7.3 miss - Ford Powerstroke Diesel Forum
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post #1 of 15 Old 10-27-2007, 07:04 PM Thread Starter
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Unhappy 7.3 miss

Im working on a early 99 7.3, has a slight miss at idle when you start to accelorate it realy starts missing bad. Ran injector buzz test OK,run cylinder contribution test #8 cyl didnt pass. Pulled #8 out found orings burnt so replaced orings. Run motor to get air out of fuel & oil engine run better but still has miss, run same tests came back #8 cyl. Replaced injector still same. Tested all wires,harness, everything OK. Removed ECM & IDM out of & used a donor truck parts still has miss.Any help would be appreciated.

99 F350 4x4 dually
7.3 w/K&N af
4" exh into 6" Aussies stacks
4"lift &35" tires
CC mod HP crossover line
Beans stage II 120hp injectors
D66 turbo
ITP regulated return
reburn on TS= 25,high idle,60,100,120,140hp
updated ecm (2000 model)
Dyno#'s 360hp and 965 ft lbs trq
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post #2 of 15 Old 10-27-2007, 07:12 PM
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Did you do a compression test on that bad # 8 cylinder,maybe you have a bad piston. Hope not, for your sake, have a look at the crankcase vent while running and see how much blowby you have.
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post #3 of 15 Old 10-27-2007, 07:14 PM Thread Starter
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Yes, that was one thing we did first. cant rember # but it close to others.

99 F350 4x4 dually
7.3 w/K&N af
4" exh into 6" Aussies stacks
4"lift &35" tires
CC mod HP crossover line
Beans stage II 120hp injectors
D66 turbo
ITP regulated return
reburn on TS= 25,high idle,60,100,120,140hp
updated ecm (2000 model)
Dyno#'s 360hp and 965 ft lbs trq
460+ is offline  
post #4 of 15 Old 10-29-2007, 08:07 AM Thread Starter
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Does anyone have any ideas?

99 F350 4x4 dually
7.3 w/K&N af
4" exh into 6" Aussies stacks
4"lift &35" tires
CC mod HP crossover line
Beans stage II 120hp injectors
D66 turbo
ITP regulated return
reburn on TS= 25,high idle,60,100,120,140hp
updated ecm (2000 model)
Dyno#'s 360hp and 965 ft lbs trq
460+ is offline  
post #5 of 15 Old 10-29-2007, 09:44 AM
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Sounds like the injector may have internal damage.

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post #6 of 15 Old 10-29-2007, 09:51 AM
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Cool miss

take the vavle cover back - off and check the wiring harness connector to the injector harness on the side of the motor that is missing....the connectors will deteriorate over a period of time and cause the miss due to bad connection to the injectors under a load.........just a thought
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post #7 of 15 Old 10-29-2007, 10:00 AM Thread Starter
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Checked all wiring is ok, ohms tested & checked all wiring from valve cover to computer.Installed new injector in#8 cyl still had miss, moved new inj to different cyl miss stayed in #8 cyl.

99 F350 4x4 dually
7.3 w/K&N af
4" exh into 6" Aussies stacks
4"lift &35" tires
CC mod HP crossover line
Beans stage II 120hp injectors
D66 turbo
ITP regulated return
reburn on TS= 25,high idle,60,100,120,140hp
updated ecm (2000 model)
Dyno#'s 360hp and 965 ft lbs trq
460+ is offline  
post #8 of 15 Old 10-29-2007, 10:10 AM
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Quote:
Originally Posted by 460+ View Post
Checked all wiring is ok, ohms tested & checked all wiring from valve cover to computer.Installed new injector in#8 cyl still had miss, moved new inj to different cyl miss stayed in #8 cyl.
Did you look for damage in the head?

You may also have a valve that is bad.

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post #9 of 15 Old 10-29-2007, 10:14 AM Thread Starter
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Did a compresion test it was close to other cylinders, useualy abent valve would show up there.

99 F350 4x4 dually
7.3 w/K&N af
4" exh into 6" Aussies stacks
4"lift &35" tires
CC mod HP crossover line
Beans stage II 120hp injectors
D66 turbo
ITP regulated return
reburn on TS= 25,high idle,60,100,120,140hp
updated ecm (2000 model)
Dyno#'s 360hp and 965 ft lbs trq
460+ is offline  
post #10 of 15 Old 10-29-2007, 10:15 AM
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im wondering about a valve or possibly a valve spring or rocker or pushrod myself...something in the valvetrain....a broken valve spring can still pass a compression test but bleed compression by when the motor is running....a bent pushrod can cause a miss as well...
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