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Fuel pressure, 1989 TBI

Discussion in 'Pre-1994 trucks, commercial vehicles' started by PCRMike, Mar 26, 2017.

  1. PCRMike

    PCRMike Well-Known Member

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    1989 D100. Factory TBI 318. Replacing with a built Magnum. Later with a dead serious poly 402. Going to use a wet manifold injection like a Sniper EFI. Calls for 15PSI. Is the factory pump up to that?
     
  2. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Factory pump puts out about 55 psi for MPFI, and I know 4-cylinders used 39 psi at one time. I don't believe any FI systems were lower than that.
     
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  3. PCRMike

    PCRMike Well-Known Member

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    I was thinking the TBI were lower than that. I can be wrong. I just couldn't find it in my Haynes.
     
  4. AllanC

    AllanC Well-Known Member

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    I referenced a 1991 factory service manual for a Dodge Dakota. The dual point (dual injector) throttle body system on the V6 and V8 operates at 14.5 psi. So the factory fuel pump system should be the correct match.
     
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  5. GLHS60

    GLHS60 Well-Known Member

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    Tell us more about Poly!!

    Is she a Plymouth A ??

    Thanks
    Randy
     
  6. pt006

    pt006 Active Member

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    Mike; keep in mind that the fuel pump is capable of putting out a lot more pressure than 14.5 psi. The regulator is in the back section of the throttle body. It returns any excess gas back to the tank.

    There was a recall for the fuel pump hose that was inside the tank. Kit not available. Mine had a borderline/intermittent pressure problem. Found the interior gasket of the pump tubes went bad. Not available. Was forced to buy a whole new fuel pump assembly. Not available. So I made an O-ring to seal the pressure side. Has been good for 2 years and counting.

    So, Poly wanna stroker????
     
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  7. ka9yhd

    ka9yhd Active Member

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    At one time there was a service bulletin on the 1987 Omni with the 2.2 and a carburetor. The service bulletin switched the fuel delivery from the mechanical pump to an electric pump in the tank.
    After the electric pump died on my friend he did some searching, found the TSB but the part numbers are long since dead and the parts are no longer available.

    But somebody here might be able to come up with something.
     
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  8. PCRMike

    PCRMike Well-Known Member

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    Awesome info. I will have to see if the regulator is on the throttle body. Had not thought of that.

    And yeah. Poly wanna stroker. Lol.
     
  9. Rick Anderson

    Rick Anderson Well-Known Member

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    From memory, I "think" typically,

    Modern MPI is usually ~55PSI
    Early MPI is usually ~39PSI, with a vacuum operated fuel pressure regulator, that would up the fuel pressure at WOT.
    TBI is usually in the teens for PSI (18 PSI comes to mind)
    Carburetor is usually in the single digits (7 PSI comes to mind)

    Sure the pumps/plumbing/regulators might be tweaked to make more or less pressure, but I'd think the most reliable service and performance would come from using the pump designed for the type of fuel system you're using.

    Check the performance aftermarket catalogs, there are plenty of universal electric fuel pumps for carburetor cars. They will make the proper pressure and fuel flow, just need to improvise the connections and wiring.

    Since the pressure difference are relatively low for fuel pump supplying a carburator, I'm confident you can mount it just about anywhere. After all the OEM mechanical fuel pumps were mounted on the engine sucking the fuel through a line the length of the car above the fuel level. MPI Fuel injection creates the delta p's/ suction that could vapor lock more easily and being at the bottom of the tank with a short suction distance help prevent that. Even fuel injection, I'm confident would work with the pump mounted near the tank, toward the bottom of the tank. After all the newest fuel pumps all have an internal reservoir, that sucks the fuel up from the tank and deposits into a smaller tank in the plastic body of the fuel pump. Assumably to always surround the pump with fuel, to keep it cooler and prevent it sucking air when the tank is near empty and going up and down hills.
     
  10. dana44

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    Yes, the book shows the TBI fuel pump is 14psi, which is greater than the stock carbureted fuel pump of 6-7psi and the EFI pumps of 37-55psi. Would suggest, given it needs to be more specific, a fuel pressure regulator to ensure the proper pressure is maintained.
     
  11. ka9yhd

    ka9yhd Active Member

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    With that TSB on the Omni the fuel pressure regulator was next to the carburetor.
     
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  12. PCRMike

    PCRMike Well-Known Member

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    Hmmmm. Cool
     

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