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1991 300TE 4Matic
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78 Posts
Discussion Starter #1 (Edited)
Good Morning all,

I had an isolated incident yesterday with the 91 300TE 4Matic on a long-ish trip I was taking. A little background as it relates to the issue. Car has 206K miles, the head was redone at about 180K for the typical valve stem leakage that the 4matics have. Oil change was up to date, plenty of fresh, amber oil. Only real issue I have seen with this is that the oil pressure gauge at idle in gear is always sitting on the peg at the bottom of the meter, but comes right up under acceleration, right up to 3 bar. If I have it is neutral it sits at the .3 or so bar that the manual says is normal.

So anyways, yesterday I passed a car at 80 mph, and when I let off the gas I saw quite a lot of blue smoke in the rear view mirror for about 10 seconds. Turned off the a/c (which had been running for 200 miles or so, cruise on at 75 mph for all of those 200, about 85 degrees ambient temp, about 85 Celsius coolant temp), pulled it over, shut it off, and let it sit for 5 minutes to check the oil. Still full, though of course the oil looked and smelled a bit hot. Started it back up, and it stumbled for about 50 feet, then was good as new again. Oil pressure was same as always. Drove the rest of the way home (about 100 miles), again at 75, with the a/c on, and not a problem, no smoke, did a hot restart or 5 just to check and make sure it didnt stumble again, and no issues. Again start it up again this morning, no smoke on cold startup, no issues at all. Anyone got anything I should be looking at here? Did I hit some screwy gas somewhere? Does this car have a problematic easy to dirty PCV system like a Volvo 850 (which causes this same problem)? Thanks for your suggestions
 

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1991 300TE 4Matic
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78 Posts
Discussion Starter #2
Just a quick update, I was driving home, still no smoke, in traffic, and the car died on me twice coming off a red light, and stumbled on acceleration another few times. Started right up afterwards and drove off ok.
 

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1995 E320
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2,507 Posts
if you're normal tune up stuff is up to date then perhaps you want to remove the spark plugs and inspect them. If nothing is evident, you probably will need to do a compression test.

I don't think the car dying has anything to do with the oil. I could be wrong though.
 

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1991 300TE 4Matic
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78 Posts
Discussion Starter #4 (Edited)
I totally agree on the oil pressure/driveability issues not being related. Went out this morning and had a total no start situation, and I know I am getting fuel (can smell it and see it on the plugs). Was hot starting fine last night after my couple of stalls. Even if the compression was a bit low it would still give me something. Had to get to work, so I couldn't see if I was or wasn't getting spark yet, but I will see. Had a full tune and check up within 5K miles with Mercedes OE parts, and the plugs show that, nice tan color on the first 3 I pulled (1,2,3), but the cap looks like it has been there for a while (they may not have cleaned the black cover off). Maybe I burned the rotor up or something. I had some burn through on some of the plug wires where it comes in contact with the dipstick tube, which I had taped up before I went on my long trip (I was getting some radio interference from them, which is why I knew about it). Maybe I was getting some cross fire in the taped bundle as well. By the way it seems like alot of people run pretty heavy oil in these engines, especially with higher miles. I know it has 5W-30 fossil oil in it right now, should I change out to 20W-50 to give it a bit more pressure? I was planning on running this car out to some serious miles, so I got a car with all the records, but this is atypical for every Benz I have driven or am in touch with. Usually if you stay on top of them they are reliable as anything (sorry guys, I had to rant because the car made me late to work this morning).
 

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Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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5,454 Posts
Aside from the stalling/no start issues, you're running 5W-30 and concerned about low oil pressure at idle? Are ya kidding me?
I run Castrol GTX 20W-50 during the warm months (or I have been since, oh, 1992). With the input of some forum members I learned that the original fill on our cars was 15W-40 (which has been my cold weather oil). I may run the Delo 15W-40 year round now, haven't totally decided. And a change is coming up on TE #1.
I wonder about that smoky discharge you first saw. My TE#1 has relatively low miles (112k) but it was poorly maintained and has had some serious issues along the way. Like fuel distributor replacement. Don't know why. When I first bought the car and was using free time to get it squared away, it would sit for weeks before I would start and move it. Once in a while it would smoke like crazy and I was sure that I would need to pull the head to do valve guides/seals. With all the other things on my plate, though, I decided to hold off on that project and wait until the car was on the road to see how bad the problem was. With about 6000 miles on the car since then (driven almost daily) oil consumption has not been a problem. And no smoke discharge has been noted.
I had to replace the throttle body to fix a bad idle/WOT switch and at that time I noted a substantial pool of oil or some other thick liquid in the lowest pat of the intake manifold (which is directly under the throttle body). It took several paper towels to wick up the stuff. You may want to blcok the throttle open and deflect the airflow meter plate to see if there's an accumulation of stuff under the throttle body.
 

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1991 300TE 4Matic
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Discussion Starter #6
Thanks for that, I was wondering why any car with 200K on it would be filled with 5w-30. I have only had the car a short while, so this was a previous owner oil change, done at a quick lube joint (go figure right). All the service was done at Hatch and Sons in Mass though. I love that delo 15W-40, ran it in all of my Audi 5000 diesels, and I think I have a few gallons kicking around. I am going to give it a shot and see if that brings up the OP on idle (that is once I get it going). I will certainly give inside the throttle body a look. The smoke was strange, but I figure if it was extra thin oil, ran at high temp for a bit, it could have snuck past a ring or seal momentarily on deceleration. It was actually pretty awesome, the dude that was riding my arse in a Lexus RX got a face full of it and you could see him cringing. Teach him to ride my family wagon like that.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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Correct oil pressure at warm idle should be about 1 - 1.5 bar. With the miles you have on the car, it might be good to replace the oil pressure sending unit. It is located on the firewall side of the oil filter block. There is a single wire lead attached to it and it's dead simple to R/R.

I tend to think that the "puff" of smoke you saw after letting off the gas was blow by from the rings. Not all that big of a deal and sometimes can happen after a sustained higher speed run.

Good Luck,

Jayare
 

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1991 300TE 4Matic
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Discussion Starter #8
I concur with changing out the sending unit as well. The movement has always been a tiny bit twitchy in the meter when accelerating or decelerating, not typical of Mercedes gauge action. I am going to give M-B a call and get a sending unit, a case of oil filters, cap and rotor (I will need them eventually) and hopefully I can get some spark out of it tonight. I am going to operate under the assumption that compression is ok, it tested OK 20K miles ago when the head was off to do the valve seals, unless it needs a retorque. Wish me luck, I think my girlfriend is going to shoot me if I have another car I am not driving in the driveway, but such is life!
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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You might try autohausaz.com, autopartsplace.com or mercedesshop for your parts. All offer excellent price and service. No tax and no shipping charge for orders of $50 or more. You'll find their cost much less than dealer prices.

As for the "spark" question... Check voltage to your coil and out. Also check your battery voltage with the car off and running. Running you should be getting 13.4 + volts. If not, the voltage regulator is most likely suspect. Easy to R/R and located on the back of the alternator, held in place by two phillips screws.

Good Luck,

Jayare
 

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1991 300TE 4Matic
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78 Posts
Discussion Starter #10 (Edited)
Ok thanks again to all for the helpful places to look for my issue. Tune up stuff was OK, plugs 1-6 nice and tan in color on the tips, cap and rotor were slightly used, I cleaned the copper up with some emory cloth just in case and put some di-electric on the rotor button center contact for good measure. Coil voltage was ok. Looked down under the throttle body, no residue. Got it fired right up last night, but it seems when I goose the throttle off of idle is where it is having an issue. After 1100 RPM it is smooth as silk. Drove it 5 miles this morning with a little 2 foot brake and throttle action with no problems. Sounds and feels like a vacuum problem. I pulled the air cleaner last night to check the vacuum lines, and was hearing a hiss coming from the general area of #3 cylinder, right about where the little molded rubber hose goes from a cold start valve/vacuum routing looking thing (silver, has a connection on it with an arrow pointing to the hose) to the engine block, down under the intake. Looks like a bear to replace, although I took my propane torch and went around the hose as much as I could with no effect. Also tightened up my intake manifold, as the bolts seemed not tight enough, this had no effect. The hose that goes from the valve cover to the air cleaner, with the small white line that goes to the fuel pressure regulator, is loose and a bit cracked at the valve cover end, plugged this and still to no avail. Anyone think that that molded hose is causing issue somewhere where I cant reach? I poked at it and thought I heard a momentary change is the pitch of the hiss, but couldn't replicate it. Got some good suggestions of where I can look? I was thinking it could be the intake manifold gasket, but it only has 20K on it, and the propane torch trick didnt seem to make any difference in idle when I ran around it too. Thanks again and sorry about the lengthy post!
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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scooter

Use the search feature of the forum and look for "air/fuel ratio adjustment". You'll find plenty to read.

Good Luck,

Jayare
 

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1991 300TE 4Matic
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Discussion Starter #12 (Edited)
Thanks for the pointer Jayare, though I do not think that this was my problem. I did the checking and adjustment by the book, actually when I hooked up the multimeter it was reading 43%-53% duty cycle with the engine warm, a/c off, and car in park. The reading with engine off, ignition to on, was 69.9%, deflected plate cycle came down to 20%, full throttle was to 10%, right in line with the specs I read. I played with the adjustments due to some people saying 70% was the sweet spot, still ran like crap. Only way to get it running with some power off idle was to put it at 90-96% duty cycle. o2 sensor readings were right in the acceptable range. One thing I couldn't figure out was when I turn the screw clockwise the duty cycle goes up, CCW it goes down, contrary to what I researched. I left it at 90 or so overnight, and now I cant get it fired up. Did the trick I read somewhere else, where you unscrew the screw to the stop, then screw back in 3 full turns, still no start. One more turn a few more times, dead in the water. Also I checked the OVP relay before I started messing with the air/fuel, and it was replaced recently, has the 2 fuse OVP in it now. Pulled the fuses and replaced them along the lines of another post where this solved the problem, still no dice. Weird thing is on the OVP is when I removed the black cover, the OVP was swinging free in there, not bolted down by the tabs. Does the relay body have to be grounded? Does me having to set the duty cycle so high mean that I may in fact be dealing with a vacuum leak? I went through all the lines I could put hands on and couldn't find a suspect, and I cant figure out if the hiss I am hearing is from the intake, or from a bad line around the intake side around #3 or #4. Does anyone think I should begin a new thread for this issue vs adding on to an oil pressure thread? Thanks
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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Well, you could start a new thread as this issue has nothing to do with oil pressure. CCW movement of the a/f adjuster screw leans out the mixture. Are all the elements of the plugs, wires, dist. cap, rotor in order? Fuel filter fresh? Pumps operating correctly? Spark strong? The "hiss" you are hearing when the engine is at idle is airflow though/past the intake plate.

Jayare
 

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1991 300TE 4Matic
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78 Posts
Discussion Starter #14
Thanks again Jayare,

I will move this thread over once I replace the fuel filter. Spark strong and doesnt seem to miss at all, and the fuel pumps seem to be doing their job just fine.
 
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