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Old 12-24-2003, 10:22 PM
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Post Voltage on disconnected coil wires with the ignition switched "on"

Would anyone know off hand what the voltage on disconnected coil wires with the ignition switched "on" should read?

I have tested mine and only have one wire (out of four individual wires) reading battery voltage at the coil. Coil tests good, but the spark in the cylinders is not enough to crank engine. It had been cranking then warming up to die.....checked spark and it appears to be a red/orange color...very weak. Now, I have to remove the new spark plugs and dry them in order to get any combustion in the engine without it running properly (with injectors and fuel operating properly). Crank sensor tests good cold. OVP resolder job last week, new cap, rotor, fuel (& filter), rebuilt head ($552.06 - I believe this is the exact price I paid the machine shop)

Plugged, or unplugged EHA makes no difference....all fuses check ok....maybe someone would be able to verify that only one of the coil wires (unscrewed from the coil) should be reading battery voltage. I also removed and cleaned ignition control unit, made sure all connections are clean....

Please help....thanks, and Merry Christ-mas! & Happy New Year!
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Old 12-24-2003, 11:42 PM
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I am not all that knowledgable in this area for Mercedes, but I would believe that you should have battery voltage ( about 13V ) at the coil (+). This would certainly be the case with an older standard K points ignition. In those systems there was usually a resistor in series with the coil primary voltage which was bypassed for starting, but in the circuit with the engine running. When the resistor failed, the engine would spark at crank, but fail as soon as you stopped cranking. I think with Mercedes the OVP has a similar function. If your engine has a simple ignition you need to check the points and capacitor as well as the coil and the coil ground. The coil is usually grounded through the shell via the mount and corrosion of the shell or mount can cause problems. I've also seen a case where a bad high tension wire between the distributor and the coil was bad and caused weak spark. In general, the high tension wires can break down over time, particually the carbon core type. Since the head was off the engine, recheck all the wiring and plugs. It looks like you have checked most of the obvious stuff. I hope somebody with insite on your particular engine chimes in here to help.
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Old 12-24-2003, 11:55 PM
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Question Voltage on disconnected coil wires with the ignition switched "on"

Would anyone know off hand what the voltage on disconnected coil wires with the ignition switched "on" should read?

I have tested mine and only have one wire (out of four individual wires) reading battery voltage at the coil.

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Old 12-25-2003, 10:12 AM
LarryBible
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If you are getting any spark at all, then this is probably not the cause of your no start condition. I would start suspecting lack of fuel pressure.

Good luck and Merry Christmas,
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Old 12-25-2003, 12:36 PM
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As pointed out, you should have battery voltage at one wire on the + side of the coil. Since you have that, that isn't the problem.

It also would be extremely unlikely for power to the coil to be the problem; there are no fuses for that circuit and only tyhe ignition switch would be able to drop the voltage.

In triggering the coil its the negative side that is importnat and changing. The positive side always stays hooked up if the car is switched on.

On most cars I might agree with Larry that any visable spark is probably all you need check for. As it turns out, the coils on 300Es fail in output quite often. I have probably replaced more 300E coils in the last year than all other MB coils combined in the whole of my career. (maybe it would take two years worth).

With that said, it also sounds like you might be getting too much fuel.
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Old 12-25-2003, 04:51 PM
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Smile Voltage at coil

Hi Steve and Larry - and Merry Christ-mas to you both!

I have been experiencing a weak intermittent spark, and now I have to dry the new plugs for it to do anything....too much fuel is what the problem has been, but when I checked the spark at #1, it was reddish/orange, so maybe the coil is weak. Now is this coil any different that my solid-state coil located on my Honda Accord? I believe it is the same, and would like to try it.

Rust has been my main problem, as the car had been sitting, and when I got it, the head gasket was blown since it left a shop where it had been repaired, and the cooling fan with shroud was left off the car (can you even imagine that??????).....so the car was loaned out for someone to sell, and that guy loaned it to some illegal migrant workers, and all they could do is put regular gas in it and drive it back and forth to work. Rust had build up in the gas tank, and the fuel sending unit was bad (I found out when it ran out of gas) so I removed the tank and cleaned it, replaced the fuel filter and cleaned both pumps.

When I bought the car, the overflow would boil over and the engine would start missing after warming up, and it was difficult to crank, taking about 5 to 7 revolutions to actually crank up.

The car is in great shape body wise, and the interior is almost perfect.....only if I could get the engine almost perfect...I would drive it until I sell the drivetrain, and then replace it with what I want under the hood (340 Mopar "Baby Hemi"....or maybe the 345 HP Hemi.....I'm just not sure which one I want).

I had a good reason asking what voltage at the coil wires should be (disconnected) as the cigarette lighter has a short in it. It had been used at one time to power a cell phone, so not knowing the wiring on this car, I thought the short may have something to do with low voltage at the coil wires. But if you say (Steve) that only one wire should have voltage (hot side) then I'll start tracing wires again. Fues are all good, windows are not operating properly though, so maybe a relay is bad.

Thanks for the heads up on the coils Steve. I had to replace a coil on a 89 560 about two years ago, as it was giving a very weak spark just like mine is doing now, and that cleared up the 560.

I really appreciate both of you guys and your willingness to help others here. If either of you need any web hosting or want to purchase any domain names, or even need a website, email me (through this site) and I can sure help you there (email me for details). Or if you want you current website to have more visitors of your choice, say the word. I can assist, and you guys would be on my special discounted pricing list . My site is at http://www.americanwebsiteservices.com.

Well it's Chrsit-mas day and I will be performing all the tests that I can do today, without plugging the fuel distributor and checking for leaks (thanks for your reply to the many posts in a search that I did last night Steve....you are truly a life-saver, and a good guy that has patience like I do...it is a gift from God and seeing all the kind hearted people here helping others is also a gift from God as well. God bless you all!
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