Rough Idle - 600 SEC (newbie)

[saleem3]

Hello all,

I am the proud owner of a 1993 600 SEC with only 8,000 km! Please see the attached pic. It’s a real classic.

However, the car has a problem when idling. It sounds as though it’s wheezing. The rev needle is always moving up and down as it breathes, both in “n” and in “p”. The oil needle always stays at zero (sometimes it goes up an inch when I accelerate hard). I'm sure the needle and the rough idle are related. I also notice that the accelerator has to be pushed down a lot for any real power. I believe all these issues may be related.

I do hope someone can point me in the right direction on how I can try and solve the problem.

Look forward to hearing from someone.

Regards

[Mercedes Mechanix]

Have noticed the zero oil pressure issue mentioned.... If it is zero when idling,,,,, I would definite recheck oil level, remove and check the filter for oil debris When was last change and filter r/r? The sensor may be defective, but without further info and service history.... I move on hesitant and cautious side. Lets move in this direction first....

Have you looked at alldatadiy.com and joined? Best tool u can have!

This engine, believe it or not is a beast and will run on half a bank only. Each side is feed respective firing sequence for the bank (as in six cylinders).

Would suggest investigate starting with each each bank of cylinders by group at this juncture:

1. start by pulling a single sparkplug from each side for comparison. Let us know and will submit further suggestion!

2. Oil level?

3. Last service? items serviced? Task(s) performed, replaced?

The V12 was one of the power plants that Roberts team was a definite in design concept and diagnostic overview during production and application.

He will be in a little later this afternoon.... 1540 hours I believe (ET). Will get with him for further assist...... unless someone else on the site, would liker to interact as well!

He was called by a local shop re: V12 with an intermittent ignition issue! OBD ! issues and not clearing, etc. Will let u know on that as well if u are interested?

Dietrich

Originally Posted by saleem3

Hello all,

I am the proud owner of a 1993 600 SEC with only 8,000 km! Please see the attached pic. It’s a real classic.

However, the car has a problem when idling. It sounds as though it’s wheezing. The rev needle is always moving up and down as it breathes, both in “n” and in “p”. The oil needle always stays at zero (sometimes it goes up an inch when I accelerate hard). I'm sure the needle and the rough idle are related. I also notice that the accelerator has to be pushed down a lot for any real power. I believe all these issues may be related.

I do hope someone can point me in the right direction on how I can try and solve the problem.

Look forward to hearing from someone.

Regards

[falconsprint]

You need to determine what is going on with the oil pressure first. If the engine is running without oil there will be serious damage. Look under the oil fill cap. Is there oil on the camshafts? Change the oil and filter. Don't run the engine more than 10-20 seconds without oil pressure. Its possible that the car has sat so long that the oil is old and has gunked up.

The wheezing sound you hear may be a large vacuum leak. The RPM is going up and down because the emissions/idle control isn't able to adjust the air/fuel mixture.

[bayhas]

you have 3 separate problems.

rough idle with hissing sound: you have major vaccum leak, follow the sound and you ll find the broken/deattached vaccum line

oil pressure: check oil level and viscosity, mercedes manual does not want you alarmed if the the oil pressure is 0 at idle, as long as the red light is not on, and the needle goes up in pressure as soon as you rev up. do an oil change anyway and see what happens.
if the pressure does not go up when you hit the gas, DO NOT DRIVE THE CAR AND TURN IT OFF RIGHT AWAY

hard to push gas pedal: from what you are describing, the car is in the limp home mode
if the car is idling, and you hit the gas, does the pedal travel 1/2 way to the floor before the rev goes up?

[Mercedes Mechanix]

Bayhas and falconsprint are both 100% right and Dietrich must have missed the possibility of limpmode being a possibility as well. We recently also had an issue with the pickup horn (is dependent on vacuum suction.... even being hit while driving can cause a loss of oil suction, thus reasoning for placement at oil-pan base and crown in fill horn scrren holder, etc. Address visual oil movement first under oil fil cap.... then move to rest of concerns. Have movement... then close it and move on.... no movement, check filter and think about dropping that lower pan and clearing that oil screen and possible sludge under valve covers. There are passages in both valve cover tops (similar to sinuses for the engine compartment and both have drains that need to be clear for oily vapor blowby residue to drain back). If not serviced regular or if sits for any length of time..... an issue can build!

As post stated, dependent on length sitting, that oil can wax up and cause a havoc with galley ways, drains, etc. Many of the passages are very small and at high rpm, bearing surfaces extremely dependent of good lubricant between surface faces. Remember high flow=low pressure.... low flow= higher pressure dependent on oil viscosity, dependent on temperature.... An overheating engine will many times lose it's oil pressure due to thinning of oil and very very high lubricant flow, etc. Vicious Circle my friend!

At engine operating Temperature the 120 and 119 engines require 10 wt for proper overall lubrication needs..... in fact all four cycle engines, even those using a single grade lubricant will have 10 wgt lubricant flowing in their machines at operating temperature. to be sustained.

One of our clients mentioned a site that also has this information. Someone on this site can also help with the actual site information?I picked this up in engineering, etc.

I will get with Dietrich..... please follow the previous Post advice and address the oil pressure anomaly first and Always First!!!. You may have fine oil flow and your sender is only seeing data below it's calibrated sensor engineered curve, etc.

After verifying you have actual oil flow through the oil fill cap.... then take a look at those cylinders, regarding the idle. Like Dietrich eluded too, there are a lot of sharp cookies on this site... and all have their advice to offer and you can choose from there! Well, as far as me, I'm not the sharpest tool in the shed, but I sure get used alot........ LOL

Although many of the other mechanics use 20-50 and such for their Benz... in my 94' S420 119.971 (347K miles), I utilize 0-30 SAE Mobil-1 and ensure that at start-up.... my lifters, journals, cam bearing towers are bathed in lubricant. There is nothing wrong with 20/50 SAE and many of our Senior Master Mechanics use it in their high mileage vehicles..... I just feel otherwise and if my engine gets a little noisy I will address that lifter or oil tube, etc. At least my start-up worries are satisfied.... always!

Thanks to everyone.... Robert O.

Originally Posted by bayhas

you have 3 separate problems.

rough idle with hissing sound: you have major vaccum leak, follow the sound and you ll find the broken/deattached vaccum line

oil pressure: check oil level and viscosity, mercedes manual does not want you alarmed if the the oil pressure is 0 at idle, as long as the red light is not on, and the needle goes up in pressure as soon as you rev up. do an oil change anyway and see what happens.
if the pressure does not go up when you hit the gas, DO NOT DRIVE THE CAR AND TURN IT OFF RIGHT AWAY

hard to push gas pedal: from what you are describing, the car is in the limp home mode
if the car is idling, and you hit the gas, does the pedal travel 1/2 way to the floor before the rev goes up?

[pcmaher]

There are a few vacuum hoses in the back of the engine bay, on the intake manifold that can easily come off. Happened to my V12 a lot...made it run rough. Check all the hoses.

[saleem3]

Gents,

Thank you for your replies.

The car has been sitting idle for over 15 years. It use to belong to the Royal household, so has only done 8,000km. Since I've changed the oil the pressure has made a difference. It still jumps up and down, but seems to be more consistent. The more I drive it, the better it is. I haven't changed the filter yet. That's next on my list.

Up to know the following is what I have done:

1. Disconnected the battery and re-connected it after 15mins. My understanding is that this re-sets the settings. It has made a difference to the acceleration. However, I've always driven a v8 Jeep, so not sure if the Merc is suppose to be as nippy. The car is fine in Sports mode, but find it slightly sluggish in E mode. May be it's just me.

2. Changed the oil. I also pulled out one of the spark plugs and they looked very old and tired.

Next steps:

1. Change the oil and air filters. Change all the plugs.
2. Take it to Merc to diagnose the idle problem.

Will keep you gents posted.

[Jonathan Wallin]

I have had zero oil pressure. = short curcuit in the cracked up/bad wires to the sensor.

I have had rough idle and also rough run that made the engine power less. = Broken/worn distributor cap on driver side of engine. That made the engine go in to some kinde of "limp mode".

So check distributor caps, rotors and the wires to the oil pressure sensor.

[Brett San Diego]

Originally Posted by saleem3

Gents,

Thank you for your replies.

The car has been sitting idle for over 15 years.... I haven't changed the filter yet. That's next on my list.

So if I understand correctly, you're driving with a 15 year old oil filter. Maybe it's still OK, but that's not a practice I would condone. Stop driving it and change the oil filter. And, if it's truly been sitting that long, I would just change all the oil again... along with the brake fluid, transmission fluid, coolant, power steering fluid, and suspension fluid.

Brett

[Haku]

Originally Posted by saleem3

The car has been sitting idle for over 15 years. It use to belong to the Royal household, so has only done 8,000km.

Sounds like you've stumbled upon a nice machine - congratulations!