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Unusually high compression

I have a 1986 Chevy Cavalier 2.4 that has started sputtering, and after changing the spark plugs ( the middle 2 are wet with fuel and look very clean and the outer two are dark with use ) I took it to a friend and was told, after he spent an hour on it, that the compression in the cylinders was way too high ( 280…I believe he said ) am I looking at a car that will soon be a lawn ornament until I can afford a new engine?

If 2 spark plugs are wet with fuel, I think you should focus on this. These 2 cylinders may be flooded with unburned fuel. Maybe you need 2 new fuel injectors but I don’t know.

I doubt you’re suffering from too much compression, you may want to have somebody else look at your Cavalier.

Since its the two center cylinders that are both wet with fuel, lets concentrate on what they have in common.

If this is an engine that shares the ignition coil for both of these cylinders, I would start with replacing it. I have no idea how advanced this engine was back in '86, however. If it is a distributor car, then you might want to replace the distributor cap and rotor, and spark plug wires.


You’re going to need to check if the cylinders are filled with a liguid such fuel or coolant. If this is happening, it raises the compression of the engine because a liquid can’t be compressed.


Tester is correct…There is something besides air in the combustion chambers to get a reading of 280…

Remove the O2 sensor and retest.

Is this a typo regarding the engine type? A quick look shows 2 engines available.
One is the 2.0 with TBI and other a 2.8 with FI. The cause may vary depending but it’s apparently trying to suffer from hydrolock based on the wet fuel and overly high compression readings.

It’s 24 years old…It was made during the Dark Ages of automotive development…It’s a Chevy Cavalier…

First I should say sorry…the car is 1996 not 1986…typo…OK here is what I know about the engine…there is a metal plate on top ( says 2.4 on it ) when I lift that the distributor ( this looks like 4 cow utters in a single row ) this is attached to the bottom of the plate ( I replaced this ) Inside the distributor is 2 ignition coils, each is attached to a middle and an outside plug, I replaced all of the rubbers and springs but not the coils. I also replaced the spark plugs.
The engine has no power, last week I could hit 70 MPH in 3rd gear, now, I can not pass a loaded logging truck going up the smallest hill. The car also sounds like it is ready to die at every stop light and I used 1/4 a tank of fuel to go about 160 miles, then this problem started and I just hit 260 miles and am empty ( same tank of gas…) so that is 3/4 tank of fuel = 100 miles…I am frustrated…thank you all for your patience and time and input!

It’s a Quad-4… Pull the O2 and retest the compression.

I will get them to try this Tuesday and post results, thank you

I guess he meant Thursday the 22.

And I was really curious on this one. I felt somewhat sure that the exhaust was obstructed.

Hi, OK here is what they actually did ( and the car surprisingly runs better than it did before all this mess started happening ), Changed the fuel filter, , the coil ( ignition ), and did something called a BG fuel induction…it seems that it may have been several small problems…I recently added some goop to the fuel tank that was supposed to clean the injectors, and by doing this I loosened up all the junk that has settled on the bottom of the fuel talk over the last several years ( 10 or so ) and in doing this I clogged up everything…fuel filter , fuel lines , etc, etc…I guess the BG fuel induction, blows out everything and cleans out all the crud that I loosened up…OH, they also cleaned out the fuel tank, I was on empty so it was less than 2 gal. loss…I did see the bucket of crud that they pumped out of the lines…( looked like raw sewage ), but the car runs great now…I know that you all can tell me if any of this made sense, or if they just replaced some tiny nothing part and charged me for all the other stuff…here is what I had done though…
BG fuel Induction 89.95,
diagnostic time ( 2 hours ) 110.00,
fuel filter ( with labor ) 47.30,
coil ( ignition ) 77.72,
fuel tank straps ( I asked for this because one was corroded though ) ( with labor ) 65.33
for a total of ( with tax ) 401.57
I hope that this helps someone else who may have this problem in the future, thank you all for your time

Since it was a DIS system, they replaced the defective coil, and cleaned out your Fuel Injection system.

I had a feeling your car wasn’t an '86 when I originally ready your post last week.

I’m glad its running great again for you.


Yes, this all makes sense.

The ignition coil pack was likely what was causing the two nonfiring cylinders, which possibly combined with leaky injectors were being flooded out with fuel. Liquid doesn’t compress as well as air does, so that can affect compression readings.

It’s a good thing that they did by cleaning our your gumped up fuel system. The work will pay for itself in improved efficiency.

It’s also good that you had them change out those tank straps.

It sounds like they did well by you. It’s nice to hear a good story for a change.

Sincere best.

Good to hear all is well now. Thanks for the post.

If they somehow got a “Bucket of raw sewage” out of the gas tank, then someone must have dumped a bucket of raw sewage IN the gas tank…Now, what about that 280 PSI compression?

Is THIS the engine in your car??

You should get an oil change because it’s possible the oil was contaminated with fuel.