72 280SEL 4.5 no spark - PeachParts Mercedes-Benz Forum

jkeith72 · #1 10-08-2009, 06:25 PM

Hi,

I am new to this forum and have an issue. My 4.5 has no spark. I suspect the ignition module, since the other components are newish. Is there a way to test that module specifically? Thanks in advance!

Jason Keith

sjefke · #2 10-08-2009, 08:00 PM

Did you replace the coil? Any wires loose? iI you still have point in distributor, are the points sparking like they should?

Bert

Graham · #3 10-08-2009, 08:56 PM

Quote:

Originally Posted by jkeith72

Hi,

I am new to this forum and have an issue. My 4.5 has no spark. I suspect the ignition module, since the other components are newish. Is there a way to test that module specifically? Thanks in advance!

Jason Keith

I assume you have checked points gap (should be about 0.014"). And that green wire from distributor is properly connected. Coil could also be faulty.

If after checking everything, you still suspect the ignition module, you might consider buying a Pertonix replacement. Under $100 alone or $150 with new coil and it replaces both points and ignition module.

Tomguy · #4 10-08-2009, 09:03 PM

If you suspect the ignition box and other items check out (coil, points gap, condenser wire to the box is unbroken & not shorted, condenser itself not connected, etc) here's how I test:

A 12v bulb on the wires that connect to the coil. It'll flash during cranking if the box is good. If not, it won't. That simple. Of course, don't keep the wires on the coil, it uses too much juice and the bulb won't light.

Most common cause of failure? Leaving the key on the "Run" position with the car off.

Graham · #5 10-08-2009, 09:53 PM

Quote:

Originally Posted by Tomguy

condenser wire to the box is unbroken & not shorted, condenser itself not connected

I once had this wire somehow move and rest against the exhaust manifold where the insulation melted and it shorted

. I was on major highway, but luckily it just got me to a service center. Took me a while to figure out what was wrong!

meltedpanda · #6 10-09-2009, 10:11 AM

Tomguy
I have always wondered how to test the ignition box. Not that mine is bad , but for future reference
12V bulb from the wires coming out of ignition box that go to coil with everything connected, would that not just test the coil?
What am I missing
And BTW , I once had the green wire from my condensor short to the dist housing, I did not see it and searched for days looking at why I did not have spark ( on my 220) '
so do check that out...

Tomguy · #7 10-09-2009, 01:02 PM

Ron it tests both! Light flashes, bad coil. Light doesn't, bad box! Pretty easy diagnosis

jkeith72 · #8 10-09-2009, 07:29 PM

Thank you for the great responses. I havent had time to work on it yet, but I now have a great starting point thanks to you guys!

Jason

jkeith72 · #9 10-19-2009, 04:37 AM

Well, I finally had some time to work on the ignition system. I first inspected all the wires and connections to the naked eye. Everything lookd decent and green wire from points has good continuity. Next, I did the light bulb check and it did not flash through cranking. Damnit...was hoping it would...lol. I looked in the shop manual to make a few confirming checks. I have voltage on 15 and 16 of the "switchgear" connector (good). With points open, I have battery voltage at lug 15 on the coil (good). With the points closed, I am supposed to have between 8.2 and 9.6 vdc on terminal 15, and 4.8-6.3 vdc on terminal 1...failed. Manual says "transistors no longer switching through".

I know its from the manual, but does this sound like its definately the box? Hope thats not a silly question, forgive me if it is. This is my first Mercedes, and definately the oldest car I have owned.

I very recently bought this car from a co-worker, and have not heard it run. Im the 3rd owner and it only has 69K. Is there a way I can override the transistor box without buying the kit to elininate it? I would like to make this thing run, just for piece of mind.

Thanks again for the feedback, and sorry in advance for my lack of knowlege.

Jason

jkeith72 · #10 10-19-2009, 04:54 AM

OK, so if the box is my issue, which pertronix kit would work? Anyone have one installed? I was looking at the models on their site, only 1 is advertised to eliminate "the box", but has limited applications (Ignitor III).

thanks!

Jason

Tomguy · #11 10-19-2009, 08:27 AM

Pertronix does eliminate that box. To make sure it's "That box" you can bypass it using an old-fashioned points and condenser setup to do the switching instead of the transistor box. Basically the green wire should go to the first ballast resistor's input where the line from the box currently goes. I am not 100% sure if you should bypass 1 or both resistors but I do believe if you do this it'll at least start.

meltedpanda · #12 10-19-2009, 02:23 PM

what is the part number on your box, I may have one

jkeith72 · #13 10-19-2009, 09:56 PM

Well, I had some time today. I did like you said and put the green wire to the points side of the upper resistor (I think its the .6 ohm). I left the lower one alone. When I cranked it, I could tell there was some spark because it sputtered a bit a few times. I think it quickly flooded out. Im letting it sit for a bit before I crank it again...and let the starter cool. Its great to hear it do something besides crank. Crossing my fingers.

As for the switchgear, Mine has no part numbers on it. According to my manual, I have chassis #108.068. The part number should be either 0 227 051 013 or the model that replaces it 0 227 051 016. Hope that helps.

Once again....THANKS!

Tomguy · #14 10-20-2009, 07:52 AM

Your timing might be off. The points are set for dwell on an ignition box and not really for a direct setup. Just check to make sure, with a std timing light, you're "In the neighborhood" of TDC while cranking.

GGR · #15 10-20-2009, 08:56 AM

I think there's also a question of coil voltage. The blue coils mated with that ignition box need something like 1.8 volts, while standard set ups with the points and condenser directly connected to the coil use coils that need 12V. So connecting the system directly to a 1.8V coil may not work that great. But again there are these resitors on the way and I do not understand much in electricity...