1998 Ford F-150 engine miss

Tiny
BASHLAND
  • MEMBER
  • 1998 FORD F-150
  • V8
  • 4WD
  • AUTOMATIC
  • 95,000 MILES
PROBLEM:
PCM CODE PO304, 1998 FORD F-150 4.6L VIN CODE “w" 95,000 MILES.

ENGINE ALWAYS STARTS NORMALLY HOT OR COLD. IDLE IS GOOD WITH A SLIGHT MISS ONLY SOMETIMES WHEN WARM. IDLE RPM IS NORMAL IN NEUTRAL AND IN GEAR, WITH AUTOMATIC XMSN. (4R70W)

ENGINE RUNS GOOD WHEN COLD, MISS ON #4 CYL ONLY WHEN ENGINE IS WARMED UP, AT LOW RPM (1700+-) IN TOP GEAR ON SLIGHT LOAD AND MINIMUM THROTTLE (UP SLIGHT GRADE) DEFINITE MISS ONLY UNDER THESE CONDITIONS+ MIL LIGHT ON.

ENGINE RUNS STRONG AND WELL UNDER HEAVY THROTTLE IN 1-2-3-4th GEAR HOT OR COLD. UNABLE TO CHECK TOP GEAR HIGHER SPEEDS OR HIGH SPEED STEADY STATE DUE TO SNOW/ICE ON ROADS.

HAVE CHANGED PLUGS AND WIRES, BOTH COIL PACKS, AND ALL EIGHT FUEL INJECTORS. FUEL FILTER WAS CHANGED 5,000 MILES AGO. NO VISIBLE HEATER H2O LEAK AROUND #4 CYL AREA. ALL OTHER DASH GUAGES ARE NORMAL.
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Thursday, November 27th, 2008 AT 10:13 PM

11 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the compression for cyl no. 4
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Thursday, November 27th, 2008 AT 10:35 PM
Tiny
BASHLAND
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WILL CHECK COMPPRESSION BUT BELIEVE THE ENGINE IS SOUND. DOES NOT USE OIL. COULD THIS BE A OPEN/ CLOSED LOOP FUEL TRIM PROBLEM? OR EGR CARBON DEPOSIT PROBLEM? TRUCK IS DRIVEN SHOORT DISTANCES IN TOWN
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Friday, November 28th, 2008 AT 11:46 AM
Tiny
RASMATAZ
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Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel
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+1
Friday, November 28th, 2008 AT 11:51 AM
Tiny
BASHLAND
  • MEMBER
  • 5 POSTS
Checked compression for cyl no. 4=125 psi.

No visible coolant leaks from heater hoses, but the spark plug boot was very wet. Dried plug well and boot, engine runs like new. Where is the moisture coming from?
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Tuesday, January 20th, 2009 AT 8:08 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Is this a 4.6? 5.4 may be included as well, but Ford was replacing the upper intake manifolds for leaking. Do a radiator pressure test.
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Friday, January 23rd, 2009 AT 1:06 PM
Tiny
BASHLAND
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WILL DO PRESSURE TEST WHEN I FIND A PUMP&PRESS. GUAGE. DO THE INTAKES OF THE UPPER & LOWER MANIFOLDS BOTH CONTAIN COOLANT? HOW IS THE H2O MIGRATING TO THE SPARK PLUG AREA?
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Saturday, January 24th, 2009 AT 6:19 PM
Tiny
RASMATAZ
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The air goes thru the intake manifold and thru the intake valves into the combustion chamber.
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Saturday, January 24th, 2009 AT 6:41 PM
Tiny
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  • 5 POSTS
ANSWER DOES NOT APPLY TO THE QUESTION THAT IS BEING ASKED.
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Saturday, January 24th, 2009 AT 10:05 PM
Tiny
RASMATAZ
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DO THE INTAKES OF THE UPPER & LOWER MANIFOLDS BOTH CONTAIN COOLANT? HOW IS THE H2O MIGRATING TO THE SPARK PLUG AREA?

Umm! Its water/coolant not O2 were talking about here, in the combustion chamber if the intake gasket is gone it will leak into the cylinder/s to include a blown headgasket into the cyl no.4
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Saturday, January 24th, 2009 AT 11:11 PM
Tiny
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THIS IS AN EXTERNAL MOISTURE LEAK SUSPECTED FROM SEEPING INTAKE MANIFOLD GASKET(S). THE PLUG WIRE AND BOOT GETS WET. THEN THE PLUG SHORTS OUT AND WILL NOT FIRE. PLEASE READ THE ENTIRE PRIOR POSTS. THE HEAD GASKET IS NOT BLOWN. NEITHER ARE THE HEATER HOSES SHOWING ANY SIGNS OF LEAKING OVER THE #4 CYL. AREA TRUCK RUNS PURFECTLY UNTIL THE WIRE AND EXTERNAL PLUG WELL ARE WET. HAVE USED DIELECTRIC GREASE ON THE PLUG AND BOOT WHICH HELPS. THIS IS NOT 02 PROBLEM BUT H2O (COOLANT) SEEP PROBLEM. RADIATOR LEVEL BARELY SHOWS LOW AFTER SEVERAL DAYS
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Sunday, January 25th, 2009 AT 12:49 AM
Tiny
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I'm stumped here -External moisture leak seeping in the intake manifolds and end up wetting the wire and the boot-If the intake manifold that has a coolant runner and the gasket blows it will probably do that. But moisture?

Please await for another expert to assist or request for refund
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Sunday, January 25th, 2009 AT 5:03 PM

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