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Old 01-01-2008
Thread Starter
Join Date: Jan 2008
Location: Colima, Mexico
Posts: 1
Icon4 engine compression low???

what´s the normal engine compression???
I just had my truck tested and has 90psi , is this normal ??
I own a ranger 94 auto v6 3.0 2wd ext cab no mods 130k
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Old 01-01-2008
Join Date: Dec 2007
Location: idleyld Park , oregon
Posts: 40
That figure is low .
You need to do things to make the right test .
Start engine , run till operating temp .(heat coming out the heater , and defrost )
Remove all 6 plugs .
Then start on either side of the engine , and block the throttle all the way open .
You Need To see the needle of the gauge leap 4 to 5 times for each cylinder .
As I said record this reading on a piece of masking tape attached to your hood .
Now note which of the figures are low .
then determine who low they are compared to the highest ones .
should be no more than 10-15% difference.
Next add 1 teaspoon of oil to the cylinder that is low , If you have more than one tht is low , do them one at a time . now record your readings
THis is where it get's hard .
The cylinders that were low , and you added oil to , should have come up in reading , IF THE compression ring ,is bad , the oil helps to seal .
If nothing happens , it may be a valve not sealing in the seat .

You can also use a vaccum gauge to " READ the engine" http://sbftech.com/index.php/topic,3020.0.html
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Old 01-01-2008
Rev's Avatar
Rev Rev is offline
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Join Date: May 2005
Location: San Diego, CA
Posts: 1,179
I believe the book calls for at least 100 psi min and no more than 15 psi difference between lowest & highest cylinders
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Old 01-02-2008
Join Date: Dec 2007
Location: Taylorsville Ky
Posts: 289
When they get to about 50-60 psi it probably won't start and it don't have to be all of them either.

It depends on the comp ratio of your engine as to what the engine will pump when new or rebuilt.

When I sold my '93 3.0L last summer it had 220,000 miles on it and it still runs fine. I can't remember what the last comp check was. A friend owns it now.
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Old 01-02-2008
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Join Date: Jun 2004
Location: Kennett Square, PA
Posts: 10,620
I know lots of 3.0's that run for 200-300K easy. Hoping for that from mine. Nearly 100k on it and it still runs strong -- for a 3.0 that is!
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Old 01-02-2008
Mark98xlt's Avatar
Join Date: Jun 2004
Location: Parma Ohio
Posts: 13
eh I got about 115k out of my 98's 3.0 before it locked itself up and I always properly maintained it and never ragged on it.

the cam syncronizer gear ate itself up starved the engine of oil and locked itself up.

common prob on the 3.0's might want to replace it if its a higher milage 3.0
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Old 01-02-2008
n3elz's Avatar
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Join Date: Jun 2004
Location: Kennett Square, PA
Posts: 10,620
Thanks, Mark, for that heads up on the cam synchro problem. Good thing to know as I work my engine pretty hard and I'm approaching 100K now.
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