Cause of no compression CYL #6 3FE

Joined
Dec 9, 2019
Messages
38
Location
Frisco Co
Hey all,
I was running a compression test on my 3FE and found pretty consistent numbers; cylinders 1-5 are within 5 psi of each other, right around 120 PSI. Adding oil bumped them up to 130 psi, so a little cylinder wear.
Cylinder 6 however isn’t pressurizing at all.
The funny thing is the truck runs fine. I took it out for some high altitude wheeling with the family last weekend, and averaged 13-14 mpg.
what is the next move now that the tester is showing no compression in cylinder 6?
Thanks so much.
Bevan
 
Joined
Nov 9, 2012
Messages
9,365
Location
Olathe, KS, USA
 
Hey all,
I was running a compression test on my 3FE and found pretty consistent numbers; cylinders 1-5 are within 5 psi of each other, right around 120 PSI. Adding oil bumped them up to 130 psi, so a little cylinder wear.
Cylinder 6 however isn’t pressurizing at all.
The funny thing is the truck runs fine. I took it out for some high altitude wheeling with the family last weekend, and averaged 13-14 mpg.
what is the next move now that the tester is showing no compression in cylinder 6?
Thanks so much.
Bevan
Do a leak-down test to determine if it's valves related or rings related.

Do a radiator compression test to see if it's HG related.
 
Joined
Dec 9, 2019
Messages
38
Location
Frisco Co
Haven’t adjusted the valves yet. Just getting the rig baselined after purchase. I don’t have a leak down tester, so I might just get a valve cover gasket and adjust the valves/check for any funny business.
 
Joined
Dec 8, 2006
Messages
9,082
Location
New Jersey
 
 
I seriously doubt that the truck would be "running fine" on 5 cylinders. If there was really no compression on #6 she would have let you know.
I suspect that the compression tester was not seated correctly in #6.
 

flintknapper

SILVER Star
Joined
May 22, 2004
Messages
7,787
Location
Deep East Texas
 
 
 
Jon, thanks. That was my feeling too. I had already reattached the gauge twice but the third time was the charm. Got my last compression number: 120 psi in cylinder 6.
Good way to end the day.
@jonheld is smarter than your average bear. Figured he had it right as soon as I saw his post. #6 cylinder is a bit hard to reach and get it to seal correctly.

Good job guys!
 
Joined
Dec 8, 2006
Messages
9,082
Location
New Jersey
 
 
Haven’t adjusted the valves yet. Just getting the rig baselined after purchase. I don’t have a leak down tester, so I might just get a valve cover gasket and adjust the valves/check for any funny business.
The 3FE wants a valve adjustment every 15K miles according to the factory service manual (FSM). Personally, I never did mine that often. However, if yours haven't been done in the last 30 years, they're more than a bit overdue. Have a look at this document. Individual parts are available from Toyota, and Wits End sells a complete kit using OEM parts.

 
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