Fuel pressure too high

[turbolimited]

What are the good reasons I haven't thought of or found in search that would result in seeing high pressures (not lower than 48 psi, vac line off)? New Walbro 340 pump, stock sending unit and lines, multiple AFPRs all with same result. The car was down for like 8 years before this problem arose. I installed a new fuel tank, new pump, but everything else on the car is how it was when it ran, normal pressure.

I have "flushed" the all the fuel lines, backward and forward with compressed air. The return seems free of any blockage or restriction. It acts like the pump is just too big for the factory lines, but it is just a little ole 340.

Combo, if it matters: stock block, ported irons, small flat tappet cam, ported lower intake, champion upper, 70 mm. TB, RJC front mount, Razor's Alky kit, TE 45A, 60 lb. injectors, new Accufab, old Accufab, old Bosch AFPRs, stock fuel rail, stock lines, new filter and sock, Walbro 340, stock sending unit.

It has to be a restriction in the return line, right? I have pretty much ruled out a restriction, which means the pump is too powerful, but that doesn't make sense to me either given its size. Anything else to try before replacing the return line or dropping the tank to check and see if this is really a 340 in there?

 

[dynoman]

Maybe you kinked the return line when replacing the tank . Try dropping it down a little to check . You can try running a line straight from the return at the rail to a bucket and turn the pump on with the jumper near the alternator . This would verify if the factory return is the problem .
Air through the lines flows much easier than gas .

 

[turbolimited]

Thanks, Sam! In the process of blasting the lines, I did drop the tank and ran compressed air from the lines at the sending unit forward. I didn't see any kinks. I'll try the straight line off the return into a bucket and see what is happening. I'm not totally opposed to running a new dedicated return line from the rail all the way to the tank, but would like to save the effort and expense if possible.
thanks again!

 

[THensley]

fuel pump to large for the return line and stock hanger

 

[THensley]

255 is all needed for 60's

 

[BRAD_PADGETT]

A new larger fuel pump can reveal restrictions on the fuel return lines at the threaded connections. Open the connections and make sure the line is clear. I had this problem with the Hellcat pump. In my case cleaning the lines was not enough.

 

[SPOOLFOOL2]

Are you still running the stock fuel lines at the tank? Might try replacing them with some high PSI fuel lines. Make sure the bends are no tighter than they have to be. You still may be able to use that pump with that combo. Many others have, including myself.

 

[turbolimited]

Are you still running the stock fuel lines at the tank? Might try replacing them with some high PSI fuel lines. Make sure the bends are no tighter than they have to be. You still may be able to use that pump with that combo. Many others have, including myself.

Yes, sir. I replaced all those when I put the new tank/pump in the car. I had the same set up before, but the lines were old and crusty, even had a 340 in the tank before, and didn't have this issue. I've somehow created a restriction, or the new pump is flowing harder than the previous 340 I guess. I'll poke around some more on the return line front to back, then ultimately replace it I suppose if I can't uncover my issue. Thanks all for your feedback.

 

[turbolimited]

A new larger fuel pump can reveal restrictions on the fuel return lines at the threaded connections. Open the connections and make sure the line is clear. I had this problem with the Hellcat pump. In my case cleaning the lines was not enough.

There's the threaded connection at the base of the regulator, and another one at the front crossmember. Any other threaded connections on the return line besides those two on the way back to the tank?

 

[BRAD_PADGETT]

There's the threaded connection at the base of the regulator, and another one at the front crossmember. Any other threaded connections on the return line besides those two on the way back to the tank?

Its' been four years since I did this -I seem to remember there being on more in the return line. I cleaned out these restrictions and still the fuel pressure was at 40 line off will the Hellcat fuel pump. My problem was solved (not by me) by having the ECUGN control the fuel pump. Slow the fuel pump down at ide/low rpm and ramp it up at higher rpm. This eliminated the need to replace the return line.

 

[salvageV6]

Condensation and ice buildup would do that, in the return line, probably not in TN though....

 

[turbolimited]

Thanks again for all the replies and suggestions. In the coming days, I plan to inspect and clean all the threaded connections in the return line again (or maybe for the first time, if I find a connection I haven't previously disconnected). The car is stored in a conditioned garage, and while temps have been cold outside, the garage never falls below 60 degrees.

Assuming that doesn't solve the issue, it occurred to me that the new sending unit that came with the tank could be a restriction in the hard return line. I'll inspect that next.

 

[xlr8ngn]

Not saying this is your issue, but something to check. Pressure gauges don't like vibration, and consumer gauges we can afford tend to be very cheaply made. Liquid fill helps mitigate vibration, but they still don't like it. Good practice is to tube up two gauges together and test 3 different pressures in the range you use it and see if they match, and even better is to use a calibrated gauge to verify.