goofy symptom, W126 420SEL - PeachParts Mercedes-Benz Forum

davestlouis · #1 02-19-2006, 06:25 PM

I'm stumped...my 420SEL has has an intermittent stumble,rough running problem ever since I powerwashed under the hood about 30 days ago. It would initially not run at all, then ran OK sometimes, then would stumble and stall under load, but there was no rhyme or reason to it. Today I went for a spin...ran fine for 15 miles or so, a mix of Interstate and surfaace streets. In the past, it seemed to be worst trying to accelerate from a stop, that was when it was most prone to stalling and running funny. It was fine. I drove it several hours later, and it stumbled several times...the new symptom is this: I heard a clicking from the dash each time it stumbled...the recirc button on the dash would light up and click in rhythm with the engine stumble. I pushed the switch "off" and it didn't do it any more, pushed it "on" and it stumbled once, but never again when I manually switched the recirc on and off. Any thoughts and suggestions?

jhodg5ck · #2 02-20-2006, 10:49 AM

I'd check your klima relay and your fuel pump relay..perhaps they got moisture in them from the power washing.

Pull the klima and take the car for a spin..see what's what.

Jonathan

softconsult · #3 02-20-2006, 11:00 AM

Not sure about your problem, but hope you have learned not to spray high pressure water on your engine and it's associated vulnerable electrical parts.

Steve

davestlouis · #4 02-20-2006, 07:39 PM

Yep, lesson learned. BTW, I work in a high volume luxury dealership bodyshop, and the porters spray off engines all the time, with no ill effects. I'd much rahter deal with a constant failure than an intermittent one, it's easier to trace.

jhodg5ck · #5 02-20-2006, 07:41 PM

I've been pressure washing engines for years... You just have to be selective about what you spray.. sensative items are either wrapped in plastic or carefullt avoided. No Ill effects as of yet

Jonathan

davestlouis · #6 02-20-2006, 09:52 PM

so....where are the relays I'm looking for? Are they the same as the ones on my "organ donor" 1988 300SE?

wbain5280 · #7 02-21-2006, 12:46 AM

You didn't happen to slice through any ground wires, or any other wires for that matter? How about rubber vacuum lines or boots?

Look at the wiring diagram and various ground points in the engine compartment area. After reading your post again, it sounds like a ground problem.

http://mb.braingears.com/126_DISC2/program/ETM_420SEL.htm

davestlouis · #8 02-21-2006, 08:28 PM

I haven't looked yet...I concentrated on washing the left apron near the power steering pump...it was the PS leak that got this whole debacle started. Every connection I've touched seemed intact.

stephenson · #9 02-21-2006, 10:51 PM

I recall seeing a few comments on Klimas that pointed to them rarely being the cause of this sort of thing - I also recall a thread or two that did point to OVPs as being a major cause of this sort of thing.

davestlouis · #10 02-21-2006, 11:03 PM

What exactly does the OVP do? Where is it? I read an old thread that said there is a connection between a bad OVP and the ABS light coming on...

Monomer · #11 02-21-2006, 11:25 PM

Quote:

Originally Posted by davestlouis

What exactly does the OVP do? Where is it? I read an old thread that said there is a connection between a bad OVP and the ABS light coming on...

OVP is the thing in the fusebox with the red top/ red fuse.

pop it apart and look for any bad solder joints.

Stan Pittman · #12 02-21-2006, 11:32 PM

Blow the water around the spark plugs out.

wbain5280 · #13 02-22-2006, 02:00 AM

Quote:

Originally Posted by davestlouis

What exactly does the OVP do? Where is it? I read an old thread that said there is a connection between a bad OVP and the ABS light coming on...

OVP stands for 'OverVoltage Protection' and is a relay to supply power to the ABS and CIS computers. If the car's voltage exceeds 22 volts, the internal zener conducts blowing the fuse(s) on top protecting the computers. Internally, solder joints can become brittle with vibration and crack.

Resolder it, like the fuel pump relay.

davestlouis · #14 02-23-2006, 11:27 PM

I'll take a look at this over the weekend...keep your fingers crossed

davestlouis · #15 02-25-2006, 03:32 PM

OK, my red box with red fuse is free-standing on the firewall. When I pull it out, the idle speed increases and the car continues to run. When I first started the car with the box plugged in, the clicking from near the ACC controls was there, and the idle was low, und12 1K at cold idle on a 45 degree day. There were maybe 3-4 clicks, and then it stopped. This time, the red light on the recirc button did not visibly light up in time with the clicks.