1997 Chevrolet Monte Carlo



January, 17, 2008 AT 4:27 PM

Engine problem
1997 Chevy Monte Carlo 6 cyl Two Wheel Drive Automatic 123000 miles

My timing belt broke & I'm trying to change it. I'm at the stage where the manual says to turn cranshaft to TDC for #1 on exhaust stroke. My question is - How do I know or tell the difference between the exhaust stroke and compression stroke - since the cams are not controlling the valves at this time the air coming out of the piston is the same.
I have a 3.4 DOHC engine. It has the Ingition Control Module which has 3 coils, each sends a spark simultainously to 2 spark plugs - one is called a waste spark which goes to the spark plug on the exhaust stroke and the other to the spark plug on the compession stroke (ie: spark plugs 1 & 4, or 2 & 5 or 3 & 6).
Your reply stated looking at the ignition rotor, which this car dosent' have. I did double check the Haynes repair manual and it does state " Exhaust stroke". The Chilton Rapair manual does not specify exhaust or compression - just says TDC on # 1 cylinder.
I wondering if the timing is somehow adjusted by the cam sensor working with the cranshaft sensor, then sending this info to the Ignition Control Module and the Powertrain Control Module - which than knows the position of the valves and therefore whether its the compression or exhaust stroke.



2 Answers



January, 17, 2008 AT 11:43 PM

Are you sure it says the exhaust stroke? It's probably the compression stroke or there is a misprint in your manual. Anyway, the easiest way to be sure that the piston is on the compression stroke is to bring it up to TDC, or real close to it. Take the distributer cap off. Look to see if the rotor is pointing to the number one cylinder. If it is then you are at TDC on the compression stroke. Normaly, as the pistion is coming up on the compression stroke air will blow out of the spark plug hole more forcefully that when on the exhaust stroke. Oh yea, if you want the piston at TDC on the exhaust stroke, bring the piston to TDC and look at the dist. Rotor if it's pointing at number one cylinder, turn the engine one complete turn (360 degrees), or if the rotor is pointing somewhere else then you are at TDC on the exhaust stroke. I understand that air is forced out every time the piston comes up, however on the compression stroke you will feel a noticable difference.
Triple check that TDC exhaust stroke.



January, 18, 2008 AT 7:06 PM

It's actually pretty simple. If the belt broke, the crankshaft doesn't know the difference between exhaust and compression, unless it has a crank sensor. If this is the case (having the sensor) the crank pulley shound have a series of teeth on it. There should be a tooth missing. This is TDC. The computer should determine Cylinder ID based on the cam sensors. The crank is no longer an issue. Then you just set the cams for exhaust stroke nd install the belt. If you have further questions, I would be happy to help.

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