460 jumped timing?
Thread Starter
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Mountain Pass
Joined: Nov 2013
Posts: 239
Likes: 7
460 jumped timing?
Hi everyone,
I went to start my 85 F250 today and it is running terribly, the engine starts and barely stays running. If I snap the throttle open at idle in park, it backfires and stalls and the same thing happens if I put it in gear and accelerate. It's been running great for me up to this point, I drive it every day with no issues. It has a newer Holley 4160 600 cfm carburetor on it and an Edelbrock performer intake which I installed about 2 years ago. It has dual electric in tank fuel pumps, both are fairly new. When I switch between the tanks, it runs the same. I am thinking maybe the timing chain is loose and may have jumped a tooth.
I have another good Holley carburetor which I swapped over and I have the same problem, no change in the way it runs. I also replaced the fuel filter today thinking it may help, but it didn't. I checked the engine vacuum at idle with a gauge and it is reading about 14 Hg. When it was running fine before the vacuum reading was 20.
Does this sound like maybe the timing chain jumped?
I went to start my 85 F250 today and it is running terribly, the engine starts and barely stays running. If I snap the throttle open at idle in park, it backfires and stalls and the same thing happens if I put it in gear and accelerate. It's been running great for me up to this point, I drive it every day with no issues. It has a newer Holley 4160 600 cfm carburetor on it and an Edelbrock performer intake which I installed about 2 years ago. It has dual electric in tank fuel pumps, both are fairly new. When I switch between the tanks, it runs the same. I am thinking maybe the timing chain is loose and may have jumped a tooth.
I have another good Holley carburetor which I swapped over and I have the same problem, no change in the way it runs. I also replaced the fuel filter today thinking it may help, but it didn't. I checked the engine vacuum at idle with a gauge and it is reading about 14 Hg. When it was running fine before the vacuum reading was 20.
Does this sound like maybe the timing chain jumped?
Thread Starter
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Mountain Pass
Joined: Nov 2013
Posts: 239
Likes: 7
Thank you for replying, I live in Michigan. I guess I will have to look elsewhere then, maybe there is a vacuum leak somewhere. I did not find any when spraying carb cleaner around the carburetor base or intake gasket area but will keep looking.
Moderator
Joined: Jan 2001
Posts: 56,999
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From: Virginia
I agree, I have never seen them run when the timing chain jumped. Put a rag beside the carb on the pass side and pull the site plugs. If fuel pours out the fuel bowls are overflowing and dumping raw fuel into the engine. You probably have dirt in the fuel system.
Thread Starter
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Mountain Pass
Joined: Nov 2013
Posts: 239
Likes: 7
I just tested the compression and have 120 psi on all eight cylinders. If there was a timing chain problem the compression values would be off right? One more thing I noticed, the new fuel filter I installed is clear plastic and when the engine runs, it only fills the fuel filter canister about half way. Normally when the engine is running, the fuel filter should be full of fuel going through it right?
FTE Legend
Joined: Nov 2015
Posts: 30,941
Likes: 4,126
From: Angier, NC
I asked if raining or say vary damp? It has been raining where I am for almost a week. I know other places also got rain or snow, read damp, and that can cause issues.
You get condensation under hood when you shut down the motor.
If the wires are boarder line good and leak spark, it only takes a little dampness for the spark find its way to ground and have the motor run like crap.
To check if the plug wires are leaking start the motor when it is dark and look at the wires if you see them sparking. Sometimes spraying them with water they will spark.
Don't forget to look under the cap, condensation can build in there also and cause cross fire that can do what you have.
Just something to check now and let us know if you find anything.
Dave ----
You get condensation under hood when you shut down the motor.
If the wires are boarder line good and leak spark, it only takes a little dampness for the spark find its way to ground and have the motor run like crap.
To check if the plug wires are leaking start the motor when it is dark and look at the wires if you see them sparking. Sometimes spraying them with water they will spark.
Don't forget to look under the cap, condensation can build in there also and cause cross fire that can do what you have.
Just something to check now and let us know if you find anything.
Dave ----
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It isn't unusual for a fuel filter to show air in it, not a cause for concern so long as pressure and volume at the carburetor inlet is at spec.
There is a way to check valve timing on a V8. When the #1 cylinder is at TDC compression, #6 cylinder valves will be at overlap, and the opposite is true also.
There is a way to check valve timing on a V8. When the #1 cylinder is at TDC compression, #6 cylinder valves will be at overlap, and the opposite is true also.
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Thread Starter
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Mountain Pass
Joined: Nov 2013
Posts: 239
Likes: 7
I asked if raining or say vary damp? It has been raining where I am for almost a week. I know other places also got rain or snow, read damp, and that can cause issues.
You get condensation under hood when you shut down the motor.
If the wires are boarder line good and leak spark, it only takes a little dampness for the spark find its way to ground and have the motor run like crap.
To check if the plug wires are leaking start the motor when it is dark and look at the wires if you see them sparking. Sometimes spraying them with water they will spark.
Don't forget to look under the cap, condensation can build in there also and cause cross fire that can do what you have.
Just something to check now and let us know if you find anything.
Dave ----
You get condensation under hood when you shut down the motor.
If the wires are boarder line good and leak spark, it only takes a little dampness for the spark find its way to ground and have the motor run like crap.
To check if the plug wires are leaking start the motor when it is dark and look at the wires if you see them sparking. Sometimes spraying them with water they will spark.
Don't forget to look under the cap, condensation can build in there also and cause cross fire that can do what you have.
Just something to check now and let us know if you find anything.
Dave ----
But regarding the compression, if the compression readings are constant on all 8 cylinders then the timing chain shouldn't be a problem right? If it is off on the chain, the compression should be off?
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Joined: Mar 2008
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From: douglasville
I think fuzz face may be on to something with the ignition wires and all you need to do to check them is wait til dark, raise the hood and start the engine. If the wires are leaking spark you will be able to see them sparking in the dark. Another thing to check is the advance mechanism in the distributor which can get stuck in the fully advanced position which will make it run badly at low speed and idle terribly if at all. Had it happen to a 390 back last summer and like to not made it home. Like others i dont think its the timing chain but if you want to check it without disassembling anything all you have to do is pop the distributor cap off and take a rachet and turn the crank in its normal direction a few degrees, then reverse the rachet and see how far you have to turn the crank before the rotor button starts to turn the other way. More than a couple of degrees rotation and you will know that a timing chain and gears will soon be needed and i am sure there is a video somewhere to give you better instructions than i can. Good luck with it.
Thread Starter
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Mountain Pass
Joined: Nov 2013
Posts: 239
Likes: 7
Can someone please help me with the spec for what the fuel pressure should be on the carbureted 460 with dual tanks and hot fuel handling? I measured 4 psi on my pressure gauge going to the carburetor. Is this within range?
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
It is somewhat damp, but here in Michigan it's damp 90 percent of the time. Mostly seems like my engine is extremely lean considering the low engine vacuum reading and backfiring, like it is starved of fuel. Tomorrow I will check the ignition timing and see how that goes.
But regarding the compression, if the compression readings are constant on all 8 cylinders then the timing chain shouldn't be a problem right? If it is off on the chain, the compression should be off?
But regarding the compression, if the compression readings are constant on all 8 cylinders then the timing chain shouldn't be a problem right? If it is off on the chain, the compression should be off?
Compression can be fine if the valve timing is off.
Di you do the ignition timing check .? That will give you the definitive answer if the timing chain has jumped.. I have seen a single tooth on more than one occasion. A single tooth jump can give the symptoms you are seeing.
Thread Starter
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Mountain Pass
Joined: Nov 2013
Posts: 239
Likes: 7
Thank you all for the replies and for helping me out with that info. That clears up a lot of my confusion knowing now that the timing chain can be off and compression can be unaffected. I spent more time yesterday trying to figure out the problem, I started the engine and while it was running poorly I advanced the ignition timing slightly and it ran better. I opened the throttle and it backfired through the carb and stalled. When I tried to restart the truck it would not start, so I took off the distributor cap and noticed the rotor was no longer spinning when turning the engine. I then took out the distributor and saw the pin holding the distributor gear was broken, so when the distributor shaft was spinning sometimes the broken part of the pin would catch and spin the rotor and sometimes it would not. So I put a new pin in the distributor, lined up the timing mark on the harmonic balancer at TDC compression and aligned the distributor to point to the #1 spark plug and have not been able to start the truck since. Today I'll try to stick a straw in the spark plug hole and make sure the #1 piston is at TDC compression and see where the mark is.
Moderator
Joined: Jan 2001
Posts: 56,999
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From: Virginia
Compression can be fine if the valve timing is off.
Di you do the ignition timing check .? That will give you the definitive answer if the timing chain has jumped.. I have seen a single tooth on more than one occasion. A single tooth jump can give the symptoms you are seeing.
Di you do the ignition timing check .? That will give you the definitive answer if the timing chain has jumped.. I have seen a single tooth on more than one occasion. A single tooth jump can give the symptoms you are seeing.
To the original poster; As you are messing with it and turning the engine over, check once in awhile to see if the rotor is still turning. Sheared pins and broken dist teeth are sign the oil pump is locked up.
FTE Legend
Joined: Nov 2015
Posts: 30,941
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From: Angier, NC
Thank you all for the replies and for helping me out with that info. That clears up a lot of my confusion knowing now that the timing chain can be off and compression can be unaffected. I spent more time yesterday trying to figure out the problem, I started the engine and while it was running poorly I advanced the ignition timing slightly and it ran better. I opened the throttle and it backfired through the carb and stalled. When I tried to restart the truck it would not start, so I took off the distributor cap and noticed the rotor was no longer spinning when turning the engine. I then took out the distributor and saw the pin holding the distributor gear was broken, so when the distributor shaft was spinning sometimes the broken part of the pin would catch and spin the rotor and sometimes it would not. So I put a new pin in the distributor, lined up the timing mark on the harmonic balancer at TDC compression and aligned the distributor to point to the #1 spark plug and have not been able to start the truck since. Today I'll try to stick a straw in the spark plug hole and make sure the #1 piston is at TDC compression and see where the mark is.
Once when on TDC compression stroke the other is on the EXH. stroke.
I find it best to pull #1 plug and hold my finger over the hole and bump the starter. A remote starter button work great for this.
When your finger gets pushed off the hole check the timing mark if on TDC and go from there.
Now why did the dist. gear pin break is the real question?
Dave ----