DodgeTrucks.Org

[RangerJoe]

OK, guys, you may remember me. I was on here about a month or so ago griping about how my truck still consumes oil even after the Hughes Plenum install.

I've also done a full tune up - cap, rotor, wires, PCV, 180 thermo, hoses, serp belt, even pulleys. I put in a brand new K&N Air filter system. I did EVERYTHING that was easiest to get to with the manifold off. I've even bought a UV oil dye detection kit and I'm about to check that out too. Since the tune-up and plenum pan, the truck burns about half as much oil - instead of 2 qts every 1,500 - 2000 miles, I seem to burn about a quart (based only on about 2 trials.) There has really been no worthy change in MPG - still mostly between 11 - 12.

So, a month later, I'm still burning oil, and some folks on here say that it can only be 2 things: rings, or valve guides.

In the interest of testing the rings, I did a compression test today. I used the guidelines for the the test laid out in the Daimler-Chrysler 2000 Shop Manual for this truck. I did five tests on each cylinder. Here's the results, as they appeared:

Cylinder 1:
#1 - 140 lbs (abberative)
#2 - 110 lbs
#3 - 110 ibs
#4 - 110 lbs
#5 - 110 lbs

Cylinder 2:
#1 - 125 lbs (slighty abberative)
#2 - 110 lbs
#3 - 110 lbs
#4 - 111 lbs
#5 - 111 lbs

Cylinder 3:
#1 - 128 lbs (slightly abberative)
#2 - 115 lbs
#3 - 109 lbs
#4 - 117 lbs
#5 - 110 lbs

Cylinder 4:
#1 - 115 lbs
#2 - 112 lbs
#3 - 111 lbs
#4 - 111 lbs
#5 - 111 lbs

Cylinder 5:
#1 - 101 lbs
#2 - 102 lbs
#3 - 101 lbs
#4 - 105 lbs
#5 - 103 lbs

Cylinder 6:
#1 - 110 lbs
#2 - 115 lbs
#3 - 110 lbs
#4 - 110 lbs
#5 - 110 lbs

Cylinder 7:
#1 - 110 lbs
#2 - 110 lbs
#3 - 110 lbs
#4 - 109 lbs
#5 - 109 ibs

Cylinder 8:
#1 - 110 lbs
#2 - 110 lbs
#3 - 111 lbs
#4 - 111 lbs
#5 - 110 lbs

So, there you have it. Everything is OK by D-C specs. Here's the odd thing. None of the plugs were badly fouled. They all looked fairly clean. The only things I noticed worth saying is that the #4 plug had some oil on the ceramic insulator for the electrode, and there was some oil (though not a lot) on the threads of the plug. On the #8 plug there was a large amount of oil on the threads of the plug, but none on the ceramic. This was dark, wet oil.

It seems to me that my rings are in good order. (Thank God.) Is this a valve guide/valve seal problem? And, if I am burning this amout of oil, why am i not seeing it in smoke or on the plugs? Maybe, _I_ am the head case, and I should stop worrying about this? Do these trucks just burn oil like this? I don't SEEM to be burning it. I JUST DON'T GET WHERE IT'S GOING!!!!!

A friend suggested installing a catch can on the PCV line, just to see what I'm pulling through there. Does anyone see any value in this?
_________________
Look, would it help you if I just gave up and went mad now?
__________________________
2000 Dodge Ram 2500 QuadCab
5.9L V8 (gas)
137,500 miles
5-spd
4.11s
K&N GENII FIPK
Hughes Engines Plenum Pan

[amc racer]

If I read it right, that's a quart within 1,500~2,000 miles?
Pretty much within allowances of most auto makers.
With the oil on the threads, any seepage from the valve covers?
_________________
69 AMC 12.79@105.9 4,200 lb barge with a 33 year old engine (Car Craft June/05)
99 Ram 2500 CC/LB CTD 4X4 , full Magnaflow stainless 4", Edge EZ, AFE
There's no such thing as too much truck.

NAMDRA Officer/Member#2923

[BR]

the shitty thing is that they should be up around 150lbs. so down to 110 is something wrong to me. your valve guides could be a bit burned causing it. or your rings worn. does it burn a lot of oil out the tailpipe? on the pressure gauge, did the pressur spike up fast and then slowly gain? or did it take a bit to get up to the final pressure? you can use that to somewhat determine where your problem is. a leakdown test also helps a lot more.
_________________
03 2500 quad cab, HO CTD, 6 speed, 2" daystars, 35x12.5x17 ST's, Pro Comp 1079s, herculiner'd bed. tis all for "now"

[mrclean]

One quart per 1500-2000 miles is acceptable per GM and most others. Personally, I don't find it acceptable, but that's just my opinion. I'd say check compression again. Only check each cylinder, record the reading, then squirt some oil down into the cylinder and check it again. If the numbers go up, you've got a ring problem. To check the valve guides, you'll need to do a leakdown test. Unfortunately, most home mechanics don't have the proper gauge for this(myself included). Have a friend follow you down the road @50mph. Let off the fuel. Your friend should look for blue smoke out the pipe when you let off. Blue smoke under closed throttle coast points to bad valve guides.HTH

[schmedly]

I'm not familiar with the houghs plenum, so don't jump on me if this is really stupid. Is there any chance that there is something wrong in your plenum repair? Those compression readings may not be great, but they don't sound bad enough for that kind of oil consumption.
_________________
'98 Ram 1500 4X4 5.9

[twilson]

A vacuum gauge fluttering on the needle will tell you if your valve guides are worn.


If you dont have excessive blow by coming out of your valve covers then I would say your rings are fine.

Todd

[HankL]

Are those 110 psi tests on the first 'puff' of the tester?

Here's an old post on my test results:
I did a compression test on my 1995 Magnum 5.9V8 this afternoon.

This engine was broken in for the first 18,000 miles with conventional oil and
switched to Mobil One synthetic. It presently has the Mobil One 15w-50 but
has used the 5w-30 and 0w-30 in the past.

Engine has about 142,000 miles on it.

I did the compression test because about 3000 miles ago my 2nd catalytic
converter plugged and created excessive exhaust backpressure - so much so that
the truck would not go above about 25 mph for the 8 miles it took to get to
the muffler shop. This excessive backpressure ruined the EGR modulating valve
diaphram, which was replaced, as was the O2 sensor.

I was worried I might have burned an exhaust valve.

The engine has been running 'ok' but seems to get slightly less mpg than
before.

I changed 2000 miles ago to NGK NGK ZFR5F11 (stock number 2262) just after the
bad cat, and the engine idle seems more uneven. Previous plugs were Autolite
3923.

In the figures that follow, 'Oil Added' means a squirt of Mobil One Gear Oil
75w-90 was put in the cylinder using a rubber hose on the end of the gear oil
bottle. The engine was cranked 5 revolutions and then the compression on that
cylinder was read again. It would have been better to have used a plunger
style oil can and put a consistent 3 shots into the cylinder. It might be
possible that the 'Oil Added' compression psi's are not consistent because the
amount of gear oil varied.

Engine was cool from sitting overnight.
Outside air 75 degrees.
Throttle bores were propped wide open during cranking.
All sparkplugs were removed.
Readings were taken on the 5th stroke and the compression tester had a
'shraeder valve' that held pressure on the gauge until pressed. Typical first
stroke compression numbers were around 100 psi and climbed to steady maximum
shown below by the 4th stroke.

Results:

Cylinder 1 - dry 145psi - oil added 175
Cylinder 2 - dry 145psi - oil added 165

Cylinder 3 - dry 150psi - oil added 185
Cylinder 4 - dry 155psi - oil added 185

Cylinder 5 - dry 155psi - oil added 180
Cylinder 6 - dry 150psi - oil added 170

Cylinder 7 - dry 160psi - oil added 175
Cylinder 8 - dry 148psi - oil added 165

Average dry: 151 psi
( # 7 is 6% high, # 8 is 2% low)

Average Oil Added: 175 psi
(#3&4 are 6% high, #2&8 are 6% low)

Additional information:
All 8 NGK sparkplugs looked clean after 2000 miles of mostly interstate
driving and had extremely white insulators on the relatively long 'projected
tips' of this design plug. Cylinder 6 had just bit different looking deposits
on the ground strap electrode - the other 7 plugs grounds looked normal 'dry
flaky' and this one looked slightly 'greasy'. When I changed out Cylinder 6
on the Autolite 3923's used previously cylinder 6's white insulator had more
black carbon deposits on it and looked just a bit oily. At the time I took
this to be because I had just sprayed a can of Mopar Combustion Chamber
Conditioner into the engine.

Engine does not seem to be using any coolant. Oil consumption is about 1
quart every 2000-3000 miles and there are slow drips from both front and rear
engine crankshaft seals.

Cylinder 7 may have more carbon deposits. I had previously found some time
ago that spraying Mopar Combustion Chamber Conditioner in cylinder pairs 7&8
got rid of pinging temporarily, maybe the problem is just cylinder #7.

The 1995 Ram FSM is not too helpful on what 'proper' compression readings
should be - it just says 100 psi on page 9-108 of my model year 1995 book.

This 100 psi seems to me like a 'cop out' number from DC listed to counter
angry customers who have a low reading cylinder. Or perhaps it is an
unchanged 'carry over' spec from 1978-1984 LA 360 V8s that had only 8 to 1
compression?

This 360 V8 engine is supposed to have a 9.1 to 1 compression ratio, as listed
on FSM page 9-81. {I hear later model 1996+ 5.9V8s were lowered to 8.9 to 1
compression ratio because of numerous owner pinging complaints.

On page 9-142 the 1995 FSM says the 1995 8.0L V10 with 8.4 to 1 compression
ratio is supposed to have 170-190 psi compression test numbers. Go figure?

The Engine Analyser 3.0 software from Performance Trends estimates that a 1995
Magnum 5.9V8 engine with 9.1 static compression ratio and the cam specs in the
1995 FSM should have 180 psi 'theoretical' cranking compression.
----------
In this month's Car Craft Steve Dulcich did three warmed up engine compression
tests on a 400 hp 9:1 Chevy 350 engine.

First one on worn engine rings that had done 100 dyno runs and the compression
test ran 160 psi.

Second test Steve did on brand new file-fitted conventional rings ran 165 psi.

Third test was on the 'Total Seal Gapless Rings' and those ran 185 psi.
-------
RUNNING COMPRESSION TESTS

This is a summary of the responses to a question about a "Dynamic
Compression Test" sent out via the i-ATN e-mail list and posted on
Compuserve's "For Techs Only" forum. It seemed to ring a bell with the
most techs as a "running compression test," so I will use that name
here. Call it what you will, this test is an accurate if slightly
esoteric and time-consuming test of cylinder breathing. It is in fact
recommended by Detroit Diesel instead of a traditional static
compression test, it is included as part of Delmar's ATTP program, and
several instructors use it as part of their state emission training
programs.

HOW TO PERFORM A RUNNING COMPRESSION TEST

1. Start with a normal ("static") compression test. To eliminate rings,
valves, holes in pistons, that sort of things.
To do this: Unscrew all sparkplugs, disconnect fuel injector plugs,
disconnect coil primary plug, and have another battery nearby in case the
cranking of this engine runs its battery down. Prop open the thottle bores
being carefull not to drop anything in them. Carefully screw in your
compression tester (the press on type gauges are vastly inferior) to one
spark plug hole. Crank the engine over. Record the compression tester
reading on the first revolution of the engine and the fifth revolution.
Write these values down and go onto the next cylinder.
If you suspect you have bad rings, repeat the entire test above but
this time put an eyedropper full of SAE 70W gear oil in each cylinder
before screwing in the compression tester. 30 psi higher readings on a
cylinder on this 'oil-seal-assisted' second test indicates that cylinder
has worn out or broken rings.

2. The Dynamic Compression Test:
Remove prop from throttle bores. Put all spark plugs but one back in and
reconnect all electrical plugs taken off in step one above.Ground that plug
wire to prevent module damage. Disconnect that injector on a port fuel
system.

3. Carefully thread your compression tester into the empty hole. The test
can be done without a Shrader { press to release } valve, but most people
recommended leaving the valve in the gauge and "burping" the gauge every
5-6 "puffs".

4. Start the engine and take a reading. Write it down

5. Now goose the throttle for a "snap acceleration" reading. Reading
should rise. Write it down NOTE: Don't use the gas pedal for this snap
acceleration. The idea is to manually open then close throttle as fast
as possible while without speeding up the engine. This forces the engine
to take a "gulp" of air.

6. Now write down your readings for at least the bad cylinder (if there
is a single bad cylinder) and maybe 2-3 good ones. Make a chart like
this:
..........STATIC COMPR /IDLE -RUNNING COMPR / SNAP
Cyl1 ...........150 ..................75 ..........................125
Cyl 2 ..........175 ..................80 ..........................130
Cyl 3 ..........160 ..................75 ..........................120

7. ANALYSIS: Running compression at idle should be 50-75 psi (about half
cranking compression). Snap throttle compression should be about 80% of
cranking compression.

EXAMPLE 1 - RESTRICTED INTAKE
CYL STATIC COMPR IDLE -RUNNING COMPR - SNAP
Cyl 1 150 ...................75 ...............................80
If Snap reading is low (much less than 80% cranking
compression), look for restricted intake air- severely carboned intake
valve, worn lobe on cam, rocker problem, "shutters" mispositioned in the
runners. (Toyota, Vortec etc. with variable runner length) Comparing
measurements between cylinders is important.

EXAMPLE 2 - RESTRICTED EXHAUST
CYL STATIC COMPR IDLE -RUNNING COMPR - SNAP
Cyl 1 .......150 ...........75 .............................180
If snap measurements are significantly higher than
80% of cranking measurements, look for restricted exhaust on that
cylinder-such as worn exhaust cam lobe, or collapsed lifter. Or, if they
are all high, look for a clogged cat converter.

WHAT IS GOING ON?

When you do a normal compression test, you are checking cylinder
sealing, not cylinder breathing. When you check engine vacuum at the
manifold, you are looking at the breathing of the entire engine, by
checking vacuum at a common (plenum) source. You aren't testing a
specific cylinder. This test looks at the breathing of an individual
cylinder.

Say the engine is running at 18 inches vacuum. Atmospheric pressure is
about 30 inches, so the difference (30 inches - 18 inches = 12 inches)
is what the engine is sucking in. 12 inches mercury is equivalent to
about 6 psi absolute air pressure. Compressed at an 8 to 1 ratio, you
should get CONSIDERABLY MORE THAN 6 x 8 = 48 psi pressure if all the air
makes it into the cylinder and then gets pushed out. So your idle reading
on running compression is about 55 to 75 psi.
Contary to popular belief, an 8 to 1 compression ratio will give you
MORE than eight times the pressure. It would give you exactly eight times
the pressure - but only if you compressed the air and then gave the now-hot
air a few minutes to cool. Fast compression in an engine gives
considerably more pressure because the air doesn't have time to cool. This
kind of compression is called "adiabatic" which is a fancy name for "no
loss of heat."

When you snap the throttle, the manifold vacuum drops, so the absolute
air pressure going into the cylinder increases.

In fact, you can do running compression tests at various constant
manifold vacuum readings (by brake-torqueing the engine momentarily),
and the running compression should roughly correspond to the manifold
vacuum. For example, at 10 inches vacuum, engine should be breathing in
about 10 psi air pressure, so you should see a running compression
reading of about 80 psi (at 8 to 1 compression ratio).

If one cylinder reads low running compression compared to the rest it
means that the air didn't make it in. If one cylinder reads high, the
air didn't make it out (and the next pulse of air raised the pressure).

Many thanks to the people who responded through both Compuserve and
i-ATN. Special thanks go to Bruce Amacker, Bob Cammarano, Chris Chesney,
Troy Croskey, Don Hazlett, Rick Jensen, Greg McConiga, David Palin, &
Thomas ??(whose last name I seem to have lost)

[HankL]

Are those 110 psi tests on the first 'puff' of the tester?

Here's an old post on my test results:
I did a compression test on my 1995 Magnum 5.9V8 this afternoon.

This engine was broken in for the first 18,000 miles with conventional oil and
switched to Mobil One synthetic. It presently has the Mobil One 15w-50 but
has used the 5w-30 and 0w-30 in the past.

Engine has about 142,000 miles on it.

I did the compression test because about 3000 miles ago my 2nd catalytic
converter plugged and created excessive exhaust backpressure - so much so that
the truck would not go above about 25 mph for the 8 miles it took to get to
the muffler shop. This excessive backpressure ruined the EGR modulating valve
diaphram, which was replaced, as was the O2 sensor.

I was worried I might have burned an exhaust valve.

The engine has been running 'ok' but seems to get slightly less mpg than
before.

I changed 2000 miles ago to NGK NGK ZFR5F11 (stock number 2262) just after the
bad cat, and the engine idle seems more uneven. Previous plugs were Autolite
3923.

In the figures that follow, 'Oil Added' means a squirt of Mobil One Gear Oil
75w-90 was put in the cylinder using a rubber hose on the end of the gear oil
bottle. The engine was cranked 5 revolutions and then the compression on that
cylinder was read again. It would have been better to have used a plunger
style oil can and put a consistent 3 shots into the cylinder. It might be
possible that the 'Oil Added' compression psi's are not consistent because the
amount of gear oil varied.

Engine was cool from sitting overnight.
Outside air 75 degrees.
Throttle bores were propped wide open during cranking.
All sparkplugs were removed.
Readings were taken on the 5th stroke and the compression tester had a
'shraeder valve' that held pressure on the gauge until pressed. Typical first
stroke compression numbers were around 100 psi and climbed to steady maximum
shown below by the 4th stroke.

Results:

Cylinder 1 - dry 145psi - oil added 175
Cylinder 2 - dry 145psi - oil added 165

Cylinder 3 - dry 150psi - oil added 185
Cylinder 4 - dry 155psi - oil added 185

Cylinder 5 - dry 155psi - oil added 180
Cylinder 6 - dry 150psi - oil added 170

Cylinder 7 - dry 160psi - oil added 175
Cylinder 8 - dry 148psi - oil added 165

Average dry: 151 psi
( # 7 is 6% high, # 8 is 2% low)

Average Oil Added: 175 psi
(#3&4 are 6% high, #2&8 are 6% low)

Additional information:
All 8 NGK sparkplugs looked clean after 2000 miles of mostly interstate
driving and had extremely white insulators on the relatively long 'projected
tips' of this design plug. Cylinder 6 had just bit different looking deposits
on the ground strap electrode - the other 7 plugs grounds looked normal 'dry
flaky' and this one looked slightly 'greasy'. When I changed out Cylinder 6
on the Autolite 3923's used previously cylinder 6's white insulator had more
black carbon deposits on it and looked just a bit oily. At the time I took
this to be because I had just sprayed a can of Mopar Combustion Chamber
Conditioner into the engine.

Engine does not seem to be using any coolant. Oil consumption is about 1
quart every 2000-3000 miles and there are slow drips from both front and rear
engine crankshaft seals.

Cylinder 7 may have more carbon deposits. I had previously found some time
ago that spraying Mopar Combustion Chamber Conditioner in cylinder pairs 7&8
got rid of pinging temporarily, maybe the problem is just cylinder #7.

The 1995 Ram FSM is not too helpful on what 'proper' compression readings
should be - it just says 100 psi on page 9-108 of my model year 1995 book.

This 100 psi seems to me like a 'cop out' number from DC listed to counter
angry customers who have a low reading cylinder. Or perhaps it is an
unchanged 'carry over' spec from 1978-1984 LA 360 V8s that had only 8 to 1
compression?

This 360 V8 engine is supposed to have a 9.1 to 1 compression ratio, as listed
on FSM page 9-81. {I hear later model 1996+ 5.9V8s were lowered to 8.9 to 1
compression ratio because of numerous owner pinging complaints.

On page 9-142 the 1995 FSM says the 1995 8.0L V10 with 8.4 to 1 compression
ratio is supposed to have 170-190 psi compression test numbers. Go figure?

The Engine Analyser 3.0 software from Performance Trends estimates that a 1995
Magnum 5.9V8 engine with 9.1 static compression ratio and the cam specs in the
1995 FSM should have 180 psi 'theoretical' cranking compression.
----------
In this month's Car Craft Steve Dulcich did three warmed up engine compression
tests on a 400 hp 9:1 Chevy 350 engine.

First one on worn engine rings that had done 100 dyno runs and the compression
test ran 160 psi.

Second test Steve did on brand new file-fitted conventional rings ran 165 psi.

Third test was on the 'Total Seal Gapless Rings' and those ran 185 psi.
-------
RUNNING COMPRESSION TESTS

This is a summary of the responses to a question about a "Dynamic
Compression Test" sent out via the i-ATN e-mail list and posted on
Compuserve's "For Techs Only" forum. It seemed to ring a bell with the
most techs as a "running compression test," so I will use that name
here. Call it what you will, this test is an accurate if slightly
esoteric and time-consuming test of cylinder breathing. It is in fact
recommended by Detroit Diesel instead of a traditional static
compression test, it is included as part of Delmar's ATTP program, and
several instructors use it as part of their state emission training
programs.

HOW TO PERFORM A RUNNING COMPRESSION TEST

1. Start with a normal ("static") compression test. To eliminate rings,
valves, holes in pistons, that sort of things.
To do this: Unscrew all sparkplugs, disconnect fuel injector plugs,
disconnect coil primary plug, and have another battery nearby in case the
cranking of this engine runs its battery down. Prop open the thottle bores
being carefull not to drop anything in them. Carefully screw in your
compression tester (the press on type gauges are vastly inferior) to one
spark plug hole. Crank the engine over. Record the compression tester
reading on the first revolution of the engine and the fifth revolution.
Write these values down and go onto the next cylinder.
If you suspect you have bad rings, repeat the entire test above but
this time put an eyedropper full of SAE 70W gear oil in each cylinder
before screwing in the compression tester. 30 psi higher readings on a
cylinder on this 'oil-seal-assisted' second test indicates that cylinder
has worn out or broken rings.

2. The Dynamic Compression Test:
Remove prop from throttle bores. Put all spark plugs but one back in and
reconnect all electrical plugs taken off in step one above.Ground that plug
wire to prevent module damage. Disconnect that injector on a port fuel
system.

3. Carefully thread your compression tester into the empty hole. The test
can be done without a Shrader { press to release } valve, but most people
recommended leaving the valve in the gauge and "burping" the gauge every
5-6 "puffs".

4. Start the engine and take a reading. Write it down

5. Now goose the throttle for a "snap acceleration" reading. Reading
should rise. Write it down NOTE: Don't use the gas pedal for this snap
acceleration. The idea is to manually open then close throttle as fast
as possible while without speeding up the engine. This forces the engine
to take a "gulp" of air.

6. Now write down your readings for at least the bad cylinder (if there
is a single bad cylinder) and maybe 2-3 good ones. Make a chart like
this:
..........STATIC COMPR /IDLE -RUNNING COMPR / SNAP
Cyl1 ...........150 ..................75 ..........................125
Cyl 2 ..........175 ..................80 ..........................130
Cyl 3 ..........160 ..................75 ..........................120

7. ANALYSIS: Running compression at idle should be 50-75 psi (about half
cranking compression). Snap throttle compression should be about 80% of
cranking compression.

EXAMPLE 1 - RESTRICTED INTAKE
CYL STATIC COMPR IDLE -RUNNING COMPR - SNAP
Cyl 1 150 ...................75 ...............................80
If Snap reading is low (much less than 80% cranking
compression), look for restricted intake air- severely carboned intake
valve, worn lobe on cam, rocker problem, "shutters" mispositioned in the
runners. (Toyota, Vortec etc. with variable runner length) Comparing
measurements between cylinders is important.

EXAMPLE 2 - RESTRICTED EXHAUST
CYL STATIC COMPR IDLE -RUNNING COMPR - SNAP
Cyl 1 .......150 ...........75 .............................180
If snap measurements are significantly higher than
80% of cranking measurements, look for restricted exhaust on that
cylinder-such as worn exhaust cam lobe, or collapsed lifter. Or, if they
are all high, look for a clogged cat converter.

WHAT IS GOING ON?

When you do a normal compression test, you are checking cylinder
sealing, not cylinder breathing. When you check engine vacuum at the
manifold, you are looking at the breathing of the entire engine, by
checking vacuum at a common (plenum) source. You aren't testing a
specific cylinder. This test looks at the breathing of an individual
cylinder.

Say the engine is running at 18 inches vacuum. Atmospheric pressure is
about 30 inches, so the difference (30 inches - 18 inches = 12 inches)
is what the engine is sucking in. 12 inches mercury is equivalent to
about 6 psi absolute air pressure. Compressed at an 8 to 1 ratio, you
should get CONSIDERABLY MORE THAN 6 x 8 = 48 psi pressure if all the air
makes it into the cylinder and then gets pushed out. So your idle reading
on running compression is about 55 to 75 psi.
Contary to popular belief, an 8 to 1 compression ratio will give you
MORE than eight times the pressure. It would give you exactly eight times
the pressure - but only if you compressed the air and then gave the now-hot
air a few minutes to cool. Fast compression in an engine gives
considerably more pressure because the air doesn't have time to cool. This
kind of compression is called "adiabatic" which is a fancy name for "no
loss of heat."

When you snap the throttle, the manifold vacuum drops, so the absolute
air pressure going into the cylinder increases.

In fact, you can do running compression tests at various constant
manifold vacuum readings (by brake-torqueing the engine momentarily),
and the running compression should roughly correspond to the manifold
vacuum. For example, at 10 inches vacuum, engine should be breathing in
about 10 psi air pressure, so you should see a running compression
reading of about 80 psi (at 8 to 1 compression ratio).

If one cylinder reads low running compression compared to the rest it
means that the air didn't make it in. If one cylinder reads high, the
air didn't make it out (and the next pulse of air raised the pressure).

Many thanks to the people who responded through both Compuserve and
i-ATN. Special thanks go to Bruce Amacker, Bob Cammarano, Chris Chesney,
Troy Croskey, Don Hazlett, Rick Jensen, Greg McConiga, David Palin, &
Thomas ??(whose last name I seem to have lost)

[RangerJoe]

The compression tests were done according to the Daimler Chrysler manual, which says to let the engine make 3 complete revolutions. The manual notes an acceptable level of 100 psi. My Dad monitored the rotations via a mark on the crank pulley while I cranked the starter motor.

Now, as a goof, and just to see if there was a ceiling on the pressurse for any or all cylinders, my Dad suggested going beyond 3 rotations. We did it for three cylinders, which I cannot unfortunately name for you. When we went to 4 full rotations of the crank, we got 145 PSI every time. On one cylinder, we went 6 rotations and still got 145. But because the manual called for only 3 revolutions, I did it that way and I was happy with the results.

Here's the direct quote of the policy from the D-C Manual for my model year:

"Ensure the battery is fully charged and the engine starter motor is in good operating condition. Otherwise the indicated compression may not be valid for diagnosis purposes.

(1) Clean the spark plug recesses with compressed air
(2) Remove the spark plugs
(3) Secure the throttle in wide open position
(4) Disconnect the engine coil
(5) Insert a compression pressure gauge aand rotate the engine with the starter motor for three (3) revolutions
(5) Record the compression on the third revolution. Continue the test for the remaining cylinders.

Refer to Engine Specifications for the correct engine compression pressures."

If you then refer to that section, you find that the book says the "5.9L ENGINE SPECIFICATIONS" call for a "Compression Pressure of 689.5 kPa (100 psi) (Minimum)"

That's where I got it from, gents. I was just following orders.

This is from the "2000 Service Manual Ram Truck 1500 - 3500 2 Wheel Drive/4 Wheel Drive" copyright 1999 DaimlerChrysler Corporation.
_________________
Look, would it help you if I just gave up and went mad now?
__________________________
2000 Dodge Ram 2500 QuadCab
5.9L V8 (gas)
137,500 miles
5-spd
4.11s
K&N GENII FIPK
Hughes Engines Plenum Pan