fuel pressure/trouble shooting?

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i am doing some trouble shooting and i have some questions. On the dyno the truck would show around 31psi of fuel pressure at idle. when they would start the pull the pressure would go up to 40psi and then start to bleed off back to around 30psi. So today i am going over my fuel system. I just hooked up a fuel pressure gauge to the stock fuel rails and it shows 28psi when i turn the key to the on position/no start. when the truck is at idle it shows 32psi. What psi should the truck be showing in these conditions? i was running jdm's fuel rail kit on the dyno and it was showing around the same numbers so i assume this means my pressure problem is not releated to the FPR or rails. also how hard should the hi/low fuel pump relay be to remove? i can not pull it out with my hands. i have a new relay and resistor but do you think it is my fuel pump(s)? how can you test the pumps to see if they are working? any help would be great.

thanks brian

 

I recently did a fuel pressure test on my 2000L. With key on, engine off it spiked to about 38 psi. At idle it`s 36 psi. Of course when you rap the throttle it spikes higher. With the engine now off, it would maintain the 36 psi for hours and then bleed down. I used a Mac-Tools pressure guage.

 

If the relay has never been out, it can be a bit tough, at least thought mine was.
I''ve never checked my pressure so can't say on the other question

 

just got the relay off and ran a jumper wire to trip the pumps to run at high only. when i turn the key to on it only goes to 32psi. looks like i will pulling the pumps again.

 

installed the new relay and zip tied the fuel pressure guage to the windshield wiper and took the truck around the block. no boost driving the gauge would show between 35-40psi. As soon as i got into the boost the needle would go up to 40psi and stop and bleed back down to 35psi.

 

Maybe a hose connection is bad in the tank? or the regulator is not working?
If your pressure increases when you connect the jumper wire to give full voltage to the pumps, it sounds like the pumps are working. You could fabricate a hose that connects the fuel line from the tank to a fuel pressure gauge and cap off the fuel rail connections and the return line and check the pressure at key on. The pressure should build up quickly and if you turn the key to off, the pressure should stay at the high point for some time before bleeding down. I have not done this on my L so I am not sure what pressure you could expect. I think I would want to have someone turn the key on while I watched for any leaks and to monitor the gauge.

Naturally you would only turn the key to "on" for a very brief period as the pressure is not regulated.

I like to have a fire extinguisher handy and do fuel system work outside of my garage.

If the pressure builds up to higher than 50-60 psi and is maintained I would doubt you have a hose connection problem in the tank; however you may still have a pump problem or a restriction in the fuel line as described in Sal's thread many months ago.

An alternative would be to cap off the fuel rail return line at the rail and at the tank return line and see what the pressure was at key "on" and if the pressure could be maintained after you turn the key to "off".

I would be interested to know what you find, whatever you try.

 

would you know the link or title of sals thread? thanks for the info.

 

https://www.f150online.com/forums/sh...=Sal+fuel+line
I don't think this is your problem but it was an interesting thread.

 

wow that sucked lol.

 

Definitely sounds like you have a leak in the tank and it's bleeding off fuel. Pull the pumps and check the hoses, clamps, and Y connector. If you need to change the hoses, make sure you get the special Gates submersible fuel injection hose, not regular fuel injection hose.

 

i had this same problem beginning of the year.. only my truck would not start and had no preasure.. my low preasure hose popped of the pump.. once re-installed the truck ran like new.. maybe your hose popped off your high preasure side..

 

pulling the pumps tonight so lets keep our fingers crossed for a popped hose.

 

just got done pulling the pumps. all the hoses looked okay and were tight. i went ahead and replaced the lines with the gates line. installed everything and tested the fuel pressure. same problems as before. i have replaced the lines, relay, filter, and put the stock rails and regulator back on. i guess the only thing left to do is to replace the pumps.