420 SEL died - PeachParts Mercedes-Benz Forum

Das Benz · #1 01-07-2014, 06:36 PM

Hey folks,

I just need a quick opinion on something that happened to me today. So we got -20c weather going on, with a wind-chill of around -38c. Nothing too out of the norm, we have had pretty warm winters the past few years.

Anyways, there's been a few cold morning so far, and my 420sel has had no problem starting. She fires up like nothing is going on, and im off to work.

Today though, put a twist in that. And the first time the car left me dead on the side of the road. So I was on my way back tonight, havoc going on outside (blowing wind, snow), as I cruse down the roads in comfort and soothing seat heat. Thinking, how nice this car is and quiet, as terror is going on outside. I slowly coasted down to a light, and watched the tach settle (I usually do for some odd reason

), however, it slowly went below 500rpm, and dipped down to 0 as I came to a stop. Oh oh.. I thought!. I hope my chain didn't skip!.

So I cranked the car over as the light was red, and it turned over fine, just no fire. So, my memory started to kick in, and I tried to remember what ive read here on the forum that could cause a no start. OVP, EZL?..

I turned the key off for a few seconds as the light was still red, and slowly turned it to on so I could try and hear the fuel pumps. Sure enough I could hear the pumps.. Hmmmm...

Thankfully one of the guys I work with was driving by, recognized my car and help me push it across the street into a gas station. I quickly checked fuses, OPV relay fuse, EZL if any wires came off, and air cleaner if there was any built up ice. Nothing.

And I now I had cell service.. Call up pops, he came by, about 10 min later. As soon as he pulled in, I tried to crank, and the car fired right up. No hesitation or anything..

Any ideal what it could of been. Pops thinks it was probably a frozen fuel line.. luckily I had some isopropyl alcohol in the trunk for electronic projects, I dashed a bit of it in the fuel tank. Car ran fine on the way home.

Anything I should look at guys before I take the car to work tomorrow. Should be around -12 tomorrow.

With the wind chill while traveling at 80km/h. could cause freezing issues.?

Randy · #2 01-17-2014, 11:21 PM

Crank position sensor; it gets temperature sensitive when it starts to fail. Has yours ever been changed? Not a bad job, esp. if you are agile.

Das Benz · #3 01-18-2014, 06:16 PM

Ok thanks, ill look into that.

So far since that day, car has been running fine. No hiccups. Hopefully she can last till i can megasquirt it in the spring

We have some more cold weather on its way. But i now have my oil pan heater, should help with cold starts; not that ive had a problem with cold stars, even at -27c. But any bit helps

pawoSD · #4 01-18-2014, 06:35 PM

I agree it sounds like crank position sensor issue. Easy first item to replace especially if its never been changed before. My 300E had the same issue.

Das Benz · #5 02-02-2014, 09:14 PM

Well folks found out what was causing the issue.

So I cant remember where I read it; somewhere on the net, but there was a fellow who his wife was driving his w126 on the hwy during a cold day in Michigan. The car died on her, and by the time he was able to reach her, the car started up like there was nothing wrong. He noticed that the intake had some ice frost.

So a few weeks ago we had -28.5c weather, and whataya know the my car started to get cranky. After my 25min drive, I got into town and at low speed it was sputtering and overall pissed

Pulled into the driveway at work, and once I parked it would almost die, then rev up to 1500rpm, then die and rev up. A quick blip of the throttle, and it cleared up like there was nothing.

Ok, drive back home from work, same thing before pulling into the driveway. So I quickly popped the hood and took the breather off, sure enough, there was a good chunk of ice buildup on the air plenum valve, holding it slightly open, causing the car to run rich. Where did this ice come from, well the breather hose was contributing to a good amount of vapour into the intake, and -30 temps caused it to freeze before getting into the engine. The ice would build up at my 50mph speeds, then hold the plenum open when I slowed down in town, causing the car to run poor, and almost stall. That first night, it must of really built up and flooded it at the stop light.

So I just disconnected the case vent from the intake, its just breathing out to the atmosphere for now, I put a breather filter on it so nothing gets into the engine. once the warmer weather shows up ill put it back on the intake.

Goofy car

pawoSD · #6 02-03-2014, 01:53 PM

Seems like that would only happen if there was a fair bit of moisture in the crank case. Does the car get fully warmed up/highway driven much? It should be running at 82C....

Could wrap the tube in heated tape with a sensor/relay to turn it on below a certain temp

INSIDIOUS · #7 02-04-2014, 04:25 PM

If the air inlet is open too much is that a rich condition or a lean one?

Das Benz · #8 02-04-2014, 06:24 PM

Quote:

Originally Posted by pawoSD

Seems like that would only happen if there was a fair bit of moisture in the crank case. Does the car get fully warmed up/highway driven much? It should be running at 82C....

Could wrap the tube in heated tape with a sensor/relay to turn it on below a certain temp

Yea my car gets fully warmed up every trip. I do about a 30min drive each direction every day at around 50-55mph (80-90kmh). Plus I have a oil pan heater that ive used every day since the temps have dropped below freezing. She does have almost 400,000km so there might be a bit more blowby then new. But it really only happens when its like -20c or lower. And after a long stretch of high speed driving as I slow down and come into town.
Once I do my EFI swap in the spring all should be well.

We have had a lot of funky weather this year, and its been relatively very humid, so that could add to the issue. one day +5, next -30c

Quote:

Originally Posted by INSIDIOUS

If the air inlet is open too much is that a rich condition or a lean one?

Rich, as you move the flow plunger down (on the MB V8's), it adds more fuel.

INSIDIOUS · #9 02-04-2014, 06:51 PM

Quote:

Originally Posted by Das Benz

.... Rich, as you move the flow plunger down (on the MB V8's), it adds more fuel.

That is interesting. Is there no electronic feedback anywhere in the system that regulates fuel? Why bother with an O2 sensor?

pawoSD · #10 02-04-2014, 08:14 PM

Quote:

Originally Posted by INSIDIOUS

That is interesting. Is there no electronic feedback anywhere in the system that regulates fuel? Why bother with an O2 sensor?

There is, the electronic EHA valve on the side of the fuel distributor can adjust the fueling via the computer.

INSIDIOUS · #11 02-05-2014, 01:21 PM

Quote:

Originally Posted by pawoSD

There is, the electronic EHA valve on the side of the fuel distributor can adjust the fueling via the computer.

Wouldn't that prevent the supposed rich condition caused by the ice?

Das Benz · #12 02-05-2014, 06:01 PM

Quote:

Originally Posted by INSIDIOUS

Wouldn't that prevent the supposed rich condition caused by the ice?

The EHA can only compensate soo much. If you totally disconnect the EHA, the engine will still run.

Think of the EHA and O2 sensor combo as the "fine tuning" of the fuel ratio. And the K-tronic "flow plunger" whatever technical term its called; It does rough fuel ratio adjustment.

pawoSD · #13 02-05-2014, 07:24 PM

Yeah the EHA is a very small fine tuning of the fuel injection. A chunk of ice holding the air flap would be huge in comparison.

INSIDIOUS · #14 02-05-2014, 08:38 PM

Quote:

Originally Posted by pawoSD

Yeah the EHA is a very small fine tuning of the fuel injection. A chunk of ice holding the air flap would be huge in comparison.

So then why doesn't excess air result in lean? Assuming the flap doesn't cause throttle position sensor read?

Das Benz · #15 02-07-2014, 09:20 PM

Quote:

Originally Posted by INSIDIOUS

So then why doesn't excess air result in lean? Assuming the flap doesn't cause throttle position sensor read?

After the flow sensor, is the actual throttle body. Which directly controls air flow into the engine via your throttle pedal. It has a simple throttle position sensor, however if im not mistaken that specific sensor only tells the ecu if its WOT, or idle.

The flow plate has a variable sensor on it to tell the ecu a semi accurate value of actual air going into the motor. Pushing the flow plate in by hand has no effect with allowing more air into the motor. Its just for measuring the ammount of air flow, and coarse mechanical fuel metering via a push plunger into the fuel distributor.