420SEL Randomly Stalling? - PeachParts Mercedes-Benz Forum

JamesDean · #1 05-25-2013, 11:30 AM

Alright everyone,

My mom's 420SEL is evidently having some random stalling isses that I've been unable to reproduce myself.

Initially I thought it was due to a vacuum leak as the car was stumbling a lot when you would give it throttle. I replaced the two air distribution lines, the crossover line and one of the PCV lines. I also replaced the hard vacuum line to the EZL.

Replacing the above solved the stumbling/stuttering problem and the car now drives well (aside from the stalling) and has good power.

Things I've noticed:

The fuel pumps sound a bit louder than what I recall them sounding like when we first got the car. It has some 220,000 on it now.

The spark plugs were last changed around 208,000 (so they have 12,000) on them. As well as a the distributor and rotor.

I do not recall changing the wires. They are BREMI wires right now, and one of my friends was moving the coil wire around and was able to get it to make a purple arc to the ABS bracket. The wires do physically look bad.

My mom said, when it stalled, the cluster went dark, no indicator lights, needles fell to their default off positions. Perhaps that points to the OVP relay failing, cutting power to electronics which drive the cluster.

pawoSD · #2 05-25-2013, 12:45 PM

Sounds like it needs new spark wires and OVP relay. What is the system voltage at idle?

JamesDean · #3 05-25-2013, 01:51 PM

Car came home now so I got a chance to play with it.

My mom said when it died everything went out. Radio included. That strikes me as odd as the only thing that would kill the radio would be switching off the key. Right?

I shook/tapped on all the electronic components to see if a loose connection was the problem. No effect.

I removed the OVP relay, the car's idle climbed to 1500 (As the IACV lost power). Even with the OVP remove the car remained start-able after 2-3 seconds of holding the key down.

Reconnecting the OVP restored the idle.

I have a newer 9-pin double fuse unit from KAE sitting here that I could put in however I don't think that is the problem.

I probed the X11 connector and the engine is running around 39-45 % duty cycle. It floats in that range.

Voltage @ battery @ idle is 14.2V

Edit:

Just took it for a second test drive, about 10 miles, no problem. No stalling, etc. The only things I heard was some ticking from the heads. Probably lifters. Doubt that is any way related to this stalling problem.

I am going to grab a new set of wires from the AutoZone, Duralast brand is all they have, they do have a resistor in them, and spec wise they meet whats currently in the car, so I think they'll be OK. I also have new NGK plugs so I might as well change those as well.

JamesDean · #4 05-25-2013, 04:41 PM

Alright, new wires installed. No real big difference. Maybe it starts up quicker. Didn't really expect huge results. I know that I have never changed the wires on this car. I would have used more zip ties than whomever did it before me.

I have no record of the wires ever being changed. However my records are not 100% complete and it seems unlikely that these wires are 220k old.

I also changed a vacuum line, it goes between the two pipes that connect to the IACV. For some reason my "old" pipe was pinched at one end preventing air flow.

JamesDean · #5 05-25-2013, 06:35 PM

Ha it finally happened to me.

I was driving along this rural road and all of a sudden it started slowing down. I gave it more throttle and watched the economy gauge tank. I looked at the tach and it was gone.

I threw on the 4-ways and pulled over. I tried to start the car back up but it would not have it. I turned the key on/off and I do not recall hearing the fuel pumps kick on briefly as they normally do.

After 3-5 minutes, I was able to get it back running. I drove home and pulled the fuel pump relay (002 545 15 05, 8Zyl 6000) and noticed that there was a cold solder joint formed on the connection to pin 87, which just so happens to connect to the fuel pumps.

So perhaps this was the cause. It certain sound fits.

Here are some pics:

http://imgur.com/a/u3wVc

pawoSD · #6 05-26-2013, 12:39 AM

Quote:

Originally Posted by JamesDean

Alright, new wires installed. No real big difference. Maybe it starts up quicker. Didn't really expect huge results. I know that I have never changed the wires on this car. I would have used more zip ties than whomever did it before me.

I have no record of the wires ever being changed. However my records are not 100% complete and it seems unlikely that these wires are 220k old.

I also changed a vacuum line, it goes between the two pipes that connect to the IACV. For some reason my "old" pipe was pinched at one end preventing air flow.

The "pinched" vac tube between the IAC lines is on purpose, that was a revision made in 1988 onward, on 86/87 its open. Mine is pinched shut also.

Sounds a lot like a failing fuel pump relay. I have records for my car showing it being replaced about 5 years ago for the same issue. I replaced my fuel pumps last year as they were quite noisy and pulling higher amps, which can destroy the relay. May be the same issue on your car...

JamesDean · #7 05-28-2013, 01:01 PM

Quote:

Originally Posted by pawoSD

The "pinched" vac tube between the IAC lines is on purpose, that was a revision made in 1988 onward, on 86/87 its open. Mine is pinched shut also.

Sounds a lot like a failing fuel pump relay. I have records for my car showing it being replaced about 5 years ago for the same issue. I replaced my fuel pumps last year as they were quite noisy and pulling higher amps, which can destroy the relay. May be the same issue on your car...

I re-installed that pinched vac tube and my idle was more "under control."

In park, it sits about 850-950 RPM, probably a bit high....
In drive, it sits about 600-650 RPM.

I think it might be running on the rich side, duty cycle reported about 38-43%.

rayhennig · #8 05-28-2013, 01:22 PM

Quote:

Originally Posted by JamesDean

They are BREMI wires right now, and one of my friends was moving the coil wire around and was able to get it to make a purple arc to the ABS bracket. The wires do physically look bad.

Oh gosh, I've just seen the 'B' word.

I had Bremi cap and rotor on mine and the rotor failed after 18 months. After that, I replaced both with the original 17 year old cap and rotor until I bought new, MB original.

To my mind, HT on these cars should be MB original or, failing that, Beru or Bosch. For mine (1991 300CE-24), it's cheap copper, non-resistor plugs from Beru, Bosch or NGK.

Economising on the HT is the road to misery!!

Good luck.

RayH

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