jay-h

My wife's 107 (560SL) is running pretty well, however recently it will OCCASIONALLY stumble/stall typically when making a sharp turn (talking city blocks, not high speed cornering). when it does stall it can be restarted without issue.

My first guess is maybe fuel filter.

Anything to point me in the right direction will be helpful.

billygoat33

Full tank of gas or partial?

jay-h

At this time it's a good solid 1/2 tank

jay-h

Back to this issue. The unexpected stalling was not specifically related to making turns, but would happen when letting up on the gas.

Frequently idles and drives fine. It will restart easily cold or hot. If the stalling occurs when stationary, it surges up and down (about 1/2 second cycles) and then stalls.

I've been checking all sorts of things (but I'm very cautions about changing anything that I don't fully understand)

I checked the duty cycle (pins 2-3 on the diagnostic plug) and read a duty of about 25%/75% OFF/ON, where it's supposed to be about 50% and a quick check with a scope shows a clean square wave. What am I actually reading at that port. What is that signal actually doing.

95_993

Have you tried checking the throttle control solenoid?

jay-h

I did swap out the idle control valve, however I know that was not the real issue because when this occurs it stumbles badly at all throttle positions.

Anyhow I just received the Bosch fuel pressure /callibration tool and will start setting things up from scratch.

jay-h

here we go, more details.

I got the pressure test set (connections to coldstart and test port with shutoff valve and gage).

When I first started the car to warm it, it idled ok for a while but started surging... low almost stall, then quite high then low again

anyhow i disconnected the electrical line to the EHA (surprisingly it seemed to run smoother, but that might be just coincidence) and ran the test as outlined by Pierre Hedary on youtube. The weird thing is I got the SAME pressure (6.7 bar) regardless of the position of the selector valve, and the engine insisted on running fast. Is this telling me that the EHA is bad?

4/1/22 Correction: Checked the pressure readings again, and got 6.7/6.3 bar. That seems right. So it's probably not the EHA

jay-h

Still messing with this problem, done studying and some testing.
Fuel pressure and differential is good (6.7/6.3 bar)
Idle control valve has been swapped with no real chang.
resoldered the OVP (old 5 pin type, hard to find). That seems to have cleared up periodic ABS light
Throttle position switch is correct.
When idling it will abruptly chase up, or drop down. Signal to the idle valve keeps hovering in the 4.3/4.7 range which seems ok. I put a 'scope on the line also and there seems to be very consistent square wave... no erratic excursions. Since doing all this, when it idles, it's pretty good. steady a little over 500, accelerates without stumble -- until it decides to misbehave. If it stalls, it can be immediately restarted without issue...
the duty cycle is about right, though I've read (from someone who seems to actually know) not to attempt to set duty cycle until everything else is dead right.. Apparently people wind up making things worse by reckless duty cycle adjustments.


Any additional thoughts, or links to information are appreciated.

[this has been quite a learning experience.

jay-h

I'm finally posting this after spending a lot of time getting the car running right (and learning a lot about Bosch KE in the process), in case it will help others.

FIRST RULE of diagnosis: If it seems to make no sense, you are probably looking at multiple issues. In my case the fuel filter was a MESS, the rubber elbows at the Idle Air Controller were cracked, the OVP was erratic, and the electronic idle controller was intermittent.

Replaced filter and the rubber elbows.
Found broken spark plug connector on one wire, installed new set (as well as plugs)
Confirmed fuel pressure was correct (had to order the special connection hose set from Amazon)
Re-soldered corroded connections in the OVP (cured the ABS light issue)
Swapped out the Idle Air valve. Not sure it was bad or not, but now I have 2
Found out that the Idle Controller module would intermittently shut down. Wound up sending it to ProgRama in Florida. They refreshed it and now things are running well.

Bill Dormandy

Good for you! Great advice for all of us. I can add that for me ProgRama has been great to work with and never a problem with their rebuilds.

Rob350SL

Check voltage readings from the EHA and even though you cleaned up/re-soldered electrical connections....you did not mention ground points which are just as critical since it is the return path for current flow. You will be surprised how small things like this can have nice results.
Many "fuel issues" in FI can be traced to electrical problems.