Question about Pontiac Grand Am

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My 93 grand am seddenly started making a knocking sound which got louder upon acceleration and it hesitates and wants to dog out when at low - idle speeds, my first thought was it was low on oil however it was only about a qt low. my intrerior check engine light was on but its been stuck on since last car repair and the check oil light isn't lit up! my car is need of an oil change and have had problems with the plunger in the IAC valve before. what do you think my cars malfunction could be? lifter shot,head blown, oil filter grimy??

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  • loni grindle Apr 18, 2009

    thanks for the feedback! checking the actual oil pressure was also on the very long list of possibilities to check!

  • loni grindle Apr 19, 2009

    i,ve had a few grand am's before and many issues go wrong with them including replacing a head gasket but have never had to have a oil pressure test done specifically that i can remenber.what i don't ubderstand is that the car ran just fine with no knock or indication that there was anything wrong, 30 minutes later get back in it and it started knocking acceleration and hesitating when in idle speed!? any other suggestions would greatly be appreciated! how is the oil pressure test done and with what device ( if it can be done diy), should i have it brought to a shop for this?

  • Bradley Hynes May 11, 2010

    a gut feeling would tell me that it would be your head gasket. what size of motor do you have?

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  • Pontiac Master
  • 6,982 Answers

Knocking in an engine is never a good thing. I'd check three things: engine bearings, valve lifters and timing chain, all of which can make noise. First thing though, is to put a mechanical gauge in place of the sending unit and check actual engine oil pressure. this will give you a good idea what is going on. low readings can be bearings, normal readings can be the other two items. I could give you a definite idea by listening, but I really can't hear it from here.!(one of the frustrating drawbacks to doing this online) An experienced tech can listen and tell you pretty much what's going on.

Posted on Apr 18, 2009

  • Richard Scordino Apr 18, 2009

    Remember...check pressure first...If pressure is bad, you will do more harm while looking around at other items and running it.

  • Richard Scordino Apr 19, 2009

    You will need to buy or borrow a mechanical gauge. To use it, you remove the oil pressure sender and attach the gauge line there. Once installed, just read the pressure on the gauge. Cold, at idle pressure will read 30lbs or higher...What is of most concern is hot pressure which should never be below 15psi (I prefer to see 20 or better) This is absolute low pressure at idle in gear. There is no "quick repair" if the pressure is low. It indicates that there is a pressure loss inside the engine that needs to be dealt with.

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If its a knocking sound:

A KNOCKING SOUND IN THE ENGINE IS MOST LIKELY CAUSED BY ONE OF THE FOLLOWING
1. PISTON SLAP: Makes a sharp metallic noise. Idle engine and short out each cylinder plug. The noise will disappear when plug with bad piston is shorted. Noise will also disappear at acceleration. This can be caused by worn or out of round cylinder, or broken piston ring. Correct problem by re-boring cylinder and/or replacing piston.
2. VALVE NOISE: Makes clicking or rattle noise. Caused by excessive wear on valve stem or lifter, out of adjustment, or stuck valve. Correct by adjusting valve clearance, replace worn valve or lifter, regrind cam, replace valve guide and /or valve. A stuck valve can sometimes be loosened by passing oil through the carburetor while engine is running.

3. ROD BEARING KNOCK: Makes sharp metallic noise similar to a piston slap. Detection is opposite of piston slap. Rod knock is not heard at idle. Knock becomes louder as engine speed is increased. Caused by excessive rod bearing clearance. Correct by adjusting rod bearing clearance to .0015 inches by removing shims. May require re-pouring rod bearing.
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