460 Miss
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5th Wheeling
Joined: Sep 2003
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460 Miss
Hey everyone, I've got an 88' F250 with the fuel injected 460. I just rebuilt the motor, has all new everything but the wiring harness (new injectors, sensors, plugs, wires, etc...). It's only got 800 miles on it. 2 days ago it developed a miss when at an idle. I started pulling injector plugs to find which cylinder and found it to be #7. So I started by swapping plugs, still #7. Then wires, still #7. The injectors, still #7. The plug is dry with slight color. The injector has fuel in it, and is firing by what I can tell with a stethoscope. I went to my mechanic who plugged an injector plug tester into it, and the light flashed like normal. Pulled the fuel rails and cranked it and fuel came out of all the wholes.
I'm stumped. The weird part is that as soon as you up the rpm's the motor smoothes out and runs fine. I double checked this by driving it up the driveway with the #7 plug wire disconnected and it was really rough when driving. So I'm guessing I have a wiring problem of some sort. Maybe the injector's not getting 12 volts at idle??? Or am I missing something else simple? Thanks.
I'm stumped. The weird part is that as soon as you up the rpm's the motor smoothes out and runs fine. I double checked this by driving it up the driveway with the #7 plug wire disconnected and it was really rough when driving. So I'm guessing I have a wiring problem of some sort. Maybe the injector's not getting 12 volts at idle??? Or am I missing something else simple? Thanks.
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5th Wheeling
Joined: Sep 2003
Posts: 28
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Ok, so a buddy of mine asked if I can swap injector plug wires to see if it's the wiring. So I looked up the wiring diagram for my truck and sure enough the computer fires injector #6 and #7 at the same time. So I swapped them and it still misses on #7. So that eliminates wiring.
I just want to reiterate that the miss is only at idle. As soon as the RPM's go over 1000 it smoothes out just fine. So it's not the injector or the wiring, fuel sprayed out normal when pulled the rail....so now I'm leaning towards spark. But what haven't I checked??
I just want to reiterate that the miss is only at idle. As soon as the RPM's go over 1000 it smoothes out just fine. So it's not the injector or the wiring, fuel sprayed out normal when pulled the rail....so now I'm leaning towards spark. But what haven't I checked??
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5th Wheeling
Joined: Sep 2003
Posts: 28
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Yeah, I'll do that in my process of elimination. I'm pretty sure it does go away though as when I pull the spark plug wire it idle, it makes no difference in the idle....but when I drive I can definitely feel the miss, not the case when the plug wire is on.
I hope my compression and cam are fine as the bore, pistons and cam only have 800 miles on them.
I hope my compression and cam are fine as the bore, pistons and cam only have 800 miles on them.
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Theprospector428
1994.5 - 1997 7.3L Power Stroke Diesel
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