Loss of power when driving

Tiny
BARBARA MCALLISTER
  • MEMBER
  • 1988 FORD F-250
  • V8
  • 4WD
  • AUTOMATIC
My Ford F250 won't go over 25 mph. I have so far changed the vacuum modulator and that doesn't seem to help. What next?
Barry Jackson
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Sunday, March 27th, 2011 AT 11:38 PM

7 Replies

Tiny
CJ MEDEVAC
  • EXPERT
Is it really running rough/ smoking/ etc. While trying to accelerate? Investigate a Stopped up Catalytic Converter.--The Medic
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Sunday, March 27th, 2011 AT 11:46 PM
Tiny
BARBARA MCALLISTER
  • MEMBER
I don't know if this matters, but, it runs at 4,000 rpms when the engine is cold. Once it gets warmed up, it drops to 2,500 rpms. Do you still think catalytic converter?
Thank you for your time, Barry Jackson
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Monday, March 28th, 2011 AT 12:05 AM
Tiny
CJ MEDEVAC
  • EXPERT
Any other observations? Does your Check Engine light work at start-up. Is it/ Has it been on constantly?--The Medic
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Monday, March 28th, 2011 AT 1:59 AM
Tiny
BARBARA MCALLISTER
  • MEMBER
No, just loses power once it gets warmed up. Anything else besides the catalytic converter? Thanks Again, Barry Jackson
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Monday, March 28th, 2011 AT 2:00 AM
Tiny
CJ MEDEVAC
  • EXPERT
Attempting a solution for your problem. Trying to get you one soon, as to get you ridin' again. I did leave a message for another Expert to assist, If I cannot come up with a solution soon.---The Medic
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Monday, March 28th, 2011 AT 2:15 AM
Tiny
BARBARA MCALLISTER
  • MEMBER
Thank you so much! I appreciate all your help. Barry Jackson
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Monday, March 28th, 2011 AT 2:38 AM
Tiny
RASMATAZ
  • MEMBER
For your idle problem

NOTE: A change in idle speed occurred because of a problem elsewhere. Enter this procedure after eliminating the possible causes listed below:

Contamination within the throttle bore and/or idle speed control device.
Throttle sticking or binding.
Engine not reaching operating temperature.
Vacuum leaks (air intake, vacuum hoses, vacuum reservoirs, power brake booster, etc.)
VERIFY:

Transmission is in PARK (A/T) or NEUTRAL (M/T).
Parking brake is APPLIED (automatic brake release is DISCONNECTED where applicable).
Wheels blocked.
Cooling system is filled to proper level.
Engine is at operating temperature.
All accessories (heater, radio, lights, etc.) OFF.
Throttle lever is resting ON the throttle plate stop screw.
Ignition timing is set to specification.
Perform EEC-IV diagnostics and resolve any vehicle malfunctions that are indicated by service codes. (Ignore this step if sent here from an EEC-IV Pinpoint Test step).
Engine OFF, disconnect the negative (-) terminal of the battery for 5 minutes minimum, then reconnect it. NOTE: Memory to radio, phone, and other programmable accessories may be erased when the battery is disconnected.
Idle Speed Setting

PROCEDURES

With engine OFF install specified feeler gauge between throttle plate stop screw and throttle lever. Automatic transmission.030 inches, manual transmission.030 inches.
Unplug SPOUT line and verify that ignition timing is 10 +/- 2 BTDC.
Disconnect idle speed control-air bypass solenoid.
With transmission in NEUTRAL (M/T) or PARK (A/T):
Allow engine to idle for 2 minutes.

Check/adjust idle rpm: Turn the throttle plate stop screw to 780 +25 rpm automatic transmission, 730 +25 rpm manual transmission.
NOTE: If you must turn the throttle stop screw IN, turn engine OFF, make estimated adjustment. START engine and repeat Steps 4, 5, and 6 before continuing.

Remove feeler gauge from throttle plate stop screw and throttle lever pad.
Reconnect SPOUT line.
Turn engine off and reconnect idle speed control-air bypass solenoid, verify the throttle is not stuck in the bore and linkage not preventing throttle from closing.
START engine and stabilize for 2 minutes then goose engine and let it return to idle, lightly depress and release the accelerator. Let engine idle, if problem exists, see Diagnosis by Symptom (Diagnostic Routines.)
NOTE: A condition may occur where the engine rpm will oscillate. This can be caused by the throttle plates being open enough to allow purge flow. To verify this condition, disconnect the carbon canister purge line and plug it. If purge is present, the throttle plates must be closed until the purge flow induced idle oscillations stop.

On Automatic Overdrive Transmission (AOD) applications check TV pressure adjustment, See Automatic Transmissions

Won't accelerate over 25mph-check and test the Airflow meter/sensor and throttle position sensor also check he fuel pressure -

**** What vacuum modulator did you replace -is for the tranny? Could very well be the transmission slipping
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Monday, March 28th, 2011 AT 4:10 AM

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