i've been fighting fuel problems for awhile now. this thread will explain alot of it. but the current issue has been intermittant priming. sometimes it'll take 10 turns of the ignition switch to get it to finally prime the rail and when it does, the damn thing won't stop until it hits 90-100 psi. i've got a hypertech psi guage hooked to the rail and i'm back probing the tan wire on the fuel pump relay with my test light and it's the computer keeping it hot or not sending the signal (which ever way it is behaving at the time) because i've back probed the green wire too.

btw, i have autometer electric oil psi gauge and no oil pressure switch. i know the oil pressure switch provides power to the pump if the relay fails, but mine isn't wired with a switch.

if you didn't read the other thread, the relay and pump are fairly new. i replaced them in the winter. i know the relay and the pump were bad when i replaced them. the pump is an inline parts store brand pump. fuel filter was replaced then as well. i replaced the FPR with a stock one a few weeks ago and i blew it out again today when it hit 100 psi.

can anybody tell me why it might be doing this? is it the computer? is it possible that something external to the computer is "telling" it to prime too long or not prime? (depending on which it is doing at that time) i've been doing alot of reading and searching, but still haven't gotten the full picture of which different things influence the operation of the fuel pump.

 

anybody got any insight on the ecm's control of the fuel pump? i've done alot of reading but only find one reply in a thread in which vader says that the ecm primes the pump for 2 seconds if the key has been off for more than 20 seconds. are there any other requirements like this for the ecm?

 

Just like Vader said. The fuel pump will prime for 2 seconds if the key has been off for more then 20 seconds. The fuel pump primes with en ecm grounds the signal wire to the relay.


The pump should then start running when the ECM see a RPM signal.


100PSI? That is what the FPR is for, to keep it at the right pressure. IT sounds like your return line is clogged and you are dead-heading the pump.

 

I agree, I don't see how it could hit 100PSI, even if the pump ran non stop...gotta be something going on with your return system. Did you cout the lines when you did the pump or drop the tank?

Now, if you are having a low pressure problem, check for restricted fuel lines, or clogged filter. If you are using a old tank from a tpi car and it has been sitting around, it may have enough sentiment to clog the filters, the fuel pump "sock" and the in line filter. If the pressure checks out at this point, block or pinch off the fuel return line, and apply 12V to the fuel pump test connector and note pressure. If it goes above 45 psi, replace fuel regulator. If it below 40 psi, check for a faulty in tank pump coupling hose, pulsator, wrong inlet filter, or even wrong fuel pump.

An excess pressure problem can be checked this way: disconnect the fuel return line at the pressure regulator side and install a 5/16" flex line, insert other end in a gas can, and look at the pressure within 2 seconds of fuel pump prime. If the pressure is between 40-47 psi, correct restricted fuel line to tank. If the pressure is still high (above 47 psi) check for restricted line from pressure regulator to point line was disconnected. If the line checks our, replace the regulator.

The above is from:
http://chevythunder.com/fuel%20injec...g%20pg%20D.htm

 

thanks for the replies guys, i'm leaning towards what ya'll are suggesting with it being a return line issue. i haven't had time to check it out yet, my son is having football practice 3 nights a week right now. the motor is installed in a nissan pickup using the stock tank. i just cut the lines under the cab to install the pump, hindsight is suggesting that i should have done this differently. my starting plan is to disconnect where the hoses connect to the hard lines under the hood. i should have enough slack there to run it into a gas can and check that way. of course i'm sure that will be fine and i'll end up dropping the tank and replacing it with a fuel cell. it'll make it alot easier and i've been needing to ditch the stock tank for clearance issues anyway.

i really appreciate all the help i get from you guys here. i know next to nothing about this stuff, but i can read for hours on all the great info here. i'd have sold out and gone to a carb by now if it wasn't for this place.

 

ok, i disconnected the return line under the hood and it primed to about 50 psi or so. so it's somewhere aft of there.....which is right were i didn't want it to be lol. again, thanks for the help guys.

 

That makes more sense...track it down and you are good. Maybe you can hook some compressed air to the return line and blow it out?