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

 

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.

 

When I accelerate or find myself in any load condition it starts to miss. I haven't changed the Condensor. Sounds like some cheap troubleshooting. Yes I am using Points. Thanks for the Troubleshooting Tips. I will post tomorrow when I have more info..

 

Look that up on the forum, folks have a lot of trouble with cheap import condensers. I would just put a Pertronix kit in, but I understand if you want to keep it original with points.

 

Original is not an Issue. I think I am going to give the Pertronix a Try. Thanks.

 

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.

 

JEFFFAFA, Thanks for this information. I had no Idea you could use a Vacuum Guage to troubleshoot like this... I will get to doing some shooting and see what I come up with. Thanks Again...

 

You're welcome. Just don't forget to post your results and findings.

 

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.

 

Read the instructions for the coil. It should specify to mount it vertically. We've had another member in the past few months catch fire and now he's been catching hell from the Ole truck.

 

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.

 

I know only the after market coils like MSD Blaster ll oil filled should not be mounted Horizontally that over heat an can short out and can cause a fire if the oil gets on the exhaust manifold/pipe.

Also Accel big yellow oil filled coil has a o-ring top that can leak if mounted up side down.
Orich

 

sorry double post

 

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"?

 

I kept the RPM constant at a higher RPM. It held steady for probably 5 sec and then dropped to 16 and stayed there. May not have even been 5 seconds. I will do the Wet Test and see what happens. Sure hope its not the Rings. The only reason I said it was probably a Leaky Valve was because it was the indication of the Vacuum test sheet that was Provided. Guess I should set up my Vacuum Guage when I time it today and see if maybe the timing is off a bit. Thing is with all the other Cylinders being so Consistant it seems like it has to be a problem in #6 Cylinder.