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Spark plug question


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#1 Fbird79

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Posted 3 weeks ago

So they guy I got the car from said he changed the spark plugs not to recently. I pulled them off and they were completely rusted, so Im thinking that isnt the case, anyone know how to check if these are the right plugs? Im going to replace them but I dont want to get the same ones if theyre wrong

#2 ZumpTA

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Posted 3 weeks ago

If they are more of a brown than a rust, that is a good color. If they are actually rusty in appearance, that is an indication of running too lean.  Lean air fuel mixtures also being a cause of the engine running hot AND running on. It occurred to me this morning that throttle blades not closing far enough can cause run on too, but your plugs are most certainly pointing to air/fuel issues so start there.  Also, all auto parts stores know what the proper plugs are for your engine.  Tell them what you have and pick a brand. Do ask what the gap should be and verify before installation.


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#3 Injuneer

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Posted 3 weeks ago

When asking them to look up the correct plug, make sure you tell them its a base 301 engine, and not the 301T turbo engine from the 1980-81 models.  Also, don't let them sell you expensive "gimmick" plugs.  Stick with AC Delco or NGK.  Before installing, make sure you know the correct gap, and check each plug to insure it has that gap.


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#4 Fbird79

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Posted 3 weeks ago

Okay so the plugs are definitely rusted not brown, and I pulled the carb off and I noticed the what controls the gas is pretty sticky, but the valves all seem to flow freely. I know forsure Im using ACDelco plugs, Im thinking I might need new cables for the plugs too as they look pretty worn and have been sitting on the heads so theres some burn marks in places. Okay by checking the gap what do you mean? I thought all should be the same gap? Also does anyone have a schematic for how the plugs should be ran from the relay to the block? Im thinking the guy I got it from just pulled them all and put them back in however he wanted.

#5 Injuneer

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Posted 3 weeks ago

A spark plug has to match the engine's required heat range, and have a gap width determined by the design of the ignition system.  The parts store, assuming the person behind the counter is competent, should be able to find the correct plug, which carries the required heat range.  But each engine and specific build of that engine has a recommended plug gap.  They are not all the same.  The plugs may come with a gap that's close to the engine manufacturer's spec, but you still have to check it to make sure each plug is correct, and did not suffer damage in shipping and handling.

 

Hopefully someone with a currently running engine similar to yours can help you with the gap.  I haven't touched a Pontiac engine that old in many decades.

 

I'm not sure what "how the plugs should be ran from the relay to the block?"  Do you mean how the plug wires should be run from the distributor to the plugs?  If the wires had just been run at random by the previous owner, the engine would be running very poorly, or possibly not at all. 

 

If the engine is running smoothly and correctly, most likely the wires are installed in the correct order and routing.  It's best to buy a pre-cut/assembled set of wires specifically for the engine.  That way they will have the correct length of each wire, and the correct boots on both ends.  Remove the old wires one at a time, and replace before going on to the next one.  If the engine is running poorly, to the extent that you think the wires are not routed correctly. you have to match the firing order of the cylinders up to the numerical order on the distributor, starting at the correct #1 terminal.

 

Here's a typical source for a wire set:

 

https://www.firebird...WIRES_s/413.htm

 

 

 

 

 



#6 sea dog

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Posted 3 weeks ago

I had to use 78 service manual for specs as I don't have the 79. But all 78  301 engines use a .060" plug gap.

 

2bbl carb models used AC R46 TSX plugs. 4bbl carb cars used the AC R45 TSX plugs. The only difference between the 2bbl & 4bbl plug types is the heat range.



#7 Fbird79

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Posted 3 weeks ago

A spark plug has to match the engine's required heat range, and have a gap width determined by the design of the ignition system.  The parts store, assuming the person behind the counter is competent, should be able to find the correct plug, which carries the required heat range.  But each engine and specific build of that engine has a recommended plug gap.  They are not all the same.  The plugs may come with a gap that's close to the engine manufacturer's spec, but you still have to check it to make sure each plug is correct, and did not suffer damage in shipping and handling.
 
Hopefully someone with a currently running engine similar to yours can help you with the gap.  I haven't touched a Pontiac engine that old in many decades.
 
I'm not sure what "how the plugs should be ran from the relay to the block?"  Do you mean how the plug wires should be run from the distributor to the plugs?  If the wires had just been run at random by the previous owner, the engine would be running very poorly, or possibly not at all. 
 
If the engine is running smoothly and correctly, most likely the wires are installed in the correct order and routing.  It's best to buy a pre-cut/assembled set of wires specifically for the engine.  That way they will have the correct length of each wire, and the correct boots on both ends.  Remove the old wires one at a time, and replace before going on to the next one.  If the engine is running poorly, to the extent that you think the wires are not routed correctly. you have to match the firing order of the cylinders up to the numerical order on the distributor, starting at the correct #1 terminal.
 
Here's a typical source for a wire set:
 
https://www.firebird...WIRES_s/413.htm
 
 
 
 
 



Awesome super helpful, is there any chance my distributor could be corroded on the bottom? Or are the a copper/brass base?

I had to use 78 service manual for specs as I don't have the 79. But all 78  301 engines use a .060" plug gap.
 
2bbl carb models used AC R46 TSX plugs. 4bbl carb cars used the AC R45 TSX plugs. The only difference between the 2bbl & 4bbl plug types is the heat range.




Thank you, I have a 4bbl so the R45, But now wouldnt the gap change between the two?

#8 Fbird79

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Posted 3 weeks ago

How am I able to find out the firing order? Im not really trying to start it up as I got the carb pulled

Edited by Fbird79, 3 weeks ago.


#9 sea dog

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Posted 3 weeks ago

I'd consult the 78 Pontiac service manual located in the 2nd gen tech section. After 2nd gen tech page opens, hit master index near top. When new page opens scroll down until you find 78 service manual.

 

If you pulled all your plug wires off car without noting where # 1 cylinder is on distributor, you'll have to do a lost timing search. This involves pulling cylinder 1 spark plug. Then rotating engine by hand until timing mark on crank damper comes up to top dead center with compression being felt with your finger blocking spark plug hole.

 

If you also pulled distributor from engine, your in a world of poop. But you can overcome that also. On the check for # 1 cylinder at TDC of firing stroke you can reinstall distributor. Where ever rotor of distributor is pointing, that can be cylinder # 1. You then replace plug wires following the cylinder firing order you found in service manual. Be sure to note direction of distributor rotation when starter turns engine over. So you will correctly place spark plug wires into cap.

 

All 301 engines use .060 gap for 78 at least. I suspect 79 is the same.



#10 Fbird79

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Posted 3 weeks ago

I'd consult the 78 Pontiac service manual located in the 2nd gen tech section. After 2nd gen tech page opens, hit master index near top. When new page opens scroll down until you find 78 service manual.
 
If you pulled all your plug wires off car without noting where # 1 cylinder is on distributor, you'll have to do a lost timing search. This involves pulling cylinder 1 spark plug. Then rotating engine by hand until timing mark on crank damper comes up to top dead center with compression being felt with your finger blocking spark plug hole.
 
If you also pulled distributor from engine, your in a world of poop. But you can overcome that also. On the check for # 1 cylinder at TDC of firing stroke you can reinstall distributor. Where ever rotor of distributor is pointing, that can be cylinder # 1. You then replace plug wires following the cylinder firing order you found in service manual. Be sure to note direction of distributor rotation when starter turns engine over. So you will correctly place spark plug wires into cap.
 
All 301 engines use .060 gap for 78 at least. I suspect 79 is the same.


Awesome, this is super helpful, and no I only pulled the carb off to clean it, Im pretty sure the guy I bought it from was screwing with the spark plugs and wires. The distributor is still on the car I havent touched that. Im gonna buy new plugs and probably wires, then check the timing before I pull the old plugs and replace them

#11 NOT A TA

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Posted 3 weeks ago

Firing order for your engine is 18436572 in counterclockwise rotation on distributor. the # 1 spark plug wire terminal on the distributor does not necessarily have to be located where it is in the pic below depending on distributor installation in the block but that's where they came from the factory on most cars. Cylinders are "numbered" differently by different manufacturers so don't presume that this is typical of all V8's. Pontiac is drivers front #1, pass side front #2 and so on.

 

CCF08032012_0000.jpg?width=450&height=27


  • ZumpTA likes this

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#12 Fbird79

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Posted 3 weeks ago

Firing order for your engine is 18456372 in counterclockwise rotation on distributor. the # 1 spark plug wire terminal on the distributor does not necessarily have to be located where it is in the pic below depending on distributor installation in the block but that's where they came from the factory on most cars. Cylinders are "numbered" differently by different manufacturers so don't presume that this is typical of all V8's. Pontiac is drivers front #1, pass side front #2 and so on.
 
CCF08032012_0000.jpg?width=450&height=27


Thank you so much! This is very helpful! Ill probably be rebuilding the carb today, and if not Ill go check the timing and put new plugs in

#13 sea dog

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Posted 3 weeks ago

Only problem with the diagram is distributor shows firing order being  18436572 rather than posted 1845672 firing order. I don't believe Pontiac engines have a screwy distributor cap like later lt1 engines have.



#14 Fbird79

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Posted 3 weeks ago

Only problem with the diagram is distributor shows firing order being  18436572 rather than posted 1845672 firing order. I don't believe Pontiac engines have a screwy distributor cap like later lt1 engines have.


Okay so go with the 1845672? And I know the caps bolted on, not screwed

#15 Fbird79

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Posted 2 weeks ago

So I rebuilt the carb, checked the timing, threw new plugs and wires in, it started to problem without my foot on the gas, but now it wants to idle very fast, almost like it wants to drive off..lol i shut the ignition off and had to manually kill it. And did she ever smoke lol but I set all the fuel and air screws to 3 turns back, and adjusted from there. Is there maybe a problem with my choke? Or are my vac lines hooks up wrong? Im stumped here

#16 tjs

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Posted 2 weeks ago

18436572,dont count on your cap to match where #1 is on the dizzy!That could have been rotated over the years.



#17 JoePeek

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Posted 2 weeks ago

Plus, it doesn't really matter where the #1 plug is on the cap, as long as the rotor is pointing at the #1 wire on the cap when the #1 piston is at TDC compression, then the rest of the wires can go around the cap in the firing order. That being said, if you get a set of plug wires, that are pre-made length, the location of the #1 wire on the cap could effect if the wires reach the distributor cap location.



#18 Fbird79

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Posted 2 weeks ago

Okay so pull the cap and check to make sure the #1 is going to #1 and then the firing order, remember I have to do this without starting the car so Ill need to manually turn it.

#19 NOT A TA

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Posted 2 weeks ago

Only problem with the diagram is distributor shows firing order being  18436572 rather than posted 1845672 firing order. I don't believe Pontiac engines have a screwy distributor cap like later lt1 engines have.

It is 18436572 I screwed up typing too quick. Silly ole man.......

 

And as Joe mentioned it doesn't really matter where #1 is for start but the factory put the distributors in most Pontiacs I've seen so that #1 is in the spot in my crude drawing.


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#20 Injuneer

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Posted 2 weeks ago

It is 18436572 I screwed up typing too quick. Silly ole man.......

 

And as Joe mentioned it doesn't really matter where #1 is for start but the factory put the distributors in most Pontiacs I've seen so that #1 is in the spot in my crude drawing.

 

 

I edited post #11 for you.






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