1981 Ford 400, Need Help

chukarhunt · 04-18-2008, 11:30 AM

Hi. I have a 1981 Ford F-150 with the 6.6L 400 engine. The rebuilt engine has possibly 30,000 miles on it. It runs really bad. It is a very rough idle, when it is cold it has no power, it knocks and pings very bad while driving down the road when you hit the throttle, and when I sit in park and rev the engine really high it stutters badly. I have ideas to what could be wrong. This is what I believe I need to do:

-GM Top Engine Cleaner
-Ignition Coil
-tune up distributor
-plugs and wires
-clean carbeurator

Does anyone know exaclty what is wrong with this engine, or know of anything else I could do to help it? Thanks for the help.

jonmark1985 · 04-18-2008, 12:29 PM

First thing I'd do is verify the firing order is right, and set the timing with a light.

chukarhunt · 04-20-2008, 08:51 PM

I just used the GM Top End Cleaner and it helped a lot. It does still run rough, but I can tell a difference. I have been messing with the timing for a long time, and I have it advanced quite a bit. It runs better that way. I will check the firing order again. I am pretty sure it is right. Thank you.

jonmark1985 · 04-21-2008, 05:20 AM

Are you using ported or vaccuum advance? Are you unplugging your distributor's vaccuum advance when you're setting the timing?

chukarhunt · 04-21-2008, 09:34 PM

It is vacuum advance. I do pull the vacuum when I change the timing. Is it possible that it is the ignition coil? Most of the parts are original. I also noticed on the rotor that there is wear in the middle of the tip and wear on the side of the tip. I figure the middle wear is normal, but how about the wear on the side? Thanks.

jonmark1985 · 04-22-2008, 02:12 PM

Fuel can ony burn so fast inside a cylinder. At higher RPM the ignition needs a headstart in order to get peak cylinder pressure around 10° after TDC durning powerstroke. Under heavy load advance is very dangerous, and can lead to pinging and spark knock.

Most distributors are equipped with vaccuum and mechanical advance. Mechanical involves centrifigual weights that turn the distributor cap to advance timing. Vaccuum advance is mounted on the side of the distributor and sources vaccuum from the intake or carb.

When setting your timing with a light you should do it with the vaccuum advance unhooked at around 2000 rpm. Or at least thats how I do it.

chukarhunt · 04-22-2008, 11:17 PM

I understand what your saying. The factory setting is 6 degrees BTDC. When I was messing with the timing a while ago I set it at 6 degrees and it had no 'get up and go'. That is why I advanced it to like 11 degrees. At 2000 rpm, should I set it to the factory setting?

jonmark1985 · 04-23-2008, 04:59 AM

I'd try setting it at 12° @2000 with the vaccuum advance unplugged.

chukarhunt · 04-23-2008, 10:40 AM

alright, I'll try that. It will be a couple of weeks before I can get to it. I'll let you know how it went. Thanks for the help.

jcoberley · 04-26-2008, 08:41 PM

Check the inside of the dist cap for hair line cracks. I would just replace it and the roter. Secnd thing I would do is make sure all the plug wires are good. I have seen them burned in the ends where the clip is crimped on. And for gods sake make sure there held in place with the clips. There cheep and they save shorting. You might want to go out in the pitch dark night and start it open the hood and see if you have any sparks jumping from plug wires and on the coil conections. Thats my thought and I agree set the timing to 12' with the vacum unhooked and at 2000 RPM. Thats just good advice he gave you!