FPR solenoid

[silvercoupe97]

Ok, I've searched in here and out there for this question/answer and I'm worst off than before.
At this time I've got my stock fpr SOLENOID removed from vacuum (yes it's still electrically plugged in). It does take an extra second or two to start even after waiting for the CEL light to turn off before I turn the key to start. Will leaving the stock solenoid attached to vacuum and to the AFPR help? I have read here or somewhere that the stock solenoid isn't needed for hot starts because that there's enough pressure from the 255 pump to overcome the vapor lock. Then I read that it's there for a reason and wouldn't hurt keeping it connected. So now I'm even more confused.
Can someone clarify this for me? Why keep it connected? Or...why disconnect it? I know the single most popular reason why to disconnect it....but what else? I know the single most popular reason why to leave it connected...but what else?
Will keeping the solenoid attached also help keep pressure in the line? My gauge shows the pressure drop to zero after my car is shut off...immediately! Not a few minutes or even a minute...immediately. Or is that another issue with a leak somewhere else, because I'm not leaking fuel in the engine bay...bad fuel cap maybe?
Clarification on this would be helpful to me and anyone that searches "FPR solenoid". Btw, it's been two hours of searching before frying my brain and posting.

Thanks guys for the help,
John

 

[Denji]

Ok, I've searched in here and out there for this question/answer and I'm worst off than before.
At this time I've got my stock fpr SOLENOID removed from vacuum (yes it's still electrically plugged in). It does take an extra second or two to start even after waiting for the CEL light to turn off before I turn the key to start. Will leaving the stock solenoid attached to vacuum and to the AFPR help? I have read here or somewhere that the stock solenoid isn't needed for hot starts because that there's enough pressure from the 255 pump to overcome the vapor lock. Then I read that it's there for a reason and wouldn't hurt keeping it connected. So now I'm even more confused.
Can someone clarify this for me? Why keep it connected? Or...why disconnect it? I know the single most popular reason why to disconnect it....but what else? I know the single most popular reason why to leave it connected...but what else?
Will keeping the solenoid attached also help keep pressure in the line? My gauge shows the pressure drop to zero after my car is shut off...immediately! Not a few minutes or even a minute...immediately. Or is that another issue with a leak somewhere else, because I'm not leaking fuel in the engine bay...bad fuel cap maybe?
Clarification on this would be helpful to me and anyone that searches "FPR solenoid". Btw, it's been two hours of searching before frying my brain and posting.

Thanks guys for the help,
John

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I really think that this is a problem somewhere else in your fuel system, It could be a variety of things, but the giveaway is that it drops straight to zero. I never really paid attention to mine, but i just went out and tried turning mine on and then off, it sat right where it was when driving for as long as i watched.

My Fuel pressure solenoid went bad on my car once, it didnt make as much of a difference as your speaking about, very minor, maybe 1 second.

How long ago were these fuel mods done? Is the a problem that came about directly after installation or later on? We had a similar problem on my friends car and it turned out to be a problem with the fuel pump o-ring.

 

[silvercoupe97]

Thanks for the reply Denji.
I've had the injectors and fuel pump in the car since the swap completion in Nov 05, the AFPR/gauge were installed in Feb 06 perhaps. I noticed the drop instantly after I installed the AFPR and the gauge. I found that my AFPR was leaking after I primed it, but it's never leaked again after I put thread sealant on the fittings, but pressure still dropped like a rock. I read that it should at least hold pressure in the line for awhile. The cap does relieve pressure when I open it before a fill up though. One thing that I do notice, or don't notice should I say is that I don't smell gas at anytime under the hood in the car or even outside of it.
It never occurred to me that it's not right until recently because I've been losing timing during boosted acceleration but no knock, so I cracked the hood to troubleshoot and then the fuel pressure was put into the limelight again. I've read that the gas cap can be a culprit but I suppose that it can be anything that has an o-ring or seal.

 

[alex99gst]

My understanding is that whenever you shut the car off, the pressurized gas just goes out the return line and back into the tank. I have never seen my AFPR gauge at anything above 0 with the car off. I also removed the solenoid with no ill effects or hot startup problems.

 

[silvercoupe97]

I have never seen my AFPR gauge at anything above 0 with the car off.

How long does it take to go to zero for you Alex? Mine just drops...not literally, but I would say it drops 5psi per second approximately.
I'm going to have to try and reconnect the solenoid to see if that does anything for me.

 

[Denji]

My understanding is that whenever you shut the car off, the pressurized gas just goes out the return line and back into the tank. I have never seen my AFPR gauge at anything above 0 with the car off. I also removed the solenoid with no ill effects or hot startup problems.

I can certainly tell you that my car retains a certain amount of pressure for a good while after the car is off. This would be unrelated to the fuel pressure solenoid, which works during start up to raise fuel pressure temoporarily. I'm not sure what the reasoning behind my fuel pressure not immediately dropping, but its not only my car that does this, my best friends car also retains fuel pressure for a reasonable amount of time.

 

[silvercoupe97]

I'll check the obvious and easiest things first...pump gasket, gas cap, solid line that runs under the car, and the engine bay again. I don't smell fuel in there though. Maybe I have the fittings on my afpr too tight to where the fittings touch and hold the little ball open too much (or whatever that is/was that covers the opening to the return line). Sorry if that's a sad description, it's been too long since I put mine on.

 

[Denji]

I'll check the obvious and easiest things first...pump gasket, gas cap, solid line that runs under the car, and the engine bay again. I don't smell fuel in there though. Maybe I have the fittings on my afpr too tight to where the fittings touch and hold the little ball open too much (or whatever that is/was that covers the opening to the return line). Sorry if that's a sad description, it's been too long since I put mine on.

yeah, i was going to mention the line under the car, since you wouldnt smell that.

 

[silvercoupe97]

Well, I was under there today and I didn't see or smell anything. I didn't turn my car on today though, so checking may have just been a moot effort . The fuel pump lid may be loose or it may just have a bad seal. That was the last thing I touched that was fuel related. I'll check that next and the hardline again (with the car on next time, ).
I'll definitely post the resolution to my pressure loss issue.

 

[FORMONTOYA]

I would look at the o-ring in the fuel pump hat as to why the pressure is falling off so quickly. You could have twisted or tore the o-ring. I use a silicone grease to install o-rings.

When you first installed the 255 you mention that it was a few months later that the AFPR was installed and then you immediately started having problems. The OEM FPR can't bypass enough fuel at idle and normal cruise conditions, so it will build up pressure quicker even with a slightly leaking seal. After the AFPR install you had a fuel system setup that would bypass enough fuel that the pressure isn't building up fast enough and it takes a couple extra cranks to fire it up.

When I first installed my 255 plus AFPR I had the same issue with the fuel pressure dropping to zero in about 2-3 minutes and taking a couple extra spins to fire up. Later found that I twisted the o-ring in the fuel pump hat and now when I shut the car off it will fall to 30psi and take about 2 hours to fall off to zero.

I have read that the FPS is not required with a 255 also. However, I live in Houston, Texas where we have 2-3 months at 100F with about 95% humidity. My FPS is hooked up as I believe it can use all the help it can get. Your call.

 

[silvercoupe97]

I would look at the o-ring in the fuel pump hat as to why the pressure is falling off so quickly. You could have twisted or tore the o-ring. I use a silicone grease to install o-rings.

When you first installed the 255 you mention that it was a few months later that the AFPR was installed and then you immediately started having problems. The OEM FPR can't bypass enough fuel at idle and normal cruise conditions, so it will build up pressure quicker even with a slightly leaking seal. After the AFPR install you had a fuel system setup that would bypass enough fuel that the pressure isn't building up fast enough and it takes a couple extra cranks to fire it up.

When I first installed my 255 plus AFPR I had the same issue with the fuel pressure dropping to zero in about 2-3 minutes and taking a couple extra spins to fire up. Later found that I twisted the o-ring in the fuel pump hat and now when I shut the car off it will fall to 30psi and take about 2 hours to fall off to zero.

I have read that the FPS is not required with a 255 also. However, I live in Houston, Texas where we have 2-3 months at 100F with about 95% humidity. My FPS is hooked up as I believe it can use all the help it can get. Your call.

Awesome, that's something most will overlook...definitely including myself! I will look into that while I have the lid off. Hell, I'll probably do the rewire too.
I haven't seen temps like that in Hawaii yet because I just moved here, but it does get pretty warm. I may just hook it up since it doesn't hurt either way. I'm not worried about vacuum leaks from it only because I read the same with and without it (19-20hg).
Thanks for your reply FORMONTOYA.

 

[FORMONTOYA]

And another thing is when I received my 255 the o-ring was real loose. Even if you didn't twist or tear it, a new, better fitting o-ring would do worlds of good as far as building pressure quicker at startup.

One would have to think that if the seal is leaking at idle, ~34psi, that when you're in boost and the fuel pressure rises accordingly, the leak would get worse and potentially cause a leaning out effect of the fuel system.

 

[silvercoupe97]

...and I don't run lean at WOT, which, like you said should indicate a leaner A/F reading but at WOT I still show 11.9-12.0 AFR both on DSMLink and the AEM. My issues are at start up, both cold and "warm". I say "warm" because it still starts up like it's cold because of my fuel pressure or lack thereof. I do idle at 34psi too, it used to be 38psi and of course 43psi with the vac line off and plugged, but it's dropped. So something is getting worse. Another thing to consider about what I just typed is that the weather is getting hotter here too. I installed the AFPR in Feb so it was still...umm, cool out. The lowered pressure started when it started to get warmer out.

I will definitely look at the o-ring though. That wasn't even something I would have thought of...probably would have torn the car apart first, .

 

[FORMONTOYA]

Yea, I'm not saying it will cause you to run lean if the seal is messed up, just that it's a possibility. Your idling fuel pressure is correct. At 43-44psi hose on running 20inHg you will loose 10psi worth of fuel pressure (2inHg=1psi) for a fuel pressure reading of 33-34psi.

But your correct that the biggest effect will be at startup with 0psi fuel pressure. The pump has to build up pressure and if the seal is also acting as a regulator of sorts bypassing fuel also, it will take a couple of extra spins for the pump to "catch up" and fire up the engine.

And yea, I took apart and put back together the fuel system a few times before I figured it out myself.

 

[silvercoupe97]

I see what you're saying FORMONTOYA.

I may have to take my fuel system apart too to find the leak. The issue will probably be the last thing I replace too, .

 

[silvercoupe97]

Well, I haven't gotten to troubleshoot the leak yet, but I have reconnected the FPR.
I will be testing this for two weeks, with the solenoid connected and without again, this week being the first.
With solenoid connected...
-The first couple days with the solenoid have resulted in smoother cold start ups. Starts up with less effort after being driven around after being shut off, then restarted.
-I've noticed that I didn't have to put my foot on the gas during the initial start for any amount of time because it didn't die or surge on me.

That's it for now, more on my research later.
*Note that I've got the EGR, ISC, and FIAV blocked off.*

The solenoid may be just a bandaid to my fuel pressure leak, nonetheless....maybe this will be a "if you have a fuel pressure leak + how to temp fix it" thread...WTF