Hello all, new to the forum. I have a 91 dodge P/U auto with a 318 engine that will not hold fuel pressure. I have replaced the fuel pump twice with in a week, Napa brand. Both pump done the same thing. It will crank and run, at idle it will hold 15lbs of pressure. but as soon as you give it throttle you can see the fuel pressure drop and it will stall. You have to cycle the ignition switch a few time to get it to build the pressure back up. Thanks for any help.

Later TW

 

Air in the system, or does that year have a pressure relief valve? When the fuel pressure gets to a preset limit, the valve opens and allows the pressure to relieve itself to the return line. The diesels have it, a gasser may as well.

I would first check the integrity of the fuel lines themselves. Down along the frame or behind the tank is where you'd probably see the most corrosion.


Just my guess.


Good luck.

 

Double D thanks for the quick responce, I am not for sure on the pressure relief. But I would think that it does have one. I have blocked off the return line to make sure it wasn't bypassing the system with no changes. I have also changed out the pressure regulator with the same results. I haven't visually inspected the lines underneath the truck. I blew air threw the pressure and return lines to make sure no restriction where present. I have good voltage to the new pump. I'm about to the point to start pulling my hair out.

 

My only other thought is something loose in the tank perhaps?

Good luck.

 

Maybe you got a bad injector that isn't sealing and letting the gas go into the intake port on one or more of the cylinders, because if your pump isn't draining back and there isnt' any leaks and return is blocked then thats about all it can be.

 

I have the bed off the truck now, there is no leaks in the tank and the fuel line has been changed inside the tank. Both injectors have been changed out from another running truck. I have also change out the coil to eliminate spark issues, I have run out of options. Thanks again for the help.

 

welcome to DF...

could it be a vacuum leak and the fuel pressure drop is it dumping fuel trying to keep up? not to familiar with the 1st gen trucks but I had a similar problem with a carb setup and it was the base gasket causing a problem. ran fine with the choke closed but as soon as you hit the gas, it wanted to die.

 

Steve thanks for the welcome, I did take off the TB today, but didn't have much time to mess with it. The base gks. is dried up, I will replace it once I get a chance to inspect the TB. I even tried a 4-14 pound 12 volt electrical booster pump to see if it would help out, but it did not help in any way. Does this model have a pickup in the distrib. to signal the fuel pump?

 

I honestly dont know. I know the magnum motors have a cam position sensor in the distributor which is responsitble for injection timing. but it sounds like yours is a 2brl throttle body type injection with 2 injectors on it so I dont know how they control the injection timing.

did you check for a relay in the fuse box? maybe one test would be to short the pump on and see if it runs that way. at least you'll know if something is killng the relay (if it has one.).

 

Yes it is a 2 barrel TB. I have swapped the relay and have bypassed the relay all together with no changes. I have done everything I could think of to try and eliminate the problem and have come up empty. Again thanks for the help