82 380SL no power when engine cold

[300sdToronto]

Starts from cold no problem - fires and idles

Stumbles and hesitates if you try to drive it until operating temp reached

Then runs OK

Any suggestions please - I am totally new to the 380SL and a search suggested several possible components could be faulty.

Shop manual is on order....

[ctaylor738]

Classic symptoms of a bad warm-up regulator. You need to check your control pressure to be sure.

[UT_Tech]

We have a loaner gauge you can use. It takes only a few minutes to check if your cold start control pressure is OK. It probably isn't. Take a look at this thread:

http://www.peachparts.com/shopforum/showthread.php?t=221171

You can download the manual for the control pressure gauge that Tim used from the UnwiredTools website. There's a detailed explanation there about Control Pressure, how it's used, how to measure it, etc.. The fuel injection system for your car is easy to work on if you have the right tools.

[300sdToronto]

Overvoltage Protection Relay bad - replaced and we're off to the races. Glad it was so cheap a part.

[Kimolaoha]

Originally Posted by 300sdToronto

Overvoltage Protection Relay bad - replaced and we're off to the races. Glad it was so cheap a part.

I'm having a similar issue. Can you elaborate please?
If I recall, the OVP is in the passenger footwell and accessible via the fuse panel? I also recall a fuse? Did you replace the whole OVP or just the fuse?
My car starts fine, but after a minute or so wants to die unless I can coax it to operating temp.
Any other thoughts?
Thanks
Mike

[Kimolaoha]

Originally Posted by Kimolaoha

I'm having a similar issue. Can you elaborate please?
If I recall, the OVP is in the passenger footwell and accessible via the fuse panel? I also recall a fuse? Did you replace the whole OVP or just the fuse?
My car starts fine, but after a minute or so wants to die unless I can coax it to operating temp.
Any other thoughts?
Thanks
Mike

PROBLEM RESOLVED -

For those that may run across this thread in the future, my issue turned out to be the 25 cent 10-AMP ATC Fuse in the overvoltage protection relay (OVP). I suspected this to be the case because of the odd "burp" that occurred when I was jumping the battery over the weekend.

It is amazing (but not necessarily surprising) how poorly the car runs when the OVP has disabled the various fuel/ignition boxes. The car would start fine but bog down badly after a minute or so -- to the point that it was dangerous to even try to pull out onto the road. After it warmed up a bit -- say five minutes -- it would accelerate, albeit poorly, and it was still missing badly. If it did stall, though, I never had any problems restarting.

For those looking for it, the OVP (at least on an '83 SL) is in the front passenger's footwell, behind the kick panel just forward of the door, and slighly below the glove compartment. If you remove the fuse panel cover, you MAY be able to barely see it at about the 2 o'clock position, but it was not (for me) accessible through the fuse panel cavity, and I had to remove the "permanent" kick panel to get access. It MAY also be accessible through, or after removal of, the glovebox cavity.

I happened to have a spare OVP from an earlier troubleshooting exercise, and simply pulled the 10-amp fuse from the known good OVP and popped it in the installed OVP -- so it seems that the installed OVP was not fried -- just the fuse. I plan to start carrying a spare 10-amp fuse in the car -- if not the spare OVP itself.

One can only wonder how many hours and dollars have been spent by unsuspecting owners trying to chase down the drivability problems caused by a simple 10-amp fuse.

Beware when jump starting from or to your car's battery, as the blown OVP fuse appears to be a common result. But I do take comfort in the fact that the OVP does exactly what it is upposed to do, and possibly saved some of my high dollar black boxes! I'm glad to have resolved the issue.

Good luck.
Mike

[ctaylor738]

But I suspect that something else is going on here. IIRC, the OVP powers the lambda controller and the idle relay. If the mixture is properly adjusted and the warm-up regulator is working, all that the lambda system does is fine-tune the mixture. It sounds like, in your case, that the basic mix may be lean and the car needs enrichment from the lambda system to run, or that it's not getting enrichment from the WUR.

Recommend that you check your on/off ratio and control pressure, and make sure that both sides of the WUR are holding vacuum.

[Kimolaoha]

Originally Posted by ctaylor738

But I suspect that something else is going on here. IIRC, the OVP powers the lambda controller and the idle relay. If the mixture is properly adjusted and the warm-up regulator is working, all that the lambda system does is fine-tune the mixture. It sounds like, in your case, that the basic mix may be lean and the car needs enrichment from the lambda system to run, or that it's not getting enrichment from the WUR.

Recommend that you check your on/off ratio and control pressure, and make sure that both sides of the WUR are holding vacuum.

Hi Chuck:

Nice to hear from you again. I recall that we were chasing down similar climate control problems a year or so ago -- yours solved by a new CC panel/control unit, and mine by a refurb'd temp regulator.

I do not doubt that there may be something else going on under the hood, but -- to the extent that I can -- I plan to leave "well enough" alone for now. The car seems to be driving as well as it ever has, and goodness knows I'll have other maladies to keep me occupied. There can be no doubt, however, that the OVP was the root of my current woes. If there are underlying issues, I'm sure that all will be revealed in the fullness of time

Thanks
Mike