Inline fuel filter before pump

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sirrus
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Inline fuel filter before pump

Post by sirrus »

Is it a good idea to add inline filter before mechanical fuel pump? I’m replacing fuel hoses going from hard lines to pump (replaced pump couple days ago) and was thinking about adding one to keep potential crud away from the pump. I already added a transparent filter between the pump and stock filter to be able to see if I’m getting gas.

Did some online searching about filter before pump and some people say it’s fine, some say it’s a sure way to get a vapor lock. Is anyone running a filter between tank and pump?


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Kowpie
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Re: Inline fuel filter before pump

Post by Kowpie »

As long as the system is good and tight it should work fine. It tends to be easier to get air into a closed system under vacuum as opposed to pressure IMO.
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Re: Inline fuel filter before pump

Post by Stuka »

Putting a filter before a mechanical pump can really reduce your fuel pressure and flow (Which can increase the chances of vapor lock). The pump is a good pusher, a very poor puller. In some cases it can prevent the pump from being able to pull fuel from the tank.

A mechanical pump won't care much about crud and such from the tank. Which is the reason from the factory the filter is behind the pump, not in front of.
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Re: Inline fuel filter before pump

Post by sirrus »

Thanks guys, I think I won't be putting a filter before the pump then. Checking condition of a mesh sock on a fuel sender (and replacing if needed) is probably makes more sense for keeping the crud away from pump
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Re: Inline fuel filter before pump

Post by will e »

Yeah, good call. If fuel filters before a mechanical pump had an advantage the automakers would have added them. Before an electric pump is a good idea but they operate differently and 'stuff' from the tank can more easily impact them.
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Re: Inline fuel filter before pump

Post by candymancan »

Didnt older wagoneers have two fuel filters.. I remember watching a video on youtube of these guys finding a green wagoneer in a barn like from 73 or something. Dirt everyday was the channle. And they replaced two filters
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Inline fuel filter before pump

Post by sirrus »

You can say there are two filters - one between pump and carb under the hood and the other being a mesh sock on a pickup tube of a fuel sender (inside the tank).

I think older wags didn’t have a return nipple on the filter, but I’m not aware of other filters on them


Update: checked that episode about wagoneer - it had a filter before pump, but it wasn’t there from the factory. I guess it makes sense to put it there, temporarily at least, to catch most of the crud that will come out of the tank and fuel lines after sitting for so long
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Re: Inline fuel filter before pump

Post by 78basewag »

I use a inline filter between the tank and mechanical fuel pump and have had no problems.
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Re: Inline fuel filter before pump

Post by sirrus »

Another question, somewhat related - would it make sense to add a check valve like this one to a fuel line somewhere around the pump? Not sure what's better, before or after (before is easier at least). The problem I'm trying to solve is long cranking after jeep was parked for a couple days (or even a day in warmer temps). I know that's partially due to gas evaporating from carb bowl, but it can not evaporate from fuel line - so it looks like it's draining back to the tank and I think that check valve placed right before pump should help. Any opinions on that?
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Re: Inline fuel filter before pump

Post by tgreese »

How long is long? Suggest you measure it. With the bowl completely dry, it will take a lot of cranking to fill the bowl to at least the accelerator pump inlet. It's the accelerator pump that's giving you a shot of gas for starting. Also rap on the float bowl with a plastic hammer or whatever before you try to start. When the bowl is dry, the float can tend to stick closed. Then you'll crank until you run the battery flat.

Easy test - let the bowl dry out. Disconnect the fuel hose at the fuel filter and direct it into a jar. Crank the engine. The amount of time needed to spurt into the jar is proportional to how far back the fuel has drained.
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Re: Inline fuel filter before pump

Post by sirrus »

Well, yesterday after sitting parked for 1 day it took about 10 minutes of cranking (20-30 seconds of cranking and then a minute to let the battery rest and starter to cool a bit).

I think I’ll try a check valve (few bucks from amazon, not a big investment ), just not sure what is going to be the better position before or after the pump (mechanical)?


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Re: Inline fuel filter before pump

Post by tgreese »

Also - sounds like you have the factory air cleaner. Be sure that the emissions door on the air cleaner closes when the engine is off. It's supposed to seal the air cleaner and trap any vapors for recovery. The float bowl will evaporate much faster with an open air cleaner. Also, if your power valve has a hole in it, or the power valve gasket leaks, the bowl will drain away when you aren't pumping gas into it.
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Re: Inline fuel filter before pump

Post by tgreese »

There are already check valves in the fuel pump. The fuel pump won't pump without working check valves.

The TSM specs a fuel pump pressure that you can measure. I would also do a volume check - you should be able to fill a jelly jar in a mimute or two of cranking. Way more fuel than you need. If the pump is failing, that could lead to this condition.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
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Re: Inline fuel filter before pump

Post by sirrus »

tgreese wrote: Fri Jul 10, 2020 9:03 am There are already check valves in the fuel pump. The fuel pump won't pump without working check valves.
I thought about check valve in the pump - shouldn't it prevent fuel from draining back when parked?
tgreese wrote: Fri Jul 10, 2020 9:02 am Also - sounds like you have the factory air cleaner. Be sure that the emissions door on the air cleaner closes when the engine is off. It's supposed to seal the air cleaner and trap any vapors for recovery. The float bowl will evaporate much faster with an open air cleaner. Also, if your power valve has a hole in it, or the power valve gasket leaks, the bowl will drain away when you aren't pumping gas into it.
Both doors on air cleaner work as they should. The one that seals the air cleaner takes a bit longer (about 3-4 minutes) to close because I used vacuum delay valve with longer delay than stock one. I'll check the power valve, but it should be good (carb was rebuilt 8 month ago). Didn't have any backfires since then and Jeep drives good
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Re: Inline fuel filter before pump

Post by tgreese »

I have my vehicles on a schedule - every week or 10 days, each one starts and runs to full operating temp, whether I drive it or not. All the old Jeeps have 21xx carbs. I don't even mess with fuel and cranking - take the air cleaner lid off, push the choke flap open with a big screwdriver, give it a shot of starting fluid. Tap on the bowl a couple of times, and vroom. Keep the battery on a minder/tender.
Last edited by tgreese on Fri Jul 10, 2020 9:21 am, edited 3 times in total.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Re: Inline fuel filter before pump

Post by tgreese »

sirrus wrote: Fri Jul 10, 2020 9:10 am ... I thought about check valve in the pump - shouldn't it prevent fuel from draining back when parked?
In my experience, it does. There would also have to be air admitted to the line past the bowl needle for the fuel to drain back, regardless of the check valves. Many a time I've had a dry bowl, pulled a filter hose off and there is gasoline right there. I would guess there is little if any drain back, typically. Kinda think the needle seal is more of a barrier to drain-back than the fuel pump.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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