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Old 11-03-2018, 11:51 PM   #1
jemo
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Default Did you vent your fuel tank?

I took my car to the gas station for the first time this weekend, in the past I've always filled it up with the lawn mower container. I filled the tank up all the way and the fuel pump got crazy loud! Additionally, it spilled fuel all in the floor of the boot. I can't tell where it's coming from and don't remember if the filler neck maybe had a breather hole in it? After siphoning about 2 gallons from the tank, the leak stopped and the pump noise volume went down.

Mine's a '95 model and when I prepped the tank I had a 3/8" bung brazed at the bottom to feed the external fuel pump and another 3/8" bung at the top of the tank for the return line. Just wondering if this is a venting issue. Appreciate any help.
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Old 12-03-2018, 08:55 AM   #2
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Could the leak be coming from the fuel sender plate in the side of the tank if it stopped after 2 gallons were removed ?

Where is the pump ? is it an internal pump or mounted externally, and if so where is it mounted ?
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Old 12-03-2018, 08:56 AM   #3
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Could very well be a venting issue if you donít have a vent. I ran a vented cap successfully on an injection tank and blocked off the original breather as I was getting fined in the car.


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Old 12-03-2018, 07:03 PM   #4
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The pump is external mounted below the tank opening running about 12” away. I had the tank cleaned out and don’t remember seeing a vent tube. I only remember the bungs I had put in for supply and return. I drove for a short while with the cap open and it made no difference.
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Old 12-03-2018, 08:25 PM   #5
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the fuel injected tanks came with non-vented caps, because the vent was up top, around a 1/4 inch tube coming out of the top, that goes to a one way check valve, and then the hose is ran to a purge canister and that is connected somewhere onto the throttle body


i have the Honda purge system hooked up in my mini shell, because i wanted my del sol drivetrain to run the same way it did when it was in the Honda body, plus i have smog here and i dont want the state to make up some bs as to why my swap is not good
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Old 13-03-2018, 02:02 AM   #6
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I agree with InstantCustard and JoaKwin: I also think its a venting problem.

When your tank is full, the pump is very noisy, which indicates to me that the pump is cavitating. Meaning its trying to pump a vacuum which it isn’t designed to do. I think that the reason that the pump is cavitating when the tank is full is because any venting you may have had, is now below the level of the fuel, and if you have fitted the Honda purge system for tank venting its not working.

When you remove 2 gallons of fuel, the pump stops cavitating, which means the tank is now able to naturally vent again, and also with this lower fuel level it appears you have no more leaks into the boot.

Also a question does your return line run all the way to the bottom of the tank or does it terminate at the top? If you have the return line terminated at the top, it will definitely create quite a splash especially with a full tank of fuel.
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Old 13-03-2018, 02:10 AM   #7
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Thanks very much for the input. I looked at the underside of the cap and the brass looking area has a hole in it. Looking online at vented gas caps, this looks the same as mine but most of those had 2 holes, mine only has one. It has to be a vented cap.

Yes, I routed the return line to the top of the tank. That might make sense that it's splashing gas but it's not getting on the exterior of the car out of the gas inlet.

I'm having another fuel issue which might be related. The pump seems to be starving the engine. I'll give it extra throttle and the car falls on its face. Tonight I pulled it apart and verified I had an adequate pump. It's a Walbro 392 which is good for 255 lph (plenty) and a high flow filter. The filter didn't have a flow direction but just to see what happened I reversed the filter. Filled it with gas and immediately the pump was quieter. Took it out on the road and gave it a good kick and it took off with no stumble. Repeated...had same excellent results. Tried a third time and it started stumbling, pump got louder and louder.

Which external, inline pump are others using? I did read some reviews about that Walbro pump and they say it's loud and prone to fail quickly.
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Old 13-03-2018, 02:17 AM   #8
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Take the cap off ? Just easy ?
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Old 13-03-2018, 02:19 AM   #9
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yeh forgot to say on tonight's test drive I drove with the cap open. Still same loud noise. I think this pump might be a problem.

Friend of mine thinks gravity fed gas might not be supplying fast enough? I guess I'll call Walbro tomorrow and ask although I'd like to try a different brand.
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Old 13-03-2018, 09:25 AM   #10
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What filter system do you have ?

I had the same symptoms, and it turned out to be a faulty filter that was collapsing under pressure.

Try it (For a short time) with no filters in the system.

Also if possible extend the return to beside the intake, otherwise you can get aeration of the fuel, so the pump is sucking a lot of air as well as fuel.
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Old 14-03-2018, 01:52 AM   #11
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Where is your high pressure filter before or after the pump. Normally it should have something like a 100 micron before the pump (Coarse filter) and a 10 micron (fine filter) after the pump.
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Old 14-03-2018, 04:11 AM   #12
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Also have you tried a vented petrol cap vs a sealed cap ?
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Old 14-03-2018, 10:04 AM   #13
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Also have you tried a vented petrol cap vs a sealed cap ?
A bit further up he says

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I drove for a short while with the cap open and it made no difference.
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Old 14-03-2018, 08:41 PM   #14
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I commented with the above cap issue on Facebook. This as you have now tested running without the cap can hopefully be eliminated as a fault.

I am wondering if the pipe you have had braised into the tank has possibly got damaged or distorted in some way, reducing the flow. If you are sure it's right then just another thing checked.

Try getting an air line and blowing down the return. I did this on mine one time checking if it was clear and a faint pop happened like something had just been stuck in it. Again, just another thing to test.

Good luck with this but have to say, I don't believe the fuel pump itself to be the issue.
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Old 14-03-2018, 08:42 PM   #15
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I commented with the above cap issue on Facebook. This as you have now tested running without the cap can hopefully be eliminated as a fault.

I am wondering if the pipe you have had braised into the tank has possibly got damaged or distorted in some way, reducing the flow. If you are sure it's right then just another thing checked.

Try getting an air line and blowing down the return. I did this on mine one time checking if it was clear and a faint pop happened like something had just been stuck in it. Again, just another thing to test.

Good luck with this but have to say, I don't believe the fuel pump itself to be the issue.
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