Edit: My FPR also does the same thing, new FPR, new injectors, new fuel pump...All with new seals and o- rings where its needed. Is it a possibility that remaining vacuum pressure in the system will hold the gate open, releasing the fuel pressure?

Previous post deleted for Inacuracy....

I may be misunderstanding something, assault... what would vacuum pressure have to do with fuel system pressure while the car is shut off? Stock, ~21psi is supposed to be maintained in the fuel lines with the car turned off. Given that there's no vacuum being applied with the car not running, why would a vacuum leak at either of those points make any difference whatsoever?

kellbeast, I have the same thing happening with mine. Hard-starting and switched off zero-pressure after I put on the Aeromotive, starting just got worse when I put on the Walbro. Planning to take off the fuel rail, zip-tie the injectors in place and point it at a pan, then turn on the fuel pump check connector. If an injector is open without any kind of actuation signal, that'd let the pressure leak out pretty damn quick. Only other places I can think of are through the FPR (have to think of a way to test that one, some kind of a pressure source applied directly to the fuel line input on the FPR, but at 20psi so the spring shouldn't open, and see if anything leaks out the return port), or through that damn O-ring on the fuel pump, where it slides into the fuel line end on the pump bracket. Not really sure if the Walbro will hold pressure coming back through it, like the stock unit is supposed to.

This topic has been debated for a while, some say (including techs at Aeromotive) that this is normal and some say (myself included) it is not. I have personally done many AFPR/pump installs and none has ever drop to 0 immediately. That said, I have no answer as to why some of you are dropping to 0 after shutdown except checking the pump o-ring and a possible AFPR defect, Talesin did bring up some interesting thoughts on the injectors though.

Talesin said:

I may be misunderstanding something, assault... what would vacuum pressure have to do with fuel system pressure while the car is shut off? Stock, ~21psi is supposed to be maintained in the fuel lines with the car turned off. Given that there's no vacuum being applied with the car not running, why would a vacuum leak at either of those points make any difference whatsoever?.

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No, you absolutly right, I was misunderstanding. My thinking was backwards but come to think of it. If your vacuum pressure holds as the car is turned off this may be enough leave the gate open for the fuel to pass through the return line releasing the pressure....??

That's a good possibility. The other end of it, I'm thinking, is that since I don't have a FPS, when it's cranking, the vacuum is keeping the AFPR open, preventing fuel pressure buildup.

Does anyone know if the FPS is supposed to close when you switch the car off? Would that prevent the vacuum from keeping the AFPR open and bleeding down? Oh duh, obviously it does, no electricity.

Same problem here right after I installed my Aeromotive fpr kit. It has to be it because its the only item I installed at that point in time. I did have the walbro installed before and never had the startup issues untill I later installed the Aero. fpr. Maybe the Aero. fpr has a design flaw in not being able to hold any pressure when the engine is off? Anyone find out the reason for this or a cure yet?

thekellbeast said:

The other end of it, I'm thinking, is that since I don't have a FPS, when it's cranking, the vacuum is keeping the AFPR open, preventing fuel pressure buildup.

Does anyone know if the FPS is supposed to close when you switch the car off? Would that prevent the vacuum from keeping the AFPR open and bleeding down?

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Manifold vacuum doesn't hold the FPR open. It works against the spring pressure inside and reduces the fuel pressure assuming that the spring pressure is greater than the vacuum like it should be. Once you turn the car off there isn't a vacuum any more.

Steve

I'm also having the same problem. It's kind of embarrasing.

This is what I have to do so my car doesn't seem like a piece; I crank it for like 3 seconds, stop, then I crank again and it starts right up. If I initially crank without stopping, it can take up to 10 seconds to start.

Well, let me try to narrow down the issue a little bit. Out of all the people in this thread who are having problems, who has their fuel pressure solenoid removed? I'm going to put mine back on and see what happens.

thekellbeast said:

Well, let me try to narrow down the issue a little bit. Out of all the people in this thread who are having problems, who has their fuel pressure solenoid removed? I'm going to put mine back on and see what happens.

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1ST gen here with all emissions removed.

I put my fuel pressure solenoid back on, and it didn't fix anything. When I have the key in the ACC position and the fuel pump is on, fuel pressure is at 43.5 psi. Despite this, when I go to start, it just cranks and cranks. I have good fuel pressure, the solenoid is working, and everything is hooked up correctly. I just can't see why it's doing this. I've eliminated every possibility except the AFPR itself. I just can't see how that would be a problem though, since fuel pressure is good.

I'll see if I can get somebody to try to start the car while I watch the fuel pressure gauge. Maybe for some reason fuel pressure is dropping off during cranking.

I'd like to track this one down as well.
Same thing happened to me after I installed my AFPR.
I even had the FPS hooked up.
It has a little breather on it right.
It's that little oval thing on one of the ends.
All it does is open up to the atmosphere and allows no boost/vacuum source to the FPR.
Just like when you set your base pressure, you remove the vac line and your fuel pressure rises.
That's all FPS's are for, is during hot starts.

I recently installed an Aeromotive AFPR on my buddies 1gb (Stock fuel system otherwise), and now he has the same problem....
He has everything else for the fuel system, but just wanted to see what one upgrade will do at a time.
Next is a FP Rewire and a 255 Fp Install.

If you can just try putting the stock FPR back in and see if the pressure drops off.
If it does you know the problem is somewhere other than the AFPR but if it doesn't then you know that the new AFPR is leaking.

The power off state of the FPS is the outlet connected to the inlet, it requires power to the coil to connect the outlet to the vent.
As your finding out it really has no effect on how fast the pressure drops after you turn off the pump.

Steve

That's right, even with the fuel pressure solenoid, fuel pressure still drops off immedeately. This still doesn't make a damn bit of sense though.

If the car has been sitting for a while:
Pump primes for a while, fuel pressure gauge reads 43.5psi. When I go to start, it cranks and cranks unless I give it throttle.
If the car has been recently shut down.
No priming pump, fuel pressure gauge reads 0psi. Starts instantly, zero throttle.

I have everything teflon taped on the regulator - adjustment allen, vacuum nipple, and all connections. I'm positive that there's no leak there. Before somebody asks, yes, I am using the correct spring inside the regulator.

I'm also getting a bit of a hesitation at low rpm's, and I'm getting an 0300 ignition system trouble code. I traced it down to a cut spark plug wire, which I'll be replacing. I really doubt this has anything to do with the problem, but it's one more thing to fix, to eliminate the possibility.

thekellbeast said:

That's right, even with the fuel pressure solenoid, fuel pressure still drops off immedeately. This still doesn't make a damn bit of sense though.

If the car has been sitting for a while:
Pump primes for a while, fuel pressure gauge reads 43.5psi. When I go to start, it cranks and cranks unless I give it throttle.
If the car has been recently shut down.
No priming pump, fuel pressure gauge reads 0psi. Starts instantly, zero throttle.

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This is exactly how mine acts too. Its a real pain since mine isnt a daily driver now and only comes out in the evenings that I go somewhere alone. Car seats dont fit well in this car.

i've never been a huge fan of aeromotive FPR's. ive seen many of them fail, not work properly. Oh and ive seen one leak gas thru the vac port, not very pretty...I find it hard to believe that a car that does not hold pressure would even have a proper 1:1 rising rate, ive seen cars blow up because of lacky fuel systems that did not hold pressure correctly.

i will say it is not normal(AT ALL) to hard start a car and for fuel pressure to drop off immediately after shutoff, i believe aeromotives should hold pressure for at least 20 mins, and then drop off.(i think this time is pre-defined by them somehow)

Anyways, i think most of you may have an intank leak at the fuel sendung unit where the pump mounts, or a pressure leak at the sending unit seal. or there's a leak in the lines somewhere. Or the FPR itself is just a piece of crap.. especially if the problem is still there when you switch back to a stock style FPR. I suggest fixing this issue asap.

Well, I have a quiet hissing by the fuel tank after I installed my Walbro, though I had assumed that to just be the sound of the pump, as I didn't smell any fuel. Know that my fuel pump assembly gasket is sealed (better than it was before!) as it'll regularly let out a good amount of pressure if I stop and immediately open the gas cap.. scared me the first time, as it never had done it before. Planning to take out the bracket again and try to make sure that the o-ring isn't damaged or tweaked in any way.

Question for the 1G AWD guys who have put a 255hp in.. does the pump seem like it sits a little angled on the spacer at the bottom? Mine seemed to have the pump 'leaning' outward, whereas the stocker Denso unit sat square.. can only assume it's because of the size difference and output port location difference. Though the 'collar' around the output stub on the top of the pump didn't seem to fit all that tightly either, nor did the little 'cap' snap over the top.. I've been feeling like I did the install wrong, though I followed the directions that came with the install kit exactly.

From the VFAQ's Walbro pump install:

Here is the new pump in the assembly. Be careful when putting the pump up into the fuel feed line - the rubber O-ring should be lubed with some grease, oil, or spit (hey, it works) so that the O-ring slips easily into the feed line. If it does not, the O-ring can kink or tear, and the car will be hard to start after sitting a few minutes, as the kinked/torn O-ring will allow the fuel to bleed out of the feed lines. The symptom will be that the car will take several seconds to start after sitting more than a minute or 2, but starts right up if you turn it off and then immediately start it back up.

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Yup, there's the problem right there. I guess the AFPR just made the problem more apparent. When I get back in town I'll be pulling my fuel pump assembly all apart.

In case anybody was considering replacing the stock fuel pump attachments and everything with -6 AN (like I was) and a hose on the fuel pump outlet, keep in mind that an install like THIS http://www.dsmtuners.com/forums/showthread.php?t=254501&highlight=bulkhead will only work on 1g's. Apparently the 2g's have the fuel pump too close to the top of the sending unit to use a barbed fitting and intermediate hose. You have to use the stock attachment.

thekellbeast said:

From the VFAQ's Walbro pump install:


Yup, there's the problem right there. I guess the AFPR just made the problem more apparent. When I get back in town I'll be pulling my fuel pump assembly all apart.

In case anybody was considering replacing the stock fuel pump attachments and everything with -6 AN (like I was) and a hose on the fuel pump outlet, keep in mind that an install like THIS http://www.dsmtuners.com/forums/showthread.php?t=254501&highlight=bulkhead will only work on 1g's. Apparently the 2g's have the fuel pump too close to the top of the sending unit to use a barbed fitting and intermediate hose. You have to use the stock attachment.

Click to expand...

Unfortunatly I dont think thats my problem as I was running the stock fpr when I first installed the pump and I didnt have any problems. As soon as I installed the Aeromotive fpr I started having the startup issues.

Not sure if the aero. fpr is letting to much fuel return to the tank after shut down or what the deal is?

It may be that the AFPR is helping cause it, because it flows more. I'm pretty sure my issue is the pump O-ring though. I'll be able to tell for sure pretty soon - I have to pull the pump because the level sender doesn't drop below 1/3 tank.

I just pulled my pump again to double check, and no, the O-ring was good, seated properly. Actually popped off the top and was stuck inside the 'collar' the fuel pump output slides into; glad I have a set of mechanic's pick-hooks, or I never would have gotten it out un-damaged. I also removed the 'cap' which would not snap into place, and the hissing is gone... just the standard Walbro whine. Which seems louder now for some reason.

Still has the hard-starting problem.

(disclaimer) The following paragraphs are pure hearsay and conjecture based on that hearsay. They are not based on known-fact. (disclaimer)
Was told by a local DSMer that the Walbro does not maintain fuel pressure like the stock Denso... that unless it's running, fuel can trickle through it backward. I wonder if the weight of the fuel would be enough to act like a siphon, and slowly pull most of/all of the fuel in the lines back into the tank. Any fuel leak between the pump and FPR would let air into the system under those conditions, which would need to be pressurized and cleared past the FPR before the car could start. There would also be the possibility of simple fuel vapors being pulled back from the tank through the AFPR, if it doesn't make an airtight seal to the return line at full closure.
An easy way to test this would be to wait overnight so it's for-certain in the 'long start' mode, then take off the fuel rail input line. If only a little fuel spills out (or even worse, NONE), it'd be pretty obvious there would be air/vapor getting in somewhere. After that, it's just a question of where.
In the latter case, simply putting an airtight check valve on the fuel return line after the AFPR would at least prevent the fuel from 'backing out' of the lines. Still would take 2-3 seconds to pressurize the lines on starting, but the crank/recrank or 10-second-crank would be gone, if that's the problem.
If air's getting in through a fuel leak... well, that should be fixed anyway, for basic safety.
The only other real place would again be the injectors, if one 'fails open' with no signal, pulling in air from the cylinder. But that would result in variable starting times, if the 'stuck' injector was in a cylinder with all the valves closed, it would start MUCH quicker than if it landed on a cylinder with either the exhaust or intake valves open. This could also be tested (as above) by pulling the fuel rail, zip-tying the injectors in place, pointing it at a pan and connecting battery voltage to the fuel pump check connector. If one sprays with the car turned off (and still clicks when the car is running), it's failing open and needs replacement.

I also have to wonder if it would be possible to somehow attach a high-flow check valve on the line between the fuel filter and the fuel rail input. Keep fuel in there, and so long as it's airtight, keep it from backing out through the Walbro as well, thanks to the power of vacuum. And since it's before the rail (and the AFPR is keeping the pressure in the rail solid) it doesn't matter if the fuel pressure in the lines before that check valve would be slightly higher (due to the resistance of the valve).