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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
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47 Posts
Discussion Starter #1
Hello
I have a mysterious problem starting & keeping the engine running
Sometimes the engine will start and stay on for 20 min and quit and other times it won’t start with strong cranking.
When it doesn’t work I have power to the pump for 3 sec and pump is priming, the relay clicks but no start I even jumped the relay, what do you think might be causing this behavior? Thanks mike
 

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Registered
1992 400SE
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191 Posts
It sounds like there may be an issue with the throttle body. Mine can be temperamental at times. (first thing in the cool of the morning)

But I'm just guessing.

Can you get the car to an older Mercedes sympathetic mechanic?
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
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47 Posts
Discussion Starter #3
Updated post

I run into a wall and totally puzzled the Benz it's a 1994 S420 with 85K miles it gives me a fault code 19 and 7 now the 7 don't show up any more all i get is the 19?
I did the following tests
Fuel pump working pressure good
Spark plugs good
Spark plug wires good
Wire harness good, it was changed
Distributor caps good, a note here (Before the removal and cleaning of the distributor cap I was able to start the engine and kept it running for 20 or so minutes now it won't start at all)
And last I check the the vacuum lines all hold pressure except one from the ICM (ignition control module) the rubber at the engine side was cracked replaced and still won't hold pressure.

Thanks ....Mike
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
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47 Posts
Discussion Starter #4
I am surprised that now one has any input on this problem or willing to help......
 

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Registered
W140 Mercedes 500 SE, 1992, European, 410.000 km
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3,602 Posts
And last I check the the vacuum lines all hold pressure except one from the ICM (ignition control module) the rubber at the engine side was cracked replaced and still won't hold pressure.
can you please explain this more precisely? do you speak about vacuum line from engine to pressure sensor in EZL module? BTW there is vacuum in this line, not pressure, if this is it.

your problem can be many things. i mean many different things in same time or only one. You definitely must check output from your crankshaft position sensor. Are you able to do it? it is not a rocket science but you need something like oscilloscope or multi meter with graphical presentation of signals. It is ideal situation now when your car does not start. so if you will measure no output from this sensor (round two-pins connector on the EZL module), then you have a culprit. you can repeat exercise with camshaft position sensor but if it is bad your car will start some moments start later ... but it will start.

after this we can go on. BTW, "i do not like" cleaning distributor caps. The rule is: replace rotors and caps after 50,000 km or every two years, which comes sooner. Everybody who neglect this has problems !!!!!! No cleaning, no saving money in this case. Trust me. You can get both rotors and caps for decent money. I am extremely satisfied with BREMI caps and BERU rotors. In my mind they are much better than BOSCH.

in parallel you can also check if you have a spark at all. remove one spark plug and somehow test it. be careful not to kill yourself or somebody else and do not make any long tests ... use a spark plug not a spark plug wire directly onto the earth of the car.

i definitely gave you two relevant ideas. it is up to you now .... :).
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
Joined
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47 Posts
Discussion Starter #6
can you please explain this more precisely? do you speak about vacuum line from engine to pressure sensor in EZL module? BTW there is vacuum in this line, not pressure, if this is it. Yes you are right it is a vacuum line but don't holed vacuum and the line is fixed

your problem can be many things. i mean many different things in same time or only one. You definitely must check output from your crankshaft position sensor. Are you able to do it? it is not a rocket science but you need something like oscilloscope or multi meter with graphical presentation of signals. It is ideal situation now when your car does not start. so if you will measure no output from this sensor (round two-poles connector on the EZL module), then you have a culprit. you can repeat exercise with camshaft position sensor but if it is bad your car will start some moments start later ... but it will start.

after this we can go on. BTW, "i do not like" cleaning distributor caps. The rule is: replace rotors and caps after 50,000 km or every two years, which comes sooner. Everybody who neglect this has problems !!!!!! No cleaning, no saving money in this case. Trust me. You can get both rotors and caps for decent money. I am extremely satisfied with BREMI caps and BERU rotors. In my mind they are much better than BOSCH.

in parallel you can also check if you have a spark at all. remove one spark plug and somehow test it. be careful not to kill yourself or somebody else and do not make any long tests ... use a spark plug not a spark plug wire directly onto the earth of the car.

i definitely gave you two relevant ideas. it is up to you now .... :).
Yes thank you at list I have something to work on
 

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Registered
1997 R129 SL600, 1998 W140 S600
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17 Posts
Drive authorization? Sorry just a wild guess, I don’t know how the car behaves with no signal from keyfob transponder, whether it cranks or doesn’t do anything at all.
 

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Moderator
1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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1,642 Posts
After a month of fiddling about... You should probably take it to a mechanic.
I agree. I know many people here like to DIY for the satisfaction and to save money, but there comes a time when you hit a wall and you're really just wasting money throwing parts at the problem, hoping that something does the trick.

When you get to that point, it's probably time to bring the car to a specialist -- if for no other reason than to give you a confirmed diagnosis. A few hours in a professional shop can save weeks of guesswork. And then if you choose to do the repair yourself after you receive guidance, that's up to you.

These forums are a great resource but there are limitations; it's very hard to diagnose complex/intermittent problems over the internet. And while these cars are DIY friendly, there are definitely some things even the more accomplished home mechanics need to go to a shop for.

Drive authorization? Sorry just a wild guess, I don’t know how the car behaves with no signal from keyfob transponder, whether it cranks or doesn’t do anything at all.
There is no transponder in pre-facelift cars. And if it was an issue like that, the car wouldn't even try to start.
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
Joined
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47 Posts
Discussion Starter #10
These forums are a great resource but there are limitations; it's very hard to diagnose complex/intermittent problems over the internet. And while these cars are DIY friendly, there are definitely some things even the more accomplished home mechanics need to go to a shop for.
Yes you are correct and thank you, a good mechanic will help but I leave 50 miles from a good mechanic besides the car is not working so I have to keep searching till I stumble on a fix...
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
Joined
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47 Posts
Discussion Starter #11 (Edited)
Update

can you please explain this more precisely? do you speak about vacuum line from engine to pressure sensor in EZL module? BTW there is vacuum in this line, not pressure, if this is it.

your problem can be many things. i mean many different things in same time or only one. You definitely must check output from your crankshaft position sensor. Are you able to do it? it is not a rocket science but you need something like oscilloscope or multi meter with graphical presentation of signals. It is ideal situation now when your car does not start. so if you will measure no output from this sensor (round two-poles connector on the EZL module), then you have a culprit. you can repeat exercise with camshaft position sensor but if it is bad your car will start some moments start later ... but it will start.

after this we can go on. BTW, "i do not like" cleaning distributor caps. The rule is: replace rotors and caps after 50,000 km or every two years, which comes sooner. Everybody who neglect this has problems !!!!!! No cleaning, no saving money in this case. Trust me. You can get both rotors and caps for decent money. I am extremely satisfied with BREMI caps and BERU rotors. In my mind they are much better than BOSCH.

in parallel you can also check if you have a spark at all. remove one spark plug and somehow test it. be careful not to kill yourself or somebody else and do not make any long tests ... use a spark plug not a spark plug wire directly onto the earth of the car.

i definitely gave you two relevant ideas. it is up to you now .... :).
Ok I was able to test the crankshaft position sensor and it checks out to 0.02 v and the EZL has power with key on. Spark plugs are all sparking. The only problem is I don't get vacuum on the line from the EZL to the engine
Any other arias to check? Thanks
 

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Registered
W140 Mercedes 500 SE, 1992, European, 410.000 km
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3,602 Posts
Ok I was able to test the crankshaft position sensor and it checks out to 0.02 v and the EZL has power with key on. Spark plugs are all sparking. The only problem is I don't get vacuum on the line from the EZL to the engine
Any other arias to check? Thanks

Ok, you wrote that you have spark on all spark plugs. Somehow this tells us that crankshaft sensor is working. However saying that it shows 0.02 V is totally wrong. I am confused now. output from this sensor is DC current which has peaks and valleys at ca. + 12 V and -12 V of course. I attached a picture of my measurement of this signal. It is blue line (yellow line is camshaft sensor). I am not sure if this is situation during cranking or during idling ... not important now (I need a minute or so to calculate it out of time scale)! There is no Multimeter in the world which can show you proper functioning of this sensor. Only an oscilloscope (i.e., A/D converter) can show you reality. I guess you connected voltmeter on the sensor and someone cranked the engine. 0.02 V is maybe a RMS value of the signal over several seconds but I cannot be sure. So, you (we) are not 100% sure if all is right at the source of spark, which definitely crankshaft sensor is. Like I wrote, according to the fact that you have sparks on spark plugs one can say that everything is OK with crankshaft sensor, but this is really not scientifically ...

You write you do not get vacuum from EZL to engine. BUT engine creates vacuum and vacuum controls the pressure sensor in EZL module. The car should start and work pretty well without this line connected from engine to EZL. This line serves for optimal combustion in your engine only.

if there is everything ok with spark then something is wrong with fuel delivery. And do not forget that timing of sparks is maybe totally wrong (due to unknown reason) in your case. So, presence of spark does not mean that sparks are delivered in proper time. As you can see, solving of your problem demands an organized approach. You must go step by step and have everything under control. of course you can go forward randomly, try different things, etc.
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
Joined
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47 Posts
Discussion Starter #13
Ok, you wrote that you have spark on all spark plugs. Somehow this tells us that crankshaft sensor is working. However saying that it shows 0.02 V is totally wrong. I am confused now. output from this sensor is DC current which has peaks and valleys at ca. + 12 V and -12 V of course. I attached a picture of my measurement of this signal. It is blue line (yellow line is camshaft sensor). I am not sure if this is situation during cranking or during idling ... not important now (I need a minute or so to calculate it out of time scale)! There is no Multimeter in the world which can show you proper functioning of this sensor. Only an oscilloscope (i.e., A/D converter) can show you reality. I guess you connected voltmeter on the sensor and someone cranked the engine. 0.02 V is maybe a RMS value of the signal over several seconds but I cannot be sure. So, you (we) are not 100% sure if all is right at the source of spark, which definitely crankshaft sensor is. Like I wrote, according to the fact that you have sparks on spark plugs one can say that everything is OK with crankshaft sensor, but this is really not scientifically ...

You write you do not get vacuum from EZL to engine. BUT engine creates vacuum and vacuum controls the pressure sensor in EZL module. The car should start and work pretty well without this line connected from engine to EZL. This line serves for optimal combustion in your engine only.

if there is everything ok with spark then something is wrong with fuel delivery. And do not forget that timing of sparks is maybe totally wrong (due to unknown reason) in your case. So, presence of spark does not mean that sparks are delivered in proper time. As you can see, solving of your problem demands an organized approach. You must go step by step and have everything under control. of course you can go forward randomly, try different things, etc.
Thanks and I love a good conversation exchange.
Ok now you given me more useful info You are right on the voltage all i dit checked the output of the CS to see if the magnet working and producing DC current I will check further and come back with it.
On the spark plug situation like i said I remove the distributor caps and rotors and just dustem off looked clean but putting them back maybe switched locations? because upon doing that the call never start it again like it used to do prior to cap and rotor remove and replace. I have to go and recheck if there in the proper location, question; "just follow the numbering on the caps?"
You say; if there is everything ok with spark then something is wrong with fuel delivery.
I have checked the fuel delivery and is delivering the pump is pumping, that was the first thing I checked.
Thanks
 

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Registered
W140 Mercedes 500 SE, 1992, European, 410.000 km
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3,602 Posts
On the spark plug situation like i said I remove the distributor caps and rotors and just dustem off looked clean but putting them back maybe switched locations? because upon doing that the call never start it again like it used to do prior to cap and rotor remove and replace. I have to go and recheck if there in the proper location, question; "just follow the numbering on the caps?"
You say; if there is everything ok with spark then something is wrong with fuel delivery.
I have checked the fuel delivery and is delivering the pump is pumping, that was the first thing I checked.
Thanks
Yes of course, you must verify if caps and corresponding spark plug wires are correctly positioned. Every single wire: follow the numbers, be careful L means left, R is right :) in direction of driving. BTW, like I wrote these caps and rotors are extremely sensitive to injuries (I guess due to high voltage), so it is really good to replace them frequently. If you want to drive the car then you cannot save your money on caps and rotors. Bad caps and rotors will affect your adaptation values as well ... and wrong adaptation values can easily burn your catalytic converter, etc. So saving money on caps and rotors is extremely bad for your valet and for the car. Many time saving means more money at the end ...

Correction: if there is (really!) everything ok with spark, then fuel delivery and/or timing of fuel injectors is wrong. So i forgot to mention timing of fuel injectors. But this is just to be precise. My impression is that these cars rarely have problems with engine management, so first check the position of spark plug wires, then replace the caps and rotors if you want to keep the car and if they were not replaced within last two years or 50,000 km. If this will not work, you can go back to more deep analysis (crankshaft position sensor signal and fuel injectors timing). It is more or less clear, according to your words, that you have messed with the spark plug wires ... and that your current caps and rotors should be in the garbage bin.

More for fun I have attached a new picture. Yellow trace is voltage at a certain injector and blue trace is "spark plug primary voltage" at the ignition coil.
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
Joined
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47 Posts
Discussion Starter #16
Yes of course, you must verify if caps and corresponding spark plug wires are correctly positioned. Every single wire: follow the numbers, be careful L means left, R is right :) in direction of driving. BTW, like I wrote these caps and rotors are extremely sensitive to injuries (I guess due to high voltage), so it is really good to replace them frequently. If you want to drive the car then you cannot save your money on caps and rotors. Bad caps and rotors will affect your adaptation values as well ... and wrong adaptation values can easily burn your catalytic converter, etc. So saving money on caps and rotors is extremely bad for your valet and for the car. Many time saving means more money at the end ...

Correction: if there is (really!) everything ok with spark, then fuel delivery and/or timing of fuel injectors is wrong. So i forgot to mention timing of fuel injectors. But this is just to be precise. My impression is that these cars rarely have problems with engine management, so first check the position of spark plug wires, then replace the caps and rotors if you want to keep the car and if they were not replaced within last two years or 50,000 km. If this will not work, you can go back to more deep analysis (crankshaft position sensor signal and fuel injectors timing). It is more or less clear, according to your words, that you have messed with the spark plug wires ... and that your current caps and rotors should be in the garbage bin.

More for fun I have attached a new picture. Yellow trace is voltage at a certain injector and blue trace is "spark plug primary voltage" at the ignition coil.
Hi I got some good news and then some not so good

This morning start it working on the car again

I start it with testing the sparkplug wires again from the beginning the first one was the left bank rotor wire as I was testing see wanted to start so I insert it back and got the car running for the first time in two weeks I let it run for a minute and restart it again 3 times the last time was 3 or 4 minutes that’s when I decided to give it little gas see responded but when I let go of the throttle the engine died I put the air intake back on, hoping that the computer need it to readjust itself but no! I haven’t been able to restart it.
While all this was happening I erase the code “mined you I never had a CEL no” now after got it running I recheck and had no codes.
So now I know, at list I thing I know the pump working, the firing is correct, and that see don’t like the extra fuel in the intake manifold, I hope this sheds some light on the problem
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
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47 Posts
Discussion Starter #17
Update: the car runs in idle for around 25 min and cuits.
After testing the spark plugs wires and spark -OK, replace distributor caps and rotors OK, check and test the crankshaft position sensor OK, vacuum lines no leaks, test it the electrical fuel pump system, replace primary and secondary fuel pump including the filter at a mercedes mechanic suggestion he is 40 miles away and do not dare to drive it there, the car runs in "idle" for around 25 min very smooth no misses no knocking and then cuits. After all that work and expense the car acts the same as if I didn't do anything to it. did I miss something?
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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3,602 Posts
engine management.
consequently and most probably but not necessarily the crankshaft position sensor will not give out any signal. you can test it with oscilloscope in a minute. without an oscilloscope you have no chances. or you at least need a voltmeter with graphical presentation of the signal.

next suspicious thing is EZL module, so the main computer/actuator of engine management. it manages and provides energy into coils (spark plugs).

But you must start a diagnosis with your crankshaft position sensor and things will be much clearer. Now with no working engine you have a great opportunity to measure output at this sensor.
 

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Premium Member
1987 300D turbo 237.000, 1994 S420 80.000K
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47 Posts
Discussion Starter #19
consequently and most probably but not necessarily the crankshaft position sensor will not give out any signal. you can test it with oscilloscope in a minute. without an oscilloscope you have no chances. or you at least need a voltmeter with graphical presentation of the signal.
What you are saying is that the crankshaft position sensor sometimes stops working while the engine is running?
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,708 Posts
Yes, they do. I had one on a Porsche 944 Turbo that worked when cold, but when it got hot, the engine just quit. Had to wait for it to cool down to restart. Replacing it cured the problem.

Jon
 
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