Car sputtering, air is coming out of the exhaust

Tiny
AHMED_RHAB62
  • MEMBER
  • 2009 CHEVROLET OPTRA
  • 1.6L
  • 4 CYL
  • 2WD
  • MANUAL
  • 135,000 MILES
After timing belt replacement the compression test shows one piston is not giving pressure, but there is no misfire or black smoke coming out of the exhaust. The millage of the car is very low. The engine is knocking at low RPM but when I drive it at higher speed it get smoother and remains a bit smooth at low RPM while the engine is hot. But when the engine cools down a bit it starts jerking again.
Monday, July 8th, 2019 AT 11:05 AM

4 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

When an engine has a knock to it this usually is a bearing failure, specifically a connecting rod bearing. The fact that you have no compression in this cylinder would be from worn or damaged compression rings, which could be scoring or may have worn out the cylinder wall of the block. It really is just educated guessing until you get into the engine and see what is really going on. Here are a couple of links for you to go to:

https://www.2carpros.com/articles/the-reasons-for-low-compression
https://www.2carpros.com/articles/engine-noises

Please go through these guides and get back to us with what you decide to do. We are here to help with instructions and step by step directions for whatever your vehicle may need.

Thanks,
Alex
2CarPros
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Monday, July 8th, 2019 AT 11:50 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
As a quick question, was the belt replaced on a running engine or did the belt fail and then it was replaced? If the latter the knocking and loss of compression could both be from a piston hitting a valve in that cylinder. It's even possible in the first situation if it wasn't timed exactly correct.
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Monday, July 8th, 2019 AT 1:33 PM
Tiny
AHMED_RHAB62
  • MEMBER
  • 5 POSTS
The timing belt was replaced on a running engine but the mechanic tried many times to get the car started he also replaced the water pump which made it hard for him to adjust the timing belt again. I did not know that he did not have experience for changing the water pump my concern is do I have a bent valve? Because I don't want to open the engine to replace the bent valve and find something else causing this trouble, I double checked the timing of the belt with other mechanics they said it was timed correctly, the computer check shewed no bent vale issue and no incorrect timing of the belt it shows TIPS input voltage low and fuel ejectors 1, 2, 3 input voltage low I had the fuel injectors cleaned but the problem still persists I also cleaned the TIPS the car performance has improved a bit but the air is still coming out of the exhaust.
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Tuesday, July 9th, 2019 AT 1:19 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
No need to open the engine, you can easily test for a bad valve by doing a leak down test. You put the engine at top dead center for one cylinder, then lock it so it cannot turn, now you apply air pressure through the spark plug or injector hole. Now you just listen for air. If both valves are closed you should hear nothing in the intake or exhaust, toy will hear some in the oil fill/dipstick as no engine has a perfect seal in the rings. If you hear air hissing in the intake or exhaust you have a valve issue. You proceed through the cylinders and test each one. While doing this you can also watch the coolant, if you see a bunch of bubbles you have either a head gasket issue or worse a cracked head/block.
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Tuesday, July 9th, 2019 AT 4:59 PM

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