ad3.152 compression psi?

[jfharper]

I'm losing power on my engine that I recently rebuilt and wanted to check the compression...is the general rule anything above 250 psi is good? Also, I read that there is not supposed to be more than 10% difference...does that mean 10% difference between cylinder readings?

I've never taking a compression test before...is there a method about holding the tester on for a bit to check for leakage after a few cranks?

Also, I don't have a tester, but have seen some on Amazon for an affordable price...would one of these testers work? I'm guessing I need one with a rubber adapter.

I've been gradually losing power in the tractor, and today I couldn't get the engine to throttle high at all...wouldn't go above 700-800 rpm with pedal or throttle arm maxed out.

I'm guessing maybe my CAV injector pump is failing and needs to be rebuilt, but I wanted to check my compression to see if that was OK.

 

[Joe Ferguson]

To start average diesel engines need 400 PSI @70˚F
If you use an usual compression tester over the
injector hole it will fly trough the shop roof and
NASA will report a new UFO.

To test compression we do a leak test cylinder at
compression stroke with an adapter in place of
injector and put air @ 150 PSI and close the air
valve. If some air escapes in intake manifold
intake valve is defective. If air escapes in
exhaust manifold then exhaust valve is defective.
If air escapes in pan vent tube or in oil filler
tube then compression rings are defective. If air
escapes (bubles) in radiator then head
gasket..sleeve seals or other water jacket
problems. Same tes may be done on gas engine with
an adapter fabricated with an old spark plug.

Normaly lack of compression will not afect engine
RPM. First symptom of low compression: the engine
will not start...but will start if tractor is
pulled then the engine will turn faster and will
built more compression.

My humble guess is that you have fuel starvation
due to clogged vented fuel tank cap clogged fuel
filters and/or old fuel and/or
sediments in the fuel tank. Esy test is to
disconnect fuel line at the inlet of the prime
pump and see if you have good steady fuel flow for
at least one minute. The prime pump may be
defective too.

My 2¢

Joe Ferguson

 

[jfharper]

Joe,
Thanks for your comments and humor.

Where can I get the air adapter you referred too? Also, my compressor only gives air to 100-110 psi...will this work?

I have gone through the fuel system as you mentioned, a number of times...it was a long story...it is fine, and there is plenty of fuel, all clean, filters clean, new electric fuel pump etc.

The fuel back pressure is supposed to be 6-10 psi. The electric fuel pump gave me 8-9 psi. This made the engine run bad with lots of black smoke. I took the air cleaner hose off to see if there was lack of air, but that didn't change the black smoke.

I also put a fuel pressure gauge on so I could see what the fuel pressure is.

I then put a fuel pressure regulator on, and reduced the fuel pressure to about 1.5 psi. This made the tractor run better, but not great, and fixed the black smoke issue.

I've been running it for a couple weeks like this until today when the symptoms above happened.

Since the tractor starts fine, very quick on second or third rotation, I'm leaning towards the CAV pump.

There is a regulator piston valve toward the end of the CAV pump. This is the end where the fuel first enters. The piston has two springs on each side of it. This regulates the fuel that enters the pump from it's back pressure. The extra fuel exits from the front of the CAV and goes back into the secondary fuel filter.

When my fuel back pressure was higher than 1.5 psi, I would get black smoke and terrible running. My guess is the piston was allowing too much fuel to enter the CAV pump.

This the end of my knowledge on the CAV pump...

 

[Joe Ferguson]

For the air adapter we made it from an old
injector.

For primary pump pressure...I'm realy surprised
that few more PSI causes engine smoking...how 20
PSI at the injection pump inlet can affect
injection pump output pressure which is ~ 2500
PSI.

Smoke may be caused by fuel dripping in cold start
system in intake manifold (if equipped)...bad
injection pump timing...blocked injector return
line to the tank.

If you rebuilt the engine it wd be good to take
your injectors to a diesel repair shop to have
them tested & adjusted.

Old contamined fuel may cause many problems.

My 2¢

Joe Ferguson

 

[jfharper]

Thanks.

This engine has no cold start system in intake manifold and the fuel is new and clean...I've drained the tank three times and the fuel comes out perfectly clean.

That's a good idea about the injectors...I'll call the shop and see about that.

I mounted the injector pump with both timing lines lined up. There is one line on the pump flange and the other on the rear timing cover...I lined both up. I could try adjusting this a bit, perhaps rotating the injector pump at a few different spots to see if this resolves things.

I'll also check the injector return line for blockage...I didn't think about that.

 

[Joe Ferguson]

I had ISP interruption in middle of my previous
post
forgot to mention:

The primary pump will supply more fuel volume than
needed at the injection pump as explained in the
text you attached in your second message the fuel
in surplus is bypassed and returned at the succion
side of the primary pump. If you had to control
the fuel volume/pressure from the primary pump to
stop engine smoking the metering valve in the
injection pump may be stuck open or defective.
If stuck open it may be corrected by putting 1
quart of 2 stroke engine oil in a full tank of
fuel or 1/4 quart in 1/4 full tank etc.It will
dissolve gum and varnish or surface rust if water
reached the pump. Worst injection system ennemy is
water in the fuel.

If you do not find solution you may bring your
pump with your injectors for testing. Injection
pumps may be adjusted & repaired by specialists we
have no tool no test jigs and no know how.

Good luck !

Joe Ferguson

 

[Joe Ferguson]

Also forgot to mention the lines on the casting and on the pump are reference...they may be perfectly alined but....if the lines are not perfectly aligned when removing the pump we must put our own marks to be sure the timing is exacly the same as it was when the pump was removed.

Another 2¢

Joe Ferguson

 

[Jerry/MT]

Check for fuel delivery. Your tank outlet could be clogged or your fuel filter. If the weather is cold it could be an iced filter.
If you"re going to do a compression check, bring the engine to operating temperature and make sure th air filter is not restricted.
Most diesel have compression pressures above 350- 400 psi.

 

[jfharper]

(quoted from post at 08:47:38 03/04/11) Check for fuel delivery. Your tank outlet could be clogged or your fuel filter. If the weather is cold it could be an iced filter.
If you"re going to do a compression check, bring the engine to operating temperature and make sure th air filter is not restricted.
Most diesel have compression pressures above 350- 400 psi.

Thanks for the tips.

No ice or cold weather...65 degree F outside in California.

I've checked the tap and screen, both new and perfectly clean. New filters on...lots of fuel flows out all bleed spots, including two screws on inj pump.

 

[Jerry/MT]

If compression was the problem it would be hard starting but you would still be able to get better than 7-800 rpm out of it with no load and just advancing the throttle. You"d be down on power under load but you should be able to make higher engine speed. You"d also see some blow by and possibly some blue smoke. You haven"t said you had any of that.

You can check the compression if you like, but your problem is most likely caused by the injection pump not providing enough fuel when you advance the throttle lever. Either the governor is stuck or there some failure in the pump

 

[jfharper]

Thanks. Maybe I'll skip the compression test.

The funny thing is, when I increase fuel back pressure, I get a lot of black smoke and the tractor runs terrible and rpm will not go above 5-600 max.

 

[Jerry/MT]

What do you mean "...when you increase the fuel back presure...."?

Black smoke means either too much fuel or not enough air. What"s the air cleaner look like?

 

[jfharper]

Hey Jerry,
I outlined the answer to your question above in my second message. Thanks.