617.95 engine diagnosis - PeachParts Mercedes-Benz Forum

sedecrem · #1 04-02-2007, 09:13 PM

Hello all

If anyone has any input as to my engine diagnosis I would appreciate the input.

Vehicle is a '82 300SD with 290k on a working odometer. I got it last August and have driven it about 2,500 mi since then. Last time I drove it was on a trip from Sacramento to San Francisco on December 30th. I cruised down most of the way at around 70 and the car seemed to run fine. As I got down to the East Bay(about 15 mi from S.F.) I ran into some traffic, and I slowed down to a stop. At this time the engine started shaking and smokeing pretty bad. It also seemed to have lost a lot of power and only eccelerated very slowly. I managed to coax it into to S.F. over the Bay Bidge in stop and go traffic smoking like crazy all of the way and could not get it to go more than 55 on the flat and 45 on any kind of a grade( those of you who know the East Bay are probably either cringing or laughing right about now). When I got there the the engine was shaking violently and black smoke was pouring out of the tail pipe. A mechanic friend of the family's came over and I was able to start it up but again it would barely run and was shaking and smoking very bad. There was quite a bit of blowby comming out of the breather hose between the camshaft cover and the air cleaner and tghe air cleaner had a lot of engine oil in it. I had it toed home(courtesy of AAA + menbership) and it has sat until now.

Today I finally got around to dioing a compression check on it and this is what I found: Cold and dry #1 350 psi., # 2 350 psi., #3 40 psi., # 4 380 psi., #5 325 psi., I rechecked every thing after putting a couple cc's of MMO down the injector ports and got the following: #1 360 psi., #2 385 psi., #3 60 psi., #4 395 psi., # 5 350 psi..

From what I have read the compression in every cylinder except # 3 looks pretty good. The spread from # 4 to #5 is kind of wide, but #3 obviously has a valve issue. Can anyone give me some insight into what is going on and the best way to procede from here. Is it worth my time to do a valve adjustment(have not done one on the car at all yet). Could a cylinder get as bad a #3 with out the valve being completely burnt. The engine always started O.K. but had a little trouble below 45 degrees F. At idle the engine would sometimes shake a bit but usually ran pretty smooth at speed.

By the way when I took out the injectors to do the C test, there was no errosion around the pintle and there was not a lot of lumpy carbon build up but there was a fair amount of soot

Any suggestions would be appreciated.

Thanks

kerry · #2 04-02-2007, 09:32 PM

Valve adjustment is pretty simple so I would definitely do it and recheck the compression.
Have you replaced the fuel filters? Lots of black smoke is unburned fuel, so I don't really think it's a filter problem, but it's a basic item that is easy to do.
I don't think one low compression cylinder would cause the bad running you describe if other people's symptoms of bad cylinders are any indication. Perhaps it is a combination of problems such as bad fuel filters and one maladjusted valve.
Check the timing chain stretch when you are doing the valve adjustment.

GRIESL · #3 04-02-2007, 10:19 PM

I had two holes at 120 and 100 and the car ran fine on the road, idle was rough only when burning cetane 40. If I put in 45 ran great. My low compression was causing fuel smoke, but not black. It was more like a stinky whitish grey, mixed in with some blue (cause the valve guides were real sloppy). So I don't think even one hole at zero (bgkast had a tight valve and got a reading of nada on one cylinder) would produce black smoke. Obviously, you should adjust valves and check again, but like suggested, you have a different problem. What kind of mileage did you get on your roadtrip? It sounds like the IP is pumping fuel in that can't be burned. Maybe check your ALDA. I'd do a search on "black smoke" and see what you turn up. Good luck.

BTW, I've driven that stretch of road around the Bay, and I was the one cringing. Yikes!

300SD81 · #4 04-02-2007, 10:27 PM

Do a valve adjustment, sounds like you have a valve stuck open with compression that bad..

sedecrem · #5 04-02-2007, 11:57 PM

Thanks every one for the suggestions. I will go ahead and do a valve adjustment. I just got through bending some 14 mm wrenches I got from Habor Freight to make a set of adjusting wrenches based on some drawings one of the members of this board posted. They were pretty easy to bend with a vise and propane tourch. There is a sale at Harbor Freight right now and a set of 9 metric wrenches from 6mm to 19mm is only $6. I bought two and used the 14 mm wrenches to make the adjusting set. Beats the $80 I have seen for sets advertized on eBay. Not that I think the people that are offering those are ripping anyone off. If I had to pay myself wages I would probably have to charge something like that too to put a set on the market. Still, it shows what you can get by with for a little thought and some work.

Any way, I will do the valve adjustment and recheck the compression. If the compressin in # 3 comes up appreciatively I will try changing the filters and see If I can't get it to start. I was preparred to change out engines, but if a little adjustment will work it will save me quite a bit.

Thanks every one for the help.

bgkast · #6 04-03-2007, 12:07 AM

I agree, sounds like a tight valve. Does the engine miss at idle? (sounds like a chugging at the exhaust outlet)

sedecrem · #7 04-03-2007, 12:14 AM

I tried to start it after I got it back home but it would not start. However the weather was pretty cold then and I have not tried since. When it was running it would sometimes idle rough and then at other times smooth.

I am still on the steep end of the learning curve with these engines but from what I have read on this board and other places it does sound like a combined fuel and valve problem. With three cylinders @ 350 psi or greater and four over 325 psi it should at least start.

Knightrider966 · #8 04-03-2007, 12:58 AM

Black smoke is a symptom of an overly rich fuel condition. I'm not sure how a bad valve could cause this, but do your valve adjustment anyway. something is going on in your fuel system.

bgkast · #9 04-03-2007, 01:37 AM

Tight valve = no combustion in that cylinder = raw fuel passing into exhaust = Smoke!!!!

Knightrider966 · #10 04-03-2007, 02:01 AM

Quote:

Originally Posted by bgkast

Tight valve = no combustion in that cylinder = raw fuel passing into exhaust = Smoke!!!!

Yeah, but black smoke? No combustion in that cylinder should produce white smoke. And the amount of smoke coming from the tailpipe according to the poster would indicate an overly rich condition in all cylinders. Clouds of black smoke would be like flooding an engine with fuel. i would have to see this to make a better diagnosis. Not starting could be too much fuel in the engine.

bgkast · #11 04-03-2007, 02:02 AM

You make a good point. When my valve was so tight it was hanging open I was got loads of blue/grey smoke.

sedecrem · #12 04-03-2007, 04:41 PM

Have not adjusted the valves yet but planning to today or tomorrow. I did check the EGR valve. It apparently is not working as it does not hold a vacumm and does not move when the vacumm is applied. Could this be at least part of the problem? If it was on it's way out for a while could that have been the cause of the intermittant rough idling?

GRIESL · #13 04-03-2007, 05:11 PM

Quote:

Originally Posted by sedecrem

Have not adjusted the valves yet but planning to today or tomorrow. I did check the EGR valve. It apparently is not working as it does not hold a vacumm and does not move when the vacumm is applied. Could this be at least part of the problem? If it was on it's way out for a while could that have been the cause of the intermittant rough idling?

Oh, bygolly, I think you've found the problem. I remember that a previous thread talked about huge black clouds and the EGR was the problem. I knew it was something else, just couldn't remember. Good work checking it for vacuum!

rrgrassi · #14 04-03-2007, 05:28 PM

EGR could be stuck open, and also check the banjo bolt and turbo switch over valve, as well as the lines running between the ALDA and the banjo bolt on the rear of the intake. After the valve adjustment, do another compression test.

If #3 is still extremely low, do a leak down test. Also check the oil for coolant contamination and the expansion tank for oil. Also look at the dip stick for any traces of water. Could be a burned valve, blown head gasket, cracked head, or just a too tight valve. The too tight valve would be addressed by the valve adjustment.

Kuhlrover · #15 04-03-2007, 06:18 PM

Here is something else to consider. With a lot of engine blow by and driving the car at high rpm's, you may have oil soaked your air filter. This would result in choking the air from the engine and causing a lot of black smoke. As the other folks have said, black smoke is caused by too rich of a fuel mixture which is also not enough air for the fuel being injected. I don't know if the Alda would completely compensate for the restricted air flow.

TimK