My 400E has been running rough as of late.
Today I had a emissions check and almost failed. HC reading was 193 ppm.
CO2 reading was 14.59 %.

Can't really pinpoint symptoms other than every thing seems pretty normal.

Gas mileage not unusally high, Temp runs around 80c during all types of driving.

Issue is that under certain times when I pull up to a stop light. The engine feels like it has lost 3 cylinders and stumbles/ chugs hard. The taletale sulphur odor is omnipresent. 90% of the time the car runs like a champ. Smooth idle, plenty of power,etc. I can shut the car off when running rough then start back up and it returns to normal. LAst month I figured it needed a tune up and changed plugs and cap and rotors. Ran better but problem persistend.

The sulphor/rotten egg smell is noticable while driving. (i.e fumes come back in the S/R opening with side windows closed.

I know something is wrong but need a hint as to where to start.

Any ideas?

Thanks, Mike
92 400E

I've experienced EXACTLY what you have been talkin' about in my '95 MB E420...I've never been able to pinpoint the problem though...and it went away after my last service check...I always assumed that it idled rough because I don't drive the E420 very much...but when I was readin' through this forum, somebody else w/ a E420/400E experienced the same problem too...tell me if you have any luck!

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-= 1995 Mercedes-Benz E420 (W124 - Black Pearl/Black) =-

Do you experience any hard start?? Maybe there's a bit of carbon build up in the engine...try rev the engine, run it hard on highway couple times, see if it will get better....

Andy Kuo

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• 1992 Mercedes-Benz 400SE
  
• Pearl Grey/Black Leather
  

ICQ#26950002
Mercedes Owners ICQ ActiveList ID#61730549
Mercedes S-Class Page
http://akry.homestead.com

Andy,

I doubt anyone needs to tell Mr. Mullins to go thrash his cars!! I'd bet my 500E he's taken care of that already

Maybe this is a WAY outside chance, but check your motor wiring harness...they've been known to get brittle on M119 motors and could cause an intermittent screw-up (I hope I'm way off).

Otherwise, no educated guess; sorry! Good luck Mike

Since speculation seems to be the issue here, I'm not sure that testing would be of any interest. The only reason to "tune" one of these cars for a performance problem would be to observe the plugs from an analytical sense.

The word "tune" as used in these forums always gives me a chuckle. That engine management system tunes every variable at least twice a second. It does timing so well that it varies each cylinder each stroke to a total of fifteen degrees variation cyl to cyl. If it don't work right its broke. It can't be "tuned" ROFLMAO. IT CAN BE TESTED though.

The first test I would do would be to monitor the O2 sensor both for closed loop operation and switching times. I would also check for codes on the self diagnostics and check the adaptation factor set in the diagnostics. I think the cars adaptation is limited to 20%. It gives diagnostic insite to view the additive and multiplicative addaption values in the controller. The engine and the fuel system change as they age and the control system recenters itself (adaptive value). By knowing the overall value (rich or lean and the amount)a direction for diagnostics is gained.

Actual values of all sensors are read using a scanner. These often need to be confirmed by scope or other means to verify the controllers interpretation.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Well the "tunability testing: is constantly in use. If it's not me, the wife is a leadfoot to the nth degreee.

Michael is right in that I've noticed the connectors on the solenoid's on the cams are brittle. Are these replaceable by themselves? along with others I haven't noticed?

Steve, I heard what you said, can I do some of the testing with home tools, i.e. Fluke Multimeter, or am I looking at a shop specialty tool?

I have a electronics and computer background and am not afraid of trying anything.

Any help in getting started testing would be greatly apprciated.



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Mike Mullins
71 250 Coupe
92 400E Sedan
90 944/S2 Cabriolet

Mike,

Sorry if I misleaded you to push your 400E hard on Highway....it solves my problem after I let my car sit for too long.... :p

Stupid me, how can I over-look the connectors between wires and plugs...I had a the same problem(caps)a while back ago, and I saw your post about changed caps, and thought it might be something else.

Anyways, the connectors between wires and spark plugs are changable, it's about 20 buck canadian each....change them all, just in case.....

Andy Kuo

------------------

• 1992 Mercedes-Benz 400SE
  
• Pearl Grey/Black Leather
  

ICQ#26950002
Mercedes Owners ICQ ActiveList ID#61730549
Mercedes S-Class Page
http://akry.homestead.com

I started earlier to write a test but I had to verify which connectors your car would have. It turns out that your car should be early enough to have the diagnostic connector on the left fender (X11). After July 1993 it was removed.

We usually would use a scanner on your car and I couldn't remember. If you use your multimeter set on duty-cycle you can monitor the on-off ratio that is used to monitor closed loop operation. If you monitor pin# 3 you should get a duty-cycle that ranges up and down around 50%. It should oscillate within 20% maximum. In other words it shouldn't go above 60% or below 40%. The rapidity of the oscillation is important but not quantifiable.

With a scanner one can also monitor the actual O2 sensor voltages, which are rather difficult with out break out boxes or leads.

If you are real adventuresome I will describe again a method for pulling fault codes from the diagnostic connector (on right fender) without an impulse counter or scan tool.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by stevebfl (edited 05-28-2000).]

Steve , Tell me more.
When you refer to duty cycle on the multi meter, you are referring to?
Ohms, volts, etc? and Scale?

As far as the adventure part, I'm all ears. The connector is on the front fender under a screw on cap.

As far as a scanner, any particular model?

Mike M



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Mike Mullins
71 250 Coupe
92 400E Sedan
90 944/S2 Cabriolet

I guess you will need a different multimeter. Duty-cylce is an extended feature of frequency. Frequency is how many times an event happens. Duty cycle refers to the caracteristic of an event.

An example: Dwell. In old points systems a six cylinder engine running at 2000 rpm would have the points openning 6000rpm or 100 times a second or 10ms for each event. Duty-cycle would be the portion of the time that the points are open vrs the time they are closed. If the points open larger their dwell and duty cycle will increase.

If you watch the event with a scope the duty cycle can be measured on the screen. Good multimeters now have frequency, rpm, and duty-cycle.

The modern automobile uses many duty-cycle related functions for control. The frequncy valve in early Lambda control systems was a valve that leaked fluid to lower a pressure. It buzzed at a constant frequency. The amount of fluid it passed related to duty-cycle. If during one cycle the valve was closed 90% and open 10% it would flow much less than if it was open 50% and closed 50% etc.

In the case of on-off ratio, the signal is a square wave at constant frequency and the duty-cycle fluctuates. On earlier cars with K-jet the duty-cycle showed relative mixture setting, closed loop condition and showed self-diagnostic faults by holding a designated constant duty-cycle, ie: 10%, 20%, 30%, 40% etc. Each had a particular meaning. Closed loop was indicated by oscillating values up and down (not constant).

By 1992 self diagnostics had improved to where the car not only could read codes but actual values to a scan tool. MB has been very tight with their equiptment and software. The only scanner sold to the public that works from company programming is the Bosch KTS300. A number of aftermarket companies have reverse engineered scanners that do varying amounts of whats possible. None of them do a fraction of what the factory scanner HHT (hand held tester) can do. MB has recently made their newest laptop scanner available to the aftermarket for the small sum of $27,000. Not bad for an IBM thinkpad. BTW there also is an $8,000 yearly subscription fee (that is included in the $27k for the first year).

We use the Bosch KTS300, an Assenmacher AST Retreiver, and an Impulse counter. We are working on the $27k.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician