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Greg, import technician
Category: Hyundai
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Experience: 27 year and 16 year as shop owner, import technician
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hyundai elantra: my car has 90 psi compression when i add oil

Customer Question

my car has 90 psi compression when i add oil it doesnt change compression timing belt marks looks good car runs good but stumbles on aqcceleration and a lot more when a/c is on. compression should be around 170 to 225.

Submitted: 11 months ago.
Category: Hyundai
Expert:  Greg replied 11 months ago.

Name is XXXX XXX i will assist you the best i can, please Only accept if you are happy with my answer.

Doing a wet and dry compression is to check if you have a problem with the piston rings to valves .
So the idea doing the wet test is testing the rings if compression stays the same at 90 psi then you have
Bad inlet to exhaust valves
To see which valves are bad you could do a leak down test ,this is where you applie air to each cylinder when at TDC
(valves in the fully closed position) then you can hear if Its is leaking out the exhaust do inlet valves .
If your car is high mileage then this is probably your issue ,
What you could try is seafoam and see if cleaning the valve this way improves the compression ,this is worth trying before doing the head repair .

Need further assistance with this issue then please get back to me with the reply tap.

Kindest regards Greg

Customer: replied 11 months ago.

The thing that gets me is that it runs really good as soon as you get past the stumble on acceleration. so what you think is the valves are corrided be cause if you had a bent valve the compression would not be the same. How can it run so good if it only has 90 psi. I just purchased engine from lkq it had 90 k miles. Thet said compression was 195 cold.

Expert:  Greg replied 11 months ago.

An engine with all cylinders at the same pressure will still run well and smooth ,but will lose power when needed on hills ,overtaking etc,when it comes under too much load then it could stall .

Take a reading of the compression test and show them the results and work on a replacement engine under the warranty.

Regards Greg

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