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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4794
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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, my C240 wont start just changed out the plugs cranks

Customer Question

hi
JA: Thanks. Can you give me any more details about your issue?
Customer: my C240 wont start just changed out the plugs cranks but wont start, 1/2 tank of fuel and has I keep cranking I smell fuel
JA: OK got it. Last thing — Mercedes Mechanics generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: Mercedes
Expert:  Lou P. master tech replied 1 year ago.

hello , did the issue happen after you changed the spark plugs?

Customer: replied 1 year ago.
No, I parked the car over night and it ran fine that day. In the morning it would not start. I checked the battery and even tried to jump it with me truck battery. ((One note with that was the negitive cable got vey hot after several attempts to start). I changed the plugs made sure all the connections were solid and tried to start it but nothing engine cranked but did not turn over. I also smelled fuel after trying to start it several times.
Expert:  Lou P. master tech replied 1 year ago.

Ok thanks for the reply. So does the car crank fine but it just will not catch and start ?have you tried starting fluid to see if it would start ? How many keys do you have ? Have you tried them all?

Customer: replied 1 year ago.
One key will try starting fluid today and let you know.
Expert:  Lou P. master tech replied 1 year ago.

Ok, also pull one plug out and check for wetness. That would determine if fuel is spraying or not. And if we have spark or not. Also did you fill up fuel recently before this happened ?

Customer: replied 1 year ago.
car has 1/2 tank of fuel. I will pull a plug and check. I'll get back to you in a little while.Thank you.
Expert:  Lou P. master tech replied 1 year ago.

No problem. What I meant was did you fill the fuel right before this happened ? To make sure it's not a case of bad gas.

Customer: replied 1 year ago.
Pulled plug (looking at the engine on the left side 1st plug) it was wet. Can't really tell if it sparked, I would say no. My nephew is bringing a diagnostic tool to read codes. I'll let you know.
Expert:  Lou P. master tech replied 1 year ago.

Ok. Hopefully the scan tool can read values. We need to know if the crank sensor is working.

Customer: replied 1 year ago.
Ok no codes and it's not sparking.
(Using a Auto Link A519)
Expert:  Lou P. master tech replied 1 year ago.

Ok sounds like crank sensor. You will have to access and replace the crank sensor that would be what I would check first. Unless the scanner can read data then we need to read the rpm as it cranks.

Customer: replied 1 year ago.
I believe it can read the rpm data it has a live data module.
Customer: replied 1 year ago.
Ok just ran test. RPM in cranking go 150-160.
Expert:  Lou P. master tech replied 1 year ago.

Ok crank sensor is good. Now check all the fuses in drivers side engine bay fuse box.

Customer: replied 1 year ago.
Ok checked all 18 fuses all are good
Expert:  Lou P. master tech replied 1 year ago.

Ok , unplug one of the ignition coils and check the wires. There should be 2 powers and 1 ground. I'll have to verify but check a few coils.

Customer: replied 1 year ago.
There are 3 yes. And I have a voltage meter ready.
Expert:  Lou P. master tech replied 1 year ago.

Ok I'm checking the diagram now.

Expert:  Lou P. master tech replied 1 year ago.

What is your vin

Customer: replied 1 year ago.
WDBRF61J34F50785
Customer: replied 1 year ago.
504785
Customer: replied 1 year ago.
Missed the 4
Expert:  Lou P. master tech replied 1 year ago.

Ok great thanks. One second.

Expert:  Lou P. master tech replied 1 year ago.

Ok the middle pin is key on power. So make sure you check with the key on. It's also power that comes from fuse 48 in the fuse box.

Customer: replied 1 year ago.
Ok how many volts am I looking for?
Expert:  Lou P. master tech replied 1 year ago.

The outer two wires are also voltage but only when cranking. You are looking for 12v or greater on center and any kind of voltage on outer ones when cranking.

Customer: replied 1 year ago.
No voltage on crank and almost nothing from middle power. Very low reading. .05 v meter is set to 20 v max
Customer: replied 1 year ago.
Fuse 48 - 15 amps is good.
Expert:  Lou P. master tech replied 1 year ago.

Ok , and the fuse has power ? Being good and having power are two different things

Customer: replied 1 year ago.
Let me check.
Expert:  Lou P. master tech replied 1 year ago.

Ok I have to leave for a few minutes. I'll check back asap

Customer: replied 1 year ago.
No voltage. :(
ignition is on
Customer: replied 1 year ago.
Could this be a battery problem? I keep jumping with my jeep, and a battery jumper. Jeep battery at 14 v and the Benz is at 12v but dies after a few starts. However not with cables connected to my jeep.
But I guess I with my truck connected the battery I should have gotten voltage at the fuse.
Expert:  Lou P. master tech replied 1 year ago.

Oh ok so the fuse does not have voltage ?

Customer: replied 1 year ago.
no voltage on either side of the fuse
Expert:  Lou P. master tech replied 1 year ago.

Ok check for negative then

Customer: replied 1 year ago.
Negitive?
Expert:  Lou P. master tech replied 1 year ago.

Yes. Flip flop your lead from ground to a positive source and that means you are testing for negative or ground.

Expert:  Lou P. master tech replied 1 year ago.

Relay P is the one that activated the circuit for that fuse. I'll get you the location.

Expert:  Lou P. master tech replied 1 year ago.

I will submit a offer for a phone call as the next couple of steps will be hard to type out.

Expert:  Lou P. master tech replied 1 year ago.

Essentially we need to determine if the relay is bad or if the module is not activating the relay.

Customer: replied 1 year ago.
Hold on.
Jut checked all the fuses
# ***** no voltage
#48 11.25 v
Expert:  Lou P. master tech replied 1 year ago.

Ok checking for what it is

Customer: replied 1 year ago.
11.55v at the plug to the coil.
Expert:  Lou P. master tech replied 1 year ago.

Yes 52 is also controlled by that same relay circuit

Customer: replied 1 year ago.
11.55v on the plug going to the coil. No cables hooked up for a jump.
Customer: replied 1 year ago.
Still not starting.
Customer: replied 1 year ago.
All the fuses in that bank have 11.55v except #52 the first one.
Expert:  Lou P. master tech replied 1 year ago.

Ok pull the cover off of relay P and you will be able to squeeze the contacts closed and see if it starts while the relay is closed.

Customer: replied 1 year ago.
Ok give me a few with that.
Expert:  Lou P. master tech replied 1 year ago.

Go for it. I have to break for a while. Family time. Wife says take a break 😉

Customer: replied 1 year ago.
Lol ok.
Customer: replied 1 year ago.
Ok relay is working when I started the car it engaged the contacts. Only fuse # ***** did not have power all the others were just under 12 v 11.55 etc.
then the battery went dead again. Will have to charge it up again tomorrow.
Expert:  Lou P. master tech replied 1 year ago.

Ok so check the terminals inside the fuse box at that fuse. Make sure they are not burnt. Maybe the fuse terminal melted or got weak tension. Do you know how to ohm ?

Customer: replied 1 year ago.
It's dark right now going to have to pick this up tomorrow. The fuse block Looks good when I was pulling the fuses to check them. Can't understand why them at one fuse has nor voltage. #52
Expert:  Lou P. master tech replied 1 year ago.

Did you physically activate the relay ? Or see it activate ?

Customer: replied 1 year ago.
it did, my wife was starting the car and when she turned the key it activated.
Expert:  Lou P. master tech replied 1 year ago.

Ok I'm going back over the diagram. Something doesn't make sense.

Customer: replied 1 year ago.
Fuse 31, 52 and 57 are start enable
Expert:  Lou P. master tech replied 1 year ago.

Fuse 48 check fuse 48.

Customer: replied 1 year ago.
It's has 11.55 v
Customer: replied 1 year ago.
My car is a c240 2004.
Expert:  Lou P. master tech replied 1 year ago.

52 is for the starter and will only have power when cranking. If there is power at fuse 48 then we should have power at the coils center wire.

Expert:  Lou P. master tech replied 1 year ago.

I think we strayed too much onto the starter circuit. We were after coil power.

Customer: replied 1 year ago.
that we do the coil connector center feed is 11.55 volts
Expert:  Lou P. master tech replied 1 year ago.

Ok then when cranking the outer wires will display a voltage as they are fired.

Customer: replied 1 year ago.
is that voltage to low, and when I hook up cables to jump I get no power on the center pin.Ok I am going to have to check that
Expert:  Lou P. master tech replied 1 year ago.

Ok if the voltage matches the battery voltage it's fine. It's possible the jumper is too much power so the control unit is not activating circuits as a protection.

Customer: replied 1 year ago.
Ah ok. So I have to charge the battery. What should be the normal voltage.
Expert:  Lou P. master tech replied 1 year ago.

12.6 -12.8 is normal battery voltage.

Customer: replied 1 year ago.
Is the 11.55 volts too low for it to start.
Customer: replied 1 year ago.
I'll try it tomorrow. Might be that the battery in NG. What else might it be?
Expert:  Lou P. master tech replied 1 year ago.

11.55 is not that low. 10 or under is low. So once we verify spark or coil activation then we may look into the fuel. Maybe the fuel is of poor quality

Customer: replied 1 year ago.
I always get fuel at the same location, never had a problem, It did not seem that the plugs fired. But that's when I had the jumper cable hooked up to it, could have shut the circuit off as you stated. I'll charge the battery or get a new one and give it a go tomorrow.
Expert:  Lou P. master tech replied 1 year ago.

Ok. And don't confuse fuel octane rating with quality of fuel. Every once in awhile water or diesel gets mixed in.

Customer: replied 1 year ago.
OK so I changed the battery, nothing.....Checked the pressure at the rail for fuel with my finger, good pressure, fuel shot out.Took out a spark plug and still no sign of a spark. The voltage at the center is 12.8 volts (New Battery)How can I check the coil pack? or see if voltage it getting to the plug?Thanks
Joe
Expert:  Lou P. master tech replied 1 year ago.

if voltage is getting to the coils then they should be sparking, did you verify once again fuse 48? to see if it had power?

Customer: replied 1 year ago.
I'll Check now
Customer: replied 1 year ago.
With key in the on position fuse 48 had 12.30 volts both sides.
Expert:  Lou P. master tech replied 1 year ago.

ok, good, then we should have voltage in the center wire of the coils correct?

Customer: replied 1 year ago.
Customer: replied 1 year ago.
All center pins have 12.3 volts.
Expert:  Lou P. master tech replied 1 year ago.

ok good, then test the outer terminals as the engine is cranking, it should show something.

Expert:  Lou P. master tech replied 1 year ago.

also, on the drivers side of the head, the wire that has the 3 plugs for the coils may be rubbing against the screw for the valve cover near the oil fill cap, verify the wiring is ok right there. the harness comes off the intake and has a bend and then goes back toward the coils, let me know if you see what i am talking about.

Customer: replied 1 year ago.
Ok. Give me a few.
Customer: replied 1 year ago.
They show nothing no voltage.
Customer: replied 1 year ago.
Wiring harnes looks good on both sides.
Expert:  Lou P. master tech replied 1 year ago.

ok, do you have a scan tool to check for codes?

Customer: replied 1 year ago.
I do and it can do live testing as well.
Expert:  Lou P. master tech replied 1 year ago.

ok, did we already check for rpm? i tried to read through our chat, also are there any codes now

Customer: replied 1 year ago.
Ok.
Customer: replied 1 year ago.
RPM cranking was 150 -160
Expert:  Lou P. master tech replied 1 year ago.

ok, does it show a cam shaft sensor value?

Expert:  Lou P. master tech replied 1 year ago.

sorry this is taking so long, im trying to wrap my head around what is happening. cam and crank sensors are responsible for spark and fuel. seems like we are missing spark and the ecm should be activating the coils.

Customer: replied 1 year ago.
No codes. What am I looking for. In the live test for the CPS?. Seems like it wants to start but just not getting there.
Expert:  Lou P. master tech replied 1 year ago.

dont abbreviate lol, what sensor you talking about?

Customer: replied 1 year ago.
Ok. From the live test.
Short term fuel trim bank 2 sensor 1 = 0
Short term fuel trim bank 2 sensor 2 = 99.2Load PCT 88.5
ECT 55
Customer: replied 1 year ago.
Crank position sensor.
Expert:  Lou P. master tech replied 1 year ago.

ok for the crank we just needed to know it was picking up rpm, now that we know that rules that out. does it show a camshaft sensor value?

Customer: replied 1 year ago.
Nope.
Expert:  Lou P. master tech replied 1 year ago.

ok....... unplug the cam sensor. its in the front of the passenger cylinder head. its a 3 pin plug. only one there.

Customer: replied 1 year ago.
I know the Crank position sensor was changed. But never the cam sensor.
Expert:  Lou P. master tech replied 1 year ago.

ok, well if the cam sensor is faulty it can stop engine starting, but if its unplugged the car will bypass it so try unplugging it.

Customer: replied 1 year ago.
Where is it?
Expert:  Lou P. master tech replied 1 year ago.

the front of the passenger side head

Customer: replied 1 year ago.
Ok. It almost started.
But then a loud pop from the engine and now smoke coming from the manifold. Oh boy.
Customer: replied 1 year ago.
Looks like it back fired. Smoke is less but no burning smell smells like exhaust. Could be it was flooded?
I get a strong smell of gasoline when I try to start it. At least it did something. lol.
Customer: replied 1 year ago.
when I disconnected the cam sensor. Souls like it was starting and the pop. Lots of smoke. :(. Looks like someone cracked under the manifold. See pieces broken off.
Guess I have to take it all apart to see what's up.
Customer: replied 1 year ago.
Uggg this car is giving me fits.
Customer: replied 1 year ago.
looks Like the manifold exploded, what would cause that?.Ugggg OK have to change that now but I think the Camshaft sensor as well.
Expert:  Lou P. master tech replied 1 year ago.

oh man, that does not sound good. maybe back fire or flooded with gas

Customer: replied 1 year ago.
OK well its the hard way to find out, lol so I guess it was the camshaft sensor, other wise it would have done the same thing.So new intake manifold and new cam sensor
Expert:  Lou P. master tech replied 1 year ago.

seems like it, man sorry that happened. you can find them used pretty easy to change as well.