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Old 01-29-2002, 12:15 PM
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My Mercedes quit and I need some ideas

The other day my wife was driving my Mercedes on the expressway when it suddenly lost power in the high speed lane. She proceeded to move over to the right lane and by the time she got there it quit altogether. Repeated attempts to start it failed, and we towed it home.

When I got it home, I couldn't get the engine to turn over. As I had been having some trouble with the battery, I immediately replaced it with a new one. Unfortunately, that didn't fix the problem although the engine will now turn over when I hit the starter - although, sometimes, it seems reluctant. When the engine turns over, I can hear a squeak (just a single squeak) after every third or fourth revolution. The squeak seems to come from the bottom of the engine.

The question is how to diagnose the problem. Can you give me any ideas about where to start? The car is a 1981 Mercedes 300 D(iesel). It has about 215,000 miles. To date it has given excellent service and I have had no major problems, the only thing I've ever had to replace other than wear components (brakes, etc.) is the alternator. Except for the squeak, I'd suspect the high pressure fuel pump. Is there a recommended way to check that out? I'd appreciate any help you could give on this.
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Old 01-29-2002, 01:15 PM
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I would start by doing a compression test. Something may have turned loose inside the engine. If you have good compression, crack open an injector line while cranking to see if fuel is making it to the injector.

This is very uncharacteristic for one of these cars. Did it have oil pressure when it laid down? Does it build oil pressure when you crank it for a few seconds?

Good luck,
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Old 01-29-2002, 01:44 PM
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3 turns then "squeek"?? Sounds like something amiss with one cylinder on compression stroke (assuming it is every fourth revolution. If the sound is coming from the bottom of the engine -I'd suspect a turned shell on the crank on one cylinder (hence the squeek every 4th revolution) when it is on the compression stroke and exerting great pressure on the shell. Is there any oil pressure - that will be the first step. I would not start the engine until I found what goes "squeek" as it could then go "ka-chunk" in the wallet.
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Old 01-29-2002, 02:27 PM
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Oil pressure

After turning the engine for several seconds (it did not start), the oil pressure gauge registered no oil pressure at all. How much pressure should register on the gauge under those conditions? If memory serves, the oil pressure gauge usually doesn't register pressure until the engine is started and running for a few minutes.
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Old 01-29-2002, 02:39 PM
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If you didnt get oil pressure immediately after engine start, there is something wrong. If what you say is true about taking minutes to build oil pressure, that might indicate that you were low on oil and the engine may have been damaged as a result.
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Old 01-29-2002, 02:50 PM
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1) check your compression
2) drop your oil pan and using a shop stethoscope probe around the oil pump, crank, etc while someone turns the key to find out what is going squeek.I get the queasy feeling that you spun a shell causing the oil pressure to fall causing your pistons to "smear" from no lubrication resulting in poor compression. I hope not -but..... if the car lost power on the expressway - it sounds like your compression was failing from lack of lubrication until she could go no more. You might want to smell the exhaust while cranking the engine to see if you can smell raw fuel meaning that the injectors are supplying fuel. Good luck - I pray I am wrong.
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Old 01-29-2002, 03:03 PM
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I've had escaping air sound like squeeks cause it was whistling.
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Old 01-29-2002, 03:07 PM
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Hi Jim - same here - the only worry I have is that he says it is coming from the BOTTOM of the engine which could mean metal on metal.
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Old 01-29-2002, 03:30 PM
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Oil pressure gauge

Sorry, I didn't mean that it took minutes for the oil pressure gauge to register pressure. I should have said seconds and it takes no more than one or two seconds for it to come up after the engine starts - if memory serves. Sorry, everyone, for the mistake.
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Old 01-30-2002, 12:40 AM
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I would go the fuel route first before I had any big worries. Only fuel will cause a diesel to quit like that (unless there is more to the story than you are telling).Likely a plugged screen, filter or supply pump gone bad.
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Old 02-10-2002, 01:16 PM
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Compression Test

First, I want to thank everyone for their ideas on this problem. Due to an unexpected problem, I haven't been able to do anything on this until now. I'm about to start, but I have a question on the idea of doing a compression test on this 5 cylinder engine.

I don't have a lot of experience working on diesel engines, but it would seem to me that to do a compression test, one would have remove an injector and use a compression test gauge in the injector bore. However, from the discussion, I got the sense that perhaps there is another way. Could anyone clear this up?

It seems to me that if you did that you would also know immediately whether or not fuel was getting to the injectors. Am I right? Would appreciate anyone's comments.
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Old 02-10-2002, 01:43 PM
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I hope it is something minor, but this sounds eerily familiar to the way I lost my 80 300D back in 1991. It was a high pitched metal squeel. Mechanic indicated bottom end failure.

Good luck. I hope its something else as the bottom ends of these motors are generally bulletproof.
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Old 02-11-2002, 09:40 AM
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If you want to know if fuel is reaching the injectors - take the metal tube from the fuel distributor/pump to any one of the injectors off at the injector. put a small container under it and have someone crank the engine - fuel should spurt out. If it does - continue to remove injectors and check compression. Remember the compression is a lot higher in diesels than gas engines - do not use a pressure guage that goes up to 300 psi - it is not high enough. Get the right guage for this job.
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