Compression Pressure
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Joined: Feb 2002
Posts: 2,404
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From: Cleveland, WI USA
Compression Pressure
Man, I wish I could tell you what the specs say it should be at, but I can only tell you what my 71 460 was at.
I had a range from 70psi to 135 psi. The instructions in my tester say you shouldn't have more that 5-10 psi different between the cylinders. I'm re-ringing it tonight as my parts just arrived.
I was once told that 120 psi was good. Did you try a search on this site?
Kevin K.
I had a range from 70psi to 135 psi. The instructions in my tester say you shouldn't have more that 5-10 psi different between the cylinders. I'm re-ringing it tonight as my parts just arrived.
I was once told that 120 psi was good. Did you try a search on this site?
Kevin K.
Elder User
Joined: Aug 2001
Posts: 508
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Compression Pressure
Numbers from an 88 7.5 EFI:
Test 1 (engine hadn't turned over in 6 months): I can't find my numbers, but they were all over the place - like 60 to 145.
Test 2 #1 to #8: 160, 150, 150, 145, 150, 145, 125, 145
Test 3: 165, 145, 50, 125, 165, 165, 160, 145
Test 4 dry: 155, 140, 135, 125, 140, 140, 150, 140
Test 4 wet: 170, 170, 145, 145, 155, 150, 170, 150
In test 3, #3 was really low because the lifter had collapsed due to not enough engine oil.
PS These tests are with a cold engine. I see no way to pull the plugs on a hot engine without burning myself.
PPS I'm having to use a little extention on the tester. The extra volume of the extention must drop the result a few psi.
PPPS This engine has an extreme oil consumption problem that I'm trying to diagnose: Like 3 qts in 100 miles, or 3 qts in 3 minutes of high idle.
Test 1 (engine hadn't turned over in 6 months): I can't find my numbers, but they were all over the place - like 60 to 145.
Test 2 #1 to #8: 160, 150, 150, 145, 150, 145, 125, 145
Test 3: 165, 145, 50, 125, 165, 165, 160, 145
Test 4 dry: 155, 140, 135, 125, 140, 140, 150, 140
Test 4 wet: 170, 170, 145, 145, 155, 150, 170, 150
In test 3, #3 was really low because the lifter had collapsed due to not enough engine oil.
PS These tests are with a cold engine. I see no way to pull the plugs on a hot engine without burning myself.
PPS I'm having to use a little extention on the tester. The extra volume of the extention must drop the result a few psi.
PPPS This engine has an extreme oil consumption problem that I'm trying to diagnose: Like 3 qts in 100 miles, or 3 qts in 3 minutes of high idle.
Thread Starter
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Senior User
Joined: Jun 2003
Posts: 213
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From: Edmonton Alberta Canada
Compression Pressure
still, getting upto 170 for compression, that is I beleive what these engines are suppose to be getting for compression, and the '93 foes through a little bit of oil itself, my Bronc with the 88 460 burns a bit in the morning, especially under full throttle, but I beleive that it is the valve seals leaking, hope to rebuild in the next year, and hoping for at least 400-450 out of the EFI
Elder User
Joined: Aug 2001
Posts: 508
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Compression Pressure
An update:
I found and fixed my oil burning problem: The intake manifold gasket was leaking, probably around the #4 port. With a new gasket it no longer smokes! Plus, engine braking has improved remarkably. Going down a steep hill in 3rd without brakes the truck actually slows down.
I found and fixed my oil burning problem: The intake manifold gasket was leaking, probably around the #4 port. With a new gasket it no longer smokes! Plus, engine braking has improved remarkably. Going down a steep hill in 3rd without brakes the truck actually slows down.
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Senior User
Joined: Jul 2003
Posts: 121
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From: Black Hills SD.
Compression Pressure
86 F250 460 200Kmiles (unknown engine milage)
all plugs removed, throttle blocked open, engine almost stone cold.
148-152 in all cylinders. The variance you have listed is way out of spec, I would agree that 10 lbs between highest and lowest is the MOST variance you would want and still consider giving it a clean bill of health.
Tony
all plugs removed, throttle blocked open, engine almost stone cold.
148-152 in all cylinders. The variance you have listed is way out of spec, I would agree that 10 lbs between highest and lowest is the MOST variance you would want and still consider giving it a clean bill of health.
Tony
Senior User
Joined: Jul 2003
Posts: 121
Likes: 0
From: Black Hills SD.
Compression Pressure
I had no idea Ford allowed so much variance, this is surprising to me but I do not presume to know more than the manufacturer! hehe
My own experience has shown me that such variance might leave an engine with some drivability or performance issues and has without fail indicated a bit of wear, I NEVER buy a vehicle w/o first performing a comp. check, EVER.
I have never personally seen a tight engine exhibit more than about 10% variance, this netted from my experience with various Ford 4cyl, Ford V8 and VW air cooled. This is only from my experience and of course, your milage may vary.
Ford has been very good to me, damn good equipment. I will not question their specs. Enjoy the torque!
Tony
My own experience has shown me that such variance might leave an engine with some drivability or performance issues and has without fail indicated a bit of wear, I NEVER buy a vehicle w/o first performing a comp. check, EVER.
I have never personally seen a tight engine exhibit more than about 10% variance, this netted from my experience with various Ford 4cyl, Ford V8 and VW air cooled. This is only from my experience and of course, your milage may vary.
Ford has been very good to me, damn good equipment. I will not question their specs. Enjoy the torque!
Tony
Elder User
Joined: Aug 2001
Posts: 508
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Compression Pressure
You might have noticed that my highest and lowest numbers kept moving around. The lowest in test 2 was one of the highest in test 4. I suspect that the leaking intake gasket allowed various amounts of oil to enter the cylinders, causing the readings to vary. I was also doing the tests with a totally cold engine - parked overnight or possible even several days. I'm sure that the lifters which were holding a valve open had plenty of time to leak down.
Senior User
Joined: Jul 2003
Posts: 121
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From: Black Hills SD.
Compression Pressure
I hear ya on the lifter bleed down. I let mine run for a while, let it cool for a couple hours, when I did my test it was still a little warm but touchable. I thought I had a burnt valve or something very ugly, a harsh missfire that turned out to be just a couple weak valve springs. I was shocked to see the compression consistant between the cylinders.
I would love to go to fuel injection!!! I might get something a little better than 7-9 mpg!! perhaps one day, a cell phone weilding motorist will smack his/her power stroke into a tele pole, then I can convert do diesel!!
Im glad you didnt find a hole in the piston, replacing pistons is a sucky way to spend an afternoon.
Tony
I would love to go to fuel injection!!! I might get something a little better than 7-9 mpg!! perhaps one day, a cell phone weilding motorist will smack his/her power stroke into a tele pole, then I can convert do diesel!!
Im glad you didnt find a hole in the piston, replacing pistons is a sucky way to spend an afternoon.
Tony
Junior User
Joined: Jun 2003
Posts: 50
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Compression Pressure
when checking your PSI - do it with the carb fully open. THis will give you a more accurate #. you dont drive truck with carb closed? Just disconnect the coil and have a friend hold down the pedal.
Ed
Ed