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  #1  
Old 06-24-2009, 06:33 PM
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300D Compression test

I am trying to diagnosis the true worth of continuing to patch up my 1981 300TD. Been advised to start with a compression test; searched several different ways on here and cannot find the directions in DIY links.

Someone please direct me to the step by step on this test fro a 617 engine!

Also, what readings I should find, and what lower readings mean?

Anyone local feel up to guiding a novice through this? I will do all the dirty work and lend a hand to any project you may have.....near Raleigh

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[B]1984 300TD Euro 4speed Sold
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  #2  
Old 06-24-2009, 06:57 PM
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Be simular to this:
http://www.peachparts.com/shopforum/showthread.php?t=254832&highlight=compression

above 350 would be good . . . could be less, but big thing is to look for large difference between cyl . . .
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  #3  
Old 06-25-2009, 08:21 AM
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Once you have a compression tester decide which you're going to use, injectors or glow plugs. Remove all of which ever you're going to use. Follow the instructions that come with the tester.
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300D Compression test-compression-tester-instructions.jpg  
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  #4  
Old 06-25-2009, 11:01 AM
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I always go for the injectors, give you a chance to clean and inspect.
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  #5  
Old 06-25-2009, 01:26 PM
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Thanks for the responses folks. I read some older threads about best affordable sources for compression tester; any recent purchases that someone would like to recommend?

If I go through the injectors; hot or cold engine??? I read both schools

How can I "clean them up" and what can I "inspect" on the injectors?
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1990 300D 2.5Turbo, two tank WVO, daily driver 300,911
1992 E300 gaser, 150k. Parts only, For Sale

[B]1984 300TD Euro 4speed Sold
1977 300D Elsbett SVO single tank Sold
1981 300TD "Silver bullet" 285k ran B100 Sold
1981-5 300D x 5 cars stripped and reused, parts for sale

Other toys:
1995 Dodge 2500 Cummins 12V P7100 Bosch mechanical pump with 2 tank veggieconversion kit, only 120k!
1959 Cadillac Dad's legacy, needs finishing
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  #6  
Old 06-25-2009, 01:48 PM
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The HF one works. Hot engine always. You can clean the carbon buildup off the tip and let is soak in a cleaning solution over night. Inspect for nailed pintles and inspect the prechamber. If you want to spend the money go ahead and have the injectors poptested and cleaned while they are out.
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  #7  
Old 06-25-2009, 02:56 PM
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I'm not much of an mechanic but I was able to do a compression test on my 240D. Here are the steps I took;

1)Remove the metal fuel injector lines coming from the injection pump

2)Remove the return fuel lines, those are the braided lines that connect to each injector

3)To crank the engine, I bought a remote starter, which a tool that connects one wire to the negative battery terminal and the other side to the starter solenoid. Real easy to connect. I bought it from autozone for $15 and it allowed me to crank the engine from the engine bay with the key in the ignition all the way to the right. Pretty cool tool. Otherwise, you can have someone crank the engine for you.

4)I bought a diesel compression tester from Ebay for about $40 shipped.

5)At this time, you can remove the injectors one by one and test them. Only have the injector that you are testing out of the engine. Under the injector, you will find a heat shield. It's a metal gasket looking piece. That needs to be replaced with a new one when you reinstall the injector.

6)With the injector out, plug in your compression tester with the injector adapter and tighten.

7) Crank the engine or use the remote starter to get a reading. About 6 to 8 cranks should give you the compression reading. I rested the compression tester, cranked the engine with the remote starter in one hand and the other hand pushing the "stop engine" lever so that the engine doesn't start.

8)Now you should have a reading!

9)Unplug the compression tester and reinstall the injector with a NEW heat shield. Make sure the heat shield is facing the right direction. Just make a note to see what direction the original heat shield was before you removed it.

10)Now, to the next injector and so on.

11)When all done, you should reinstall the metal injector lines that connect one end to each injector and the other to the injection pump. You should also replace the braided return lines(those are the plastic lines you removed) with new ones. They sometimes leak when reinstalled. Plus they are pretty cheap to replace. You can buy the line for all the injectors for probably $8.

12)Leave the connection coming from the metal injector lines to the injector loose. Now with everything tight except those five connections, crank the engine until all five of them are leaking out a little fuel. Once that happens, tighten those connections and the engine should be back to normal.

-A couple notes. Some people suggest you test compression on a warm engine, others say a cold engine. Others suggest if you get a low reading (probably under 290), you should squirt a bit of engine oil in the injector hole and then test the compression again. If you get a low reading, then you probably have bad or worn rings.

-Badly adjusted valves will also give erratic readings.

-You need to buy heat shields for each cylinder, new injector return line, a compression tester. A breaker bar helps free the injector from the engine. Not sure what the size the fittings on the metal injector lines are.

Hope that helps!
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  #8  
Old 06-25-2009, 10:49 PM
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Quote:
Originally Posted by brownrice78 View Post
I'm not much of an mechanic but I was able to do a compression test on my 240D. Here are the steps I took;

1)Remove the metal fuel injector lines coming from the injection pump

2)Remove the return fuel lines, those are the braided lines that connect to each injector

3)To crank the engine, I bought a remote starter, which a tool that connects one wire to the negative battery terminal and the other side to the starter solenoid. Real easy to connect. I bought it from autozone for $15 and it allowed me to crank the engine from the engine bay with the key in the ignition all the way to the right. Pretty cool tool. Otherwise, you can have someone crank the engine for you.

4)I bought a diesel compression tester from Ebay for about $40 shipped.

5)At this time, you can remove the injectors one by one and test them. Only have the injector that you are testing out of the engine. Under the injector, you will find a heat shield. It's a metal gasket looking piece. That needs to be replaced with a new one when you reinstall the injector.

6)With the injector out, plug in your compression tester with the injector adapter and tighten.

7) Crank the engine or use the remote starter to get a reading. About 6 to 8 cranks should give you the compression reading. I rested the compression tester, cranked the engine with the remote starter in one hand and the other hand pushing the "stop engine" lever so that the engine doesn't start.

8)Now you should have a reading!

9)Unplug the compression tester and reinstall the injector with a NEW heat shield. Make sure the heat shield is facing the right direction. Just make a note to see what direction the original heat shield was before you removed it.

10)Now, to the next injector and so on.

11)When all done, you should reinstall the metal injector lines that connect one end to each injector and the other to the injection pump. You should also replace the braided return lines(those are the plastic lines you removed) with new ones. They sometimes leak when reinstalled. Plus they are pretty cheap to replace. You can buy the line for all the injectors for probably $8.

12)Leave the connection coming from the metal injector lines to the injector loose. Now with everything tight except those five connections, crank the engine until all five of them are leaking out a little fuel. Once that happens, tighten those connections and the engine should be back to normal.

-A couple notes. Some people suggest you test compression on a warm engine, others say a cold engine. Others suggest if you get a low reading (probably under 290), you should squirt a bit of engine oil in the injector hole and then test the compression again. If you get a low reading, then you probably have bad or worn rings.

-Badly adjusted valves will also give erratic readings.

-You need to buy heat shields for each cylinder, new injector return line, a compression tester. A breaker bar helps free the injector from the engine. Not sure what the size the fittings on the metal injector lines are.

Hope that helps!

The FSM specs are with the Engine at operating temp; a min of 70 C.
If you do the Compression Test with the Engine Cold it tells you something but you cannot compare your readings accurately to the FSM specs for a hot Engine.
If you remove all of the Injectors before you start cranking it is easier on the Starter/Battery and easier for the Engine to turn faster so that you get a good test.
I believe I also read that you want crank at least 8 revolutions per each cylinder tested.
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  #9  
Old 11-29-2011, 01:04 PM
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I may be missing something, but if you crank the engine and the fuel injector LINE is loose, how do you avoid fuel being spit out by the injection pump? There's something I am not understanding.

Or could I disconnect the fuel pre-filter and then run the engine until it stalls, to clear the injection pump of any fuel (before disconnecting any lines). This is after the car is at operational temperature of course.
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  #10  
Old 11-29-2011, 01:23 PM
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I've used my Harbor Freight compression tester several times. It works well, and is cheap. If you're going to use it a bunch I'd buy a good one. If you're only using it once in a while the HF tester will work. Make sure you get a Diesel Compression Tester not a Gas one.

Cold verses Hot - To me it depends on what you're troubleshooting. If you're having hard starts. Then cold compression will tell you what the engine is working with when you try to start it. If you've got rough idle or lots of smoke then hot compression might tell you why. High cold compression is only going to go up when the engine is hot.
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  #11  
Old 11-29-2011, 01:48 PM
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I bought a HF compression tester and my overall impression is that it is junk. Not worth $25.00

I am making a SUPER HIGH quality compression tester by taking the lower half of a fuel injector body, treading a bolt in it that had a hole drilled thru the bolt (bolt goes into the lower half and the lower half as threads on the inside of it) and NPT threaded the hole in the bolt. Then, simple hose with a GOOD Gauge. I guess the above sounds super confusing. I will get my pictures out there soon.

I am shopping for Gauge right now since that is the real meat and potatoes of the tool.

Any interest out there in buying the injector body part of the compressoin tester ???
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  #12  
Old 11-30-2011, 09:19 AM
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Quote:
Originally Posted by tomas_maly View Post
I may be missing something, but if you crank the engine and the fuel injector LINE is loose, how do you avoid fuel being spit out by the injection pump? There's something I am not understanding.

Or could I disconnect the fuel pre-filter and then run the engine until it stalls, to clear the injection pump of any fuel (before disconnecting any lines). This is after the car is at operational temperature of course.
Depending on your car, either hold the STOP lever down, or apply vacuum to the shut off actuator, this should prevent more fuel from being dispensed.

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