low fuel pressure

[boarderlib]

Let me start off by thanking you guys in advance for your help.

I have a 92 GSX 5spd, that is completely bare bones stock. My issue is with my fuel pressure. I went to Summit Racing and got a B&M fuel pressure gauge, because I'm having serious running issues. I put the gauge on the fuel filter and started the car. The gauge is saying I'm running idle at about 19 psi. I refered to my haynes manual and it says that my car should be between 36-38 psi vacuum hose detached or 26-28 psi vacuum hose attached. Everything I've read on here says I should be about 37.5 psi. Now obviously I'm running really low, if the gauge is correct. As I gave the car some throttle, the pressure dropped down to about 16 psi. When I let off the gas the pressure went back up to about 19 psi. After about 30 minutes of the car sitting turned off the gauge has dropped to about 16 psi.

The reason I'm testing is because the car runs like its on 3 cylinders between idle and about 3000 rpm. After that it smooths out but doesn't have anywhere near the power it had. I tested my injectors and have 3 with a 3 ohm resistance, and 1 at 5 ohms.

My first question is what vacuum hose is the guide refering to? Second if anyone has any ideas as to why this is happening, please feel free to jump in and help me out.

Thanks again! You guys RULE!!!

 

[mlstraw]

I have been going through similar issues. My fuel pressure finally dropped to zero letting me know for sure it is the fuel pump that is bad.

Mike

 

[boarderlib]

There's no other options that could cause low fuel pressure?

 

[mlstraw]

Low fuel pressure can be caused by:

Clogged strainer
Clogged Filter
Low Voltage to fuel pump
Clogged fuel rail
Inoperative fuel pressure regulator
Incorrectly adjsted pressure regulator
Internal leak in fuel lines
Bad pump ( like mine)

 

[boarderlib]

Thanks for the list of possible causes.

Quick question as I was running through some tests on the fpr, I went to hookup a vacuum pump to the port on the fpr and it wouldn't hold any vacuum. I would pump it up to about 17 hg, and it would just slowly release the vacuum. I pulled the pump off the port and stuck my finger over the hose, and pumped it back up and it held vacuum. With all this considered would I be safe to assume this is at least part of my problem (fpr)? I'm thinking that the spring went bad or the seal isn't seated properly inside the fpr, causing the vacuum to leak out into the fuel rail. Since I'm no expert in the matter, I lean towards your experience with these cars.

 

[mlstraw]

The regulator should hold vacuum. However , if your pressure measured with the hose disconnected is out of spec, then you have more problems than just the regulator. You might be able to pinch off the return hose to see if the pressure comes up. If the regulator is leakng through and not holding pressure, the hose pinch test will tell you.

Mike

 

[boarderlib]

I pinched the return line off and the pressure didn't do anything. The pressure stays steady. The only way I can get it to move, with or without vacuum is pinching off the in line before the rail. Then it will spike up about 2 or 3 psi, that's it.

Let me guess we keep heading towards the pump?

I appreciate your time for helping me out with this.

 

[mlstraw]

Sounds like you have to pull the pump. I just ordered a Walboro for mine. Hope to install it this weekend.

I found this guide helpful in pulling the pump:

FAQ Locator Fuel

MIke

 

[boarderlib]

Yea I was trying to avoid that, because of the output line coming out of the sending unit is probably going to snap. I jbwelded it awhile back to get it to stop leaking. Now I gotta break that line loose. Come on PB Blaster!

Just in case any ideas where I might be able to find a sending unit?

 

[KewlWinter]

Try the classifieds or one of our supporting vendors that deal in used parts like Miller Imports or DSM Graveyard.

 

[mlstraw]

I had to take mine loose at the fitting under the car. I could not get the one accessed from the top loose at all. I even tried several tricks that normally work in the vise after I had it out with no luck. That bugger is stuck good.

Mike

 

[boarderlib]

Well I have confirmed my feelings about why I never take my cars to mechanics. Don't get me wrong, I'm sure there are some good mechanics left. I just don't know any. I took my car to a mechanic right after I got to have him put a gas tank in. I pulled my pump today and guess what I find, no strainer on my pump. Oh yea and the input of the pump had what appeared to be long strands of nylon in it. I wonder why the pressure was low. And on top of that I snapped that output line off just as suspected.

I did manage to find a sending unit without to much hassle, so that's a plus.

 

[mlstraw]

Hope you get it running again soon. I hope to install my new fuel pump in the morning.

Mike

 

[boarderlib]

That makes 2 of us. Its killing me. I hate not being able to take her out for a drive, especially since the weather has been so nice around me lately. Mid 80's for the most part.

Does anyone know what the thread is coming off of the fuel sending unit? The feed line coming out of the top, had a fitting that went into a high pressure line. The fitting going into the hpl is the threads I need to find out, so I can replace the line going to the fuel filter. It looks like 18 npt, but I'm not sure of the size. 1/4, 1/2, etc.

 

[boarderlib]

Have any of you guys gotten a bad Walbro pump? I finally got everything back together. New pump, new lines from the tank to the fuel filter. I tried jumping the pump to see if I could hear it kick on, but nothing. I have 12 volts at the sending unit, but no fuel pressure.

 

[billyt]

did you resolve your problem? I'm in the same situation. I have low fuel pressure on my 97gst. For now I have ordered the filter on the pump and another oem in line fuel filter from extreme psi. When I get them I will replace and see if that solves my problem.

 

[boarderlib]

Yes, it ended up being the pump. I replaced it, the sending unit, and the fuel line up to the filter. Now it fires right up, and runs like a champ again. Yay!