Why does my car idle better with AFPR vacuum hose off?!

[hofmania]

I've been working over the past days on my 96 GS-T auto fwd in hopes of getting it running. I have everything bolted up and am now going back through piece by piece until it's all working nicely.

Yesterday was spent on boost leak and compression testing. Had a ton of leaks! The day before I redid the mechanical timing. Today I had some issues with a few of the An connectors with my AFPR and now I'm attempting to set the fuel pressure.

Current pressure - ~35psi - it does not change when I take the vacuum line off. In fact, if I leave the vacuum line connected the car will eventually stall and turn off at idle. If I remove the vacuum line, the car idles quite well. Two questions...

1. Why does the car idle better with the vacuum line off? Running wally 255 + stock injectors at the moment

2. Why will the fuel pressure not rise or fall by cranking the allen wrench bolt on the AFPR? I've taken apart the AFPR and things looks fine.

I have Bosch 1000s waiting to be installed, but I wanted to get everything working smoothly before tossing on some mega injectors for my 16g/20g that's coming.

Thanks in advance!

 

[BogusSVO]

Does the AFPR vac line look wet, or smell of gas?

The diaphragm may have failed.

Commonly it will pump fuel out the vac line if it is bad, causing raw gas to be pumped/sucked into the IM

 

[hofmania]

Does the AFPR vac line look wet, or smell of gas?

The diaphragm may have failed.

Commonly it will pump fuel out the vac line if it is bad, causing raw gas to be pumped/sucked into the IM

I read about that originally when I was searching. And no, there is no fuel in the vacuum line. I took apart the AFPR just to check the diaphragm health and it looked good to me. No cracks, tears, holes, etc.

 

[Diamond Star Werks]

What is your fuel pressure on and off?
If its 35psi that's 8 psi too low. With the line off fuel pressure should be 43 and on at idle vacuum 40.

 

[BogusSVO]

Did you install the spring properly when you reassembled it?

You may have flubbed that and that's why you are not getting adjustment.

http://www.dsmtuners.com/forums/articles-engine-fuel/399037-replacing-diaphragm-your-afpr.html

http://www.dsmtuners.com/forums/new...le-fuel-pressure-regulator.html#post152724177

 

[miguelmcv]

When you say disconnecting the line, do you mean disconnected and plugged, or disconnected and letting it hang down with out plugging it, I will assume plugged., The only thing that comes to my mind is, because is not adjusting the AFPR, it holds higher psi of fuel forcing the injectors to spray a little more fuel, obviously with more fuel, it will idle better.

My suggestions is, you might have a bad AFPR as stated (BOGUS),,,, The diaphragm not necessary needs to be bad for the AFPR to fail, Check under the diaphragm and look at the hole where the ball shots the fuel, some times the hole is not rounded and the ball doesn't shot completely causing a constant leak,,.
If all inside the AFPR looks OK, then you might have a bad fuel pump valve, or the O ring is not keeping up, remove the fuel pump and check if there is any abnormal somewhere,.

When the AFPR is not adjusting is,
A,-Because the AFPR it self is bad, or B,- because there is a leak on the line, or a leak back in the fuel pump.

Check all that and report back what you find.

 

[dilbertgonebad]

I had a similar problem this summer as well, Turned out that the o-ring between the fuel pump and the fuel pump housing / mount had been torn during the installation. The result was it would build about 35 lbs of pressure but that was all the rest of the fuel would just bleed out in the tank.

 

[hofmania]

First off, thanks for the quick replies!

What is your fuel pressure on and off?
If its 35psi that's 8 psi too low. With the line off fuel pressure should be 43 and on at idle vacuum 40.

Same pressure regardless, about 38 PSI

Did you install the spring properly when you reassembled it?

You may have flubbed that and that's why you are not getting adjustment.

http://www.dsmtuners.com/forums/articles-engine-fuel/399037-replacing-diaphragm-your-afpr.html

http://www.dsmtuners.com/forums/new...le-fuel-pressure-regulator.html#post152724177

Always a possibility! Seemed pretty straight forward, but I've thought that before and been way off.

When you say disconnecting the line, do you mean disconnected and plugged, or disconnected and letting it hang down with out plugging it, I will assume plugged., The only thing that comes to my mind is, because is not adjusting the AFPR, it holds higher psi of fuel forcing the injectors to spray a little more fuel, obviously with more fuel, it will idle better.

My suggestions is, you might have a bad AFPR as stated (BOGUS),,,, The diaphragm not necessary needs to be bad for the AFPR to fail, Check under the diaphragm and look at the hole where the ball shots the fuel, some times the hole is not rounded and the ball doesn't shot completely causing a constant leak,,.
If all inside the AFPR looks OK, then you might have a bad fuel pump valve, or the O ring is not keeping up, remove the fuel pump and check if there is any abnormal somewhere,.

When the AFPR is not adjusting is,
A,-Because the AFPR it self is bad, or B,- because there is a leak on the line, or a leak back in the fuel pump.

Check all that and report back what you find.

1. Plugged or not plugged it's the same reading
2. I'll look into those tomorrow when I tear it apart again.

I had a similar problem this summer as well, Turned out that the o-ring between the fuel pump and the fuel pump housing / mount had been torn during the installation. The result was it would build about 35 lbs of pressure but that was all the rest of the fuel would just bleed out in the tank.

Dang...sounds like I might have just got a bad bunch of stuff from this forum member. Lesson learned.

 

[hofmania]

I ordered a new fuel pump install kit so that I can use all new parts.

Replaced the fuel filter today - I have a feeling it was the issue.

Installed new injectors and cleaned fuel rail.

We'll see how things go tomorrow. Fingers crossed.

 

[hofmania]

reinstalled the fuel pump
changed the fuel filter
checked all connections

Running like a champ now. Thanks everyone