Need some help troubleshooting spark knock

4Cruisers

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Is your '78 a Federal spec vehicle or California spec? The '78 California spec distributor only has a retard port, the Federal spec has two ports - advance and retard - one on either side of the diaphragm.

On your mechanical advance, there's a small bushing over the stop pin that limits the maximum mechanical advance. They are usually toast unless they've been replaced. If it's missing, the maximum advance will be greater than spec, which could lead to pinging under load. It's easy to replace - clean the stop pin (under the breaker plate assembly) and push on a nylon or aluminum bushing. The proper size is 1/4" diameter X 1/4" long, for a #8 screw. Easy to find at any decent hardware store. That could be contributing to your issue.
 

fyton2v

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Yup, that guy. I just finished redoing my 60 series dizzy with one of his new vac advance modules.
Found a piece of the hard plastic airline works for that bushing.
How attached are you to that dizzy? Thought of a replacement?
Not terribly attached, but if I can buy a small piece of plastic to fix my problem, that’s a good path. My dizzy cleaned up nice. :).
 

thorslc1977

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When I bought mine new it was 1977 and you could not get premium unleaded only 87 octane. Mine would do what yours is doing brand new. Not a lot but when you got on it uphill in fourth you got a knock. With the addition of 91 octane the problem much went away. As the distributor aged and stop pin was gone along with the main bushing wearing it came back some. Dropped in a new city racer distributor ( plug an play with the '77 coil/ignitor) and problem now only in summer using 87 octane. So I run 87 octane in the winter and the 91 octane in the summer
 

fyton2v

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When I bought mine new it was 1977 and you could not get premium unleaded only 87 octane. Mine would do what yours is doing brand new. Not a lot but when you got on it uphill in fourth you got a knock. With the addition of 91 octane the problem much went away. As the distributor aged and stop pin was gone along with the main bushing wearing it came back some. Dropped in a new city racer distributor ( plug an play with the '77 coil/ignitor) and problem now only in summer using 87 octane. So I run 87 octane in the winter and the 91 octane in the summer
Thanks for this background. It's really cool that you've had the truck since '77. Mud needs some special kind of badge for original owners. I don't think there are many members left in the Window Sticker Club.
 

thorslc1977

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Yeah, I thought about trying to do something for/with Original Owners but it is an ever shrinking circle when it comes to FJ40's. And I do still have my window sticker and original bill of sale ( pic of window sticker is on a thread in this section about window stickers). My goal is to own/drive it for 50 years - I will be 71 if I make it.
 

fyton2v

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That little spacer is all kinds of awesome. Name any item that can make a bigger performance improvement for under a buck. Go ahead, name it. :D

I really appreciate the knowledge here. The engine operates more smoothly at higher RPMs, and it makes freeway driving A LOT better. I can still cause the knock, or ping, or whatever, but it's pretty hard to do. I'd never encounter it while driving normally. Heck, just trying to make it occur probably costs me 5 bucks in gas.

Thanks everyone!
 

85roktoy

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Apr 28, 2007
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Inlet Beach, FL
Try 93 octane I bet it will disappear. Mine had a slight ping due to increased compression from a head job. Filled her up with 93 and adjusted timing to 8 degrees. It’s 98% gone.
 
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