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EFV-8 Club Forum / General Ford Discussion / Compression Test Results

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Discussion Topic: Compression Test Results

LarryK

09-04-2017 @ 4:28 AM

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Posts: 105
Joined: Aug 2012

Hello All,
My car is a stock 1939 Deluxe Tudor. I am looking for some help in interpreting recent compression test results. I did two tests back-to-back with the same results for both. The car was thoroughly warmed up after a 25 mile drive. Throttle was wide open.
Cylinder Pressure
1 145
2 125
3 95
4 95
5 120
6 115
7 120
8 120
I am concerned about cylinders 1, 3, and 4.
The car runs well. It starts readily and idles smoothly. However, I will get an occasional backfire out the tail pipe.
I also did a vacuum test. It was steady at 22 inHg.
Attached is a photo of spark plugs 1 – 4.
Thanks for your insight.

Larry

cliftford

09-04-2017 @ 6:32 AM

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Posts: 845
Joined: Jan 2014

How many miles are on the engine, and how was it driven? you could have a head gasket leaking between 3 and 4. 15 to 20 lbs. variation between cylinders is normal on a good running engine, but 50 lbs suggests some problems.

This message was edited by cliftford on 9-4-17 @ 6:33 AM

shogun1940

09-04-2017 @ 9:34 AM

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Posts: 464
Joined: Feb 2010

Time for leak down test, put #3or 4 on tdc and put shop air into the one on tdc and see if you hear air coming out of the other one

TomO

09-05-2017 @ 7:51 AM

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If the engine starts, runs and idles, I would not worry about an occasional pop in the exhaust. It could be caused by a slightly rich mixture or moisture in the gas. Moisture in the gas can be cleared up by using Heet or Seafoam.

Here is a link to a site that shows what your plugs should look like.

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/how-do-i-read-a-spark-plug

Your plugs all look normal to me.

Tom

Drbrown

09-06-2017 @ 8:32 PM

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Posts: 570
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All good info here. In addition, recommend putting a good vacuum gauge on it to check condition of valves and their workings. Attached is a good article on the subject of interpreting vac gauge readings.

http://www.secondchancegarage.com/public/186.cfm

This message was edited by Drbrown on 9-6-17 @ 8:37 PM

alanwoodieman

09-07-2017 @ 5:26 AM

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Posts: 868
Joined: Oct 2009

#1 cylinder with higher compression could be carbon build up caused by rich mixture or a weak spark plug. what do the plugs "read" color, deposits, etc

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