2003 Buick Regal poor idling. Error code PO300.

Tiny
STEPHEN KARANJA
  • MEMBER
  • 2003 BUICK REGAL
  • 3.8L
  • 6 CYL
  • FWD
  • AUTOMATIC
I did a headgasket replacement about a year ago on this car. Everything else runs fine no overheating, and at speeds over 10mph the car runs fine. The only problem is the idling. Took your advice and checked vaccum lines and intake manifold no leaks. The only thing I have been able to find is low compression reading on #1 cylinder of about 70 to 90 while other cylinders are around 120. My question is.I know their could be several factors causing this. Piston rings, valves etc. How do you narrow it down, can the push rods in this vehicle cause this problem?Is it also possible the head gasket is leaking air?Your opinon will greatly be appreciated.
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Wednesday, October 14th, 2015 AT 2:00 PM

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Tiny
CARADIODOC
  • EXPERT
The test you need is called a "cylinder leakage test". Once the compression test shows low compression, this test will tell you why it's low.

The tester uses compressed air that goes through the tester and is regulated. The hose looks like the hose for a compression tester but it doesn't have a check valve in it. You pump in compressed air through the spark plug hole. The gauge on the tester will show percent leakage, but then you can listen at various places to find out where the leak is. If an exhaust valve is leaking, you'll hear a hiss at the tail pipe. For a leaking intake valve, you'll hear the hiss at the throttle body. With leaking piston rings you'll hear the hiss at the oil cap or dip stick tube. With a leaking head gasket or cracked head, you'll see a stream of tiny bubbles in the radiator.

The piston for the cylinder being tested has to be at top dead center. That is easy to find if you use a whistle screwed into the spark plug hole. It will stop whistling when the piston reaches top dead center on the compression stroke. Check at an auto parts store that rents or borrows tools to see if they have the tester and whistle.
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Wednesday, October 14th, 2015 AT 8:20 PM
Tiny
STEPHEN KARANJA
  • MEMBER
Thankyou very much Caradiodoc.I will try to use the test you recommend.
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Thursday, October 15th, 2015 AT 1:09 PM

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