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Ram Diesel Injector Pump Problems

 Injector Pump Overflow Valve Diagnosis

See TSB 14-07-96 for additioanl fuel pressure and overflow valve tests.

Overflow valve location  The most common problem related to the injection pump is the Overflow valve, located at the return line connection. Look for this connection at the front of the injection pump on the engine side of the pump.

Subject:   Re: Low fuel pressure
From:       "Fest3er" <>

> I've had a couple responses on the question of low fuel pressure, but
> still not the answer I need.   Can someone tell me the process of
> analyzing whether the problem is the valve or the lift pump?  I am
> taking the pressure reading on the output side of the fuel filter.
> Where exactly is the pressure valve?

According to my '98 manual, the overflow valve is on the left side of the fuel injection pump, near the front. It says the valve opens at about 22 PSI; the transfer (list) pump supplies fuel to the injection pump at about 25 PSI.

Skipping to the Diagnosis and Testing section (paraphrasing)....

For symptoms:

  1. check fuel shutoff solenoid adjustment. If it's not right, fuel pressure could be low
  2. check supply and return lines for kinks, etc., that could restrict fuel flow
  3. check fuel filter/screen (which you say are OK)
  4. check lift pump pressures. S/b about 22 PSI at idle and 25-30 PSI at 2500 RPM. Install Spec. Adap. Hose Tool 6539 in the return line, then pinch the adapter's rubber hose and see if there's any change; book suggests a smooth-jaw vise-grip.
    1. If there's change, first ensure the overflow valve is installed at the OUTLET of the injection pump, *not* the inlet; if that's OK, the overflow valve most likely needs replacing. However, the valve is matched to the injector pump during (re-)manufacturing.
    2. If no change in power is noted, then the lift pump needs replacing or the cam lobe is worn.  Note: *don't* pinch the regular return line; outside may be rubber, but the inside is not.
  That's it in a nutshell: three pages condensed to a half page. Given the medium complexity of the diagnosis process, it would be wise to have a copy of the service manual handy (I *did* leave out a lot of detail, wanting to relate the ... high points of the procedures).

Good lock,


Replacement overflow valves are available from Piers Diesel Research Inc.
18940 -94th Avenue, Surrey, B.C.

Phone   604 888 4159

New valve installed on pump New on left / old on right
Use a 3/4" wrench to unscrew the valve. Make sure that you do not lose the
sealing washers on each side of the fuel return line fitting.


Last edit to this page: April 11, 2003