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Walbro 255lph acting up, (noisy, fixed!)


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I've had my Walbro fuel pump (same one as everyone else uses) for a good 20k miles with no problems whatsoever, nice quiet operation. My car has been in the body shop for the past month with the gas tank out, and when I picked it back up today, the pump is much, much louder, and I'm getting some pretty bad fuel starvation (will sometimes rev okay to 4000rpm, sometimes it practically dies in the intersection). Replaced my fuel filter, redid my fuel lines (I had SS braided lines to put in anyways), no change. Fuel coming from the tank is perfectly clear, tank itself is clean. It's wired on its own relay with good connections (the pump wasn't touched at the body shop AFAIK). When I redid the feed lines it definitely primed well, and sounded completely normal, but after about 45 seconds it went right back to screaming. I'm guessing it's about to die completely, but does anyone know of something I can check/do before I just buy a new one?

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I have the same pump and it has about 15K miles on it. It is definitely louder than when it was new. It makes a hammer/rattle sound, almost like a cavitation, but I am getting good flow confirmed by my AFR's. I thought it could be the fuel damper gone bad but I have no way to confirm either. It is actually becoming annoying. I was thinking of shopping for a replacement. Let me know what you find. I can't think of any easy tests other than flow testing on a bench at various head pressures.

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I've had my Walbro fuel pump (same one as everyone else uses) for a good 20k miles with no problems whatsoever, nice quiet operation. My car has been in the body shop for the past month with the gas tank out, and when I picked it back up today, the pump is much, much louder, and I'm getting some pretty bad fuel starvation (will sometimes rev okay to 4000rpm, sometimes it practically dies in the intersection). Replaced my fuel filter, redid my fuel lines (I had SS braided lines to put in anyways), no change. Fuel coming from the tank is perfectly clear, tank itself is clean. It's wired on its own relay with good connections (the pump wasn't touched at the body shop AFAIK). When I redid the feed lines it definitely primed well, and sounded completely normal, but after about 45 seconds it went right back to screaming. I'm guessing it's about to die completely, but does anyone know of something I can check/do before I just buy a new one?

 

 

Hey-

Check the last chance filter at the pump itself. Should be where the inlet line connects to the filter itself, looks like a fine mesh screen. If it gets clogged with debris, it will start to starve and cavitate.

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Good call on the pump screen, I'd forgotten about that. I checked today, it seemed clear, though it was hard to see much through the inlet threads. I sprayed it out with carb cleaner, then with a bit of WD-40. Same thing happened when I hooked everything back up, it primed, ran fine for 30-40 seconds, then got loud again. I filled up the tank (it was at about 5 gallons) to see if not having to suck uphill would help, but it made absolutely no difference. I checked the voltage at the pump with a DMM, it's got a solid 12.9v at idle.

 

Cygnus - FWIW, I've never run a fuel damper.

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Alright, it's not the pump. I put in a brand new one today, everything was fine for about 15 minutes, then it started getting louder and louder and then I ran into the same problems as with the other pump (super loud, not enough fuel flow to barely go 45mph). It's definitely not a blockage before the pump, it's done this with two totally separate pick-up systems, and the fuel flowing from the tank is perfectly clear. It's not a wiring issue, I've got 13v there at all times. It can sometimes get so bad that I can't even accelerate past idle in 1st gear; when that happens, if I shut it down for 2-3 minutes, I can resume driving and have enough fuel flow for 45-50mph.

 

When it does almost die at idle or near idle, the pump sounds like its working super-hard, but the pressure at the fuel rail drops to near nothing. The only thing I can think of is a blockage between the pump and the rail, but what? And why would it reset after a 3 minute shut down?

 

 

EDIT: I removed the rail feed line and pointed it into an open bucket. When I turn the pump on, a huge steady stream of fuel comes flowing out like a garden hose, and the pump is super quiet. This means there is a clear, normal path for the fuel to travel from the tank, to the pump, to the rail, no obstructions. Also, I checked the rail by disconnecting the regulator and blowing through it, it was perfectly clear. I'm 100% completely out of ideas.

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I've run some more tests, still haven't figured it out. I can bring the car in when the pump is screaming, disconnect the return line from the regulator and route it into a 5 gallon race jug, run the car, and the pump is super quiet, and flows 60gal/hr (timed with marks on jug and stop watch). This lead me to believe there was a blockage farther back in the return line, but I couldn't find anything, and if I disconnect the AN return line from the tank and run it into the jug, I get the same thing, quiet pump and 60gal/hr fuel flow.

 

I tried a spare stock FPR that I had and it made no difference at all.

 

I can run the pump manually without the engine on, and it will pump well and stay quiet for a half hour (longest I've tried it), but it gets loud after 3 minutes of driving. If I just start it up and let it idle, it will idle all day without the pump getting loud. But if it gets loud while I'm driving, it stays loud at idle, or even when the engine is off (if I manually turn on the pump).

 

I've used two totally separate feed routs from the the tank to the pump, as well as two totally separate return routes from the hard line to the tank.

 

Absolutely any suggestions are appreciated, I'm supposed to drive this car to San Diego tomorrow morning, but won't be able to without solving this.

 

Edit: I just ran another test. Let the car idle for about 15 minutes, pump was quiet, all was fine. Jumped in and drove around the block (no more than 1/4 mile) and by the time I got back the pump was screaming again. The only thing that changed was that I drove around the block.

 

Edit #2: I ran this same test again, same results. When I parked it and the pump was screaming at idle, I felt it to see if it was hot. It wasn't even warm to the touch, it was ambient temperature all over.

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Nothing in the engine bay has moved, and the lines out back actually got moved farther away from the exhaust than they were.

 

I ran yet another test. I put a pressure gauge right at the outlet of the pump to compare with the pressure gauge on the fuel rail. They both read the same under all conditions, when the pump is dead quiet and when the pump is howling. This means there's no blockage in the fuel system or anything like that that's causing the pump to have to work hard to push fuel.

 

I retested voltage when it was loud - 13v.

I filled the tank up again to be sure it wasn't having to suck too hard up-hill - no help.

I felt the pump again while it was loud - not hot.

 

The only thing that changed from when I dropped the car off at the body shop to when I picked it up was that I had taken the tank home and welded in a sump, that's all (the process can be seen in my build thread). When I drove it home from the body shop it was doing this, and it was still hooked up the exact same way it had been before, with the stock 240z pick-up and the lowest vent line for a return.

 

Absolutely any more suggestions are welcome, I'm totally stumped.

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Tried running errands with the gas cap off, it didn't help. Also, I parked the car (still running, pump still loud), unbolted the pump, and lowered it to the same level as the bottom of the tank. No help either. I shook the pump as hard as I could and tapped the feed line, but the sound remained constant.

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Sean, Have you tried blowing compressed air back through the line at the tank, that feeds the pump?.

 

This seems like a tank issue.

 

I had a fuel starvation problem above 3500 a few years ago after I installed a new fuel level sender and replaced the fuel fill hose. I was draining the tank to recheck everything and fuel started coming out slower and slower. I blew through the drain hole and fuel started pouring out of the drain hole like it was supposed to. I blew air through the lines coming out of the tank and the problem went away.

 

After all that I cleaned out my tank again after doing it a few months earlier. No problems with this issue since then and did my turbo swap after fixing this.

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Yeah, I checked to make sure they were clear. Both separate feed systems were fine.

 

I don't know if this is taking its toll on the new pump or what, but now it's not passing the flow test even after it's had time to sit. I checked it after running some new pressure lines, only 30gal/hr (should flow 60). I let it all sit for a few minutes and checked again, only 45gal/hr.

 

Edit: I just remembered I have a known-good stock 280zx pump that should still flow enough for my motor (I know Prox was running a stock 280z pump at something like 17psi with his 440cc injectors). I'm going to swap that in and see if it makes a difference.

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I have had good results with the msd 2225 pump.

 

I'm thinking the walbro pumps need bigger fuel lines to run right.

 

I had one of those a while back, it crapped out on me within a few months.

 

The guy at my local hot rod shop said the same thing, a lot of them have problems with cavitation, and that they need like a -8 or -10 feed line, even though the threads on the inlet are only 10mm. Weird that my first one would go for over a year on a 5/16" feed though, then decide to act up.

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Bo, how long is your feed line? Mine is ~4'.

 

 

Turns out the 280zx pump hasn't totally fixed the problem either. 3/4 of the way from Tucson to San Diego it started acting up in a similar manner. Shut the car down for two minutes and restarted, made it the rest of the way. Here in SD it's been working fine.

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Sean, my Walbro is literally right next to my tank. I am using the stock 240z tank but I had the pickup and returns lines resized to 3/8-in. SS lines with AN fittings. The pickups were extended to the bottom of the 240z tank near the "sump".

 

The SS braided hose from the pickup tube to the pump is maybe 8 to 10 inches long.

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I think I have it fixed for good. I now have a Carter P4070 fuel pump back by the tank acting as a lift pump, pushing fuel up to the Walbro 255lph in the engine bay. So far, so good, I've got about 90 minutes on this set-up with no issues.

 

I guess considering the problem I had with the stock zx pump though, I won't know for sure 'til the MSA show when it'll be running for hours straight.

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