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Low compression on two cylinders

Tiny
DARRELL BARTON
  • MEMBER
  • 1995 FORD F-150
  • 4.9L
  • 6 CYL
  • 2WD
  • MANUAL
  • 214,000 MILES
Did compression test dry 30 on each cylinder did wet and went to 300 on each cylinder. What are your thoughts?
Saturday, January 25th, 2020 AT 4:28 PM

7 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This is undoubtedly because the rings are worn out on the two cylinders in question. Usually if you have two cylinders side by side that half 1/2 of the compression of the other cylinders, then that would be a blown head gasket in between the cylinders but a wet test that yields a higher compression reading is going to be worn piston rings. Please let us know what you decide to do. We have instructions available if you decide to an engine overhaul.

Thanks,
Alex
2CarPros
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Saturday, January 25th, 2020 AT 4:56 PM
Tiny
DARRELL BARTON
  • MEMBER
  • 6 POSTS
Okay, had 2 injectors stick on these 2 cylinders causing I guess what they call a cylinder wash? Could the compression rings be stuck due to all oil in cylinders being washed out by fuel? Will letting some ATF sit in cylinders un-stick these rings? It was running perfect before injectors stuck and it shut off.
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Saturday, January 25th, 2020 AT 5:50 PM
Tiny
DARRELL BARTON
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  • 6 POSTS
Hope you got my reply.
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Saturday, January 25th, 2020 AT 5:52 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

Sorry for the delay in my reply. It's possible, but cylinder wash washes away the protective film of oil from the piston walls and the ring actually go metal to metal with the cylinder wall and then they get scratched and damaged. The problem really isn't with the rings but the cylinder wall.

Thanks,
Alex
2CarPros
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Saturday, January 25th, 2020 AT 8:14 PM
Tiny
DARRELL BARTON
  • MEMBER
  • 6 POSTS
Okay, but mystery oil in cylinders let sit turned over very slow let sit another 24 hours turned over very fast to blow all oil out of cylinders did another compression test now have 190,180,180,190,190, and 180. When I was doing this# 4 cylinder was building compression then quit. This was not a cylinder that was washed. Put a little mystery oil in cylinder and started to build compression again. Turn over very fast again to get oil out of cylinder and let sit. Then did compression test and the numbers are what I have now. All the cylinders that did not get washed have improved from around 100 to 180. And #2 and #5 that got washed went from 30 to 190. Now all cylinders are only 10lbs different and have good compression. I'm really baffled on this one. Was thinking of doing a leak down test just to make sure that they hold this compression. Any ideals maybe a valve sticking then when builds compression it unsticks due to mystery oil? Help please
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Monday, January 27th, 2020 AT 7:25 PM
Tiny
DARRELL BARTON
  • MEMBER
  • 6 POSTS
Hope you got my explanation of what I'm going through just doesn't make since.
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Monday, January 27th, 2020 AT 7:27 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

No, I doubt it. The wet test usually confirms piston rings. Do a leak down test and report back with those readings, please.

Thanks,
Alex
2CarPros
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Monday, January 27th, 2020 AT 8:47 PM

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