, and left both on while driving? Or should I toss in a relay so when the ECU powers the fuel pump line, it'll cut off the 'prime' switch/button power?

 

[steve]

The "standard" rewire uses the existing fuel pump drive circuit as the trigger for the new relay so that it works just like the original setup. If you want to add a security lockout just put the switch on the ground wire for the relay coil.

Steve

 

[Talesin]

Yes, I mean adding in a second circuit to that, so that I can turn on the fuel pump independent of the ECU for priming purposes, say with an intermittent switch or button. If the ECU line-controlled relay is a lower voltage feed, I doubt that it would do the brainbox *any* good to put it on the same line with a direct 14V, if it isn't expecting it.

Then again, just running a bypass around the relay (14V->FP line bypass, that is), with the switch on that would do the same thing, and with less hassle (aside from re-crossing the firewall to locate the switch inside). Heck, if the switch had a 30-second (or so) hold on it, just hit the button and wait a few seconds, start the car. With the relay closed, it'd provide the shorter path and depower (almost entirely) the intermittent button.

Lockout, just put that on the ECU controlled wire as you said. Even if someone knows about the intermittent, the car would only run for the duration of the intermittent 'wait time', even with the turbo timer going.


Eh, KISS rule wins, probably just have a standard lockout and a prime button that I have to hold down. Or a three-position switch.

 

[steve]

The normal fuel pump check connector is just a tap on the line to the fuel pump and it doesn't harm anything when you power the pump that way.

I really think your problem is in the regulator. Possibly damaged or you have more stuff in it but you can set up a prime control if you want.

Just do the rewire. That will take all the current draw off the stock wiring. The pump will just be getting power from the relay. The you can add both a prime switch that puts 12v on the trigger wire to the relay coil or ground the input on the MPI relay that the ECU uses to activate the pump. The security switch would go in the ground side of the relay coil circuit to open the relay from ground. No ground and the relay won't switch and the pump won't turn on. No need to make yet another parallel circuit for priming the pump

Those switches will only have to handle a couple hundred milliamps rather than the 10s of amps that the pump draws.

Steve