84 500 SEC no start - PeachParts Mercedes-Benz Forum

126nut · #1 04-11-2011, 07:05 PM

Hello all,

It's been a while since I've been here but I just picked up one of the cars I have wanted for years, an 84 500 SEC which looks to be a grey market car which I like as I think it looks better but anyhow, enough of my gibberish.

The car was running when I first looked at it but now it won't which is OK with me because I got it for a better price because of the no start. The OVP keeps blowing. Not sure what all runs through this but evidently the ignition does as it has no spark. It will blow the fuse just as quick as you can turn the key. I am just now kicking myself in the ass for getting rid of all my Merc technical books, more and more over the years as I just seem to keep buying these cars as the years go on, since my first 380SEL back in 1995.

Thanks for any advice.

JohnM. · #2 04-11-2011, 07:31 PM

You have to replace the entire OVP unit. If the one in there is blowing fuses, it's already been shorted internally.

126nut · #3 04-12-2011, 12:10 AM

Thanks, I will get one ordered tomorrow. What would have caused it to short out anyhow? I am thinking somebody put the battery in wrong or maybe jumped it incorrectly at the auction where I got it maybe?

JohnM. · #4 04-12-2011, 12:12 AM

Quote:

Originally Posted by 126nut

Thanks, I will get one ordered tomorrow. What would have caused it to short out anyhow? I am thinking somebody put the battery in wrong or maybe jumped it incorrectly at the auction where I got it maybe?

That's a high probability. The OVP falls on the grenade so to speak when dumb***** like that happens. Sometimes it survives and you can get away with just replacing the fuse...sometimes not.

126nut · #5 04-12-2011, 11:30 PM

Well I got the OVP replaced and the fuse is holding up so maybe that part is squared away but she still won't start, no spark like before. There is power at the coil positive terminal but other than that I have no idea how to proceed. The parts that control spark are simply the ignitor, pickup coil in distributor and the ignition coil am I correct? The wire or lead that comes off and goes to the distributor from the ignitor is frayed rather badly, if I knew how to ohm it out maybe I could diagnose it.

Oh yeah I might have even bigger problems, when trying to crank it over it would not spin, I knew the battery was good and could hear the starter engaging but it would not turn over. I feared that it was somehow locked up, pulled the plugs and there was coolant in several holes, looked like it had been there for a while so it probably needs headgaskets or worse, who knows. This is not my first rodeo with these cars so pulling the engine and going thru it is not my preference but if that's what must happen, so be it. I would like to hear it run though before I tear it all down just to see how bad the damage is.

I used to have the tech books in bound paper, are they available on CD's now?

126nut · #6 04-23-2011, 03:44 PM

Update:

I got the manual on CD and traced the problem down to a bad igniton module (switching unit) After getting a scare on prices I found a HUCo brand aftermarket at my local wholesaler which cost me $55 versus the $750 for a Bosch OEM, what's up with that crap anyways?? The new module fixed her, looks a little different and came with heat transfer goop, now it fires up and runs surprisingly well considering the coolant in the cylinders issue but I still am looking at pulling the engine and doing head gaskets and whatever else needs to be done besides that. It would probably overheat if I ran it like it is and damage the cats, is what I am thinking.

Any thoughts on head gasket problems on these cars or am I looking at more serious damage? It actually runs pretty good for the little bit I ran it as it had no coolant. I will probably do a compression test before I tear it down. I have all the records on the car and the fella who used to own it spent some crazy money over the years keeping up with it. I am guessing it has sat for the last 4 years as the last time it was in the shop was 2007, a/c work.