Compression interpretation/ bad exhaust smoke and blowby - PeachParts Mercedes-Benz Forum

Dovetail · #1 01-01-2010, 06:34 PM

Hello all:
I have a 1980 300SD with 210,000 on it. It was previously owned by my cousin (since 1982), and was his daily driver until about 10 years ago. He meticulously cared for it up until that point, however his mechanic, although a popular independent mechanic in the Pasadena, CA area, is not someone who I would take my car to. They used 20/50 wt Pennzoil, which was regularly changed. Over the last 10 years this has been his second car, and approximately 10,000 miles were put on it over that time period, as well as run on homemade biodiesel (made by his mechanic). The maintenance was benign neglect. His wife started it oneday and it went into runaway (not traveling, but while in park). She had to call the fire dept who stopped it by blocking the turbo intake. After that the car was gladly given to me. His mechanic thought it was the fuel injector pump (stuck fuel rail), and had it partially dismantled. I found a good used injector pump, swapped it out, and got the car running. 6 degrees of off timing was noted so I rolled a new chain in. It now runs very nicely, however has a loud knock when cold (always had this), and despite new injector nozzles, still has the knock which goes away when warm. However, the most obnoxious thing is that it smokes really bad, and has significant blow-by. It is a little slower than other turbo diesels I have had, but still has respectable off the line speed and power under load (when warm). Before I put any more effort into this I figured I should check the compression. The readings I got were:

27
23
27
27
27

So the question is, is the 4 bar difference significant? Could that be the origin of the smoking grayish exhaust? The blow-by? By the way, despite several tanks of diesel the exhaust still smells like McDonalds. Do you think more time and money should be invested? I am thinking I will see if new valve stem seals will help, but I hate to invest much in it if I can not get rid of the smokey exhaust. Any comments would be appreciated,
Will

layback40 · #2 01-01-2010, 06:52 PM

An other 300D motor damaged by junk fuel!!
Blowby = ring problem.
There are plenty of threads on here about stuck rings from using junk fuel. No one on here has put there hand up to being able to have run junk fuel for say 200k miles with out damage to the motor. Years of damage from junk fuel will not be overcome by 2 tanks of proper fuel. Some have had a little success with soaking in Mystery OIL. Most likely your rings on piston 2 are jammed in the lands with varnish from the fuel. The others wont be far behind.
Mystery oil added to the cylinders and soaked for a couple of weeks may help. Other wise head & sump off eventually, pistons out & cleaned, new rings.

Skippy · #3 01-01-2010, 06:53 PM

23 bar is good compression, but the fact that one cylinder is four bar below the rest does point to something possibly going on. The cold knock and gray smoke indicate incomplete combustion. Does it smoke all the time, or just under certain conditions?

Things I would check:

1. Valve adjustment. This is an easy one and the only one of the things I'm going to suggest as first checks that could directly affect compression numbers.

2. Intake or exhaust restriction. This would explain it being slow and still smoking.

3. Turbo boost. Low boost could make low power. If the ALDA has been messed with, you could get normal fueling without normal boost, which would give you smoke.

Also, did the injectors get pop tested and balanced when the new nozzles went in? If one or more are popping off at too low of a pressure, that could give you the knocking and smoking without anything else being wrong. While you're at it, change the fuel filters if they haven't been done lately. Sometimes a fuel restriction can paradoxically cause some of the symptoms of overfueling.

My $ 0.02.

Biodiesel300TD · #4 01-01-2010, 06:54 PM

Leaking valve stem seals usually causes smoke on start up that goes away after a bit. If you are getting lots of smoke all the time the valve stem seals probably aren't the culprit. I would check the valve clearances, and run a couple cans of diesel purge through the engine. On these cars the valve clearances tighten over time which cause the valves to not close fully, which can lower compression numbers.

There isn't much you can do about blow by other than rebuild the engine.

With compression number like that you are doing pretty well. The one cylinder with 23bar is going to cause rough idling, more than anything. I'm a little surprised you have much blowby and smoke with compression numbers that high.
23 bar = 333psi
27 bar = 391psi

Is the ALDA cranks up to high? What color is the smoke?

Skippy · #5 01-01-2010, 06:55 PM

Quote:

Originally Posted by layback40

An other 300D motor damaged by junk fuel!!
Blowby = ring problem.

(Smacks forehead)

I think you're on to something. I've heard of people getting the rings unstuck by running regular diesel and performing a thorough Italian tune up. It doesn't work all the time, but it's cheap, it's easy, and it's fun to do.

Biodiesel300TD · #6 01-01-2010, 06:58 PM

Quote:

Originally Posted by Skippy

(Smacks forehead)

I think you're on to something. I've heard of people getting the rings unstuck by running regular diesel and performing a thorough Italian tune up. It doesn't work all the time, but it's cheap, it's easy, and it's fun to do.

If he had stuck rings his compression would well below 333psi.

layback40 · #7 01-01-2010, 07:27 PM

Bio,
He has blowby. I guess he has caught the problem early. No.2 is on the way out. Have you found a Merc yet that has run serious miles (200k+) continuous on junk fuel with out problems?
20 years ago I was offered a small Bio plant, not some back yard junk. It used canola or sun flower seed as a feed, it had a high pressure & temp. catalytic reactor to remove the varnish. I know a guy who bought one. After 2 years of trouble he gave up. His problems were identical with what we see on here time & time again. I use around 20,000 US gal a year of diesel, with all the best brains I can get my hands on, I, like many other larger users cant get it to work well, what hope have regular mom & dads.
You only have 160,000 miles to go on your current BIO Merc before I will see you as having some credible experience with successful running. I guess you wont keep it that long!!

Biodiesel300TD · #8 01-01-2010, 07:58 PM

Yup blame it all on the biodiesel. It's easy to pick out. Since there are issue in his 30 year old car it must be the biodiesel. It couldn't be poor lubrication, valves out of adjustment, worn rings, an engine that hasn't been run in a good while, or anything else.
You know there are other reasons for compression number that aren't all exactly the same. When I bought my wagon it hadn't seen a drop of biodiesel, or any other biofuel and my compression numbers were all over the board. The compression numbers were as follow: 310, 295, 240, 285, and 275. Can't blame it on biodiesel so what caused it?

Please don't accuse me of not having biodiesel experience. You know nothing of my biodiesel experience. Before the economy down turn I worked for a diesel shop that specialized in biodiesel, veggie oil, and MB and VW diesel repair, which started out as a biodiesel co-op for the area I live in. I've seen and worked on more than my fair share of alternatively powered vehicles. And worked with one of the people who were part of the forefront of biodiesel being brought and produced in Northwest US. I have more biodiesel experience than most here.

layback40 · #9 01-01-2010, 08:44 PM

Bio,
Down here there are diesels running diesel/LPG and diesel/LNG systems 18 hrs per day 7 days a week. No problems. I know of a fleet of Mercedes buses on diesel/LNG, It has Mercedes blessing.
I have seen the insides of a Cat truck motor that Cat sponsored a trial of Bio. on a double B on long haulage. I saw the same thing as members on here show.
I am not in the biz of selling bio or WVO conversions nor do I work for the alternate.
If the engine manufacturers cant get it to work properly I think its best left.

I dont know the history of your wagon so I cant comment.
As I continue to ask, where are the cars that have run on WVO or Bio for 200k miles. These 2 fuels have been tried for over 20 years now. If they were that good, the car/engine manufacturers would be giving their blessing.

JimSmith · #10 01-01-2010, 10:07 PM

Quote:

Originally Posted by Dovetail

Hello all:
I have a 1980 300SD with 210,000 on it. It was previously owned by my cousin (since 1982), and was his daily driver until about 10 years ago. He meticulously cared for it up until that point, however his mechanic, although a popular independent mechanic in the Pasadena, CA area, is not someone who I would take my car to. They used 20/50 wt Pennzoil, which was regularly changed. Over the last 10 years this has been his second car, and approximately 10,000 miles were put on it over that time period, as well as run on homemade biodiesel (made by his mechanic). The maintenance was benign neglect. His wife started it oneday and it went into runaway (not traveling, but while in park). She had to call the fire dept who stopped it by blocking the turbo intake. After that the car was gladly given to me. His mechanic thought it was the fuel injector pump (stuck fuel rail), and had it partially dismantled. I found a good used injector pump, swapped it out, and got the car running. 6 degrees of off timing was noted so I rolled a new chain in. It now runs very nicely, however has a loud knock when cold (always had this), and despite new injector nozzles, still has the knock which goes away when warm. However, the most obnoxious thing is that it smokes really bad, and has significant blow-by. It is a little slower than other turbo diesels I have had, but still has respectable off the line speed and power under load (when warm). Before I put any more effort into this I figured I should check the compression. The readings I got were:

27
23
27
27
27

So the question is, is the 4 bar difference significant? Could that be the origin of the smoking grayish exhaust? The blow-by? By the way, despite several tanks of diesel the exhaust still smells like McDonalds. Do you think more time and money should be invested? I am thinking I will see if new valve stem seals will help, but I hate to invest much in it if I can not get rid of the smokey exhaust. Any comments would be appreciated,
Will

Well, the compression numbers overall are very good, given the engine has less than a 20:1 compression ratio. And the high to low difference is over the 10% limit considered ok - meaning not to worry about - but the basic numbers are pretty high, so I don't think the difference is that telling. I don't think it is the primary cause of your smoking issues.

I think you need to understand why the engine ran away. I have never owned a turbo of that era and have not had to get to know the boost control system intimately. But, I have never heard of one of them or a 240D going into a runaway condition all on its own because the injection pump suddenly got unruly. I think someone was fooling with the shut-off or the Alda or some other boost control/fuel mixture sensing or feedback line to fix a performance problem. The new injection pump may be set up better, but it may still be suffering from bum control system sensors or calibration.

Given those compression numbers your smoking issues sound like a fueling system being out of calibration or an intake obstruction more than a cylinder to piston ring problem. Blow-by can be a result of the turbocharger bearing area being pressurized and then allowing some air to be pumped into the oil sump. Check general oil consumption rates. If you are getting 2k miles to a quart of engine oil, I don't think you have a an engine oil smoking problem.

Jim

4x4_Welder · #11 01-01-2010, 10:15 PM

Are there any vacuum leaks? The blowby and smoking can be unrelated, since the vacuum pump dumps into the crankcase. Perhaps the turbo is bad, and is wobbling around on it's bearings providing little boost while dumping oil..............That would cause a runaway too, if the inlet was leaking badly due to, say, a plugged air filter or something?

whunter · #12 01-02-2010, 12:08 AM

Quote:

Originally Posted by Dovetail

Hello all:
I have a 1980 300SD with 210,000 on it. It was previously owned by my cousin (since 1982), and was his daily driver until about 10 years ago. He meticulously cared for it up until that point, however his mechanic, although a popular independent mechanic in the Pasadena, CA area, is not someone who I would take my car to. They used 20/50 wt Pennzoil, which was regularly changed. Over the last 10 years this has been his second car, and approximately 10,000 miles were put on it over that time period, as well as run on homemade bio-diesel (made by his mechanic). The maintenance was benign neglect. His wife started it one day and it went into runaway (not traveling, but while in park). She had to call the fire dept who stopped it by blocking the turbo intake. After that the car was gladly given to me. His mechanic thought it was the fuel injector pump (stuck fuel rail), and had it partially dismantled. I found a good used injector pump, swapped it out, and got the car running. 6 degrees of off timing was noted so I rolled a new chain in. It now runs very nicely, however has a loud knock when cold (always had this), and despite new injector nozzles, still has the knock which goes away when warm. However, the most obnoxious thing is that it smokes really bad, and has significant blow-by. It is a little slower than other turbo diesels I have had, but still has respectable off the line speed and power under load (when warm). Before I put any more effort into this I figured I should check the compression. The readings I got were:

27
23
27
27
27

So the question is, is the 4 bar difference significant? Could that be the origin of the smoking grayish exhaust? The blow-by? By the way, despite several tanks of diesel the exhaust still smells like McDonald's. Do you think more time and money should be invested? I am thinking I will see if new valve stem seals will help, but I hate to invest much in it if I can not get rid of the smokey exhaust. Any comments would be appreciated,
Will

tbomachines · #13 01-02-2010, 12:51 AM

First off, holy crap Roy you've given that guy about a year's worth of reading!

Great post, I will book mark it along with the DIY injection links.

Second...to OP - you mentioned that you replaced the timing chain. Did you recalibrate the Injector pump timing?

whunter · #14 01-02-2010, 01:10 AM

Quote:

Originally Posted by tbomachines

First off, holy crap Roy you've given that guy about a year's worth of reading!

Great post, I will book mark it along with the DIY injection links.

Second...to OP - you mentioned that you replaced the timing chain. Did you recalibrate the Injector pump timing?

IMO; he needs to be able to make a correct diagnosis = education = study.

NOTE:
Do not try to print the thread
wont start for anything!
wont start for anything! 1985 300SD
it is over five hundred pages..

nckmsn · #15 01-02-2010, 01:30 AM

Crack the injector on the low compression cylinder and see if the smoke goes away. This should give him an idea on which way to move with the diagnosis.