2004 Fuel Pressure Question

[John Addington]

Fuel pressure test question, 2004 4.0L. When I turn the key on the fuel pressure gauge goes to 46 then slowly lowers to 43 and holds. I then started the Jeep after about 30 seconds and the gauge goes to 47 and holds. Does that appear that the pump and regulator are working correctly? I tried to upload a video but it’s too long. Thanks.

 

[Jerry Bransford]

47 is close enough, 49 psi is the factory specified pressure. The fuel pressure regulator's job is only to limit excess pressure, it does nothing to help keep the pressure high enough which is solely the fuel pump's job.

 

[John Addington]

47 is close enough, 49 psi is the factory specified pressure. The fuel pressure regulator's job is only to limit excess pressure, it does nothing to help keep the pressure high enough which is solely the fuel pump's job.

 

[John Addington]

Cool thanks.

 

[HarleyMick]

47 is close enough, 49 psi is the factory specified pressure. The fuel pressure regulator's job is only to limit excess pressure, it does nothing to help keep the pressure high enough which is solely the fuel pump's job.

Question for you, Jerry. I have a 99 Jeep Wrangler Sahara and I recently changed the engine to a 4.7L Stroker. It is balanced with Chevy valves and springs and a CompCam with a basic operating range of 800 - 4800 RPM. It also has a header with low restriction Flowmaster exhaust, a 62 mm throttle body and 24 lb. Mustang fuel injectors.

With 35" tires, a 6" lift and 4.88 gears to go with the AX15 5 spd trans I am afraid to bring it out of the hole, but will occasionally do a 5 -10 mph punch and it pulls the front wheels. I'm very happy and I'm working hard to finish the touches needed for car shows.

Here's the problem: At about 4,200 RPM it sputters and looses most of its power until I let off the gas. It does this at any rate of acceleration and in any gear. I used a Hypertech programmer to add 500 RPMs with 91 octane gas. The camshaft pretty much demands the timing to be set at 15 degrees BTDC wich forces me to use 95 octane to keep the valves quiet. I checked the fuel pressure and it levels out at 42 psi, which is less than the 43.5 minimum required by the injectors.

What do you think? Am I running out of fuel pressure due to a week fuel pump or is it a ECM/PCM issue? I'm retired and hate to just throw more money at it. There is a company I could send the computer to with all the info I gave you and a little more to reprogram it specifically for my setup. But what if it's the fuel pump instead? Any ideas or advice would be greatly appreciated. Anyone?