i have an 86 420 sel v8 gas,i was driving and the car died,i checked the fuses first,then coil,then wires,then crank sensor,finally module all replaced,still no fire what else could be my problem,i also check the timing and its fine?please help!!!!

How do you know it's no fire and not no fuel?

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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

im getting fuel and i can here the pump,plus i can take off any wire from anything and theres no spark

Sorry, I had to ask. Most no-starts are fuel-related

Are you getting power to the coil and ignition unit while cranking? Did you check the continuity on the green wire from the ignition unit to the coil? Do you have an alarm system that might have gone TU?

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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

i have checked all of those as well and i don"T know what else to check. maybe it would help if you could tell me what is the very first thing that gets fire? then i could possibly go from there,thank you chuck

I'm not bailing on you. I don't have my CD with me at the moment, and I don't want to give you bad information.

Suggest that you try a Search. The ignition system is more or less they same for the 86-89 cars.

One thing, have you looked at the cap and rotor?

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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

yes ive looked at the cap and rotor and anything i could think of,but this is my 1st nercedes so im not sure where the fire originates?

Hi there,
I would suspect the fuel pump relay if you were driving and it just cuts out.
Normally they restart,though. You can take out the relay and then jump terminal 30 with 87. That should make the fuel pumps run and, if it is the relay, the car should start.
There is a lot in the archives, so a search might help.
Good luck

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Reinhard Kreutzer
1987 420 SEL (126)

I took a look at the CD. The spark sequence starts with the crank sensor. There are four signals sent each revolution of the flywheel, so each cylinder fires once in two turns of the crank. The each time a segment passes it, the crank sensor sends a high-low signal. It is supposed to be 1.5V at cranking speed. The ignition unit gets this signal, fires the coil and spark goes to the plug. Once the engine is running the ignition unit looks at temperature, load, and other information and adjusts the timing.

So if you changed the sensor, coil, and ignition unit and still no spark, then I would say you have a wiring problem. The only other possibility that comes to mind is that someone changed the position of the distributor so that the spark is occurring when the rotor is not aligned with the lug on the cap. But this works if you are getting spark from the coil.

Do you have power and ground to the ignition unit?

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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

From what I have been looking into, there are two sensors
one at the fly wheel and one at the crank but not sure what the rear one does except cost more than the front one that does regulate the spark

There is a sensor on the back of the engine that reads the flywheel this also sends the rpm signal if this sensor is not reading it will not fire. If you go to www.egermanparts.com
you can find any part you need for your mercedes.

I have a 1986 420 sel that I just fixed a cracked valve and Head gaskets, I have good compression on all cylinders. I have bad spark knock and it idles rough,can anybody help.

Yes there is a sensor on the back of the engine that reads the flywheel,
it also sends the rpm signal, if there is a problem with this sensor or wire it will not fire. You can find all the parts you need for your mercedes at
www.egermanparts.com

How do you tell if it is the front sensor or the rear sensor that is keeping it from firing?