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Compression and Starting

 
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  #1 (permalink)  
Old 19 Jun 2016, 05:31 pm
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Join Date: Jun 2015
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Default Compression and Starting

Hello, again! So I have finally gotten around to messing with the PT again. I truly wish I could get it running again as I love the car. My question is would zero to no compression cause a no start? I did a compression check and there is 25lbs on each cylinder. I would Ass-ume that it would start but just run very poorly but that could be a dumb assumption.

If it is possible, than I will proceed to replacing the head and gaskets. Thanks for all of the past and present help.
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Old 19 Jun 2016, 06:11 pm
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Default Re: Compression and Starting

Quote:
Originally Posted by Dahoopd View Post
Hello, again! So I have finally gotten around to messing with the PT again. I truly wish I could get it running again as I love the car. My question is would zero to no compression cause a no start? I did a compression check and there is 25lbs on each cylinder. I would Ass-ume that it would start but just run very poorly but that could be a dumb assumption.

If it is possible, than I will proceed to replacing the head and gaskets. Thanks for all of the past and present help.
First of all the engine will not fire with only 25 lbs.

Is the starter cranking normal or slow?

Did you do the compression test properly? Proper cycles? Throttle body open? All spark plugs out?

Have you checked your ignition timing yet?

I would advice not pull the head until you do a full diagnosis on what is causing the low compression and not starting.
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Last edited by ptcruisersteve; 19 Jun 2016 at 06:17 pm.
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Old 19 Jun 2016, 06:12 pm
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Default Re: Compression and Starting

Where are you located? Perhaps another member could help. Compression numbers that low are definitely not good.
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Old 19 Jun 2016, 06:50 pm
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Default Re: Compression and Starting

You will want to do a wet and dry compression test to see if it is the head or the rings. Out of curiosity, are the cams turning during crank?
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Old 20 Jun 2016, 07:36 pm
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Default Re: Compression and Starting

Quote:
Originally Posted by ptcruisersteve View Post
First of all the engine will not fire with only 25 lbs.

Is the starter cranking normal or slow?

Did you do the compression test properly? Proper cycles? Throttle body open? All spark plugs out?

Have you checked your ignition timing yet?

I would advice not pull the head until you do a full diagnosis on what is causing the low compression and not starting.
Thank you for the help and replies. I will save on posts by consolidating replies.

The starter is cranking normal although it does seem to kill the battery rather quickly while doing so. I can run the compression check on the cylinder twice before the battery wont turn it over anymore. The battery is tested and good.

Cycles? I put the compression gauge on each individual cylinder and cranked the motor over for a few seconds with TB open and the gauge stops at 25-30lbs. Only the cylinder being tested has the plug removed.

Timing is correct at cams and crank. The cams and cam gears turn correctly.

I live near Baltimore, Maryland.
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Old 20 Jun 2016, 07:47 pm
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Default Re: Compression and Starting

Quote:
Originally Posted by Dahoopd View Post
Thank you for the help and replies. I will save on posts by consolidating replies.

The starter is cranking normal although it does seem to kill the battery rather quickly while doing so. I can run the compression check on the cylinder twice before the battery wont turn it over anymore. The battery is tested and good.

Cycles? I put the compression gauge on each individual cylinder and cranked the motor over for a few seconds with TB open and the gauge stops at 25-30lbs. Only the cylinder being tested has the plug removed.

Timing is correct at cams and crank. The cams and cam gears turn correctly.

I live near Baltimore, Maryland.
I would suggest a compression leak down test. You need to find out where the leak is coming from.
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Old 21 Jun 2016, 05:32 pm
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Posts: 91
Default Re: Compression and Starting

Quote:
Originally Posted by ptcruisersteve View Post
I would suggest a compression leak down test. You need to find out where the leak is coming from.
Got a question? Does the cylinder have to be at TDC on compression to do a compression test? I am thinking I may be doing something wrong. This is the down side, I have no experience when it comes to testing and diag. I used a LA screw driver to "assume" TDC and then did the compression test.

On another note, I would really like this car to run even if it means pulling a good motor and replacing it (that I CAN DO) just to put a motor in it.
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Old 21 Jun 2016, 07:50 pm
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Default Re: Compression and Starting

It doesn't matter what position the piston is in when you start. You're going to spin the engine over 4 or 5 times on each cylinder anyway. At least that's the way I've always done it. I just do one cylinder at a time. Make sure someone is holding the gas pedal all the way down so the throttle body plate is open.
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Old 22 Jun 2016, 06:37 pm
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Default Re: Compression and Starting

Quote:
Originally Posted by chuzz View Post
It doesn't matter what position the piston is in when you start. You're going to spin the engine over 4 or 5 times on each cylinder anyway. At least that's the way I've always done it. I just do one cylinder at a time. Make sure someone is holding the gas pedal all the way down so the throttle body plate is open.

Chuzz, Thanks for the pointers. I was holding the TB plate open by hand while doing it. Does it matter or does the peddle have to be depressed?
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Old 23 Jun 2016, 08:49 am
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Default Re: Compression and Starting

You can hold it open by hand, but it's a lot easier if you just have someone inside the car put the peddle to the floor while they crank the engine. I'm guessing you have a helper, right?
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