W124 Starting Problem

Tom, Well this is a real "stump the band" request.

If this car were in my garage I'd start from the beginning:

Prior to these problems had anyone worked on the car? If so, what was done, exactly?

Is the battery reasonably new and installed correctly -- to ground ++ to starter?

Check the age of the "over voltage protection relay"; it is the one with a fuse on its top. Replace it if more than ten years old.

Is the fuel pump relay original? Replace it if older than ten years.

I didn't see that the fuel filter was replaced. Was it?

Does the engine run smoothly when it runs? Or does it have misfires?

The catalytic converter could have disintegrated and the debris are blocking the exhaust passage but that's not likely. To force the engine to turn backwards the pressure inside the exhaust would be very high so high that the engine would be unable to run for more than a second or two. Water in the gas gets vaporized; it wouldn't destroy the cat. Was the car underwater? Is the exhaust pipe crushed flat?

I suspect there are two problems: An engine running problem and a starter motor problem. The engine starting and running may be cured by the aforementioned filter and relays etc. The starter motor itself is suspect, IMHO. It may not be disengaging from the flywheel when you release the key - thus the strange noises and engine rotation. Conversely, has the ignition key switch ever "acted up?"

If it were only a diesel, none of this would happen.

Tom

Thanks for your advice. The starter never occurred to me. I was even dreading the possibility of a head gasket leak into the exhaust system (though the coolant level has been stable).

If only it were a diesel, indeed. My favorite car by far was my '82 300D turbo, which, very, very sadly was totaled by a careless motorist while I was on my way to the parts store to get a new washer fluid reservoir (the old one was stained!). Such was my folly. But no longer. Now I just do what the cars need to run.

For the rest, the fuel filter was replaced when my mechanic flushed the lines the last time I had it towed in, and the fuel pump relay was replaced in 2002. The battery is four years old, the terminals are corrosion free and tight. The grounds look good too, and I sprayed them down with CRC 2-26 just in case.

If I am looking at the correct relay (10A 12V square body with a 10A spade-style fuse under a cover on top of it, located behind/next to the fuel pump and klima relays) I don't see a date stamp anywhere on it. Judging by the oxidation on the body, though (about the same as all the aluminum body relays in the fuse box, but none of them look bad at all), I think it's original. The fuse on it is fine, by the way. On a side note, I looked for a new one online and only found one (about $70 at BuyMBParts.com) with two 10A fuses in them. Would those be compatible? Any way to test the old part?

Otherwise, when the car was running it always ran smoothly. The only oddity was that sometimes it seemed to lack power when accelerating from a stop, almost like it wasn't downshifting...sometimes. The rest of the time, it was quite peppy. My wife (who drives it most) thinks that it was more likely to fail when it was peppy! I haven't seen any pattern, though.

Fortunately, the car has never been under water or driven through deep water, and the exhaust pipes look good all the way to the caty. Turning the key in the ignition has never done anything weird, except what it's doing now.

So, what would I have to do to troubleshoot the starter motor?

Cheers! Tom

Tom Dolan Williamsburg, VA

1988 560SEL 1989 260E

And once the proud owner of a secondhand

1977 300D, 1979 240D, 1982 300D, & 1985 380SE

I forgot to mention, I've had the car since May 2000, and never had it in for any major work. I replace the distributor cap, rotor, and wires in 2004, and the blower motor this past January. Otherwise, the most recent work done (other than whatever the mechanic I've been taking it to has done to the fuel system) was an oil/filter change I did in early July.

My '77 F100 pickup is looking more friendly to me every day!

Tom Dolan Williamsburg, VA

1988 560SEL 1989 260E

And once the proud owner of a secondhand

1977 300D, 1979 240D, 1982 300D, & 1985 380SE

If I am looking at the correct relay (10A 12V square body with a 10A spade-style fuse under a cover on top of it, located behind/next to the fuel pump and klima relays) I don't see a date stamp anywhere on it. Judging by the oxidation on the body, though (about the same as all the aluminum body relays in the fuse box, but none of them look bad at all), I think it's original. The fuse on it is fine, by the way. On a side note, I looked for a new one online and only found one (about $70 at BuyMBParts.com) with two 10A fuses in them. Would those be compatible? Any way to test the old part?

I'm not a "overvoltage protection relay" expert; I do know that when these get old their host cars do some very strange things - hard starting, stalling, lack power etc. Old relays have 'Siemens" stamped on them. Others here may have more information, suggest you make a new post about this relay.

The starter consists of a solenoid and a motor. My theory is that the solenoid is defective and not cutting off the current to the motor after the engine fires

- or tries to. I don't know how to test it other than listening to it while cranking the engine, especially after releasing the key. If you replace it buy a Bosch, not some "brand X" rebuild sold by a local parts store.

That said, I'd look again at the battery - a four year old battery can be weak enough to crank the engine but little else. I once spent about $400 for a new fuel pump etc. because my car's battery was a cheap (off brand), few years old and weak! An expensive lesson after "saving" $20 on a cheap battery.

I hope these ideas help get your car back on the road.

Tom

ago, then it started to

to re-start. Usually,

I had to have it towed to a

a few seconds without

seconds, but made a very

The mechanic could not

the shop. This seemed to

gas/condensation in the fuel

at the pumps and told me

flushed the fuel lines out,

it failed to start at all.

It had very little

a new one. Since they are

the fuel hoses. I know they

at least it would get rid of

system does hold

the odd run-on thing after

strange. While the

are firing. When I stop

fan change directions!

how do you diagnose more

water in the fuel, and water

catalytic converter?

The turning backward thing is proof of a serious timing issue. the compression/ combustion is pushing the Motor.

Check he timing chain is where it snould be. Check the plug wires, Make Sure they are hooked up correctly. HTH, Marty

Tom, Try to make things as simple as possible. It takes 5 basic things to make an engine run. Each needs to be checked and then the correct one fixed. Look at the following things in this order.

1. Starter turning the engine close to normal cranking speed. Just listen to it and see if it sounds normal for that car.
2. Ignition. Check for spark at the plugs and check that the ignition is at the right time (timing light).
3. Air and fuel. Remove the air filter and pour a couple of ounces of fuel directly into the fuel distributor then try to start.If it is a fuel problem it should run for a second or two.
4. Exhaust. Have someone turn the engine over with the accelerator held to the floor. Feel at the tailpipe for exhaust.

One of the above should lead you to the problem area.

Paul McKechnie PS An engine turning backward a little is nothing unusual. It is just compression in one of the cylinders pushing the piston back down.

ago, then it started to

to re-start. Usually,

had to have it towed to a

few seconds without

seconds, but made a very

The mechanic could not

the shop. This seemed to

gas/condensation in the fuel

at the pumps and told me

flushed the fuel lines out,

failed to start at all.

It had very little

a new one. Since they are

the fuel hoses. I know they

least it would get rid of

system does hold

the odd run-on thing after

strange. While the

are firing. When I stop

fan change directions!

how do you diagnose more

water in the fuel, and water

catalytic converter?

Thanks again for your advice. I put a charger on the battery overnight even though it read at full charge (or near to it), and after a few turns of the starter, it fired up. It still took a lot longer to start than usual, and the same when I started it a second and third time. So, I guess I'll get a new one tomorrow--from MB this time, though.

I think I'll take the starter off this weekend to see if the solenoid is disengaging and that the gears still mesh correctly, though.

If only I could really feel confident that it's fixed. Man, I hate intermittant problems!

Cheers!

-Tom

Tom Dolan Williamsburg, VA

1988 560SEL 1989 260E

And once the proud owner of a secondhand

1977 300D, 1979 240D, 1982 300D, & 1985 380SE

Thanks for the suggestion. The plug wires are definitely connected right, and I just got the car started, too, after recharging the battery, so I doubt the chain is the issue unless the tensioner is somehow only working sometimes.

I doubt that the car's actually fixed now, though. Unfortunately, I won't be able to do anything more with it until the weekend.

Thanks again.

-Tom

Tom Dolan Williamsburg, VA

1988 560SEL 1989 260E

And once the proud owner of a secondhand

1977 300D, 1979 240D, 1982 300D, & 1985 380SE

Thanks, Paul. I went out to try listening for the starter and to feel the exhaust, and after about 4 seconds of cranking the thing fired up! So, the exhaust is definitely not clogged (I went ahead and felt for the exhaust anyway), at least not all the time. The only additional things I did were to spray down a bunch of electrical connectors and grounding points with CRC 2-26 and put a trickle charger on the battery over night, even though it read at or near full charge.

Wish I was sure that a new battery would fix it, but the problem has been intermittant.

Anyway, thanks again!

-Tom

Tom Dolan Williamsburg, VA

1988 560SEL 1989 260E

And once the proud owner of a secondhand

1977 300D, 1979 240D, 1982 300D, & 1985 380SE

After you charged the battery the engine started? And again a second and third time? It started, why then do you want to mess with the starter? Just replace the battery and see how it goes. Don't look for problems for then YOU create problems.

I agree completely.

Marty

OK, OK. If it ain't broke don't fix it. I got it!

Thanks, guys.

Tom Dolan Williamsburg, VA

1988 560SEL 1989 260E

And once the proud owner of a secondhand

1977 300D, 1979 240D, 1982 300D, & 1985 380SE