Author Topic: s code low compression  (Read 176 times)

Offline MarkC

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s code low compression
« on: May 02, 2024, 10:49:33 AM »
s code 390 150 lbs compression except cyl 2 is at 60 lbs,but passes leak down test,any ideas

Offline RoyceP

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Re: s code low compression
« Reply #1 on: May 02, 2024, 02:57:46 PM »
Typically it means either a leaking valve or bad rings. You need to pull the heads and see which it is. Cold Cranking numbers like that on an FE are indications of trouble. It indicates low compression of course, but compression ratio is more likely calculated, not measured.
1968 W code 427 Cougar XR-7 GTE Feb 23 Dearborn C6 / 3.50 open
1968 R code 428CJ Cougar XR-7 May 13 Dearborn C6 / 3.91 T - Lock

Offline J_Speegle

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Re: s code low compression
« Reply #2 on: May 02, 2024, 10:59:36 PM »
First welcome to the site.

Not really our focus here and you may be served better on a different site but lets get some of the basics out of the way.

Was the test done wet or dry?

Has this engine been sitting for a while?

If so have you thought about putting a scope down that hole through where the spark plug attaches?
Jeff Speegle

Anything worth doing is worth doing concours ;)

Offline lightwtjet

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Re: s code low compression
« Reply #3 on: May 03, 2024, 08:58:07 PM »
As Jeff may have eluded, an engine sitting for years can develop stuck rings. Simply driving fixed mine.
Here is more of what can be learned from a leak down test.
https://www.mobil.com/en/lubricants/for-personal-vehicles/auto-care/vehicle-maintenance/h
1968 CJ - Owner and paint original. Dec 67 build in Dearborn. One of 50 135 Cobra Jets. Ford engineering used it for 8 mos. to resolve problems in the 50 early car build. Ford by-passed the normal sign off to get cars to the Winternationals drag race.