Fuel pressure?

[salmon30]

Hello, new to forum from Packer country. Got a problem.

My poor old ram isn't used much, just to pull my boat and my car hauler trailer. Only has 69K miles after 14 years. I think I get more problems from sitting around then I do from driving it.

So, I have a 2003 Ram with a 5.9 gas. When started it miss's coughs, backfires, etc. After a bit of flooring the gas pedal it clears up until the next time I start it. And cold or warm starts don't matter.

No codes on my cheapo harbor freight code reader.

Ran a bunch of gas dryer thinking water in gas, no help. New rotor and distb. cap cause they were a bit green inside.

Book talks about vacuum, I have 15in at idle and 20in with a tiny bit of throttle, nice and steady.

Book also talks about fuel pressure so I rigged up a gauge from an old Freon adapter fitting, and a very old vacuum/fuel pressure gauge. T the rail fitting I'm getting 40psi, all the time. all RPM's. Book says 47 to 51psi.

Can being 7 psi low cause all my problems? Do I need a new $250 fuel pump? $750 at the dealer.

Retired here, money is tight.

 

[usaf2006]

Id try a new or diff gauge to be sure. U said urs is old. Also check rockauto for a fuel pump. Good prices.

 

[BigSloth]

A 5.9 will run on far less than 40 psi, that's actually about the norm for the older trucks. I'd be willing to put money on it being a problem with you intake plenum gasket. The magnum engines have an aluminum intake with a steel belly pan on the bottom that goes across the lifter valley. Steel and aluminum expand at different rates, causing the gasket between them to break. It causes a hard start condition and also pinging on top end in some higher load situations.

 

[salmon30]

So, I borrowed a fuel pressure gauge, still 40psi. Ordered a new fuel pump with regulator. Got it yesterday and put it in. STILL SAME THING. 40psi. and it still misses and backfires shortly after I start it, then after stomping on it a few times going down the road it clears up until I shut it off and start it again.

About the plenum gasket, I had a 1998 Dodge that had a bad plenum gasket and it burned a lot of oil until it was replaced. My 2003 doesn't use any oil. Could it still be that gasket? It starts easy every time, cold or hot, just after it runs a bit the missing and stuff happens.