The car is a 1993 E320 with 75K miles. At random times the engine/transmission goes nuts and will not shift out of second gear. This leaves the car with a almost total loss of power (floor it and you'll get up to a wonderful 15 mph). The car has entered this state while driving down the interstate (70 to 15 with no warning and surrounding traffic - fun), after being stopped at an intersection, and even after sitting in a parking lot for an hour.

Repeated trips to multiple dealers have resulted in zero solutions. The problem does seem to surface more frequently in warm weather, and only after the car has been recently driven (i.e., never first thing in the morning).

We've taken the car to numerous dealers on different occasions (even once while the it was suffering the symptoms), but none have been able to isolate the problem.

Please help!!!

HMMMMM! This sounds like a transmission problem not an engine problem. When it acts up does the engine run fine but the trans will not change gears? Or does the engine run poorly?

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
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Have your dealer verify that the most current
part number overvoltage relay is installed before you go any further. Good Luck

Benzmac,

The engine runs fine. When the problem occurs the engine smoothly gains RPM up to the shifting point to go to 3rd (I belive it's 3rd since 1st is bypassed?) and then kicks back down. It ends up feeling like a learching motion.

Some background, since I have what I believe are full service records:

- Car is a '94 purchased 11/93. I purchased 11/96.
- Service record on 5/3/95 at 21813 miles indicates the loss of power for the first time. The dealer performed a number of engine tests at that time.
- Service record 5/17/95 indicates another episode of loss of power. Looks like they replaced the ignition coils at that time.
- No further mention of the problem in the previous owner's service sheets
- 10/1/97 Car lost power while driving on the interstate. After sitting with the engine off for a while it functioned properly. Took the car to a dealer and they replaced the overvoltage protection relay. Part number listed on the invoice is 000-540-67-45 (I do not know if that's a Mercedes's number or just the dealer's stock number).
- Since that time the car has acted up on at least a half dozen occasions, the lastest of which was this past weekend. The last time we visited a dealer they recommended letting the car sit for 15 minutes so "everything could reset." Tried both disconnecting the battery and letting the car sit for 30 minutes; neither worked... the car was fine the next morning.

The only other odd thing I've noticed is that when the car is driven for the first time on a given day, it seems reluctant to get into 3rd gear (again, assuming 1st is bypassed, so this would be the first shift for the tranny). Gradually accelerating, I have to speed up sufficiently to raise the RPM up into the 2000-3000 range to get it to make the first shift. After this first episode, it shifts smoothly at lower RPM. I this normal for these cars?

Finally, I mistakenly put down '93 in my original post; the car is a '94 E320.

Much appreciate the feedback and assistance.

The delayed upshift cold is part of the emissions system,to get the TWC too operating temp. sooner thus lower emission levels sooner. Now onto your major concern.
You state that the transmission downshifts to second gear and stays there. When this happens can the engine be reved to the rev limiter when Neutral gear is selected? Can the car be shut off and restarted with the fault immedately reoccuring? Can first gear be selected with the selector lever and the car be driven to the red line on the tach?
Has the dealer that inspected the car when this fault ocurring given you the DTC readout that was obtained? Does the car have ASR/ABS or just ABS? Does the gas pedal feel as if it has alot of travel before anything happens when fault is present? I need ansers to these question. I need first to determine of the fault is engine, transmission or traction control related. This can be very difficult without being able to access the on board diagnostic information and being able to drive the car and experince the fault. The part number you listed is the latest relay and has presented no problems that I am aware of.

Corky,

Thanks for the info on the cold start. At least that's one less thing I have to worry about.

I'll answer your other questions as best I can.

Can the car be rev'ed when the fault occurs with the shift in neutral? Yes... not positive about neutral, but definitely in park. Engine seems to run fine until an attempt is made to actually drive somewhere.

Can the car be shut off and the fault immediately reoccur? Yes. Fault continues to occur even after waiting a period of time and/or disconnecting and reconnecting the battery.

Can 1st gear be selected? Sorry, no first gear option on my gearshift... D, 3, and 2. Fault does continue to occur when manually selecting either 3 or 2.

We've only been able to get the car to a dealer one time with the fault occurring. Unfortunately, my wife had had the car in a city 3 hrs. away when it happened... no DTC readout - she was told that the computer showed no faults. On other occasions when we've taken the car in after an event, we were also told that the computer showed no faults.

The car has ABS only... no ASR (at least, no dashboard indication of such a system). Acclerator pedal feedback seems normal when the fault is occuring. But, from what I've read, the problem does seem to mimic the throttle limiting action of an ASR system.

Hope this additional info sheds some additional light. Thanks

I have seen this on one other occasion and the crankshaft position sensor was faulty. This would explain the warm up and cool off.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Steelep
Thank you for the additional information. As you maybe begining to discover there is much more involved in this than you might have expected. Forgive me of I sound abrut at times. If I do it is not intended. Intermittent faults are amoung the most challenging and rewarding problems that we face. In your replay you indicate that the engine can be free reved in park. This is as good as neutral. Disconecting the battery does nothing other than code your radio. The control units (ECM's) in your car have hard memory. When the fault occurs does the transmmission actualy shift into third gear then back to second? or does it never make it out of second. I read it that it does not make the shift.
Can the car be put into drive and while holding the brake what RPM can be achived while breifly appling full throttle?
You should see 1500-1800RPM and have a extemly high tourqe load on the brakes.
Benzmacs point on the crank angle sensor L5
is a valid possiblity. I have had a few (8-10) The primary thing that I have seen with this fault is the engine will seem as if the ignition timeing is incorrect. A DTC will be set if the sensor is faulty but it erases itself after it sees a valid signal and the engine has run normaly for a period of time.
How long I do not know. If this was the case the time that the car was at a dealer when fault was happening they should have gotten a code. Do not rule this componet out.
Another possiblity that you can look at yourself is the carpeting and floor mats around the gas pedal. Insect them for being bunched up under the pedal. While you are there look at the kickdown switch that is located directly under the pedal. (round and black) Push it down and listen for a click then release and listen for the click. If this is sticking down it could hold the transmission in gear and not allow a upshift.
It dosent sound like this is your problem but it is easy to check anyhow. Have the dealer perform a fuel pressure and VOLUME test. Volume being much more important than pressure. At the same time have them check the adjustment of all the throttle likages and set the lenghts to specification. As the transmission control pressure cable adjustment.
One last question When the fault is occuring and you attempt to drive does the engine buck choke or sputter? or does it just feel as if something is holding the car back ie as if the brakes were applied.
If you can think of anything else that might be helpfull please post. A complete history of a car is eveybit as important to the diagnostic process as it is to a Dr.

Corky,

Thanks for additional information... Let's see if I can provide further symptoms/characteristics of the problem.

When the fault occurs the car never makes it into 3rd. When it's acted up at highway speed there's a loss of power and then the car will no longer make it out of second gear. To answer your last question, when the fault occurs the car definitely chokes and sputters - almost sounds like it wants to backfire. The tach will swing rapidly between idle and 2000-2500 RPM, with an associated learching of the car (that's with the accelerator floored). However, you can just lightly press the accelerator and the car will move along fine at a slow rate of speed (as long as RPM do not get close to the shift point). But the minute you hit that point, the tach will kick right back down to idle (with an associated deacceleration of the car). It does not feel at all as if something is holding the car back (like the brakes being depressed).

It feels like taking a car with a manual tranny up in the RPM range in 1st and then taking your foot completely off the gas. Now, imagine rapeatedly pressing and removing your foot from the accelerator each time you get the the shift point with a manual transmission, and you have the feeling of what this car does when it has the fault.

Are these characteristics consistent with the L5 sensor? It did not immediately feel like a typical engine timing problem... when the fault is occurring the motor runs fine until it hits that magical RPM point.

I checked the kickdown switch... no problem there. It does not stick when depressed, and there is no carpet interference.

Do you want me to check the torque load while the car is running normally, or the next time the fault occurs? Normally will be easy - but who knows when it will die again (although my wife is travelling this week, so there's a good chance http://216.71.131.233/ubb/smile.gif ).

Again, thanks for the help... I've been trying to isolate the cause of this problem for quite some time now. You've done more in a couple of replies to help me than all the other efforts to date combined.

Steelep
The tourqe load that I want you to attempt needs to be done when the fault is present.
Based on the information that you have provided to me I believe that the next course of action would be to replace the crank angle sensor L5. It is not that expensive to do and it sounds as if this is a very likely the cause.
Good Luck
I would still suggest that the fuel pressure and voulme be check too.

The adventure continues...

I finally had the opportunity to drive the car with the fault present. Some of the information I provided previously was erroneous, so here's an accurate picture of what's going on.

The car is basically going into limp mode... Tach cycles between 1000 and 1500 RPM. The motor stays in limp mode regardless of whether the transmission is in gear or park. Torque can be placed on the transmission up to the 1500 rpm point, then the motor kicks back. Check engine light does not illuminate. Fault would seem to be related to heat... only goes away once the car cools overnight (or at least for a long time).

Dropped the car off at a dealership (unfortunately after closing). Next morning (today) no codes present. Gave them a full rundown of the conditions. They drive/test/drive/test etc., but fault won't occur. They were not receptive at all to L5 sensor suggestion... insist it would code and that all sorts of other nasty side effects would occur.

Does the above information still support the original diagnosis, or does this change the landscape?

If they can't duplicate the problem, I would probably have them sit the car out in the sun at idle with the air conditioning off. Let it run for an hour then drive. I have had to get many cars to fail in this way!! Persistance pays off in this buisness. If they still can't duplicate, just have them replace the crank sensor and let us know if that fixes the problem!!

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM