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Old July 22nd, 2015, 10:59 AM
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Replacing In-Tank Fuel Pump with External

Old July 13th, 2010, 6:24 PM
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Default Converting an intank fuel pump to an inline pump

I'm curious if you ever found that article that your referred to for making the conversion from an in tank to an inline.

I've been calling pump mfg'rs and talking to folks.
MSD claims that if the intank pump is still working that you can put their unit inline after your fuel filter and it will "assist" in bumping the pressure up and making your vehicle functional again.

That just seems like eventually the airtec pump in the tank will eventually die and cause the MSD pump to follow suit.

I talked with another company that said the extra drag pulling fuel through the pump, sock, and extra line would wipe out the new pump quickly.

However he did suggest dropping the tank, drilling a hole and installing a bulkhead connector through the tank (AN10) which will accomodate a 1/2" line.
So using a 1/2" line from the bulkhead to the bottom of the tank for your fuel pickup (without a pickup sock). Again use 1/2 line from bulkhead (outside the tank)to a prefilter mounted on your frame rail, continue with a 1/2 line from prefilter to the inline pump. Then go from the pump output to your existing fuel line which is a 5/16 or std. GM line that runs to the intake manifold.
Also recommends using a relay to supply the power to the pump. Use your existing power that goes to the intank fuel pump to activate the relay coil (low current load), but pull a wire from your fuse box to the relay contactors (higher current load to run the pump) to activate the inline pump. This will ensure you have the proper voltage/current available to run this pump and it will still only activate the pump when your key switch is turned on...like the factory setup.

another guy highly recommended if I do this to make sure the new fuel pump power was connected in line with the engine oil pressure switch to shut off power to the pump in case of an accident or rollover on the vehicle to keep fuel from spraying out and being a fire hazard.

however if you use the relay and activate the relay with the existing wiring harness going back to the intank pump, this protection/safety circuit is already in place.

You need to leave the intank pump in place (I'd have to remove it to drain/clean the tank, and for installing the bulkhead connector), but leaving the intank pump in place will still allow you to have a fuel gauge functioning AND more importantly it will still be NEEDED to provide your RETURN FUEL LINE to flow back into the tank, plus its plugging a big hole in the top of your tank to boot

Last edited by Steve L.; July 13th, 2010 at 6:45 PM. Reason: didnt include a response to the last post
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Old July 24th, 2010, 5:31 AM
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Originally Posted by Steve L. View Post
I'm curious if you ever found that article that your referred to for making the conversion from an in tank to an inline.

I've been calling pump mfg'rs and talking to folks.
MSD claims that if the intank pump is still working that you can put their unit inline after your fuel filter and it will "assist" in bumping the pressure up and making your vehicle functional again.

That just seems like eventually the airtec pump in the tank will eventually die and cause the MSD pump to follow suit.

I talked with another company that said the extra drag pulling fuel through the pump, sock, and extra line would wipe out the new pump quickly.

However he did suggest dropping the fuel tank, drilling a hole and installing a bulkhead connector through the tank (AN10) which will accomodate a 1/2" line.
So using a 1/2" line from the bulkhead to the bottom of the tank for your fuel pickup (without a pickup sock). Again use 1/2 line from bulkhead (outside the tank)to a prefilter mounted on your frame rail, continue with a 1/2 line from prefilter to the inline pump. Then go from the pump output to your existing fuel line which is a 5/16 or std. GM line that runs to the intake manifold.
Also recommends using a relay to supply the power to the pump. Use your existing power that goes to the intank fuel pump to activate the relay coil (low current load), but pull a wire from your fuse box to the relay contactors (higher current load to run the pump) to activate the inline pump. This will ensure you have the proper voltage/current available to run this pump and it will still only activate the pump when your key switch is turned on...like the factory setup.

another guy highly recommended if I do this to make sure the new fuel pump power was connected in line with the engine oil pressure switch to shut off power to the pump in case of an accident or rollover on the vehicle to keep fuel from spraying out and being a fire hazard.

however if you use the relay and activate the relay with the existing wiring harness going back to the intank pump, this protection/safety circuit is already in place.

You need to leave the intank pump in place (I'd have to remove it to drain/clean the tank, and for installing the bulkhead connector), but leaving the intank pump in place will still allow you to have a fuel gauge functioning AND more importantly it will still be NEEDED to provide your RETURN FUEL LINE to flow back into the tank, plus its plugging a big hole in the top of your tank to boot
When you install an in-line pump do you leave the stock pump in the tank and connected? Does the in-line draw throught the stock pump?

Last edited by kurtdaniel; July 26th, 2010 at 7:02 AM.
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Old July 25th, 2010, 11:33 AM
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Default Inline fuel pump VS in tank pump...how to do it?!

Originally Posted by kurtdaniel View Post
When you install an in-line pump do you leave the stock pump in the tank and connected? Does the in-line draw throught the stock pump?
MSD says you can draw through the intank pump as AN ASSIST to bump your fuel rail pressure to required pressure. AS LONG AS your existing intank pump is still functioning, but is simply providing too low fuel pressure for your vehicle to work.

Reread my original post, as most folks recommend NOT trying to pull fuel through the existing intank pump, for fear that the excess drag in doing so will cause premature inline pump failure.

I have not done this yet to my vehicle, I need to do something this week but still havent decided the exact route to take.

I will post my results and procedure as this project is completed and also post long term analysis on how this works or not.

PM me if you care to, we can chat on the tele if need be and bang our heads together to make more sense of this.

later,
Steve
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Old July 1st, 2017, 12:10 PM
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Originally Posted by Steve L. View Post
MSD says you can draw through the intank pump as AN ASSIST to bump your fuel rail pressure to required pressure. AS LONG AS your existing intank pump is still functioning, but is simply providing too low fuel pressure for your vehicle to work.

Reread my original post, as most folks recommend NOT trying to pull fuel through the existing intank pump, for fear that the excess drag in doing so will cause premature inline pump failure.

I have not done this yet to my vehicle, I need to do something this week but still havent decided the exact route to take.

I will post my results and procedure as this project is completed and also post long term analysis on how this works or not.

PM me if you care to, we can chat on the tele if need be and bang our heads together to make more sense of this.

later,
Steve

I was told it wouldn't be a problem, so I went ahead and installed an in line fuel pump.. 45-65 psi/30gph vane pump, and used the Grey lead to the existing pump in tank so the mfg protection systems would still work correctly.
I simply did not want to pull the tank out, (Was 3/4 full), and I didn't wish to cut a hole in the box bed.
My issue was it would crank over till the battery went dead and wouldn't fire. Tested for spark, had a good nice white/blue spark, so obviously no fuel. Pulled the air horn off the throttle body and pulled up the fuel line, cranked the eng over...nothing but a drip. To further confirm the faulty pump I tested pin 30 from the relay to ground for continuity, came up infinite (Open). Then even went ahead and put direct battery power to pin 30 with the fuel line out, nothing but a drip, so no question it was a failed fuel pump.
After going through the work of installing the in line pump, I managed to start the engine, it would idle perfectly, but when I moved the throttle it seemed to choke and nearly die. I could slowly increase rpm, but only until about 3000 rpm and it would die out and recover back to idle.
Even leaving it idle, it would only run for about 20 min then it would just die and be very hard to start again after.
I am now going to have to get access to the in tank fuel pump to remove it as it is clearly causing a restriction of flow. I'll be putting in a new pump in the tank after all and I recomend to anyone else... DO NOT install an In line pump as a replacement for a failed in tank pump>> it will not work!
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