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  #1  
Old 08-30-2016, 02:20 PM
is thinning the herd
 
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240D - Dead Cylinder

So my dad has a 1983 240D automatic with around 245,000 miles. He's put about 20,000-25,000 of those miles on it. Oil changed usually at 5,000 miles with 5/40 Rotella T6, he religiously runs fuel additive in the car as well.

It started running rough all of the sudden. Runs great off idle, but idles terribly. Doesn't consume oil or coolant, still gets close to 30mpg mostly highway driving.

He drove it up to my shop to pull the injectors to send off to greazzer, pulled the injectors and compression tested it.

300 - 80 - 300 - 290.

Put ATF in cylinder 2 and when you crank it over the gauge will now spike to 200psi but it won't hold pressure. So it goes 200 - 0 - 200 - 0 - 200 - 0 as it cranks over (if that's indicative of anything)

Pulled the valve cover and the valve adjustment for #2 is dead on.

Why would a diesel all of the sudden have a dead cylinder? Car is well cared for and didn't really display any "going down hill" symptoms. We just assumed the nozzles were finally worn and needed done when it was idling rough.

Just wondering if there is something we have [not] done that killed this car.

Really nice rust free southern 240D in midnight over palomino that he adores, so we will be fixing it, but its annoying to have to put an engine in a car that ran so well right up until it didn't.

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  #2  
Old 08-30-2016, 02:27 PM
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If you do a leakdown test you should be able to nail down whether it's the rings, intake, or exhaust. I would suspect something broken, like rings or valve component. The wet compression finding may be enough of a clue, though I haven't seen that specific result before.

-Rog
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  #3  
Old 08-30-2016, 02:30 PM
t walgamuth's Avatar
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Quote:
Originally Posted by Rogviler View Post
If you do a leakdown test you should be able to nail down whether it's the rings, intake, or exhaust. I would suspect something broken, like rings or valve component. The wet compression finding may be enough of a clue, though I haven't seen that specific result before.

-Rog
Agreed 100%.
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  #4  
Old 08-30-2016, 04:17 PM
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Try the gauge in another cylinder to rule out the gauge. That bouncing sounds like a gauge issue. Going from 80-200 psi sounds like a ring/piston problem..two different problems occurring at the same time?

If you are going to put pistons in, don't let them bore it until the pistons are numbered and in the machinists hands. The bore sizes are slightly different, IIRC number one has a different clearance than 2-4.

X2 on putting air in the cylinder to see where the leak is at.

Good luck and keep us posted!!!
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Old 08-30-2016, 05:04 PM
is thinning the herd
 
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Quote:
Originally Posted by Sugar Bear View Post
Try the gauge in another cylinder to rule out the gauge. That bouncing sounds like a gauge issue. Going from 80-200 psi sounds like a ring/piston problem..two different problems occurring at the same time?

If you are going to put pistons in, don't let them bore it until the pistons are numbered and in the machinists hands. The bore sizes are slightly different, IIRC number one has a different clearance than 2-4.

X2 on putting air in the cylinder to see where the leak is at.

Good luck and keep us posted!!!
It's not the gauge, it worked fine on cylinders 3 and 4. And again on 1-2-3-4 when I tried it again.

I am not sure what I am going to with the engine, if I am going to rebuild or replace.

I need to get a leakdown tester and see what the deal is I guess. Would be nice to just have a burnt valve or something.
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  #6  
Old 08-30-2016, 07:28 PM
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The benefit of a leak test is knowing what to look for before tearing the engine apart. Don't be overly concerned about a leak down tester, we already know that it is leaking too much so the amount of leakage is not critical. Where the leak is at is what we want to find out...with no tension on the rockers at all, put air in the cylinder and see where it leaks out from, the tailpipe, intake manifold, cooling system and or the crankcase/oil pan.

Was thinking about whether or not you could pull the head and the lower oil pan only to remove just the number two piston if that is where the problem is at, hone/deglaze re-ring that cylinder and go down the road. It just depends on what you want out of the car. I did the first repair size .5 mm pistons/bore on my 240 and it ran like a dream.

The bouncing gauge is puzzling. Nothing in the cylinder should affect whether or not the gauge holds a reading.
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  #7  
Old 08-30-2016, 09:02 PM
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There is a check valve in the compression gauge that makes peak pressure visible so any bouncing is a gauge system failure. The check valve is usually at the tip of the adapter so make sure the adapter isn't bottoming out on something and holding the valve open. Many compression gauges use a tire valve core with a light spring.

As a side note, removing the check valve is how one checks for even compression on a rotary engine, even bounces show all chambers are sealing.

You should be able to pull the check valve and use that adapter to pump air in for a quick leak down test. Actual numbers don't mean much, you are looking for a high volume of air leaking out relative to other cylinders

Being it still gets good fuel mileage, I'd vote for a fuel injection pump issue where no fuel is being injected. If this is the kind of pump I'm thinking of, one of the plunger barrels may have rotated shutting the fuel off or a cam roller came apart.

However, the 80 PSI kind of rules that out, unless the cylinder was low all along and it went unnoticed.

I'd work up some vials for all cylinders then crank to see if fuel volume across all 4 is anywhere believable.
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  #8  
Old 08-30-2016, 09:11 PM
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Some gauges are liquid filled to dampen out fast variations...
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  #9  
Old 08-31-2016, 12:10 AM
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One explanation is during the atf test , a piece of carbon got dislodged and stuck in the schrader valve of the compression gauge. Take out the schrader, blow clean with compressed air, inspect, put back together and try again.
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  #10  
Old 08-31-2016, 12:24 AM
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Quote:
Originally Posted by DieselPaul View Post
It's not the gauge, it worked fine on cylinders 3 and 4. And again on 1-2-3-4 when I tried it again.

I am not sure what I am going to with the engine, if I am going to rebuild or replace.

I need to get a leakdown tester and see what the deal is I guess. Would be nice to just have a burnt valve or something.
If you just want to listen to the leaking sound you can mod your compression tester adapter to take lower pressure compressed air.

If compressed air is leaking out of the Valve you would hear it in the manifolds.

If it is leaking by the piston you would hear the sound coming from the crankcase.

If you go to the harborfreight website and look at their leak back setup you will find it is only for gasoline engines and you are going to need to find a way to hook it up to the diesel. Also the site has the instructions for the setup in .pdf format.
So you can look at the instructions and see how much compressed air psi you need and so on.
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  #11  
Old 08-31-2016, 06:05 AM
t walgamuth's Avatar
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I agree on the gauge. If it makes 200 psi it makes it.....the gauge not being able to hold it seems irrelevant to me. I'd be looking at the injectors now. I'd start by moving the "dead" injector to another hole and see if it misses there.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #12  
Old 08-31-2016, 08:26 AM
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Quote:
Originally Posted by Diesel911 View Post
If you just want to listen to the leaking sound you can mod your compression tester adapter to take lower pressure compressed air.

If compressed air is leaking out of the Valve you would hear it in the manifolds.

If it is leaking by the piston you would hear the sound coming from the crankcase.

If you go to the harborfreight website and look at their leak back setup you will find it is only for gasoline engines and you are going to need to find a way to hook it up to the diesel. Also the site has the instructions for the setup in .pdf format.
So you can look at the instructions and see how much compressed air psi you need and so on.
And you will break it if you use too much. And you need to lock the engine rotation.

Yes, the HF leakdown only comes with a spark plug insert for sparky engines. The injector adaptor from the HF compression tester comes with a removeable Schrader insert you would take out to use it for a leakdown.
I went to a hydraulic hose shop with the various bits and pieces, and they sold me the ones I needed to connect them.
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  #13  
Old 08-31-2016, 12:46 PM
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Juist a thought. It usually takes a few strokes to get the actual compression of a cylinder. If the gauge would not hold what was previously presented in pressure.

You may have an artificial total single stroke readiing on that cylinder. Get the gauge operational properly and retest that cylinder. It may still be below idle running pressure but you want a usable number to make sure.

Of course 80 pounds is far too low. I have no issue with that. It just may not be accurate.
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  #14  
Old 08-31-2016, 01:18 PM
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I don't think its accurate and I don't think it could give 30 mpg if it has a dead cylinder.
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..I also have a 427 Cobra replica with an aluminum chassis.
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  #15  
Old 08-31-2016, 02:06 PM
is thinning the herd
 
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I tried and retried a all the cylinders that evening and 2 consistently misbehaved, so I'm not so sure my gauge is bad.

I will mess with it again this weekend. The car ran way too well off idle to have a cylinder under 100psi, a diesel combustion event wouldn't even occur if compression was that low would it?

I may just go ahead and send the injectors off to greazzer and see if any come up really bad.

I'll keep you guys posted, I appreciate the insights so far.

I think with my air gun and a rubber tip or some creativity and my compression tester I can probably come up with my own leakdown tester and listen for the valves.

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