Missing while Under Load or Accelerating
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Missing while Under Load or Accelerating
So today I got Hooptie from the Alignment shop and it drives so much better. The Engine seems to be missing under load but runs absolutely flawless while in Park. It feels like what I would think of as a burnt valve or something like that. Once you get it up to speed it is smooth as silk but when accelerating it sounds and feels like its missing. Has anyone had a similar issue with your Truck and if you did how did you fix it? Okay so list of things I have done. Set the Timing, Replaced the cap and rotor, Replaced the Wires, Replaced the Spark Plugs, Replaced the Carb and I think the only component I haven't changed is the Coil. I think I need to do a Compression Test and maybe a bleed down test to see if maybe I have a bad valve or something, but I sure don't hear it in the Exhaust.
Thanks For any Help!!!
JRB64
Thanks For any Help!!!
JRB64
Cargo Master
Joined: Sep 2012
Posts: 3,064
Likes: 39
From: Laramie, WY
Well...you've replaced most of the ignition system and your symptoms are very indicative of an ignition problem. Running smooth at little or no load, then missing under load. Is the miss random of very cyclic? Are you using points? If so the condenser gives a lot of trouble.
Try having someone power brake the engine while you watch under the hood after dark. You are looking for small sparking events showing where the ignition might be shorting to ground. Stand off to one side, not in front, in case the truck lurches forward.
Next, or first, in the day light do the same thing while looking down the throat of the carb. You need to wear safety glasses and you are looking to see if the fuel comes out in droplets when the engine starts running rough under a load. You shouldn't ever be able to see the fuel going into the engine during a steady throttle position. The only time you should see liquid fuel is when the throttle is moving and it is coming from the accelerator pump.
During all of this you can connect a vacuum gauge to the intake to watch for valve train problems. The needle should always be steady, unless you have a monster cam. If the needle flutters it is showing that an intake valve is allowing combustion pressure back up into the intake manifold.
Try having someone power brake the engine while you watch under the hood after dark. You are looking for small sparking events showing where the ignition might be shorting to ground. Stand off to one side, not in front, in case the truck lurches forward.
Next, or first, in the day light do the same thing while looking down the throat of the carb. You need to wear safety glasses and you are looking to see if the fuel comes out in droplets when the engine starts running rough under a load. You shouldn't ever be able to see the fuel going into the engine during a steady throttle position. The only time you should see liquid fuel is when the throttle is moving and it is coming from the accelerator pump.
During all of this you can connect a vacuum gauge to the intake to watch for valve train problems. The needle should always be steady, unless you have a monster cam. If the needle flutters it is showing that an intake valve is allowing combustion pressure back up into the intake manifold.
Thread Starter
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Senior User
Joined: Jul 2017
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Well...you've replaced most of the ignition system and your symptoms are very indicative of an ignition problem. Running smooth at little or no load, then missing under load. Is the miss random of very cyclic? Are you using points? If so the condenser gives a lot of trouble.
Try having someone power brake the engine while you watch under the hood after dark. You are looking for small sparking events showing where the ignition might be shorting to ground. Stand off to one side, not in front, in case the truck lurches forward.
Next, or first, in the day light do the same thing while looking down the throat of the carb. You need to wear safety glasses and you are looking to see if the fuel comes out in droplets when the engine starts running rough under a load. You shouldn't ever be able to see the fuel going into the engine during a steady throttle position. The only time you should see liquid fuel is when the throttle is moving and it is coming from the accelerator pump.
During all of this you can connect a vacuum gauge to the intake to watch for valve train problems. The needle should always be steady, unless you have a monster cam. If the needle flutters it is showing that an intake valve is allowing combustion pressure back up into the intake manifold.
Try having someone power brake the engine while you watch under the hood after dark. You are looking for small sparking events showing where the ignition might be shorting to ground. Stand off to one side, not in front, in case the truck lurches forward.
Next, or first, in the day light do the same thing while looking down the throat of the carb. You need to wear safety glasses and you are looking to see if the fuel comes out in droplets when the engine starts running rough under a load. You shouldn't ever be able to see the fuel going into the engine during a steady throttle position. The only time you should see liquid fuel is when the throttle is moving and it is coming from the accelerator pump.
During all of this you can connect a vacuum gauge to the intake to watch for valve train problems. The needle should always be steady, unless you have a monster cam. If the needle flutters it is showing that an intake valve is allowing combustion pressure back up into the intake manifold.
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Original is not an Issue. I think I am going to give the Pertronix a Try. Thanks.
Hotshot
Joined: Mar 2013
Posts: 14,255
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From: Phoenix, Az.
A weak spark can show up when an engine is under load.
Put a mechanic's vacuum gauge on it. That can tell you a lot.
I would give it a full tune up. check the vacuum advance to be hooked up and it's rubber diaphragm not ruptured. While the plugs are out do a wet and dry compression test. Warm engine while doing the compression test.
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A weak spark can show up when an engine is under load.
Put a mechanic's vacuum gauge on it. That can tell you a lot.
I would give it a full tune up. check the vacuum advance to be hooked up and it's rubber diaphragm not ruptured. While the plugs are out do a wet and dry compression test. Warm engine while doing the compression test.
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1. 145
2. 145
3. 142
4. 140
5. 145
6. 120
7. 140
8. 145
When I did the vacuum test it held steady at 18 and soon after fell to 16 and stayed there. So I'm Guessing the problem is in Cylinder number 6. How do you check to see if the valves are adjusted properly on these FE Motors? I am going to take the valve cover off tomorrow and do a physical inspection to see if there is anything obvious going on here. I did put a set of Pertronix 1281 Electronic ignition sensor in and it starts really nice. I also put in a Pertronix flame thrower Coil just because I hadn't replaced it and it was the only thing left not new in the Ignition System. Do you concur with my Troubleshooting? I did a Dry Pressure test so that is probably why my numbers are lower than they should be. I was looking for consistency more than anything.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
When did horizontal coil mounting become a thing? Lots of OEM did this for years and years. Heat may be an issue, but have used a Flamethrower coil on a Y block for years with no problem. Pertronix instructions doesn't say anything about horizontal being an issue afaik. Link?
Have read that when an oil filled coil is mounted horizontally it should be set with the terminals at the 6 and 9 o'clock position. The most important thing is to use a good quality unit.
Have read that when an oil filled coil is mounted horizontally it should be set with the terminals at the 6 and 9 o'clock position. The most important thing is to use a good quality unit.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
When did horizontal coil mounting become a thing? Lots of OEM did this for years and years. Heat may be an issue, but have used a Flamethrower coil on a Y block for years with no problem. Pertronix instructions doesn't say anything about horizontal being an issue afaik. Link?
Have read that when an oil filled coil is mounted horizontally it should be set with the terminals at the 6 and 9 o'clock position. The most important thing is to use a good quality unit.
Have read that when an oil filled coil is mounted horizontally it should be set with the terminals at the 6 and 9 o'clock position. The most important thing is to use a good quality unit.
Also Accel big yellow oil filled coil has a o-ring top that can leak if mounted up side down.
Orich
Cargo Master
Joined: Sep 2012
Posts: 3,064
Likes: 39
From: Laramie, WY
So if I had to guess I would say I have a Leaky Valve on number 6. I did a Pressure Test and I got
1. 145
2. 145
3. 142
4. 140
5. 145
6. 120
7. 140
8. 145
When I did the vacuum test it held steady at 18 and soon after fell to 16 and stayed there. So I'm Guessing the problem is in Cylinder number 6. How do you check to see if the valves are adjusted properly on these FE Motors? I am going to take the valve cover off tomorrow and do a physical inspection to see if there is anything obvious going on here. I did put a set of Pertronix 1281 Electronic ignition sensor in and it starts really nice. I also put in a Pertronix flame thrower Coil just because I hadn't replaced it and it was the only thing left not new in the Ignition System. Do you concur with my Troubleshooting? I did a Dry Pressure test so that is probably why my numbers are lower than they should be. I was looking for consistency more than anything.
1. 145
2. 145
3. 142
4. 140
5. 145
6. 120
7. 140
8. 145
When I did the vacuum test it held steady at 18 and soon after fell to 16 and stayed there. So I'm Guessing the problem is in Cylinder number 6. How do you check to see if the valves are adjusted properly on these FE Motors? I am going to take the valve cover off tomorrow and do a physical inspection to see if there is anything obvious going on here. I did put a set of Pertronix 1281 Electronic ignition sensor in and it starts really nice. I also put in a Pertronix flame thrower Coil just because I hadn't replaced it and it was the only thing left not new in the Ignition System. Do you concur with my Troubleshooting? I did a Dry Pressure test so that is probably why my numbers are lower than they should be. I was looking for consistency more than anything.
Those numbers look high enough for a dry test. You now do the wet test, just a couple squirts of oil into the cylinder. That will tell you if the low #6 is due to the rings or the valves. If the reading dramatically increases wet, the rings are bad. If it stays about the same the valves are bad.
The vacuum reading being steady isn't indicating a valve sealing problem. But it takes a pretty bad valve to make it flutter as much as is shown in that diagram. You can change the amount of intake vacuum by changing the ignition timing or the rpm. Was the initial 18" at a faster rpm than the later 16"?
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Those numbers look high enough for a dry test. You now do the wet test, just a couple squirts of oil into the cylinder. That will tell you if the low #6 is due to the rings or the valves. If the reading dramatically increases wet, the rings are bad. If it stays about the same the valves are bad.
The vacuum reading being steady isn't indicating a valve sealing problem. But it takes a pretty bad valve to make it flutter as much as is shown in that diagram. You can change the amount of intake vacuum by changing the ignition timing or the rpm. Was the initial 18" at a faster rpm than the later 16"?
The vacuum reading being steady isn't indicating a valve sealing problem. But it takes a pretty bad valve to make it flutter as much as is shown in that diagram. You can change the amount of intake vacuum by changing the ignition timing or the rpm. Was the initial 18" at a faster rpm than the later 16"?