Misfire

Babu Owner/Technician Virginia Posted   Latest   Edited  
Unsolved
Propulsion
1966 Mercedes-Benz 230SL 2.3L (180.954)
Misfire

no compression on number 5 , but no leak down either, i did in cylinder test looks like intake valve not opening, lots clatter on this engine, from possible valve lash not in specs, i did valve adjustment last year , need opinions on what i am seeing , this is a MWF file for UsbAutoscope. ​this benz has mechanical fuel injection 

this is at idle, i should mention that i did a cranking mechanical pressure test first,

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Dmitriy Analyst
Ontario
Dmitriy
 

Babu, could you compress the file by ZIP and then attach?

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Babu Owner/Technician
Virginia
Babu
 

i will try

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Tom Engineer
California
Tom
 

We've now added support for MWF files, so I edited your original message to have the file attached directly.

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Sadel Owner/Technician
Ohio
Sadel
 

Babu, at quick glance, in this running compression waveform it looks like you have pressure “bleed” off during the compression stroke, the tower is leaning and goes into a very deep expansion pocket and the offset between the bottom of expansion pocket to the intake plain is too great. All indications of most likely psi bleed off at one of the valves. The intake valve is opening and closing as…

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Babu Owner/Technician
Virginia
Babu
 

Height of wave compression is only 1.4 bar

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John Mechanic
Illinois
John
 

Bad valve guide causing valve to stick shut. I would imagine if you pulled the valve cover you would find a broken or bent push rod/rocker arm. An actual leak down test would tell you if you have a leak and where it is. Vacuum gauge will probably reveal a valve train issue. If you have no leak and no compression the piston is not able to pull a “charge” in from the intake and will result in low…

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Glenn Owner/Technician
Texas
Glenn
 

Hello Babu, I would thing the valve clatter is the place to inspect on this. I have had lash adjusters break at the tension lock nut several times in the past. This thing is 56 years old and has a lot of run time on it. Pull the valve cover and do a physical inspection if the customer agrees.

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Richard Mobile Technician
Florida
Richard
 

No matter what the mechanical issue is on cylinder 5 you will have to tear down the motor to see what is actually wrong with it. Try an endoscope and see what is going on inside the cylinder. A rebuild or engine replacement is probably the only solution. Take Care.

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Rudy Technician
California
Rudy
   

As some one else mentioned, the tower is leaning and the exhaust pocket is deep. You have a leak in the cylinder. I don't try to get into the weeds too much, for me that's enough to stop and get authorization for tear down.

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Agree
Darren Mechanic
Wisconsin
Darren
 

Roger that

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