99 S420 Skips Heart Beat @ 70mph - Mercedes-Benz Forum
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post #1 of 14 (permalink) Old 03-19-2018, 12:04 PM Thread Starter
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99 S420 Skips Heart Beat @ 70mph

Ten days ago+-(100 miles ago) travelling at 70mph, cruise on, the engine skipped a beat, like the fuel shut off, the ignition failed on all cylinders, or there was water in the fuel line. It was a split second event, a hiccup.

A week later it happened twice in 2 minutes, same circumstance, hiway, cruise on, 70-75 mph.

Next day it happened coming off a traffic light after I exited a freeway.

Yesterday, it happened again on the interstate, at 70mph, and then actually stalled at a traffic light a few minutes later. It restarted perfectly.
Now I have a CEL on the instrument panel.

This vehicle runs exceptionally well, shifts smoothly, no heating/cooling issues, no hesitation on acceleration, nothing to indicate a malfunction like this. It's not a single plug or wire type of miss, it's a system wide failure.

It's just a split second blip, like a miss or a tug, but it obviously is becoming more frequent. Occurs after 3-8 miles of driving.

The second time it happened I thought maybe the tranny was hunting for 5th gear, so I added a 1/2 quart of tranny fluid thinking it was possibly low. That didn't solve the issue. (Thank you Benz for eliminating the tranny dipstick!)

Has anyone else experienced this sorta' hesitation?

I've spent over an hour researching this on the forum, but nothing came up similar to my symptoms.

107k miles on the vehicle, it's a sweet ride, not a beater.
Could a wonky wheel sensor tied to the ASR cut the fuel momentarily? If I were to guess(and I am guessing!) I'd say it is an ignition issue rather than a fuel issue. MAF in very early stages of failure?
THOUGHTS??

Now how do I clear the CEL? I can't find a link on that.


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"You are what you drive!" Big Al

There is perception, and then there is reality.

'99 W140 S420 111K, '94 W124 E320 124K (sold! Repurchased 10/3/16, sold 11/17)
'14 BMW X3 XDrive 38K,
'13 BMW X1 28K (Traded). '11 BMW 328i XDrive 19K(Traded)
'08 Subaru Outback Limited Wagon 56k (Traded)
'83 BMW 320is "Sport" (48k, sold! converted to EV!)
'87 190E W201 (sold!) '85 Audi 5000 (sold!)
'76 250 W114 (sold!) '72 280 W114 (sold!)
'67 200D W110 (bartered) '62 220 W111 (buried)
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post #2 of 14 (permalink) Old 03-19-2018, 12:28 PM
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Sounds like a CPS. Timing engine sensor at the back of the engine.

Works fine cold/first start of the day, and then nothing when hot.

The CPS can be a easy 10min DIY, or 10hr or so job if it is a metal sleeve sensor that is corroded on the engine...

By the way, what are the codes..?

https://www.benzworld.org/forums/r129...ensor-r-r.html

w140 Rear Crank Position Sensor / RnR nightmare - PeachParts Mercedes ShopForum

https://www.pelicanparts.com/techart...or_Removal.htm

Martin
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post #3 of 14 (permalink) Old 03-19-2018, 01:18 PM Thread Starter
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CPS Failure Possibility

Quote:
Originally Posted by MAVA View Post
Sounds like a CPS.

Works fine cold/first start of the day, and then nothing when hot.

By the way, what are the codes..?

Martin
Thanks for the super quick response, Martin!

As I've studied this CPS issue in learning about these Mercs, I honestly cannot say this is EXACTLY what most people report for symptoms, i.e. the "Classic failure".

I do understand how this total loss of power COULD be related to the CPS, as it is an electrical choke point so to speak, however I'm not experiencing any " "hard starting when hot" symptoms. Ever!
Are you saying this "miss" is an early symptom of CPS failure?

Sorry, I don't know how to pull codes on the beast, I did seek the info provided by a HUM device attached to the plug under the dash, OBDII, and HUM tells me there are no malfunctions.

I'm not pressed to do something today, I have a back up ride.
I'll research "pulling codes" later today, and that should point me to the exact issue, correct?
My W124 had the OBD I and blinking lights so it was much easier to diagnose.

What you advise certainly makes sense, and the links were terrific. I thank you.

Al


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"You are what you drive!" Big Al

There is perception, and then there is reality.

'99 W140 S420 111K, '94 W124 E320 124K (sold! Repurchased 10/3/16, sold 11/17)
'14 BMW X3 XDrive 38K,
'13 BMW X1 28K (Traded). '11 BMW 328i XDrive 19K(Traded)
'08 Subaru Outback Limited Wagon 56k (Traded)
'83 BMW 320is "Sport" (48k, sold! converted to EV!)
'87 190E W201 (sold!) '85 Audi 5000 (sold!)
'76 250 W114 (sold!) '72 280 W114 (sold!)
'67 200D W110 (bartered) '62 220 W111 (buried)
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post #4 of 14 (permalink) Old 03-19-2018, 06:26 PM
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Go to any local auto store and ask them to scan it for you. It's free.
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post #5 of 14 (permalink) Old 03-19-2018, 09:43 PM
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I have observed the exact same thing a few times over the past 12 years, fairly intermittent and not dependent on speed, engine or ambient temperatures. Never had any check engine lights though, and STAR never showed any errors.
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post #6 of 14 (permalink) Old 03-20-2018, 12:34 AM
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Al

The car is OBDII compliant. As suggested, stop by any autoparts store and they can read as well as clear the code/codes. It's free and eliminates all the guessing.

Jim

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post #7 of 14 (permalink) Old 03-20-2018, 09:05 AM
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Al,

Mine displayed exactly the same behavior when I got it, like it shuts down for a split second and then goes on as if nothing had happened. Most of the time it doesnt cause a problem, but if it happens when your going slow it may stall completely. It used to happen once or twice a day. It didnt throw a CEL. It was the MAF sensor. SDS showed a MAF error so I swapped the one off my parts car and it's never happened again.
CEL can be cleared by most any handheld OBD2 scanner or autozone.

Hope this helps.

Mike in ABQ
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You treat that car like it's a Mercedes or something!.
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post #8 of 14 (permalink) Old 03-20-2018, 09:19 AM
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Quote:
Originally Posted by LogicalPosition View Post
Thanks for the super quick response, Martin!

As I've studied this CPS issue in learning about these Mercs, I honestly cannot say this is EXACTLY what most people report for symptoms, i.e. the "Classic failure".

I do understand how this total loss of power COULD be related to the CPS, as it is an electrical choke point so to speak, however I'm not experiencing any " "hard starting when hot" symptoms. Ever!
Are you saying this "miss" is an early symptom of CPS failure?

Sorry, I don't know how to pull codes on the beast, I did seek the info provided by a HUM device attached to the plug under the dash, OBDII, and HUM tells me there are no malfunctions.

I'm not pressed to do something today, I have a back up ride.
I'll research "pulling codes" later today, and that should point me to the exact issue, correct?
My W124 had the OBD I and blinking lights so it was much easier to diagnose.

What you advise certainly makes sense, and the links were terrific. I thank you.

Al

Everything you posted I went through with my 2002 W210, so that is why I replied to your post. Except I did not get any codes or lights.

Martin
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post #9 of 14 (permalink) Old 03-21-2018, 06:06 AM Thread Starter
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MAF Was My 1st Suspicion

Quote:
Originally Posted by Mlthoma View Post
Al,

Mine displayed exactly the same behavior when I got it, like it shuts down for a split second and then goes on as if nothing had happened. Most of the time it doesnt cause a problem, but if it happens when your going slow it may stall completely. It used to happen once or twice a day. It didnt throw a CEL. It was the MAF sensor. SDS showed a MAF error so I swapped the one off my parts car and it's never happened again.
CEL can be cleared by most any handheld OBD2 scanner or autozone.

Hope this helps.

Mike in ABQ
I've experienced failed MAF's on Subaru's. Slightly different symptoms, but that sudden BLIP, then normal behavior got me thinking.

I knew a failed CPS would give a hard start when hot symptom, but since it can shut down the electrical system, it certainly is a suspect.

I'm off this AM to an auto parts for the code check. I'll report back for an update.

Thanks to everyone with an input, I knew there had to be others with the same symptom.


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"You are what you drive!" Big Al

There is perception, and then there is reality.

'99 W140 S420 111K, '94 W124 E320 124K (sold! Repurchased 10/3/16, sold 11/17)
'14 BMW X3 XDrive 38K,
'13 BMW X1 28K (Traded). '11 BMW 328i XDrive 19K(Traded)
'08 Subaru Outback Limited Wagon 56k (Traded)
'83 BMW 320is "Sport" (48k, sold! converted to EV!)
'87 190E W201 (sold!) '85 Audi 5000 (sold!)
'76 250 W114 (sold!) '72 280 W114 (sold!)
'67 200D W110 (bartered) '62 220 W111 (buried)
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post #10 of 14 (permalink) Old 03-21-2018, 10:19 AM Thread Starter
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Update On Engine Hiccup/CEL

I went to start the vehicle to run down to the auto parts just a few minutes ago. The CEL immediately went off. Car ran the usual wonderful, and I drove to the auto parts. The very knowledgeable manager there said he couldn't check the codes since the CEL was off, and that he could not clear the codes even if he found a malfunction code. He says he cannot access a history of malfunctions. As it turns out Rico owns a '95 S600 in white/tan w/ 107K.

So I get home, and HUM had sent an email, informing me that it detected a code, P0100, MAF sensor with the CEL lamp. It didn't detect the CEL/code till I started the car today.

I think I better check my air filter. I have a funny feeling that it may be dirty, since I never checked it since purchase.


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"You are what you drive!" Big Al

There is perception, and then there is reality.

'99 W140 S420 111K, '94 W124 E320 124K (sold! Repurchased 10/3/16, sold 11/17)
'14 BMW X3 XDrive 38K,
'13 BMW X1 28K (Traded). '11 BMW 328i XDrive 19K(Traded)
'08 Subaru Outback Limited Wagon 56k (Traded)
'83 BMW 320is "Sport" (48k, sold! converted to EV!)
'87 190E W201 (sold!) '85 Audi 5000 (sold!)
'76 250 W114 (sold!) '72 280 W114 (sold!)
'67 200D W110 (bartered) '62 220 W111 (buried)
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