Video: 1978 intermittent runs rough
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Joined: Jun 2015
Posts: 50
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Video: 1978 intermittent runs rough
I put together a video of my 1978 behaving badly.
At cold idle, the car seems to run well. A slight feeling of a "miss" here and there but generally, pretty well.
As the engine begins to heat up, it will begin to intermittently start running rough. Originally it felt like a cylinder missing to me, however I'm noticing the whole engine will start to dog in general: runs smooth, kicks down and starts running rough, clicks back in runs smooth.
When it's been at operating temperature for a good 10-15 minutes, it will continuously run rough, and will barely come back to run smooth. I've replaced a lot of the standard culprits, so I'm sort of at a loss and would appreciate any insight? I'm hesitant to take it to a shop where they start replacing stuff as a shot in the dark without a good diagnosis. Thanks very much for any help.
Work that's been done over the last 6 months:
Plugs and Wires, AC Delco / premium wires routed correctly through mounts and heat shields
Distributor Cap and Rotor
Ignition Control Module
Distributor Coil
Distributor vacuum advance still holds vacuum
Complete Carburetor Rebuild including accel pump, fuel filter etc.
Valve Cover Gaskets
Fuel Pump and flex lines
Water Pump
Vacuum hoses generally checked and replaced where faulty
Alternator looks like relatively new replace by previous owner
Battery
At cold idle, the car seems to run well. A slight feeling of a "miss" here and there but generally, pretty well.
As the engine begins to heat up, it will begin to intermittently start running rough. Originally it felt like a cylinder missing to me, however I'm noticing the whole engine will start to dog in general: runs smooth, kicks down and starts running rough, clicks back in runs smooth.
When it's been at operating temperature for a good 10-15 minutes, it will continuously run rough, and will barely come back to run smooth. I've replaced a lot of the standard culprits, so I'm sort of at a loss and would appreciate any insight? I'm hesitant to take it to a shop where they start replacing stuff as a shot in the dark without a good diagnosis. Thanks very much for any help.
Work that's been done over the last 6 months:
Plugs and Wires, AC Delco / premium wires routed correctly through mounts and heat shields
Distributor Cap and Rotor
Ignition Control Module
Distributor Coil
Distributor vacuum advance still holds vacuum
Complete Carburetor Rebuild including accel pump, fuel filter etc.
Valve Cover Gaskets
Fuel Pump and flex lines
Water Pump
Vacuum hoses generally checked and replaced where faulty
Alternator looks like relatively new replace by previous owner
Battery
Last edited by 1978BackToLife; Sep 6, 2016 at 07:51 PM.
Burning Brakes
Joined: Oct 2015
Posts: 781
Likes: 113
I put together a video of my 1978 behaving badly.
https://youtu.be/fQ-ZGkyS73I
At cold idle, the car seems to run well. A slight feeling of a "miss" here and there but generally, pretty well.
As the engine begins to heat up, it will begin to intermittently start running rough. Originally it felt like a cylinder missing to me, however I'm noticing the whole engine will start to dog in general: runs smooth, kicks down and starts running rough, clicks back in runs smooth.
When it's been at operating temperature for a good 10-15 minutes, it will continuously run rough, and will barely come back to run smooth. I've replaced a lot of the standard culprits, so I'm sort of at a loss and would appreciate any insight? I'm hesitant to take it to a shop where they start replacing stuff as a shot in the dark without a good diagnosis. Thanks very much for any help.
Work that's been done over the last 6 months:
Plugs and Wires, AC Delco / premium wires routed correctly through mounts and heat shields
Distributor Cap and Rotor
Ignition Control Module
Distributor Coil
Distributor vacuum advance still holds vacuum
Complete Carburetor Rebuild including accel pump, fuel filter etc.
Valve Cover Gaskets
Fuel Pump and flex lines
Water Pump
Vacuum hoses generally checked and replaced where faulty
Alternator looks like relatively new replace by previous owner
Battery
https://youtu.be/fQ-ZGkyS73I
At cold idle, the car seems to run well. A slight feeling of a "miss" here and there but generally, pretty well.
As the engine begins to heat up, it will begin to intermittently start running rough. Originally it felt like a cylinder missing to me, however I'm noticing the whole engine will start to dog in general: runs smooth, kicks down and starts running rough, clicks back in runs smooth.
When it's been at operating temperature for a good 10-15 minutes, it will continuously run rough, and will barely come back to run smooth. I've replaced a lot of the standard culprits, so I'm sort of at a loss and would appreciate any insight? I'm hesitant to take it to a shop where they start replacing stuff as a shot in the dark without a good diagnosis. Thanks very much for any help.
Work that's been done over the last 6 months:
Plugs and Wires, AC Delco / premium wires routed correctly through mounts and heat shields
Distributor Cap and Rotor
Ignition Control Module
Distributor Coil
Distributor vacuum advance still holds vacuum
Complete Carburetor Rebuild including accel pump, fuel filter etc.
Valve Cover Gaskets
Fuel Pump and flex lines
Water Pump
Vacuum hoses generally checked and replaced where faulty
Alternator looks like relatively new replace by previous owner
Battery
Racer
Joined: Jun 2016
Posts: 336
Likes: 29
From: Il.
It sounds like when the engine is hot you have a bad lifter or maybe a broken rocker arm,could be a bent pushrod.If you still have an EGR valve and a air cleaner valve one or both could have a leak when the engine gets up to temp.Unplug one vac line at a time with the engine at temp and see if they are holding vac also pull one valve cover off than the other and check to see were that ticking noise is coming from.
Last edited by sparky77; Sep 7, 2016 at 07:01 PM.
Racer
Joined: Jan 2013
Posts: 300
Likes: 10
I put together a video of my 1978 behaving badly.
https://youtu.be/fQ-ZGkyS73I
At cold idle, the car seems to run well. A slight feeling of a "miss" here and there but generally, pretty well.
As the engine begins to heat up, it will begin to intermittently start running rough. Originally it felt like a cylinder missing to me, however I'm noticing the whole engine will start to dog in general: runs smooth, kicks down and starts running rough, clicks back in runs smooth.
When it's been at operating temperature for a good 10-15 minutes, it will continuously run rough, and will barely come back to run smooth. I've replaced a lot of the standard culprits, so I'm sort of at a loss and would appreciate any insight? I'm hesitant to take it to a shop where they start replacing stuff as a shot in the dark without a good diagnosis. Thanks very much for any help.
Work that's been done over the last 6 months:
Plugs and Wires, AC Delco / premium wires routed correctly through mounts and heat shields
Distributor Cap and Rotor
Ignition Control Module
Distributor Coil
Distributor vacuum advance still holds vacuum
Complete Carburetor Rebuild including accel pump, fuel filter etc.
Valve Cover Gaskets
Fuel Pump and flex lines
Water Pump
Vacuum hoses generally checked and replaced where faulty
Alternator looks like relatively new replace by previous owner
Battery
https://youtu.be/fQ-ZGkyS73I
At cold idle, the car seems to run well. A slight feeling of a "miss" here and there but generally, pretty well.
As the engine begins to heat up, it will begin to intermittently start running rough. Originally it felt like a cylinder missing to me, however I'm noticing the whole engine will start to dog in general: runs smooth, kicks down and starts running rough, clicks back in runs smooth.
When it's been at operating temperature for a good 10-15 minutes, it will continuously run rough, and will barely come back to run smooth. I've replaced a lot of the standard culprits, so I'm sort of at a loss and would appreciate any insight? I'm hesitant to take it to a shop where they start replacing stuff as a shot in the dark without a good diagnosis. Thanks very much for any help.
Work that's been done over the last 6 months:
Plugs and Wires, AC Delco / premium wires routed correctly through mounts and heat shields
Distributor Cap and Rotor
Ignition Control Module
Distributor Coil
Distributor vacuum advance still holds vacuum
Complete Carburetor Rebuild including accel pump, fuel filter etc.
Valve Cover Gaskets
Fuel Pump and flex lines
Water Pump
Vacuum hoses generally checked and replaced where faulty
Alternator looks like relatively new replace by previous owner
Battery
Racer
Joined: Apr 2008
Posts: 406
Likes: 46
From: Lebanon OH
I agree with Sparky about the EGR valve. The EGR valve is tied to the vacuum source through a thermal switch. When the engine is cold, the vacuum thermal switch blocks the signal to the EGR valve. As the engine heats up, the valve opens and activates the EGR. One symptom of a failing EGR is rough idle and misfire.
I would think if your problem was caused by a bad valve train component, you would hear it more when the engine is cold and the rough idle would be there regardless of temperature. Good luck, idle problems can be a bitch to find.
Maj D
I would think if your problem was caused by a bad valve train component, you would hear it more when the engine is cold and the rough idle would be there regardless of temperature. Good luck, idle problems can be a bitch to find.
Maj D
Melting Slicks
Joined: Jul 2006
Posts: 2,291
Likes: 493
From: Salmon Arm, BC
I had this same problem on a Monza I once owned.
Closed the plug gaps some and it idled nice and smooth.
I suggest closing the plug gaps to .040" and try that.....
Have you done a compression check with engine both hot and cold to see if the engine is in good health?
Closed the plug gaps some and it idled nice and smooth.
I suggest closing the plug gaps to .040" and try that.....
Have you done a compression check with engine both hot and cold to see if the engine is in good health?
Last edited by OMF; Sep 8, 2016 at 12:45 PM.
Drifting
Joined: Jul 1999
Posts: 1,542
Likes: 43
From: Plano TX
Common HEI failure mode of running good when cold and then rough like starving for fuel once hot. Pop the cap and rotor and you'll see what looks like rust on the advance mechanism from a bad rotor allowing sparks to hit the module and over time causing it to fail. Replaced rotor and modules in several cars over the years for this exact issue.
if you had electronics coolant spray you could hit the module after its hot and it would then run good until it warms back up.
if you had electronics coolant spray you could hit the module after its hot and it would then run good until it warms back up.
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Instructor
Joined: Aug 2016
Posts: 235
Likes: 28
From: Fort McMurray Alberta
I 3rd the EGR. Sounds like the engine definitely has lifter noise but that's not going to cause you "intermittent". However it certainly needs some attention.
I can just imagine the carbon build up on the EGR pintle though ! As suggested above, remove the hose and plug it. Give the EGR a few little taps on the side with a small hammer and let us know.
I can just imagine the carbon build up on the EGR pintle though ! As suggested above, remove the hose and plug it. Give the EGR a few little taps on the side with a small hammer and let us know.