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1G Walbro 255 Pump starts quiet, gets loud, then pressure fluctuates.

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mcfeat96talon

15+ Year Contributor
44
42
Jul 26, 2005
Butler, Pennsylvania
90 laser Rs turbo fwd.
Only mods are exhaust and 255 Walbro with fpr. AEM wideband and boost.
When the car starts up the pump is quiet and fuel pressure is steady at ~38psi. About 3-4 min after, pump gets loud and pressure drops to mid 20s and fluctuates from 22-30.
This causes the car to run extremely lean while driving. Basically forget accelerating, it drops to 3 dash’s on the wb.

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Additionally, when the car is cold it runs pretty well besides high rpm under load. That didn’t last long though. As soon as the pump gets loud it leans out badly.

Ive changed the fuel pump, pickup screen, fire wall filter. I thought the return was clogged, it wasn’t. 12.95v at the pump while it is whining and pressure is fluctuating.
 
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I wonder if the pump is leaking in the tank where it fits into the fuel pickup tube? That's where problems like this usually seem to happen. Does this happen even if the engine is off? (by using the check connector)

What FPR are you using? Did this always happen or did it change lately?

The Fuel pressure should vary based on the pressure or vacuum in the intake manifold but 22 psi for a 2G is too low even at full vacuum.
 
Steve, This is on my 90 laser,
Once the tank gets closer to empty, I am going to pull the pump out once again to check all hose and electrical connections.

The regulator is a Tanks INC from summit. It works great on the car I swapped it from with out an issue.

A little update...
I re-wired the pump, it still starts out quiet then becomes very loud. The pressure is slightly better but if the pump is loud, it continues to cause a lean scenario when under load. However it drives much better than before. If the pump is loud, once boost reaches roughly 6-8 psi A/F ratio gets up in the ~16 and higher.

Normal driving A/F stays right around 15 or so.

I don't currently know what is changing when the pump gets loud, but that is completely dependent on whether or not the car runs lean.
 
Maybe you have a bunch of sediment that slowly gets stuck in the fuel filter as the car runs? Just guessing here. Or maybe the pump is just worn out? It could also be a knockoff Walbro. Those are common.
 
Usually pumps get loud when there is insufficient fuel levels. It's possible that the sending unit got bent during removal and this changed the angle/position of the pump inside the tank? Then, when you are under load, i.e. acceleration, the fuel sloshes and gravitates away from the pump, causing the whine to become louder and the lean condition. Possible way to check is to fill the tank, then do a pull. See if it still goes lean.
 
Maybe you have a bunch of sediment that slowly gets stuck in the fuel filter as the car runs? Just guessing here. Or maybe the pump is just worn out? It could also be a knockoff Walbro. Those are common.
I thought the sediment as well may be a possibility. As for a fake Walbro, I cant be sure. I did put 2 different "Walbros" into it and found the same result.
 
Usually pumps get loud when there is insufficient fuel levels. It's possible that the sending unit got bent during removal and this changed the angle/position of the pump inside the tank? Then, when you are under load, i.e. acceleration, the fuel sloshes and gravitates away from the pump, causing the whine to become louder and the lean condition. Possible way to check is to fill the tank, then do a pull. See if it still goes lean.
I have noticed the tank is slightly dented, not much though. Just yesterday I filled the tank and it still leans out under moderate load. I am going to pull the pump/sending unit back out to inspect once the tank level is closer to empty.
 
From a safety perspective the best time to mess with the tank is when it's full.
I agree. The fwd 1g uses the bolt in the bottom of the tank to hold the sending unit in position. So gasoline just rushes out. Getting the bolt lined up and threaded back in while gas is pouring out is even more fun.
 
Forgot about that. I got a 1G FWD hanger once by mistake when I had ordered an AWD one and was surprised by how different it was.
Yeah, its not a great design. The 1g AWD cars and the 2gs are a much better design in regards to the fuel tank although the FWD tanks are very easy to remove. Any way, I have been driving it for 2 days now, it drives very well until under moderate load. In addition, I have an SAFC2 that I will install once the leaning out issue is resolved. I am wondering if the new in tank screen filter may be causing the issue. I have a near identical setup and car that works great but used a different in tank screen on it...
 
I just wanted to post an update on the solution to the problem I was having with my 1ga.

Turns out the tank had a bunch of rust/scale and other stuff that causes the pump screen filter to clog after the car is in motion. When the gasoline was sloshing around kicking up the rust/scale it would then cause a very bad lean situation. I had an old tank that is rusty on the outside but minty fresh on the inside. Installed it into the car, new screen filter, and it runs great again.

Thank you for the help everyone!
 
I am guessing the pump got loud when it wasn't moving fuel. Much the same way a vacuum cleaner gets louder when it's hose is plugged.
 
I am guessing the pump got loud when it wasn't moving fuel. Much the same way a vacuum cleaner gets louder when it's hose is plugged.
I believe you are correct. It was strange to me at first that, with the car not moving just idling the pump would never get loud. When it was driven on a windy road, in the more aggressive corners you could hear the pump change tone as I assume the strainer would get a little cleaner.

Anyway, thank you everyone for the help!
 
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