85 470 runs the same on 3 cylinders as 4

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ctaylor2069

Petty Officer 2nd Class
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Jul 31, 2013
Messages
131
I was checking for spark and I pulled boot off #1. Cranked over and engine fired and ran. On 3 cylinders. No miss or rough idle. Put back together and it ran fine. Then later felt like no spark again so I pulled boot #1 to check for spark, same thing, started and ran fine on only 3 cylinders. What is going on
 
jimmbo

jimmbo

Supreme Mariner
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May 24, 2004
Messages
13,656
It's running on 3 cylinders. Did you have spark on the suspected dead cylinder?

If no; What condition plug wires? Distributor cap?
If yes: What condition is the spark plug. Does that cylinder have compression? Leaky intake manifold, broken hose? Are the valves opening and closing?
 
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stonyloam

Vice Admiral
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Mar 13, 2009
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5,827
Do a compression check. In the meantime pull the other wires ( from the distributor cap) one at a time and see if the idle drops significantly with the other 3 cylinders. If it does then #1 is the problem. Take the plug and wire from #2 and swap them to #1, (you know #2 wire and plug are OK) see if this changes anything. If not then the problem is internal with #1, probably low compression, head gasket or valve. Check the color of the #1 plug vs the others. The compression test will confirm. Good luck.
 
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ctaylor2069

Petty Officer 2nd Class
Joined
Jul 31, 2013
Messages
131
Thanks for getting me started in the right direction. But can someone explain to me how it's possible for the engine to run so smooth in only three cylinders?
 
Alumarine

Alumarine

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Feb 22, 2005
Messages
3,739
There may be nothing wrong.

As someone suggested try your test with the other cylinders.
It would be different if it ran the same when you were out using it.

jimmbo probably nailed it.
 
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