SSS help on a 1988 300SEL W126 (pre-repair factsheet included)
 

I put this here because I want to be wise and not just throw parts at the problem, I just found there was one problem I was encountering that the other SSS posts were not, mine dies when the engine is hot and runs smoothes when the engine is cold in the morning.

Also lately this might be a seperate problem but lately, I will press the accelerator and the car will accelerate slowly until I get to a certain RPM then it kicks in to how it used to accelerate. and the "power" of the vehical seems to pulsate intermittenly, like when I drive down the freeway.

Can anyone give me some pointers and a direction? thanks.


SSS factsheet:

Car model: 300 SEL
Year: 1988
Chassis Model: W126.025
Engine Model: straight 6??
Mileage(km/miles): 256,000
State: TN
Last tune-up (km/miles):230,000 I think, according to last owner
-Spark plug: N/A
-S/P Cable: N/A
-Rotor: N/A
-Cap: N/A

What kind of sudden stalling do you experience?

-Deceleration, and sometimes when turning


Does all the instrument and light are working in your dashboard?

-Temp gauge: Y
-Oil pressure gauge: Y
-Tachometer: Y
-Fuel Gauge: Y
-Alternator Gauge: N/A
-Abs light: Y
-Srs light: Y
-Engine light: Y
-O2 sensor light: don't know what this is
-all the other light :

STALLING INFO:

How often does it Stall:

-Every day: useually when the engine is hot, can also do it one the first crank of the day, but now I usually hold the key down

-At a certain outside temp(specify): All

Does Any light come on or flikering before it Stall?: Not that I know of

Engine Temp when stalling: Operating Tempeture

Outside Temp when Stalling: All

Fuel gauge reading: Normal

Alternator's reading: N/A

Ac/Heater on or off: typically on

Heated seat on or off: N/A

Does it Start easy after Stalling: most of the time, a few times I've really had to gas it to start

After stalling when you get the engine running:

-The idle is rough, makes the car shake, unless I 2-foot it (specify RPM):
-The idle go up and down(specify RPM): between 7 and 10 on the tach

If the idle go up and down does it settle to normal after:

-it doesn't useually settle once it gets rough for the day

Deceleration Stalling:

-If you put the car in neutral at the same time you decelerate does it stall?? havn't tried that yet

- If you double pedal and keep the RPM over 1500 does it stall?? no

Which procedure have you follow to troubleshoot your problem? None yet


Which part(s) have you replaced and why??

none yet, didn't want to start throwing parts without at least some wise counsel. A shop I had fix my mixture (for emissions standards) told me I probably needed and Over-voltage Relay

I will second the shop's opinion, Over Voltage relay needs replacement.

PawoSD - that's amazing. How did you come up with this diagnosis for a fix? What gave you the clue?

Stalling is usually the OVP. It might have other issues as well, but the OVP is a good place to start.

So you replaced the OVP, and now the car is running well?

If not, I just had the exact same problem with my 560SEC, and it turned out to be a clogged fuel filter. If you haven't changed it in a long time, it's probably due.

Factsheet--- next step....
 

Hi tpros

Thank for using the factsheet I create few years ago.

Now you've done the first step in the troubleshooting procedure, you have to do the second step to narrow the problem to a few parts, other than that all the answer the member of this forum will give you , might cause SSS, unless you're lucky, for me this is equal at throwing parts at troubleshooting and this could be realy expensive and frustrating.

The second step is the following:

You will need 3 tools to narrow your problem to few parts.

1- A Cd or paper shop manual of your car
2- A multimeter able to read duty-cycle and mA
3- A pulse code reader ( if your car is equiped with a diagnostic socket)

These 3 tools are not expensive, Cd could be bought online from Ebay for under 20$, multimeter from Sears online model #82139, 29.99 and the pulse code reader could be built according to the Arthur Dalton design or you may use a test lamp.

When you get the tools and ready for the second step let me know.

Max

same problem!
 

Hi tpros,
i think we have the same damn problem!! have you also noted that when your car is first started in the morning the power is there until the car warms up?!
here is a youtube vid of my 500 'pulsing' at constant speed...i cant believe 2000views and no one knows the exact problem
http://au.youtube.com/watch?v=eiwKaI5Y1eE&feature=channel_page
if you find a proper fix, please let me know
nathan

88 SEL Stalling
 

I had a similar prob. (used own a 88 126). It turned out to be the fuel management computer.

I also have a 1988 300SEL (with 156k miles). Mine has never stalled until today. I pulled into a drive-thru for lunch and was waiting my turn. I had been stopped for like 20 seconds, car was running smooth and I looked down and the warning lights were on, the car had simply and smoothly stalled. I didnt even notice it had stalled until I saw the warning lights on where the engine had stopped. It started right back again, ran smoothly and never stalled again, but I am wondering if this is a sign of future and more often stalling to come? :rolleyes:

Like I really need another problem... my Lexus is already doing enough of that (overdue for costly maintainence - valve cover gaskets, mounts and now the PS pump is leaking on the Lexus), I dont need the Mercedes to start causing problems too. :o

I had a stalling issue on my old W126 ('85 380SE) and turns out it was leaking injectors. I sold that car though.

As a precaution clean out the pins on the fuel relay and OVP relay .mostly the harbringer of stall problems .i had to resolder the joints on mine when that happened.
mak
300se/90.w126

Where is the location of OVP relay on '88 300 SE?

Not sure, but I drove my car again yesterday (Thursday) without fanfare. I am sure whatever is causing it will rear its ugly head again.

The OVP, OverVoltage Protection, supplies power to the ABS computer, between the two firewalls, and the ECU inside the car. Check the fuse(s) on the red topped relay on the drivers side between the two firewalls. Take it out, open the case and relsoder the connections. It's purpose it to protect the two compters from reversed battery jumper cables. There is a zener diode inside to blow the fuse(s) over 22 volts.

There are two more relays towards the middle, one the the AC controller, called the KLIMA, and the next one is the fuel pump relay. Take the FPR out, open it and resolder the large relay pins on the back side of the PC board.

The fuel pump is before the rear axle on the passenger side. Check the wire connections at the pump. Look for leaks as well. The pump is packaged with the filter and the accumulator as well.

Curses. I spoke too soon. I drove my car (88' 300) car today on an errand and it stalled on my 3 times! First time when I pulled into a shopping center, it stalled just as I was stopping. Then when I got almost home and made a turn onto my road, it stalled again and less than a mile later when pulling into my driveway, as coming to a stop, it stalled again! Funny this issue cropped up so suddenly. Unlike the symptoms of tpros car, my car runs smooth otherwise and starts back instantly without having to depress the accelerator. All of the old and bad memories of my old 1985 380SE (that also did this exact same thing) is coming back! :(

Guess it will go into the shop next week and see how much of my savings account it can drain. :rolleyes:

Check out the idle air hoses. They get loose at the ends and start sucking in air.

Had the same problem with my car, thought it was OVP. Started out intermittent and infrequent, but slowly got worse and worse. Like you, it would always stall as I was coming to a stop - when the engine is transitioning from a running mixture to idle.

Eventually, the idle got really rough and it was obvious something was very wrong, but that was 6 months from the start of symptoms.

Good luck.

I think like me, you will find a vacuum leak somewhere under your hood if you poke around. Listen carefully under there with the motor running. You might hear hissing.