7.3 miss

[460+]

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.

[grabowskimech]

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.

[460+]

Yes, that was one thing we did first. cant rember # but it close to others.

[460+]

Does anyone have any ideas?

[Dirk]

Sounds like the injector may have internal damage.

[jwarren072]

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

[460+]

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.

[Dirk]

Originally Posted by 460+

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.

[460+]

Did a compresion test it was close to other cylinders, useualy abent valve would show up there.

[mschn99]

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...