Did something get fried?

[Por_sha911]

This is a M Benz question but the wife's `85 380SL uses the same CIS system as in the 911:
The car hadn't been driven for 2 weeks and the battery was dead. Someone tried to jump start it but put the jumper cables on backwards (musta been some sparks!). When they turned the key and got nothing, they reversed the cables but the car barely ran. I found out all that went on and thought maybe it was just loaded up and needed to be blown out. I took it down the road. At first I could barely keep it running in gear. After a few miles running in 3rd (it has overdrive) it will idle fine but has zero power and it bogs down if I just try to accelerate normally. I have to coax it to get going by running up the idle a little and then slapping it in gear (not good for the Automatic trans I know). So what do you think? Do we have an electrical problem? I thought I would pull the plugs and see what they look like. Any suggestions? I have tried to get help from a MB BBS in the past but they seem more interested in chrome wheels and new CD changers. (Porsche content: I need to stop wasting time fixing the Benz so I can drive my 911!)

[ThePointman]

I hate to say it but hooking up the cables backward sent current to where it should not go. You have a very high probability of serious damage to the charging system at a minimum.

[Por_sha911]

The car runs and holds a charge just fine. My concern is that there may be a fried brain.

[randywebb]

no brain on a CIS car; you may have burned up some ganglia tho -- i.e. any electrical component that the current reached -- cold start valve maybe - I'm not sure what else on the fuel system has an elec. connection.

You should call your ins. co. and describe what happened. Talk to the person who hooked it up wrong & get the name of their ins. co. ... This could get very expensive.

[ianc]

Later Porsche CIS has a 'mini-brain' that is used to control the O2 sensor and frequency valve. Not sure of the effects if this were hosed or even disconnected. Basically no other electronic parts though...

ianc

[randywebb]

good point - now, whether your MB has that...

[Por_sha911]

Morning bump. Any more suggestions from the brain trust out there. Rick M-you out there?

[rick-l]

Originally posted by randywebb
good point - now, whether your MB has that...

My 84 Audi with CIS had a brain to modulate control pressure (mixture) so I am sure a high end Mercedes would also.

You could see if current is still going through the valve and being modulated (there is a duty cycle).

[xlr8]

Hi Joe, I had a word-of-mouth recommendation for Aaron at Mercedes of Knoxville Classic
I was advised that the problem could likely be with the fuel pump relay, and that there is a somewhat complex procedure to jumper it for troubleshooting.

article

Link

Good Luck!

[Por_sha911]

Well since I started the thread, I figured I'd post the results. Apparently, the MB has a "Overload Protection Relay". The cute little critter is the last thing in line before the brain blows up. At least the rest of the system didn't fry.
Porsche content: Now I can go back to driving my Carerra

[randywebb]

Nice - this is an example of why the Visigoths (proto-Germans) were able to destroy the Roamn Empire...