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I have a 1989 Dodge Ram Van B250 TBI 5.2L 318ci engine. It takes about 10-15 seconds of cranking to start the engine. After it gets hot sometimes it never starts. I'm getting afraid of taking it anywhere I have to trust it to start.

My question is about how to make the fuel system work better.

If I pitch a spoonful of gas into the carb while cranking, it instantly starts. If I short the outputs of the ASD relay so the fuel pump runs continuously and then crank the engine it instantly starts. I can see that fuel does not spray into the carb for quite a while after starting cranking, and it starts when the injectors start squirting fuel.

Why does the fuel take so long to get to the injectors? Does it siphon back down while sitting and take a while to get back to the carb? I'm wondering if air in the fuel line is why it behaves worse once hot.

I tested fuel pressure at the fuel pressure regulator at the carb and it comes up to 14 psi, but really slowly (taking about 10 seconds). Once up to pressure, it's solid and the pressure regulator dumps fuel back to the tank. Safety tangent: I tried to hold my thumb over the output of the fuel return line to see if it was misbehaving and when it came up to pressure, van started and fuel came spraying out like a thumb over a hose. Yowza! Won't check things that way again.

Anyhow, I checked pressure at the output of the fuel filter - and the input to the fuel filter (from the fuel tank pump). Pressures behaved the same as I measured at the carb, but replaced the fuel filter anyhow. I also pulled down the gas tank and replaced the fuel pump.

Question: Can fuel somehow drain back down from the carb when the engine quits - leaving air in the last 5' of line or so from the fuel filter? Does that matter? Is the fuel regulator suppose to allow a backfeed of air or is it suppose to stop backflow? Any ideas appreciated!

[added] Replaced the fuel pressure regulator at the carburetor body. Same issues remain. This problem has me stumped. Everything from the pump to the regulator has been replaced. Pressure checks are the same at all points in the system (nothing is plugged). I could sure use some help...

  • I cannot find a reference for where the pressure should be, but the stock pump runs between 38-58psi, which leads me to believe the pump you have in there isn't running right. Either you have a bad pump, or you put the wrong one in. 14psi is way low. – Pᴀᴜʟsᴛᴇʀ2 Aug 11 '18 at 12:00
  • There’s generally some kind of drainback valve in the tank that’s supposed to prevent this problem. – Ben Aug 11 '18 at 12:05
  • The fuel pump is siphoning fuel back into the gas tank. replace the fuel pump. – Moab Aug 11 '18 at 15:14
  • Paulster2 - yes the fuel pump puts out a higher pressure. In fact, I called the company to check and they explained that the higher pressure was correct - I remember may 68 psi - which seemed really high to me! But they explained this is correct becuase the pressure regulator blows fuel into a return line when the pressure at the carb reaches 14 psi. I think it's just a simple spring valve like a gas regulator and when the pressure gets high enough, the excess goes out the side port back to the tank. – Brian Aug 12 '18 at 1:12
  • Ben - I can't find any drainback valve upon inspection, and I can't find any in the docs. The output from the fuel pump goes directly to the output hose that runs underbody to the fuel filter. – Brian Aug 12 '18 at 1:13

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