Help me figure out this stupid vacuum issue M103 - PeachParts Mercedes-Benz Forum

lorainfurniture · #1 10-18-2011, 12:00 PM

Ive been chasing this problem around for about 2 weeks now. I'm running out of ideas.

Car: 89 300e, m103 engine.

Symptoms: Runs like a dog, no power.

I suspected a vacuum leak, and I was right. At idle, I am only getting about 14-15hg of vacuum. Normal from what I searched is 18-22hg.

Checked the usual suspects:

1 idle air hoses: good
2 eliminated trans line, ignition advance line, and the line that goes in to the cabin: Good
3 Thinking I might have a clogged cat, I disconnected the exhaust system at the head. I basically loosened all the bolts enough to get me about 1/4 of an inch gap between the head and the exhaust manifold. drove it around the block. Still reading 14-15hg, no appreciable gain in power.
4 I thought maybe I had an ignition problem, so I swapped out the ignition coil. No change.

So now I am thinking that either my intake manifold gasket sprung a leak, or possibly my injector seals.

What do you guys think?

lorainfurniture · #2 10-18-2011, 02:43 PM

Anybody? I feel like punching my car in the face...

duxthe1 · #3 10-19-2011, 12:19 AM

22 inches of vacuum on a 103 is a pipe dream. I idle around 12. Vacuum leakage isn't going to have any bearing on a low power scenario. Look elsewhere.

lsmalley · #4 10-19-2011, 12:22 AM

Punch your car in the face first, then check your spark plugs.

ps2cho · #5 10-19-2011, 03:19 AM

Is this something new on the car?

Condition of plugs/wires/rotor + cap?

The coils on the 103's rarely go bad. They are pretty solid.

And as dux mentioned, goodluck getting anywhere 18Hg!! Both my 103's ~12-13 at idle.

lorainfurniture · #6 10-21-2011, 10:35 AM

Quote:

Originally Posted by ps2cho

Is this something new on the car?

Condition of plugs/wires/rotor + cap?

The coils on the 103's rarely go bad. They are pretty solid.

And as dux mentioned, goodluck getting anywhere 18Hg!! Both my 103's ~12-13 at idle.

At idle, I get about 14-15hg. My economy gauge went from pegged to the left at idle in park, to about 3/4 to the left.

The spark plugs, cap, wires, and rotor are about 4 years old, and have about 40k on them. It seems a bit soon for new plugs. Ill give them a try anyways.

Any other ideas?

S-Class Guru · #7 10-21-2011, 12:25 PM

Yeah, about 15-16 has been normal on mine for the last 10 years or so.
This puts the needle on the left peg when idling in neutralat normal RPM of about 700, with warm 10-40 oil. When in gear the needle will move off the peg about 1/8th inch.

I assume the engine runs smooth at idle and speed, just sluggish? If the engine has a problem and is struggling a bit, then the IAC will open more to maintain idle speed, and the vacuum will fall a bit; so that may be what you are seeing. So, the lower vacuum would be a sympton, not a cause.

You might check compression, cam lobe wear, and possibly cam timing (although the timing chains are pretty bulletproof).
A quick check of the fuel system can be done by checking the Lambda percentage as defined in some of the archives herein.

DG

lorainfurniture · #8 10-21-2011, 12:40 PM

Quote:

Originally Posted by S-Class Guru

Yeah, about 15-16 has been normal on mine for the last 10 years or so.
This puts the needle on the left peg when idling in neutralat normal RPM of about 700, with warm 10-40 oil. When in gear the needle will move off the peg about 1/8th inch.

I assume the engine runs smooth at idle and speed, just sluggish? If the engine has a problem and is struggling a bit, then the IAC will open more to maintain idle speed, and the vacuum will fall a bit; so that may be what you are seeing. So, the lower vacuum would be a sympton, not a cause.

You might check compression, cam lobe wear, and possibly cam timing (although the timing chains are pretty bulletproof).
A quick check of the fuel system can be done by checking the Lambda percentage as defined in some of the archives herein.

DG

The engine runs pretty smooth, no misfires or hiccups. Its just I have to press the pedal 80% down to get the same acceleration as when I used to press it 25%.

It feels like my car is half as powerful as it used to be.

RBYCC · #9 10-21-2011, 02:33 PM

As the previous poster stated "check your spark plugs"
The condition, gap and color will tell you where to look for any problem

You mention your accelerator pedal..have you checked your throttle linkage to see if it has full movement?
My 300CE is close to 16 @ idle:

rayhennig · #10 10-21-2011, 02:52 PM

Quote:

Originally Posted by lorainfurniture

Symptoms: Runs like a dog, no power.

I suspected a vacuum leak, and I was right. At idle, I am only getting about 14-15hg of vacuum. Normal from what I searched is 18-22hg.

If it idles like a dog I might agree that vacuum is an issue. However, if it always runs like a dog, there's something else.

Think about it. When you hit the gas, vaccum disappears and what the engine needs is fuel and spark. Vacuum leaks will be irrelevant as the butterfly valve's fully open and the engine's gulping in great globs of air.

Smooth idling is one of the most difficult situations for the management system to handle. Once you open it up, the equation becomes simpler, albeit not trivial for optimum conditions: fuel, air (which the pistons are sucking in like hell) and spark.

I've been having vacuum issues on my old M104 KE Jetronic and it's only at idle speed that problems manifest themselves.

There is something worth considering though. If you've adjusted fuel delivery duty cycle with vacuum leaks, the adjustment will be out and that could affect richness (or otherwise) under power.

That's my 2c worth.

Bon courage.

RayH

greenacres2 · #11 10-21-2011, 03:07 PM

With a 1989, i'm guessing it calls for a copper core spark plug. As mentioned by a few others, the first thing i'd look at would be the plugs/gaps. With copper, 40,000 miles probably has several thousandths of wear and could very well be at least a contributor. Distributor and rotor "should" still be good, but if the plugs are right it's the next place i'd look for signs of arcing, etc.

Might not be it, but it's one of the easiest parts of the puzzle to check and correct.

Good luck!!

lorainfurniture · #12 10-21-2011, 03:13 PM

Thanks for the replies guys. I was beginning to think a while back that my vacuum was a symptom of a different problem.. Thats why I removed the exhaust.

I have to order some new plugs, and I think I have a good cap and rotor from a spare car just in case.

Just to refresh, checking the duty cycle is pin 7 and 11? After the car is at operating temp?

Hirnbeiss · #13 10-21-2011, 08:06 PM

Also check your transmission control pressure cable, that it's connected and adjusted properly. Just an easy thing so you rule it out - doggy shifting gives doggy performance.

S-Class Guru · #14 10-22-2011, 12:07 PM

Duty cycle on the round connecter is pin 2 & 3. On the ubiquitous Sears meter, the red probe goes on pin 2, just the opposite of what one would think. The book says optimum is just a tad rich, or about 40% at idle and 2500 RPM. The guys are right, though, if you have a problem, trying to band-aid it with lambda tweaks will just throw everything off even more.

DG

benfield4 · #15 10-25-2011, 11:49 AM

Please follow through with what the others are telling you. An observation I had with my 89 300SE that has the M103 engine is that the injectors were not spraying a fine enough mist. I had a noticable increase in power when I replaced the injectors, both seals and the plastic baskets. It did not do squat to fix my low vacuum/economy guage but it sure made the car perform better!

Have you done the vacuum leak test as layed out in the "DIY Articles"? That is where you hook up your volt meter directly to the oxygen sensor and spray carb cleaner around all the rubber bits and seals to check for a change in the lambda reading. I had a noticable leak in the Throttle valve shaft seals on mine. It made the vacuum better after shelling out $300 for that. Its still not perfect but its better.

Keep on with the diagnosis and you will find it!