Engine Randomly Dying !!! HELP PLEASE !!!

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Hi here's my strange problem. I have a '91 W126 type 300SE auto. It has never missed a beat until yesterday when I was driving it along, engine at 80, cool but dry outside, ~ 30mph and the engine just cut
out! I tried restarting the car, it was turning and coughing but there wasn't enough there for it to restart.
I walked home (only about a mile) and went back with a friend to toe her home - tried to start her when I got there... perfect! Started first touch of the key, ran silky smooth all the way home. So later that day I took her out for a 5-6mile run to check she was OK, but there was a very slight juddering on deacceleration up to a roundabout after about 5 miles and a mile later she did the exact same dying trick! Waited two minutes and she restarted and I drove another mile and she died again... luckily the next restart gave me enough distance to reach my driveway!
It sounds and feels like fuel starvation. When I turn her key I can hear the fuel pump priming. There is of a tank of petrol in her. I took the two big relays out of the fuse box last night and resoldered all the joints, after which she fired straight up. But... I am worried about taking it out for a run after a voodoo fix like that; what's to say she'll be fine for a couple of miles and then start dying again!
Has anyone else heard of, or had this problem? What is going on, she is usually so reliable you could set your watch by her. My local Merc guy is backed up with cars until the start of next week - buggerations!
Mike P
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Mine behaved like that when the alternator went bad and the battery voltage dropped too low. I had to park it for the day and get a ride to work. Later that day, I met the tow truck driver there and it started right up.
When the voltage got too low, it died. The battery recovered some surface charge after sitting for a while and it started right up.
Hope your problem is a simple as mine was (I think it is). It cost about $15 for a new regulator, and it was simple five minute job to replace it.

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Sounds exactly like fuel pump relay... pull it out from your fusebox... it will say kickdown on it... look on the side, if the date is same year as your car... it is a goner.
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On Fri, 01 Oct 2004 15:24:39 GMT, "Tiger" wrote:
Thank you for your help guys!
Mike
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On Fri, 01 Oct 2004 15:24:39 GMT, "Tiger wrote:

Thanks for the pointers, I have two big relays in my fuse box They are marked as follows:
(merc symbol) 201 821 00 47 (lk) 05 8983 00 12v/2(4) x 21w Max. 6x32cp DOT SAE J590e/945b (A) 712043
-and-
(merc symbol) 126 542 03 32 5KG 004 747-09 Hella
The top one is the longer of the two, it has just solid state electronics inside. The bottom one has three small relays inside and some electrical gubbins. Which is the one that needs to be replaced? What's the other one for (just out of idle curiosity)
Thanks again Mike
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http://parts.mbz.org /
Go there and look up the part... they show picture there. But order it at Mr. Auto Part for only $61 with free shipping.
http://www.mr-auto-parts.com
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On Sat, 02 Oct 2004 14:03:01 GMT, "Tiger" wrote:

OK - I got and fitted a brand new fuel pump relay; took her out for a drive and she died after just 3 miles and refused to restart!
I can't see any reason why this should be the case - but I was wondering if the car is running OK until it hits its 'normal' working temp of around 80. It also seems to happen (awkwardly enough) when the engine is put under a load. For example this time she died when turning right (remember we're RHD over here), so she was stopped in the crown of the road and once the road was clear gentle accelerator to pull across the road and she died way over! Luckily the road was clear and I hit her into N and drifted across the junction!! She was in (E) mode on the transmission if that's any help for ideas.
Those are all the symptoms, I am still scratching my head - any ideas please.
Mike
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Ahh... didn't notice you are in Japan... Should have paid attention to email address.
Alright... we need to get down to the basic. First, what is the voltage output when engine is idling? Are you getting at least 13.5V at the battery when engine is running?
So you got a brand new fuel pump relay from your local Mercedes dealer right? Forget about checking fuel pump pressure yet... this would require a trip to a shop.
Overload relay... the one with a red fuse on the top... located in the fusebox... Take it out and give it a rap and put it back in... if your car starts, then that should be it...
My friend got 93 E300... pretty much the same engine... engine keeps dying on him anytime it want and takes at least 45 minutes before he can start again... sometime it will start up right away but randomly shut down. He changed everythign from fuel pump relay. crank sensor, cam sensor... and then he found out there was a bulletin about bad batch of Siemen overload relay... bought a new one and have not shut down on him since.
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On Wed, 06 Oct 2004 22:27:17 GMT, "Tiger" wrote:

On tick over 13.49v.

Yep; brand new from my local dealership.

The only relay I can see that looks like that is on the centre of the bulkhead - red fuse sort of buried into the top of it. I will give that a smack with something hard (like an old fuel pump relay that I seem to have suddenly aquired - lol) and see what happens. Mercedes tell me that a new one is 47 +17.5% VAT. Bugger!
Thanks again Mike
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On Wed, 06 Oct 2004 22:27:17 GMT, "Tiger" wrote:

OK - I have replaced both of these relays with brand new ones from Mercedes (160!! wife was VERY amused) and it is still no better than when I first posted this question! Arghhhhhhh!!!
The car cuts out when the engine hits 80 every time. Something happens when the car reaches 80 and it causes the car to cough then die. It is subsequently unstartable until the engine has cooled below this temp.
H E L P ! ! ! Mike
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It's still cheaper than have your mechanic do it for you to eliminate the two potential common thing that goes bad. Otherwise, it can add on diagnostic fee.

Consistently at hot engine? I can only assume it has something to do with fuel injection system... Car runs fine and smooth until then? When it reaches that temperature, does it start to slow down and sputter? Have you checked the timing? Does it die if you just let it warm up on your driveway without moving the car?
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On Tue, 12 Oct 2004 13:27:36 GMT, "Tiger" wrote:

The car starts, runs and drives flawlessly until it hits 80. It dies at the exact same spot on the temp guage, if you are driving it or if you start it from cold and just let it idle. As soon as it gets to 80 it cuts out. If you're driving it you get a cough as it dies, but that doesn't happen when it dies after idling. It doesn't lose power, it's as if someone switched the motor off; it is that instant!
I have been told that it may be worth looking at the o2 sensors (but I don't know where these are yet). The theory is that the ecu is running the fuel injection from tabled data until it thinks the sensors are up to working temp, then the ecu switches across to the sensors for data... which is when it dies because they aren't working.
Thanks for your continued help and ideas with this. Mike
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Okay Mike, don't spend anymore money... we have to search and check for potential problems. I recall a friend of mine has a car with similar situation... car is fine until operating temperature... he checked everything... in the end, it was the main wiring harness.
Now, with that in mind, it is time to check your wires to see if insulation is cracking or falling apart... the main wiring harness can be found in your driver side footwell, pull those carpets out... until you see bare metal and wires... check the wires at where it goes through the metal for any potential short.
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For the moment, take out the thermostat. I know this probably isn't what you want to hear, but with winter coming maybe you can atleast have the car usable.
I doubt it is a wiring harness issue, you have said that the problem occurs at *exactly* 80 degrees. Is this precise, or more "between 75 & 85"?
Maybe purchase a cheap electronic thermometer (one with a remote sensor on a wire as used in Fridge/Freezer repairs) - stuff that into the radiator or if possible as near to the engine block/temp sensor as possible and confirm it is a rise to a precise temperature which causes the problem.
If it is, then contact Mercedes and ask "what happens within the engine managements system at 80 odd degrees etc".
An earlier poster (sorry earlier poster, can't remember who) suggested it was some sort of problem when the ECU flips from cold/partial cold running to full warm engine.
This seems reasonable, I used to have a Volkswagen which ran better when cold than hot, turns out it was a cheap vaccum valve in the air intake which seized and couldn't react to ECU instructions to move left/right for hot/cold air intake - it was permanently stuck on cold setting.
I suspect in your case, it isn't a vacuum or mechanical valve, but something electronic - something which only becomes part of the equation at *precisely* 80 degrees or so.
Question to aim at MB tech dept: "Which electronic component failure could cause my car to stall completely? Many components can cause rough running when failed, others can invoke a complete stall. Which ones which?"
Now follow list of offered items and consider which ones only become operative once the engine is hot.
Hth Bill
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You have to remember that the not all electronic system are active until proper operating temperature is achieved... such as O2 sensor... It will remain open loop until operating temperature and then it will become closed loop... which there is actually live circuit.. so if shorted and too much current, it will overload the computer.
On MB, I keep hearing people who got a shitty running car or a car that keeps dying ended up replaicing the wiring harness... Someone wiht a proper diagnostic scanner will be able to tell. Dealer or some MB specialized shop who actually have that tool.
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Have your Indy do a simple Cranke Angle sensor test when the car is hot Common Hot Soak failure part
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Just had this happen to one of my other vehicles (not Mercedes). Turned out to be a plugged catalytic convertor.
On Wed, 6 Oct 2004, Just Mike wrote:

THE ABOVE OPINIONS ARE MINE, AND MINE ALONE. THEY DO NOT NECESSARILY REPRESENT THE OPINIONS OF OTHERS INCLUDING MY EMPLOYER(S)
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On Fri, 01 Oct 2004 10:55:26 +0100, Just Mike wrote:
This is getting stranger by the day! I can't get the car into the shop until a week on Thursday! So I have been having a bit of a poke about myself.
I called the local HomeTune guy. He's the one with the test equipment for Mercs; honestly the way some of these HomeTune guys talk you would think I was asking them to run a check on the Space Shuttle, not an old '91 petrol saloon!! As they suck air through their teeth they are chanting "Mercedes you say..." like some sort of mantra!
Anyhow, this guy assured me over the phone that if I had replaced the fuel pump relay and OVP relay then the 'only other thing it could be' was the crank sensor going bad when it was getting heated up by the engine, and then once the engine had cooled (and in turn the sensor had cooled) it would work again. At 30 for the part it seemed worth a go, so I found what I thought was the sensor, I traced the wire back up to the round diagnostics socket. I took the socket off and the end of the sensor is just part of the diagnostics socket (pins 7, 8 & 9 to be exact). They are not connected to anything! So it couldn't possibly be 'that' sensor causing the problem could it?
I hope I located the sensor properly. It is just visible looking down from above, in behind all the pullies and belts at the front of the engine. It points straight down at the timing marks on the top pully It looks like it's held in place by an 8mm bolt (guessing the size as I didn't remove it). The other end has a three hole socket attached, this seems to form an integral part of the diagnostics socket. It looks stunningly like this part (F6010-12104):
http://img.eautopartscatalog.com/live/F601012104OES.JPG
Am I a mile off here? Is that the wrong sensor? I am glad hand guns aren't legal over here in the UK as I think I would have given the car the Elvis treatment this afternoon!!! Sorry to sound like a whiner, but... HELP!!
Mike
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Wrong sensor That is speed sensor You want the crank angle sensor .. back of engine at fly-wheel Simple test is crank engine and look for low a/c volts with meter at end of cable ...
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On 19 Oct 2004 17:37:02 GMT, AJDalton7 wrote:

Thank you. I'll be out there tomorrow with my multimeter set to stun! Low AC volts.. how low? Couple of volts?
ATM I'm just trying to check all the possibilities I can whilst I'm waiting for the garage to do it properly - it'll be a month off the road by the time the garage finally get it into the workshop and I'm getting Mercedes withdrawl :-( Mike
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