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Diagnosing Fuel Pressure Loss

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Old 09-11-2017, 10:39 AM   #1
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Default Diagnosing Fuel Pressure Loss

I have a Walbro (knockoff brand) 255 fuel pump and Corvette regulator. I've only put about 35 mi on the swap since the first startup. It ran okay at lower throttle/rpms, but would choke out badly if I tried to get on the throttle. This got worse and worse until it just died and will not start now.

Plugs read lean, and I noticed the fuel pump sounded weaker than it did initially. Checked the fuel pressure last night, and it barely gets up to 10 psi and bleeds down immediately. No leaks anywhere under the car. The pump kicks on with the key, but sounds quieter and then makes a hissing sound in/near the tank as it bleeds the pressure off.

Does this sound like a bad pump, leaking feed line inside the tank, or bad FPR? How can I diagnose it? I hate throwing parts at a problem. Any help appreciated.
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Old 09-11-2017, 10:48 AM   #2
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Make sure you have the supply and return lines hooked up correctly to the FPR,mistake I made once...
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Old 09-11-2017, 11:29 AM   #3
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Pretty sure they're correct. Would it run at all if they were switched?
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Old 09-11-2017, 03:39 PM   #4
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Interested to see the responses. I get the full 60 psi when the pump is running, but I quickly bleeds down to zero once the pump shuts off. I have Tanks set-up with a Corvette FPR I sourced from an online speed shop.
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Old 09-11-2017, 03:57 PM   #5
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Me too. Are you running a Walbro or a knockoff brand pump?

My knockoff brand pump was louder and I didn't hear any hissing noises early on. I have a Tanks Inc. tank and pickup assembly, but I got the pump somewhere else.
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Old 09-11-2017, 04:54 PM   #6
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If the fuel pressure is at 10psi with the pump running, it could be either the pump or the regulator...

I don't know how you make judgement on pump sounds....

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Old 09-11-2017, 06:14 PM   #7
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Me either. Just looking for any ideas. What should the resistance be across the fuel pump motor leads?
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Old 09-11-2017, 06:33 PM   #8
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Those are the same symptoms as a empty tank .Your gas gauge could be off .
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Old 09-11-2017, 07:27 PM   #9
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Default Fuel pressure

Have you looked at the pump? Friends car was running badly, pulled the pump and it had slipped down and the short hose was actually away from the hard line. Why it ran is still a mystery to me. Heard lots of bad reports regarding off shore pumps failing quickly.
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Old 09-11-2017, 09:35 PM   #10
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Simple, fake Walbro = junk!
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Old 09-11-2017, 11:09 PM   #11
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I hate to admit this, but the fuel gauge is way off and the tank was empty. dcd215 nailed it. I'm obviously getting horrible mpg - drove it no more than 50 mi and used about 9 gal of gas. I put a few miles on it tonight with fresh gas, though, and It's still losing power at ~50%+ throttle.
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Old 09-11-2017, 11:10 PM   #12
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Pretty solid 55 psi on the FP gauge now...
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Old 09-12-2017, 07:25 AM   #13
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Quote:
Originally Posted by tracetrimble View Post
Pretty solid 55 psi on the FP gauge now...
What's the fuel pressure at 50%+ throttle and higher RPM?
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Old 09-12-2017, 11:48 AM   #14
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Quote:
Originally Posted by tracetrimble View Post
Pretty solid 55 psi on the FP gauge now...
Does it quickly drop to zero once you shut down?
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Old 09-12-2017, 07:14 PM   #15
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Here's a video of the behavior (I revved it to about 4k tops):

I also fixed my high throttle issue. The only code it was throwing was P0102 (MAF low voltage). Turns out the 3-to-5 wire MAF adapter I bought was wired wrong. No codes and running fantastic now!!
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Old 09-13-2017, 11:24 AM   #16
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That is exactly what mine does when I shut off. It doesn't seem to cause any problems as long as I let the pressure build before trying to start.
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Old 09-13-2017, 04:32 PM   #17
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a lot of aftermarket pumps don't have a check valve in them like the original oem pumps. This allows fuel pressure to bleed off back to 0. This is why once u install a aftermarket pump u usually have to prime the pump with key on and off twice. Works every time.

Aftermarket regulators are bad about bleeding off pressure as well. If it gets to annoying u can add a check valve inline after the pump. Another thing I have never had good luck with knockoff pumps. They never hold up and last much more than a few months. Install a good pump from the get go and be done with it. Just my 2cents.
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Old 09-13-2017, 10:01 PM   #18
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Good to know. I was always waiting for the pump to finish its cycle before I started the motor because it was fresh and i was geeking out on everything. I now notice I can't just hit the starter immediately - gotta let it prime first. This will be annoying in daily driving.

Thankfully, I added an access door in the trunk floor when I was building the car. A long time ago, I promised myself I'd do that every chance I got, after I had to change a fuel pump in a 92 Camaro with a full tank.
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Old 09-15-2017, 07:57 AM   #19
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I had a similar problem when i first did my swap. Ended up being the hose in the tank from the pump to the sock area came loose. Fixed with fuel injector clamps and have been good ever since. I have the corvette pressure regulator setup. I also have the no name Wallbro pump which has been awesome.
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