stalling 560SEL - PeachParts Mercedes-Benz Forum

biobenz617 · #1 07-23-2007, 01:39 PM

I have a 1990 560SEL that has an issue with stalling at idle. It only happens when the engine bay is up to operating temp and the car is restarted after a short stop. It starts and then within seconds dies. A little cranking gets her running again and no problems follow on the road.

Could this be the idle air valve sticking? The last time this happened, I pressed the pedal down 1/2 way to bypass the idle air valve and cranked, but still took a few seconds to start so I'm wondering if it is fuel related instead.

It has a somewhat rough idle with 250k on the clock (power balance test showed one or two cylinders a little low), but all maintenance has been done including timing chain/tensioners/guides/cam sprockets, except valve job. Runs about 80-90C.

Thanks,

just-n-time · #2 07-23-2007, 05:35 PM

do a search for EHA and potentiometer this might help.

biobenz617 · #3 07-25-2007, 11:06 PM

I'll check that, thanks. On that subject...

How wide of control range does the EHA have on this system? Just wondering what would happen if the CIS-E control computer or a portion of the control system malfunctioned far from home (i.e. same condition as unplugging the EHA valve). Would I be able to drive the car home normally? It seems as though the fuel distributor should still be able to meter fuel to some degree on its own mechanically, just without all the fuel trim influences such as altitude, lambda, etc.

saumil · #4 07-26-2007, 02:21 AM

Are you equipped to check some electrical parameters (voltage, current, resistance) ?

Check coolant temp sensor. If this car's temp sensor is like my 87, 260E, then when the engine is cold, you should get between 2.5 and 3.5K resistance acorss the sensor terminals. When the engine is at 80 degC, the resistance should drop to between 250 and 350 ohms.

EHA and idle control valve have been mentioned previously. Though EHA is less of a factor once the car has started and idling.

Another item is the OVP relay, when did you last check/replace it ? It supplies voltage to the idle control valve.

zcc · #5 07-26-2007, 02:05 PM

Could be the fuel pump relay.

TX76513 · #6 07-26-2007, 02:55 PM

Do you have the FSM? If yes look at the idle stabilization diagnostics. Specificaly diagram Y6 Idle speed air valve.

gmercoleza · #7 07-26-2007, 03:45 PM

Different car, but my E320 behaved the same way when it was hot and you attempted to restart it after sitting for a few minutes. Turned out to be the fuel pressure regulator - I guess the pressure leaked down over time with the car sitting, probably resulting in a somewhat lean mixture. Issue was likely masked when cold, since the mixture on cold startup is enriched.

biobenz617 · #8 07-26-2007, 11:31 PM

Quote:

Originally Posted by gmercoleza

Different car, but my E320 behaved the same way when it was hot and you attempted to restart it after sitting for a few minutes. Turned out to be the fuel pressure regulator - I guess the pressure leaked down over time with the car sitting, probably resulting in a somewhat lean mixture. Issue was likely masked when cold, since the mixture on cold startup is enriched.

That sounds likely. I haven't driven it since Monday because I'm waiting for a new blower motor to arrive to fix my HVAC. When I was verifying the blower motor was bad on Tuesday I turned the ign. key to RUN without starting and noticed that the fuel pumps ran for about 10 seconds before stopping. This was strange since they usually only run for about 1-2 sec under that condition from previous experience, so maybe the system leaked down during the day on Tuesday...possibly from a faulty regulator (or accumulator??). If that's the case, it still leaves me scratching my head why it starts and runs for a few seconds before stalling.

I'll check electrical values when I get a chance. Thanks for all the input!

This car has had problems with the idle air valve before (stalling while driving in traffic, specifically during left turns at stop lights

) but that was fixed by a shop about a year ago by cleaning the valve. The car still takes a few seconds before restarting with my foot at 50% anyway, so I ruled out the idle speed control system. Speaking about the idle valve...another tangent...is it possible to replace the wiring harness for the idle air valve and temp sensor? The insulation has cracked off at the connections of these instruments but does not touch anything or short out. I was planning on replacing those wires soon, but it seems they are just a small twig on the monstrous tree of a wiring harness and impossible to replace from end-to-end.