fuel pressure stays the same

[Tyeler18]

Yes, that's why you need to test it.

 

[ishnish]

My apologies, I thought your comment was referring to the afpr when you stated "then it's bad"

 

[Tyeler18]

My apologies, I thought your comment was referring to the afpr when you stated "then it's bad"

It was, if you have strong vacuum at the AFPR but it still wont drop pressure- the AFPR is bad. If you don't have vacuum obviously theres an issue with your t-junction or hose.

 

[ishnish]

UPDATE: I've been working a lot so haven't had too much time to give my car. Last night when I got home I had about 15 minutes so I started the car, took off the vacuum line at the Tee of the boost source. Instantly I felt vacuum from the T and so I capped it with my finger. I then just sucked some air through the vacuum line going to the afpr and also blew air into it both as hard as I could. The AFPR gauge dropped like 2-3 psi when I sucked on it and went up like 2-3 psi when I blew on it. Should I have been able to get more than this just using my mouth?

No fuel in the vacuum line either. I guess this is kinda' good news? It should mean my afpr isn't bad. I just wonder why it's not dropping as much as it should.. sadly, that's all I had time for so my next step will be to replace that line from the afpr completely. Would it be wise to just use a vac line to a dedicated source on the nipple from the intake manifold instead of the T into the boost source?

Also, upon some further research, I THINK that maybe a restriction in my fuel return could be the only other thing causing this. Any other suggestions?

Sorry for the slow progress, but I try to do what I can whenever I have a free window.

 

[1990TSIAWDTALON]

A $25 0-100 sensor and wiring it into the EGR or FPR wiring and you can log it in Link and watch it. I have one in my 92 so the remote tuner can see all that is going on!

 

[Tyeler18]

UPDATE: I've been working a lot so haven't had too much time to give my car. Last night when I got home I had about 15 minutes so I started the car, took off the vacuum line at the Tee of the boost source. Instantly I felt vacuum from the T and so I capped it with my finger. I then just sucked some air through the vacuum line going to the afpr and also blew air into it both as hard as I could. The AFPR gauge dropped like 2-3 psi when I sucked on it and went up like 2-3 psi when I blew on it. Should I have been able to get more than this just using my mouth?

No fuel in the vacuum line either. I guess this is kinda' good news? It should mean my afpr isn't bad. I just wonder why it's not dropping as much as it should.. sadly, that's all I had time for so my next step will be to replace that line from the afpr completely. Would it be wise to just use a vac line to a dedicated source on the nipple from the intake manifold instead of the T into the boost source?

Also, upon some further research, I THINK that maybe a restriction in my fuel return could be the only other thing causing this. Any other suggestions?

Sorry for the slow progress, but I try to do what I can whenever I have a free window.

Sounds like it's working. Run a dedicated NEW vacuum line and see what it does.

Also a restricted return line would prevent you from lowering pressure below your current base pressure which you mentioned being able to do.

 

[ishnish]

Thank you for replying. What you stated is what I've read, but that's the only other thing I could go off of because I've never heard of anyone having an issue of fuel pressure not going down with vacuum whilst able to still lower fuel pressure. It's been a while since I've tampered with it though, so tomorrow I will confirm whether I can lower fuel pressure or not but last I remember I was able to totally fine. Just the vac line is the issue..

 

[ist dwa]

Fuel pressure should drop roughly 1/2 what vacuum is when the line is pulled. So AFPR is set to 43 with line on, at idle vacuum reads ~14hg, when you pull the line off it should drop 5-7 psi and should read 36-38psi.

1. If this doesn't happen either your diaphragm inside the AFPR is busted...but you would know this by gas in line/afpr.

2. You don't have a good vacuum source, the line should be dedicated and short as possible.

3. In a weird world you have some screwy spring in the AFPR

 

[ishnish]

Thank you for your input! Yeah I feel like I'm in a weird world.. No gasoline in the vacuum line but I'll replace it. Maybe I can unplug the one nipple I have free on my intake manifold and run it as a dedicated port to the afpr instead of teeing the boost source. I'll actually have a day off tomorrow and see what I can do!

 

[ishnish]

Sounds like it's working. Run a dedicated NEW vacuum line and see what it does.

Also a restricted return line would prevent you from lowering pressure below your current base pressure which you mentioned being able to do.

UPDATE:
So literally JUST got done putting in a while bee vacuum line and I actually made it a dedicated vacuum line from afpr to intake manifold. This made my boost source from boost gauge to intake manifold a dedicated like too. Did not fix the issue. Fuel pressure still doesn't drop much at all from idle. I found out my base fuel pressure was higher than 43 psi though so I lowered it to 43 psi (the afpr gauges are really small and hard to read) almost exactly and when I turned on the car the fuel pressure dropped from 43psi to about 41.5-42psi. And just for the hell of it I went to the back and checked my fuel pump assembly and the return line is perfectly fine.

I then proceeded to pinch the fuel return line off of the afpr to see if this would cause my fuel pressure to spike up. Fuel pressure spiked up very quickly once I pinched the return line. This would indicate that my afpr is working correctly from what I understand. I even tightened the bolts all around the afpr just as a last ditch effort. No change..

 

[ishnish]

UPDATE:
After this whole concern of mine, I was lucky enough to get some input from Kevin who owns the rwd blue talon and he told me he's 100% sure that my fuel pressure issue was due to my walbro 450 over running the stock return line. So, I ended up buying some 3/8 " hardline, bending it myself and installing it, removing the old 1/4" return line.

Guess what? After install, I started up the car and BAM, fuel pressure at idle dropped to 37 psi or so (couldn't fully see since it was dark out). Either way, this mod worked! So anyone else who's in the same dilemma as me, there's your problem..