Question about 1992 Ford F250

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I have a 1992 E350 motorhome with a 7.5 in it. I just had to replace the fuel pump. After replacing the pump it idles rough and runs rich. I did pick up an engine light and after getting the codes replaced the oxygen sensor. Problem still exsists. I am thinking my next step would be the fuel pressure regulator. I appreciate any help I can get.

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There is a few options but first I am hoping with your fuel pump replacement that you replaced the fuel filter if not do it first.
next have you checked you throttle body idle speed control device... See below on diagnostics
The curb and fast idle speeds are controlled by the Engine Control Assembly (ECA) and the Idle Speed Control Bypass Air Valve (ISC-BPA) . The ISC-BPA valve is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow this device to control the speed.
The idle speed setting procedure has been revised considerably to reflect the expanded application of the Self-Test idle speed options and because the throttle body incorporates an orifice in the throttle plate to control idle airflow as part of the sludge tolerant design.
I have a 1992 E350 motorhome with a 7.5 in it. I - dak408_14.gif

Throttle bodies with sludge tolerant design are clearly identified with a Yellow/Black decal. This decal warns that the throttle plate stop screw must not be adjusted counterclockwise (backed off), as this will not reduce the engine speed but may cause the throttle plate to stick in the bore. Backing out the screw may be required if the throttle body has been previously serviced (a plug in the throttle plate orifice may be present) or the plate stop screw tampered with (TPS Self-Test output out of range). The decal also warns that the throttle body must NOT be cleaned inside the bore, as this cleaning will impair the sensitive coating. The sludge accumulation will not affect the idle air flow. The cleaning procedure for the ISC-BPA still applies.

A change in idle airflow can occur not only at the throttle body but other areas as well. You should enter the idle speed procedure only after other possible causes in the following areas are eliminated.

  • Contamination within the idle speed control device
  • Lack of fuel system control (excessively rich or lean)
  • Throttle sticking or binding
  • Engine not reaching operating temperature
  • Incorrect ignition timing
  • Incorrect or clogged PCV system
  • Vacuum leaks (intake manifold, vacuum hoses, vacuum reservoirs, power brake booster etc.

  • Transmission is in PARK (A/T), or NEUTRAL (M/T)
  • Parking brake is applied (automatic brake disconnected where applicable)
  • Wheels blocked
  • Engine at operating temperature
  • Proper fuel pressure and no exhaust smoke
  • Correct and clean PCV system
  • Heater, A/C, and other accessories OFF
  • Ignition timing is set to specification
  • EEC-IV diagnostics have been performed and vehicle malfunction indicated service output codes have been resolved.
With the engine OFF, connect a tachometer, according to manufacturer's instructions. Disconnect the negative (-) terminal of the battery for 5 minutes, then reconnect it.
START the engine and let stabilize for two minutes. Goose the accelerator and let the engine return to idle. Lightly depress and release the accelerator, then let the engine idle.
If the engine is not idling properly, turn the engine OFF, and proceed with this procedure.
Disconnect Idle Speed Control Air Bypass Solenoid.
START and RUN the engine at 2500 rpm for 30 seconds.
Place the transmission in PARK (A/T), or NEUTRAL (M/T).
Using a tachometer, verify the idle speed is at 650 +/-150 rpm.

NOTE: A plug in the throttle body orifice will decrease idle rpm. Where as an orifice without a plug will increase idle rpm. Orifice plugs and installation tools are available in service kit # FOPZ-9F652-A.

  1. DO NOT clean the throttle body, check the plate orifice plug.
    • If there is no plug, turn the screw clockwise to the desired rpm.
    • If there is a plug from previous service, remove the plug, then adjust the screw in either direction as required. Screw must be in contact with the lever pad after adjustment.
  1. Turn the engine OFF.
  2. Disconnect air cleaner hose.
  3. Temporarily block the orifice in the throttle plate with tape. If the orifice already has a plug from previous service proceed to Step (e).
  4. RESTART the engine. Check the idle speed, using a tachometer. NOTE: On vehicles with Mass Air Flow Sensors, reconnect the air intake duct hose prior to rechecking the rpm. If the engine stalls, crack open the throttle plate stop screw, but DO NOT over adjust.
  5. If rpm continues to be fast, perform KOEO Self-Test.
    • If TPS output code is within range, remove tape from throttle body and check for other possible causes.
    • If TPS output is out of range, adjust screw for proper TPS code. Lever must be in contact with the screw.
    • If rpm is still fast, terminate the procedure and check for other possible causes.
  1. If rpm drops to 650 rpm or lower, or the engine stalls, turn the engine OFF, disconnect the air cleaner hose, and remove the tape from throttle plate.
  2. Install an orifice plug with proper color code according to the throttle plate orifice size.
  3. Reconnect the air cleaner hose. START the engine, and check the idle rpm using a tachometer. Turn the throttle plate stop screw clockwise until an idle speed of 650 +/- 25 rpm is achieved. NOTE: DO NOT turn the plate stop screw counterclockwise. This may cause the throttle plate to stick at idle.
Run the KOEO Self-Test for proper TPS code output.
Reconnect the Idle Speed Control Air Bypass Solenoid. Verify the throttle is not sticking in the bore, and the linkage is not preventing throttle from closing.
START the engine and idle for two minutes. Goose the accelerator and let the engine return to idle. Lightly depress and release the accelerator, then let engine idle.


Remove air inI have a 1992 E350 motorhome with a 7.5 in it. I - dak408_16.gifrom throttle body.
dak408_16.gif STEP 2
Select the proper color plug by using the Go/No-Go gauge pegs, included in the service kit (FOPZ-9F652-A).
Starting with the largest diameter gauge peg, attempt to insert through the throttle plate orifice.
If the gauge peg goes through the orifice, use the corresponding color plug.
If the gauge peg does not go through, proceed with the next smaller gauge peg for Go/No-Go Test.
NOTE: It is important that the largest Go/No-Go combination is used to determine the proper plug size.
If the smallest gauge peg does not go through the orifice, use the reamer bit and handle included with the service kit to enlarge the plate orifice. Wipe bearing grease on both sides of the plate orifice and on the reamer bit to hold the brass chips. After reaming, wipe plate clean and then return to Step 3 to determine the proper plug size.
Using the installation tool from the service kit, push the plug into the orifice until bottoming out at the throttle plate.
Open and snap closed the throttle several times to verify proper plug retention.
Reconnect the air inlet tube(s).
Reset idle rpm per engine requirement using the throttle plate stop screw.

Hope this helps

Posted on Nov 12, 2010


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