1983 300SD diagnosis help. Low power. Think you know? - PeachParts Mercedes-Benz Forum

JHogan · #1 05-30-2008, 06:26 AM

I bought this 126 300SD for the Ronal wheels. The previous owner said the car was worn out. He stated it had no power and wouldn't get out of it's own way.

Hmm, I thought, easy fix.

Change the filters and get it going. At the most clean the banjo bolt. No.

Ok, I'll adjust the valves. (Cold,.10mm,.35mm.) and try using a alternative fuel tank and see if it runs any better. Nope.

Still no power when the car is first started, wont pull a hill, barely backs out of the grass. Linkages are sloppy but go to full stop. Very slow to rev, even using the rack on the engine to rev. If I let it warm up a bit, say 5 minutes idling, it seems to have a bit more power. At least it will pull a small hill.

Car starts on 2 revolutions after glow.
Car teakettles like crazy and has low to medium-low compression. It's even across all cylinders though.

I still think it's fuel delivery, but why does it get better when the car warms up? What would you check next? I have no compunction about parting out or junking this car, but I'd like to give it a chance first.

Any suggestions would be appreciated.

Thanks, Jay Hogan

barry123400 · #2 05-30-2008, 07:31 AM

I would try to disconnect the exhaust system or just drop it at the manifold. Thats after a few checks below. The power after it warms a little is probably just the oil thinning out a little with heat.
Since it starts so easily I wonder if your description is right on compression? Some numbers might help. You are getting the injection pump opened up? Or is there too much slop in the linkage? See if the linkage fully advances the pump arm with the pedal. You would not be the first.

Brian Carlton · #3 05-30-2008, 08:49 AM

From the description, I'd be looking at the cam timing and the IP timing. If the engine was poorly maintained (likely with the low compression), the chain is probably elongated by 10° or so.

If you cure the timing issues and the engine still won't perform, I'd double check the fuel pressure with a suitable gauge.

It's possible that the low compression is a contributor to poor performance, but if it's seriously low, you'd have a bit of issues in starting it at colder temperatures. That's probably not a problem right now, however.

PNO TECH · #4 05-30-2008, 12:04 PM

I did the compression check using the gp holes without cutting off the fuel, so that may compromise the results. None of the cyliders reached 250 in the first 3 strokes, and they all took 7 to 10 to reach 400.

After we did the valves, I tried cranking it without pausing for the glowplugs,and it caught on the third revolution.
What gets me is that it takes perhaps 10 seconds to rev to 2500 rpm when cold, then, when warm, will do it in a second or so.
BTW, we did remove the teminally oil-soaked air filter.

Any insight/sugestions much apreciated

Brian Carlton · #5 05-30-2008, 12:09 PM

Quote:

Originally Posted by PNO TECH

I did the compression check using the gp holes without cutting off the fuel, so that may compromise the results. None of the cyliders reached 250 in the first 3 strokes, and they all took 7 to 10 to reach 400.

It is irrelevant how many strokes the engine requires to reach the true compression value. In your case, you achieved compression figures of 400 which is excellent. There are no compression issues with that engine.

Your problem is cam timing and/or injection timing. I'd bet on it.

81300sd · #6 05-30-2008, 06:36 PM

I second Brians opinion.
Diesels are gutless pigs that rev slower than dirt when retarded.

Bet it needs a chain.

bgkast · #7 05-30-2008, 07:00 PM

Birds nest in the Airfilter?

Brian Carlton · #8 05-30-2008, 07:10 PM

Quote:

Originally Posted by bgkast

Birds nest in the Airfilter?

.........no serious smoke........??!!

bgkast · #9 05-30-2008, 07:11 PM

Good point.

barry123400 · #10 05-30-2008, 07:24 PM

Glad to hear you have excellent compression. Turbo is spooling up and providing boost? Back to the drawing board. There are in reality quite a few possibilities. Nothing too expensive though.
After checking the timing and chain stretch etc. A set of partially obstructed injectors might be another possibility. The last is just a guess. I do not think the pump is that far out of time as the car would smoke. I suspect thats why Brian asked if it was smoking. Or at least I think it might smoke myself. Maybe it does?
Your very low power till warmed up and then only marginal power sounds like low fuel supply or again obstructed exhaust. Nothing like making suggestions so someone else gets to do all the checking things out.

One last thought. If the car has been running vegatable oil let us know.

PNO TECH · #11 06-01-2008, 09:28 PM

Checked the timing chain stretch both ways (2mm valve lift & cam mark) and got 9 and 2 degrees respectively, which is right for the 05 cam code. Guess I/we will drop the exhaust next to check for carbon buildup.

I've been searching the forum for the simplest way to check IP timing. Any leads for that procedure would be great.

J cleaned it up Sat, and now its really too nice to just part out. I just hate using up time that I could be installing MY engine. My kingdom for a 30-hour day!

Thanks for the suggestions,

Scot

94mgm · #12 06-01-2008, 10:05 PM

did you try to spin the turbo by hand?

PNO TECH · #13 09-06-2009, 09:45 PM

I figured the best thing to do was try it as a daily driver: it'll either work out or become a parts car.
Turbo does spin by hand. Power with exhaust disconnected didn't seem much better. I have to let it idle for at least 3 min before I can get out of the driveway. It won't go up an incline of 7% until the temp gauge is at least at 40. Seriously: no power! Once warmed up, it runs pretty well, with the exception that the 1-2 shift is pretty hard (and doesn't happen until 3500), and it won't shift into 3rd unless I quickly nudge the shifter up into N and back to D. I've revved it all the way past 4000 to no avail. Door locks don't work, so I'm chasing that vacuum issue. It does cut right off, though. My main concern is the lack of power when cold.
It does smoke a fair amount at idle. No idea if it was ever run on VO, but I seriously doubt the guy we got it from did anything like that.
So, is the drip test the simplest IP timing test? I really don't want to junk this without a fight.

Thanks,
Scot

Junkman · #14 09-06-2009, 10:23 PM

Every time my SD wouldn't go up hill, it's been lack of fuel. Rule that out 1st.

Brian Carlton · #15 09-06-2009, 11:16 PM

Quote:

Originally Posted by PNO TECH

It does smoke a fair amount at idle. No idea if it was ever run on VO, but I seriously doubt the guy we got it from did anything like that.
So, is the drip test the simplest IP timing test? I really don't want to junk this without a fight.

Thanks,
Scot

You've covered many bases at this point. One other..........did you ever drop the tank screen just to see its condition?

As far as IP timing, see if this IP might have the port on the side to use the A-B lights. I believe the change was made late in '83 so you might get lucky. If so, the A-B lights are the way to go for ease of use and accuracy. If not, you'll need to use the drip method.

With 400 psi compression, you've got to continue with it until you find the issue.