1993 300SL 107k miles, engine stalls out

[Benz Mondi]

I've done a search on the topic but thought that mine might be a little different. I'm hoping to narrow the possible cause or causes so that, if I can't fix it, at least my mechanic won't have to spend too much time looking for the cause. I thought I had the problem licked last month when I found a leaking EHA and replaced it.

Symptoms: From a cold start, starts right up, idles smoothly, but stumbles if the rpm's go above 2,000 or when in gear, then ultimately dies out completely. Difficult to start afterward. Wiring harness previously inspected and found to be in good condition and not in need of a replacement. Usual humming sound coming from fuel pump area after turning key, then not audible after engine is running.

Fixes so far: replaced EHA, ignition coil, idle control valve, fuel pressure regulator, battery fully charged, new dist cap and rotor, 1/2 tank of gas.

Next step planned: replace accumulator and fuel filter, then replace both fuel pumps (107K miles on them).

Any advice on what else to check?

Thanx,

Al

[tecqboy]

Check Crankshaft position sensor. Check the EGR valve for stuck or partial operation. Does your vehicle have a charcoal evap filter?

[Benz Mondi]

Originally Posted by tecqboy

Check Crankshaft position sensor. Check the EGR valve for stuck or partial operation. Does your vehicle have a charcoal evap filter?

Started it up (idled smoothly) and did a seafoam treatment after it was up to operating temp to see if the de-carbonizing would help. It seemed to help some. It idled smoothly, even at 2500 rmps, but stalled out when I put it in gear.

Replaced the EGR, idled smoothly much longer than it has since the trouble started. Stalled out when I put it in gear. Two attempts at starting and called it a day. I'm starting to think that it might be an injector issue since it's so difficult to re-start (too rich?).

I'm not familiar with how the Crank Shaft Position sensor works. If it's not functioning properly, why would it cause my symptoms (stalls under load)?

In the morning, while it's still cold, I'll put it in gear and see if stalls. In this way, I'll confirm if it stalls when only warm or not.

Thanx,

Al

[TylerH860]

I'll second crank sensor... They can cause a number of symptoms, and are not expensive/easy to change.

Mine would quit working and stall out the car when the motor started heating up.

[Genbiltstein]

That mechanic if he is worth his salt will be able to tell you the condition of the fuel pump, Fuel pressure regulator and anything else through testing through PSI.
If I were you I would be looking somewhere along temperature related.
there is a computer that regulates fuel duration during start up. If the fuel pressure is normal than I would be looking at a signal that the computer is supposed to receive concerning engine temp, air temp. that's my guess.
Intake air temperature sensor, coolant temperature sensor to name a few.

[Genbiltstein]

but stumbles if the rpm's go above 2,000 or when in gear

If it stumbles in the higher RPMs You could have fuel restriction or a lack of adequate fuel pressure to the injectors.
If the computer doesn't receive the proper RPM signal than you might not be receiving the correct amount of fuel for that rpm.

[RadioTek]

Cheap, easy test:

Check to see if you have the problem when the gas cap is removed. You may have a bad gas cap, or an obstructon in the excess fuel return system, causing a 'vacuum ' in the tank, not letting you develop enough fuel pressure.

Just a wild guess.

[Benz Mondi]

Originally Posted by TylerH860

I'll second crank sensor... They can cause a number of symptoms, and are not expensive/easy to change.

Mine would quit working and stall out the car when the motor started heating up.

Tyler, I'll try to tackle this one and if it doesn't fix it, it'll be one less thing my mechanic will have to worry about. With 107K, it's bound to need to be changed anyway. I've done a search and found that it's on the rear of the motor on the bell housing of the trans.

I've ordered the reapir manual, but it hasn't arrived yet.

How do I go about changing it?
Access is from underneath the car?
The sensor itself is a screw-in or is it a "squeeze the sides and pull off"?
To help locate the wire at the Ignition Control Unit, which plug is it attached to?

Thanx,

Al

[Genbiltstein]

Also take good note that the MAP (manifold absolute pressure sensor) functions in a manner to let the computer you need more fuel. If you are going 2000 rpms and you are stumbling then the computer is not sending more fuel to the injectors. Demand is not met.
Can you imagine that MAP sensors are still around? Refined but still with us.
The higher the engine revs the lower the vacuum. The vacuum is turned into an electrical signal that is fed into the computer.

[Benz Mondi]

OK. Went out this afternoon and started up the car for the first time of the day (cold). It started on the first crank as it has always done. I waited a few minutes, as though I was getting ready to drive to work, and then shifted into Reverse and then into Drive and proceeded to slowly drive up my driveway a little waiting for it to start stumbling. It never did. I let it idle for a few more minutes, turned on the defroster to put additional load on the system and then put it into Drive again. Again no hesitation. I let it idle for some 15 minutes until it got to operating temp (80 Celcius) and performed the same load tests. This time I detected a very slight stumble that grew worse as I repeated moving up the driveway, putting it in Neutral and rolling back down the drive a few feet and then putting it in Drive to move forward again. Before it completely stalled out. I turned the car off. I unscrewed the gas cap which released pressure (seemed like normal pressure) and was able to re-start the car, though with some effort. Leaving the gas cap off seemed to have no effect.

So it seems that my issue is Heat related.

Any info on the way to replace the Crank Position Sensor would be appreciated.

As I've noted above, I've replaced the most common source of heat related issues. What else could be heat related?

Thanx for all the info so far.

Al

[TylerH860]

I knew it was the crank sensor after pouring cold water on it after it had stalled and the car fired right up.

Here is my post on the subject.

Just bought something...

Only one bolt holds it secure, if I recall correctly, and of course the electrical connection needs to be unplugged. Slides right out and back in. One of the easiest jobs I've ever done.

[Benz Mondi]

Originally Posted by TylerH860

I knew it was the crank sensor after pouring cold water on it after it had stalled and the car fired right up.

Here is my post on the subject.

Just bought something...

Only one bolt holds it secure, if I recall correctly, and of course the electrical connection needs to be unplugged. Slides right out and back in. One of the easiest jobs I've ever done.

Tyler,

You're killing me man. Thanks for the info and the reassurance that it only takes 15 mins, but how did you change it?
From the top?
You reached down between what?
Could you see the sensor or did you feel for it to unscrew it?
Looking at the top of the engine from the driver's side, is it above, below, to right of the starter?

I can't seem to see it, even with the air cleaner off and a work light.

Thanks again,

Al

[Benz Mondi]

OK I found this our of my 300E info (seems to be the same for the 300SL).

I've also found that the plug into th EZL unit (ignition control unit) helps me identify which one is the crank position sensor wire (per the ebay listing pic's for the crank sensor and EZL, it's the only one with a one wire plug-in). Knowing this, I'll be able to trace the wire back to the where the sensor is mounted on the bell housing.

I'll know more in the a.m.

I'll report my findings and hopefully, fix!

Al

[TylerH860]

Once I had the part it just seemed obvious. With mine it was on the back driver's side of the engine protected by a shroud. Inside the shroud was the top of the crank sensor, with one bolt holding it in.

and yes from the top.

[Benz Mondi]

Of all the things... after finally locating the Crankshaft Position Sensor (see pic attached, I have a long red screw driver pointing down at the bolt between the oil filter and the vac lines), what drew my eye was the allen head... visually, it's just below the oil pressure sending unit), I went to losen the 5mm allen bolt so that I could inspect the sensor. I found the bolt very loose, and wondered if that might have been the problem. I went ahead and withdrew the sensor and cleaned the tip. Mostly because I found that the wire arrived at the Ignition Control Unit from under the intake manifold (it seemed like it was going to be a PITA to get it out), I just went ahead and put the sensor back in, added a small amount of BLUE locktite to the bolt and reinstalled the bolt.

It worked! When the car heated up, it must have expaned the losened sensor gap enough to give faulty reading to the ICU.

Here's what I've learned:

Isolate the variables-
1. Is there spark?
2. Does it get gas? (listen for the fuel pump to turn on and then turn off, losen the gas cap to listen for the pressure releasing).
3. Does it happen when it's cold or when it's at operating temperature?
4. Does it happen when it's under load (in gear and with the A/C on)?
5. Check the easy things: dist cap, rotor, crank position sensor.

Good Luck with yours!