351 mystery
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4wd Low
Joined: Oct 2025
Posts: 10
Likes: 3
351 mystery
I have an ‘84 that is driving me insane, the truck sat for 2 years ran fine before was a daily driver. Now it will not idle at all. Iv gone through the fuel system new sending unit , old one was shot and I fixed all hoses and new fuel pump. I have changed intake gaskets twice to to rule out leaks. I have a edelbrock 1406 and Holley 1850 both no idle. Its duraspark 2 system was converted before all this back when it ran. Iv checked , double checked and triple checked timing. 10 degrees up to 14 degrees. Itll start and if I rev it up it stays running as soon as I let go of the throttle it falls flat on its face. I’m running out of ideas I may have forgot something else that Iv tried but any suggestions would be great.
Lead Driver
Joined: Nov 2013
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One possibility is the timing marks may not be accurate. On the crankshaft pulley, the outer sleeve (with timing marks) may have slipped relative to the core. Checking the accuracy is easy.
Remove the spark plugs to make the engine easy to turn with a socket and breaker bar at the pulley. Bring #1 piston to Top Dead Center (TDC). Use something semi-rigid like a soda straw or piece of wire through the spark plug hole to determine the position of the piston. Do NOT use anything that could snap off, such as a screwdriver. I do not care to discuss how I learned this.
With #1 at TDC, look at the timing marks and make sure they show 0. If not, you will need to replace the vibration damper, or have your existing one rebuilt.
FTE Legend
Joined: Nov 2015
Posts: 30,992
Likes: 4,140
From: Angier, NC
Ok after doing the timing mark check lets check some other things.
I take it the gas is fresh being you replaced the sending unit in the tank, was the fuel pump in take too?
Sitting 2 years maybe fluffy got to the plug wires? Still running the same plugs, cap & rotor?
What is the compression like, give us some numbers. Maybe a stuck valve?
When you say falls on it's face I take it as stalls.
What if you turn up the idle speed to keep it running as slow as it can and pull 1 plug wire off at a time what happens?
If no change that hole is not doing it's share of the work.
If you did not want to pull 1 wire at a time get the exhaust manifolds wet and start the motor and let it run for a vary short time.
Holes that are firing should evap the water off the manifold and give a clue where to look for issues.
Dave ----
ps I have had new looking plugs in a motor that only ran to move the car around every few months / year and 1 time it would back fire out the tail pipe when giving it throttle.
Wter trick found the bad hole, new set of plugs and it ran like new.
So dont say "they looked good, measure or swap with known good parts and new parts may not be good.
I take it the gas is fresh being you replaced the sending unit in the tank, was the fuel pump in take too?
Sitting 2 years maybe fluffy got to the plug wires? Still running the same plugs, cap & rotor?
What is the compression like, give us some numbers. Maybe a stuck valve?
When you say falls on it's face I take it as stalls.
What if you turn up the idle speed to keep it running as slow as it can and pull 1 plug wire off at a time what happens?
If no change that hole is not doing it's share of the work.
If you did not want to pull 1 wire at a time get the exhaust manifolds wet and start the motor and let it run for a vary short time.
Holes that are firing should evap the water off the manifold and give a clue where to look for issues.
Dave ----
ps I have had new looking plugs in a motor that only ran to move the car around every few months / year and 1 time it would back fire out the tail pipe when giving it throttle.
Wter trick found the bad hole, new set of plugs and it ran like new.
So dont say "they looked good, measure or swap with known good parts and new parts may not be good.
Thread Starter
|
4wd Low
Joined: Oct 2025
Posts: 10
Likes: 3
Ok after doing the timing mark check lets check some other things.
I take it the gas is fresh being you replaced the sending unit in the tank, was the fuel pump in take too?
Sitting 2 years maybe fluffy got to the plug wires? Still running the same plugs, cap & rotor?
What is the compression like, give us some numbers. Maybe a stuck valve?
When you say falls on it's face I take it as stalls.
What if you turn up the idle speed to keep it running as slow as it can and pull 1 plug wire off at a time what happens?
If no change that hole is not doing it's share of the work.
If you did not want to pull 1 wire at a time get the exhaust manifolds wet and start the motor and let it run for a vary short time.
Holes that are firing should evap the water off the manifold and give a clue where to look for issues.
Dave ----
ps I have had new looking plugs in a motor that only ran to move the car around every few months / year and 1 time it would back fire out the tail pipe when giving it throttle.
Wter trick found the bad hole, new set of plugs and it ran like new.
So dont say "they looked good, measure or swap with known good parts and new parts may not be good.
I take it the gas is fresh being you replaced the sending unit in the tank, was the fuel pump in take too?
Sitting 2 years maybe fluffy got to the plug wires? Still running the same plugs, cap & rotor?
What is the compression like, give us some numbers. Maybe a stuck valve?
When you say falls on it's face I take it as stalls.
What if you turn up the idle speed to keep it running as slow as it can and pull 1 plug wire off at a time what happens?
If no change that hole is not doing it's share of the work.
If you did not want to pull 1 wire at a time get the exhaust manifolds wet and start the motor and let it run for a vary short time.
Holes that are firing should evap the water off the manifold and give a clue where to look for issues.
Dave ----
ps I have had new looking plugs in a motor that only ran to move the car around every few months / year and 1 time it would back fire out the tail pipe when giving it throttle.
Wter trick found the bad hole, new set of plugs and it ran like new.
So dont say "they looked good, measure or swap with known good parts and new parts may not be good.
I didn’t get time to get out there today but compression I did not long ago 160-180, I’ll double check to make sure the timing marks didn’t spin. Cap and rotor look good plug wires aren’t chewed up. There wasn’t much gas in the tank so I put fresh gas in about 15 gallons. Fuel pump is still the stock mechanical pump. If I turn the idle screw once it gets very high pretty much at 1500-2000 it’ll run. I replaced the plugs not long ago when I was trying to get it to go a couple months ago, now after trying for so long they’re obviously black. Will report back once I try to spray the manifold.
FTE Legend
Joined: Nov 2015
Posts: 30,992
Likes: 4,140
From: Angier, NC
I am thinking the carb needs to be pulled apart and given a good cleaning if it ran before it was laid up for 2 years.
Old gas dries up and plugs ports for the idle side and why it will not idle but if the RPM is up to 1500+ it is no longer on the idle side of the carb.
Dave ----
Old gas dries up and plugs ports for the idle side and why it will not idle but if the RPM is up to 1500+ it is no longer on the idle side of the carb.
Dave ----
Thread Starter
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4wd Low
Joined: Oct 2025
Posts: 10
Likes: 3
I am thinking the carb needs to be pulled apart and given a good cleaning if it ran before it was laid up for 2 years.
Old gas dries up and plugs ports for the idle side and why it will not idle but if the RPM is up to 1500+ it is no longer on the idle side of the carb.
Dave ----
Old gas dries up and plugs ports for the idle side and why it will not idle but if the RPM is up to 1500+ it is no longer on the idle side of the carb.
Dave ----
FTE Legend
Joined: Nov 2015
Posts: 30,992
Likes: 4,140
From: Angier, NC
I can try cleaning it again , Iv swapped between the edelbrock and Holley , unless both are still clogged , but I was also back tracking to stuff Iv put on it in the past I remember putting a new ignition module on it for no spark , and if I remember correctly that’s when no idle started ? Maybe? Have you ever heard of a module causing no idle but will run off with throttle ?
Is this the one in the distributor or on the inner fender?
But they both have been known to cause issues.
Dave ----
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4wd Low
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FTE Legend
Joined: Nov 2015
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From: Angier, NC
You said you did change it for a no spark was it a cheap one or top of the line and you have to ask for top of the line ones.
If you have a junk yard close by maybe pick up a used one for testing. At least it is easy to change out anad you dont even need to bolt it down for testing just unplug and plug in the new one.
Dave ----
If you have a junk yard close by maybe pick up a used one for testing. At least it is easy to change out anad you dont even need to bolt it down for testing just unplug and plug in the new one.
Dave ----
Thread Starter
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4wd Low
Joined: Oct 2025
Posts: 10
Likes: 3
You said you did change it for a no spark was it a cheap one or top of the line and you have to ask for top of the line ones.
If you have a junk yard close by maybe pick up a used one for testing. At least it is easy to change out anad you dont even need to bolt it down for testing just unplug and plug in the new one.
Dave ----
If you have a junk yard close by maybe pick up a used one for testing. At least it is easy to change out anad you dont even need to bolt it down for testing just unplug and plug in the new one.
Dave ----
Lead Driver
Joined: Nov 2013
Posts: 7,187
Likes: 1,179
Did somebody say slow turning starter?!!!
Oh, never mind. It’s probably just from the battery getting run down. Be sure to charge that poor battery before going any further.
Just in case the problem persists after charging the battery, you can always put out the call for Voltage Drop Man, everybody’s favorite super hero:
https://www.ford-trucks.com/forums/1...w-starter.html
Oh, never mind. It’s probably just from the battery getting run down. Be sure to charge that poor battery before going any further.
Just in case the problem persists after charging the battery, you can always put out the call for Voltage Drop Man, everybody’s favorite super hero:
https://www.ford-trucks.com/forums/1...w-starter.html
FTE Legend
Joined: Nov 2015
Posts: 30,992
Likes: 4,140
From: Angier, NC
So the battery had enough power to crank and start the truck and idle but bring the RPM up it would cut in & out?
I find that a little hard to believe. I had a points truck we would jump start to do road calls and not shut off and on the way back to the shop would start loosing power and start missing as the generator could not put out enough power for the coil and the rotating lights up top.
If you put a new / good / more power battery in check that it is charging.
Dave ----
I find that a little hard to believe. I had a points truck we would jump start to do road calls and not shut off and on the way back to the shop would start loosing power and start missing as the generator could not put out enough power for the coil and the rotating lights up top.
If you put a new / good / more power battery in check that it is charging.
Dave ----