460 Miss
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5th Wheeling
Joined: Sep 2003
Posts: 28
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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
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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??
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
I was thinking compression check also. I'm thinking maybe a push rod has bent or come loose. I know it SEEMS to smooth out after 1000 RPM, but V-8s will do that. Does the 460 have adjustable rocker arms, just curious?
Postmaster
Joined: Jan 2009
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Hey Lew , where did you learn how to spell ??? (seif) thats a good one ...forgot the other u to...
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5th Wheeling
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I've pulled the spark plug wire and there is no change in idle.
The rocker arms are not adjustable on.
I'll have to get the compression checked next I guess. It's definitely firing at higher rpms, it's really smooth. Like I said I pulled that #7 plug and the idle did not change, but it ran very rough when I drove it. It's starting to look like either compression or my cam. Bummer.
The rocker arms are not adjustable on.
I'll have to get the compression checked next I guess. It's definitely firing at higher rpms, it's really smooth. Like I said I pulled that #7 plug and the idle did not change, but it ran very rough when I drove it. It's starting to look like either compression or my cam. Bummer.
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5th Wheeling
Joined: Sep 2003
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I've switched the injectors, still #7.
But something new happened today...it fixed itself! For a little while anyways. Started up, idled fine. But Progressively got worse at each stop sign or red light until it was back to missing again! What the hell!? But that tells me it's probably not the cam or bad compression.......so it brings me back to fuel or spark. I'm gonna set it on fire!
But something new happened today...it fixed itself! For a little while anyways. Started up, idled fine. But Progressively got worse at each stop sign or red light until it was back to missing again! What the hell!? But that tells me it's probably not the cam or bad compression.......so it brings me back to fuel or spark. I'm gonna set it on fire!
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
Or a bad lifter that is collapsing when the oil warms up...
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