460 idles low and has misfire

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460 idles low and has misfire

Post  coldsteel86 on May 18th 2015, 7:09 pm

I got a 86 F-250 with the 460 in it.
About 6 years ago i replaced the timing chain in it to ford racing double roller, threw in a lunati voodoo cam,lifters and new valve springs.
Since then i have put about 30,000 miles on it,truck has 150,000 total.

Motor has ran fine ever since no major issues. The other day i was driving home from work and wound it up to about 4,500 rpm and held it for about 1/2 mile going down the interstate. When i got off at the exit and stopped at the red light the motor started idling really low like 200 rpm would barely run, it also has a slight miss at idle and revved up.
Oil pressure is good,fuel pressure is good,timing is good, i pulled the valve covers and took the pushrods out cause i thought maybe one was bent but they are straight. Rocker arms are good.

Any thoughts????

Thanks in advance.
-Daniel

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Re: 460 idles low and has misfire

Post  69F100 on May 18th 2015, 8:45 pm

coldsteel86 wrote:I got a 86 F-250 with the 460 in it.
About 6 years ago i replaced the timing chain in it to ford racing double roller, threw in a lunati voodoo cam,lifters and new valve springs.
Since then i have put about 30,000 miles on it,truck has 150,000 total.

Motor has ran fine ever since no major issues. The other day i was driving home from work and wound it up to about 4,500 rpm and held it for about 1/2 mile going down the interstate. When i got off at the exit and stopped at the red light the motor started idling really low like 200 rpm would barely run, it also has a slight miss at idle and revved up.
Oil pressure is good,fuel pressure is good,timing is good, i pulled the valve covers and took the pushrods out cause i thought maybe one was bent but they are straight. Rocker arms are good.

Any thoughts????

Thanks in advance.
-Daniel


Have you checked the wires and plugs might be loosing fire
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Re: 460 idles low and has misfire

Post  Mark Miller on May 19th 2015, 1:26 am

coldsteel86 wrote:I got a 86 F-250 with the 460 in it.
About 6 years ago i replaced the timing chain in it to ford racing double roller, threw in a lunati voodoo cam,lifters and new valve springs.
Since then i have put about 30,000 miles on it,truck has 150,000 total.

Motor has ran fine ever since no major issues. The other day i was driving home from work and wound it up to about 4,500 rpm and held it for about 1/2 mile going down the interstate. When i got off at the exit and stopped at the red light the motor started idling really low like 200 rpm would barely run, it also has a slight miss at idle and revved up.
Oil pressure is good,fuel pressure is good,timing is good, i pulled the valve covers and took the pushrods out cause i thought maybe one was bent but they are straight. Rocker arms are good.

Any thoughts????

Thanks in advance.
-Daniel

Does it have a carb or fuel injected,if carb could have fuel dripping out of the boosters or shooters if it's a holley carb?

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Re: 460 idles low and has misfire

Post  coldsteel86 on May 19th 2015, 10:01 am

Its carburetor edelbrock 750

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Re: 460 idles low and has misfire

Post  maverick on May 19th 2015, 8:03 pm

Run a compression check. That'll verify or rule out mechanical issues like bent, sticking or burned valves, bent pushrods, windowed pistons, blown head gaskets, etc...all the expensive stuff.Razz If compression checks out ok, move on to electrical and fuel systems. If compression check does NOT check out ok....well, you know. Rolling Eyes
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Re: 460 idles low and has misfire

Post  coldsteel86 on May 19th 2015, 8:14 pm

I did a compression check on it and all cylinders were about dead even on psi except for the front cylinder on the drivers side of the engine. It was about 10 pounds lower than the others.

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Re: 460 idles low and has misfire

Post  maverick on May 19th 2015, 8:33 pm

Ignition timing still where it should be?
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Re: 460 idles low and has misfire

Post  coldsteel86 on May 19th 2015, 8:36 pm

Yup

One thing i want to mention is the distributor is really old like the factory one, is there a chance something in it could if went bad to cause this???

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Re: 460 idles low and has misfire

Post  FalconEh on May 19th 2015, 9:02 pm

Is it a constant or an erratic miss ? A constant miss is more likely to be a mechanical (failed lifter, stuck valve, broken spring...or worse) or an electrical (failed plug, bad cap terminal) , the erratic is more likely the fuel system, improperly adjusted or stuck float etc. or electrical (cross firing) Check grounds too. Usually it is the pickup that fails in the factory dist. but that does not sound like your problem.
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Re: 460 idles low and has misfire

Post  coldsteel86 on May 19th 2015, 9:16 pm

Its a constant miss that keeps pace with engine rpm, misses at idle and throughout the rpm range

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Re: 460 idles low and has misfire

Post  bbf-falcon on May 19th 2015, 9:41 pm

When you pull the wires off while running,Which cylinder makes the most drop in sound/rpm?

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Re: 460 idles low and has misfire

Post  coldsteel86 on May 19th 2015, 9:43 pm

I will check it asap been busy doing other stuff.
Thanks for everyones advice!

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