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  #1  
Old 06-15-2009, 09:39 AM
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Location: Falls Church, VA
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400E Occasional Die with No Restart

I have been asked to look at a friends 1993 400E with 107K, always had good care. Normally it runs perfectly, but it has a maddening and frustrating problem.

Occasionally but recently more frequently it will begin to run rough and sometimes die and not restart after 5-10 minutes of running. This can occur at idle or while driving. This started out happening if the car had not been driven for at least 3 days but now it can occur after one day's sitting. It seems to be worse during rainy or damp weather.

The car has been cared for by an excellent local Mercedes-only indie, but they have never been able to reproduce the problem. There are no codes stored in any of the modules.

Caps and rotors were replaced, and a new engine wiring harness was installed in September 2007 with no change.

Here is my experience with the car over the last two weeks.

June 9

Replaced MAF sensor

June 11

Pulled the car into the garage. Hard start, died in gear, ran rough.

Removed one spark plug from each side – plugs were dry

Tested coolant sensor – had correct value for approx coolant temp

Went to move car out of garage, no start.

Checked fuel pressure at rail – normal

Checked spark with timing light – had spark

Swapped out Base Module for unit known to be good except for AC function – still no start. Put original Base Module back in.

Successful at re-starting by pressing down on accelerator while cranking. Engine would go rough when pedal returned to idle, went rough when moving car slowly up slope into parking space. Light throttle cured roughness.

No CHECK ENGINE LIGHT

June 13

Started the car, running perfectly. Then I noticed that the coolant light was on, so I shut the engine off and topped it up.

When I re-started the car to move it, the idle went rough, and the CHECK ENGINE LIGHT came on for the first time. Light throttle cured roughness.

Pulled the following codes:

9 – Intake air temp open or short circuit
17 – Data exchange malfunction
25 – Knock sensor or ignition control module defective

June 14

Cleared codes, started car. Ran perfectly

NO CHECK ENGINE LIGHT

So from my experience with the no-start situation, it appears that the engine has spark but no fuel. Since there is pressure at the rail, the ECU is not opening the injectors. I am thinking this is either a bad ECU or a bad throttle actuator. I have no idea why the CEL would come on suddenly with those codes.

Anybody have any thoughts?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #2  
Old 06-15-2009, 10:31 AM
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I'd start by looking at distributor caps, even though they are only 2 years old!

If they look good?? I'd try jumping the fuel pump relay, under the pass rear seat.
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  #3  
Old 06-15-2009, 11:37 AM
david s poole
 
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and even though the throttle harness was replaced,what about the electronic accelerator with it's crumbled wiring.this could be your cause.
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  #4  
Old 06-15-2009, 06:57 PM
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Great Theory!

On this car, the EA/CC/IC wiring is very accessible. It snakes up out of the intake and back to the firewall, through a grommet and to a connector by the relay box.

I slit about 4" of the sheath as close to the intake as I could, no evidence of deteriorated wiring. I started the car and shook the entire length of the wire that I could reach. The car, of course, ran perfectly through this.

Thanks, and keep 'em coming.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #5  
Old 06-16-2009, 09:19 PM
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Location: Ames, Iowa
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Used to have a car that either lost power on highway or just die suddenly, especially at the stop sign. When the engine went off, it will not start right away, but it will start back on after waiting, may be 5-10 minutes.

It turned out to be a bad Crank Shaft Position Sensor (CPS). Once it was replaced, all the problem was gone. To my understanding it will be very difficult to diagnose the problem exactly other than from signs. Because when it is running you don't find anything wrong. By the time you are running the test it may come back to normal.

CPS needs to be replaced at certain time interval. It may be another thing to look at.
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  #6  
Old 06-16-2009, 10:17 PM
arkie's Avatar
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I concur with the strong possibility of the CPS. The easiest way to check is to leave the car running for a while at idle and go out and check on it every now and then. Bad CPS shuts off fuel and also tells the EZL to shut off spark. The CPS is a hall-effect sensor, so problems show up first at low engine speeds after warmed up.
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  #7  
Old 06-24-2009, 11:37 AM
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I would agree with the CPS, except that when caught in the act, the car had both fuel pressure and spark.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #8  
Old 06-24-2009, 11:47 AM
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Wait, there's more ...

Today, after sitting for a week, the car was to go to the super-tech team at the dealer for a couple of hours of diagnosis time. So I started it and it ran badly immediately at idle. Restart and it would run fine for 10 seconds, and then start stumbling. Died when put in gear. Died and would not start after about 10 minutes.

Let it sit for a half hour, still no start. I rechecked fuel and spark, which were fine. Then I tapped very gently on the ECU with a wrench, and the car started, idled rough, but no dying in gear. Decided to have it towed to the dealer.

The truck arrived for the pick-up about 20 minutes later. And, of course, it started instantly and ran perfectly so I could maneuver it to make the loading easier.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #9  
Old 06-26-2009, 10:04 AM
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Car had it's day at the dealer yesterday. They started it, and let it run for a half hour, and of course it ran perfectly. They put it on a scope and diagnosed "carbon arcing" in the distributor caps. This was caused, they believe by "aftermarket" caps and rotors which have a poor seal, and possibly by oil vapors getting past the cam cover seal. They said this replacement was needed to go any further with the testing.

So the owner swallowed hard authorized the work and parts. Back together, it went for an extended test drive and performed flawlessly. They will park the car until Monday morning and see if it will act up after sitting for a while.

The team lead and I had a long discussion about next steps. He believes that this will fix the problem. I am skeptical because I believe the stalling is caused by the injectors shutting down and I don't see how that can be caused by ignition misfires. When it was in a no-start situation, I pulled two plugs and they were both dry, and the car has never smelled rich like it was mis-firing and loading up with unburned fuel. And that moment in the driveway when it started after a tap on the ECU was pretty compelling.

So I bet him a latte that we weren't through with this yet.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #10  
Old 06-26-2009, 01:02 PM
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Quote:
Originally Posted by ctaylor738 View Post
So I bet him a latte that we weren't through with this yet.
You are going to be drink a latte pretty soon.

But I can kind of sympathize with the techs at the dealerships, until the actually can see the car fail it's going to be hard to pinpoint the problem.
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  #11  
Old 03-06-2012, 02:59 PM
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Was there ever a solution found for this?

I have a 92 400e which has had similar problems for a number of years. In summary, if the car is used daily, it runs fine. If I let it sit for 2> days it will run fine for about 10 minutes, and then start to have a serious miss. It doesn’t matter if the 10 minutes of running fine are due to sitting at idle or running down the freeway, or someplace in between.

The cure is to either force the engine to rev higher – into the 3K range for a while (30 minutes or so), or to shut off the car and let sit for up to a couple of hours. Typically after either of these it will run fine, as long as I use it daily.

The longer the car sits, the longer, it takes to resolve this problem.

I took it to the dealer and asked them to see if they can identify the problem and hopefully resolve it. The car sat for over a week before it was taken to their shop by flatbed, and the problem duplicated for them.

They reported back that the problem may be due to any one or a combination of the following:

Wiring harnesses – they say there are 2 of them and they are both brittle.
ignition control module
throttle actuator motor

They say there were codes for both the ignition control module and throttle actuator motor.

They replaced the distributor cap and rotor. This made for no major difference. These hadn’t been replaced for probably 7+ years or so, that was okay.

They advise that they’ll have to relocate the wire harnesses to replace the ignition control module and throttle actuator motor. They say that due to the age of the harnesses (it's a 20 years old car) that this could lead to the insulation failing, requiring that the harnesses be replaced.

Any suggestions?

TIA
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  #12  
Old 03-06-2012, 04:30 PM
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Well, after the caps and rotors were replaced the car ran perfectly for almost a year. So I paid off the latte bet. Then it started again and it turned out to be the throttle actuator.

I believe that this work was done at an independent shop, and that they didn't replace the wiring harness. I also recall that they put in a rebuilt actuator.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #13  
Old 03-07-2012, 11:53 AM
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Thank you for the quick reply!

I read or rather saw a video that showed a test after a re-wire of what I think is the throttle actuator. The author implied that the mechanical parts of the unit are very stable, but that the wires are frequently the cause of the problems associated with it. http://www.youtube.com/watch?v=Ci8fz62O8ew

Another series of videos shows that replacing the throttle body is a challenge due to it being a tight fit. http://www.youtube.com/watch?v=kM4eEzsgNGI&feature=related

In talking with the SA yesterday, her recommendation was to replace the upper wiring harness as the next step on a potentially long list of parts to replace, and then to re-test for any codes. Having read many posts of failed or failing wire harnesses, this is probably a good idea.

But! I was not able to find any guides for doing the wiring harness replacement. Is it the kind of thing that’s an easy DIY or is there a lot of tear down that’s needed to access the places where the harness goes?

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