My "New" Airtex fuel pump...... A question

[EMD_DRIVER]

After all the fuel pressure problems I've had, I thought a new pump would solve them...

All this week, the pressure would immediately come up to 70PSI and hold there, for about 3-5 minutes. It would then drop sharply, depending on how much pressure I had on the go pedal. I figured my new fuel filter might already be clogged, but hadn't changed it yet.

I installed a post-pump filter this evening and had to mount it horizontally. That kept me from being able to fill it with fuel, before spinning it on. I decided to try just pushing the air through the system, and back to the tank. I temporarily have my fuel pump wired to a relay, so it gets power directly from the driver's side battery. I bypassed the relay and just let the pump run for a while. Using the OBS fuel pressure regulator allows me to hear the air, when it goes through the regulator.. Kinda cool sounding..

When I first hooked up the pump (With the truck off) It sounded nice and fast. The pressure built up and I eventually heard the air going through the regulator. After about 4 minutes, the pump started slowing down. The pressure also dropped to 65PSI. The longer it was running, the slower it got. It did keep maintaining the 65PSI though.

I'm wondering if there is a design flaw with the pump, or if it's supposed to do that. I know it wasn't my W85 fuel, since I filled up with D2 this morning.. The check valve part of the pump is still working, as evidenced by the bath of diesel I got, then I pulled the line from the pump outlet.

I'm kind of at a loss on this one.. If the pump were still wired to the factory harness, I might think it was a voltage issue. Since I'm wired directly to the battery, that rules voltage issues out.

Anyone have any ideas?

 

[94f450sd]

as long as it holds the pressure and the truck doesnt run out of power its fine.sitting there with the pump running and the engine off really isnt the best thing to do.as the pump heats up its gonna die down.

 

[EMD_DRIVER]

I shimmed the OBS FPR I'm using, with a BB and raised the pressure to 70PSI. I'll try removing the BB and reducing the pressure. Maybe that will keep the pump from having to work so hard..

 

[Double-S-Diesel]

the more pressure on the pump the harder working they will sound. Id say the draw down is normal.

 

[EMD_DRIVER]

the more pressure on the pump the harder working they will sound. Id say the draw down is normal.

I know what you are saying Nick, but it runs fast and good for maybe 4 minutes and then draws down and can't maintain the pressure. With the truck off, it could maintain 65PSI. Just starting it, would make the pressure drop to 58PSI.. 7PSI drop simply idling doesn't seem right to me.

I pulled the BB out of the FPR and it dropped the pressure to 50-52PSI. Even with 20PSI less work to do, the Airtex pump still wound down after only a couple minutes. I also checked the pump itself and it was still very cool. I had run the truck 4hrs earlier and the return line was still quite warm.

I went ahead and put the Bosch pump back in it and it drew down a bit, but nothing like the Airtex did. With the truck in gear, my foot on the brake and working it, it dropped to 40PSI. I haven't test driven it yet..

 

[94f450sd]

is it running out of power?if not i wouldnt be worried about it

With the truck off, it could maintain 65PSI. Just starting it, would make the pressure drop to 58PSI.. 7PSI drop simply idling doesn't seem right to me.

with it off the injectors are closed.with it running the injectors open and it uses fuel. each time an injector fires its gonna cause a drop in pressure.a 7 psi drop is nothing to be concerned with.mine runs about 90PSI with it off and around 85PSI idleing.im running the SD electric pump.

 

[EMD_DRIVER]

is it running out of power?if not i wouldnt be worried about it

The couple of times that the pressure dropped to around 10, she stumbled a lot. Lately, I've been watching the gauge like a hawk.. I need to tow our fifth wheel with this truck tomorrow and hope the trip is un-eventful!

with it off the injectors are closed.with it running the injectors open and it uses fuel. each time an injector fires its gonna cause a drop in pressure.a 7 psi drop is nothing to be concerned with.mine runs about 90PSI with it off and around 85PSI idleing.im running the SD electric pump.

I'd love to be able to maintain those pressures! The airtex pump would hold to within 2PSI of 70, for the first couple of minutes it was running. After that, the pressure dropped right along with the go pedal..

 

[94f450sd]

the more you step on the throttle the more the pressure is gonna drop.youre using fuel.themore fuel you use the more the pressure is gonna drop.

what truck are we dealing with here?i see you have a regulated return on the 99.is that the one we are dealing with?if so why are you using an obs regulator on it?you should be using an aftermarket regulator on it.there is a reason why the aftermarket fuel systems for the 94-97 use an aftermarket regulator.are you also using the obs filter housing?if not what did you do about blocking the hole where the regulator screen is?id be willing to bet that if you were to install an aftermarket regulator all your issues will go away.

 

[EMD_DRIVER]

the more you step on the throttle the more the pressure is gonna drop.youre using fuel.themore fuel you use the more the pressure is gonna drop.

what truck are we dealing with here?i see you have a regulated return on the 99.is that the one we are dealing with?if so why are you using an obs regulator on it?you should be using an aftermarket regulator on it.there is a reason why the aftermarket fuel systems for the 94-97 use an aftermarket regulator.are you also using the obs filter housing?if not what did you do about blocking the hole where the regulator screen is?id be willing to bet that if you were to install an aftermarket regulator all your issues will go away.

I completely understand that the pressure is directly related to how much fuel the truck is using. I just don't understand how a 7.3 can use more fuel, than the stock fuel pump can provide. I am dealing with the 99 and I have had pressure problems for quite a while.

The whole reason for the regulated return, was because I wanted to delete the factory check valves. I pulled them out and cleaned them, but there was still a lot of restriction in them. When I originally put the regulated return on the truck, I used an aftermarket regulator. With that regulator, the only time I could maintain a constant pressure was when the truck wasn't running. As soon as I started it up, the pressure would fluctuate wildly. I replaced that regulator with another one, but the results were the same. That's when a friend of mine suggested the regulator from an OBS truck. The one I used, was from a 97. I used the factory port, for the return to connect to and have the line to the tank where the 97's return line was. All the other ports on the regulator were plugged. I did not use the 97's fuel bowl.

Since I now have a post-pump filter under the truck, I would like to delete the 99's factory fuel bowl. I am also planning on installing a fuel sump on the fuel tank and run 3/8" fuel line from the tank and go all the way to the engine with it.

 

[94f450sd]

what kind of aftermarket regulator were you using?imthinking your problem is in the regulator area not the pump.i dont think the 97 regulator will work properly the way you have it.

 

[EMD_DRIVER]

what kind of aftermarket regulator were you using?imthinking your problem is in the regulator area not the pump.i dont think the 97 regulator will work properly the way you have it.

I don't remember the brand, but I couldn't afford the the more expensive one yet.

I have a friend in Texas, that owns a diesel shop. He's the one that told me about the OBS regulator idea. He runs one on his truck, with zero problems.

BTW: Thanks for your help and "Brain time" Rich!

 

[94f450sd]

still think its a regulator problem.the obs reg. wasnt designed to be intalled the way you have it.this is the first time i have ever heard of it being used like this.im still willing to bet that if you use a good aftermarket reg. your problems will go away

 

[94f450sd]

BTW: Thanks for your help and "Brain time" Rich!

 

[EMD_DRIVER]

still think its a regulator problem.the obs reg. wasnt designed to be intalled the way you have it.this is the first time i have ever heard of it being used like this.im still willing to bet that if you use a good aftermarket reg. your problems will go away

I believe we're gonna be swamped at work next week... Hopefully, I'll get enough OT to afford one of those expensive regulators..

I still want to install the fuel sump and get the larger diameter line to the engine..

One thing that gets me, is that the truck is getting great mileage now!

 

[94f450sd]

honestly as long as its running fine and not loosing power i wouldnt worry about it.

but this is the regulator that came with my fuel system from BDP.only issue ive had with it is the liquid leaked out of the gauge somehow

http://cgi.ebay.com/ebaymotors/FUEL...r_Truck_Parts_Accessories&hash=item2a134f72dc