Just bought a 1981 Mercedes 300D and it was idling really rough and a big loss of power when accelerating. It seemed like one of the cylinders wasn't firing so I took it to a mercedes mechanic and he checked the glow plugs, and the fuel injectors. He said they are both fine but cylinder number one is not firing. He thinks the cylinder is damaged and that it would take $4,000 to $5,000 to fix. Is there anything I should look for before spending more than what i paid for the car?! What else could be causing the first cylinder to fail??

Thanks! Please help!

 

Did he provide you with the compression test results? If not, and based on his price quote, he may not be all that reputable. Do you have a lot of blow by as indicated by the valve cover cap bouncing around when it is loosened? When you say he checked the injectors, did he do a pop test to actually see what the injector in number one is doing?

 

Although the car was cold, when idling the cap bounced around. When we revved to higher RPMs the cap stopped bouncing and it was smooth. Also exhaust and/or air was coming through the valve cover cap. What could this mean?

 

vwallace97,

A few things you should look into:

1.) Have you adjusted the valves on this engine? Valves that are extremely out of adjustment can lead to rough idle and lack of power. The valves on these engines should be adjusted every 15,000 miles, and if it has not been done recently, it should be. You will need a new Valve Cover Gasket when performing this service. You can get to the Valve Cover Gaskets on our site by clicking HERE.

2.) You say that the mechanic check the fuel injectors. Did he pop-test them to determine their opening pressures? If not, they should be tested in this manner. Bad injector nozzles with a poor spray pattern, as well as unbalanced injectors can lead to rough idle and poor power delivery. You may want to try a Diesel Purge (chemical made by Lubro Moly) and see if that helps improve the engines power output. After you do this, you should replace the fuel filters.

3.) Did the mechanic check the compression? If not, he should have. You cannot determine the reason for the engine running poorly without checking the compression. Also, if the valves were not in proper adjustment, the compression numbers may be off, so the best time to check compression is right after a valve adjustment. Poor compression may be caused by many different things, but try some of the less expensive remedies before spending thousands on a major engine repair. Many people find that switching the car to a synthetic oil, like Mobil Delvac 1, (meets MB Spec. 228.31 and 235.27) will help free stuck piston rings, and improve compression. This is not a guaranteed fix, but it is certainly worth a try if you are considering spending thousands on a repair that you may not need.

I hope this info helps out, and if there is anything else I can help with, please feel free to post or send a PM!

 

Get a new Mechanic, you can get a complete short block New Engine (300D) from http://www.mercedesengines.net/products.asp?cat=24
for $4350.00 or a completely brand new Long block complete for $7650.00
A mechanic should be able to fix a single cylinder for about $1000. including parts. IMHO