Poor Idle Quality, Cuts out, Misfire
 

All-
I could use some expert input/adviseideas. The following is from
my mechanic describing the problem condition and test
and diagnostic info. Any help would be much appreciated.

thanks!

-andy






1992 Mercedes-Benz 500SL

Engine: 5.0 L / 8 cyl / Gas / DOHC
Fuel: Fuel Injection / CIS Fuel Injection
Ignition: Distributor-Breakerless / Dual Distributors W/2 coils
Trans: 4-speed Automatic Transmission
Mileage: 94,000 miles
Emissions: OBD1
VIN: WDBFA66E8N

Misc Data: 500sl
Symptoms: Poor Idle Quality, Cuts out, Misfire
Occurs: After a Hot Soak
More Info: Test results & repair history included below

____________________________________________________________

The vehicle will start and run fine. After running for 30
minutes or more in hot weather..over 75 degrees.. if the
engine is shut off and sits for 10 minutes, it will restart
fine but has a bad missfire nit seems like on one cylinder
but sometimes seems like multiple cylinders. The missfire
is very easily noticed at stop when reving up the engine
and can also be easily felt when driving the car. It will
continue to miss even after hard accellerating for up to 2
minutes. Then it will smooth out and be fine for the
duration of the drive. This situation will repeat itself
always after a 10 minute HOT SOAK after driving in hot
weather. The coils and injectors and wires etc. have all
been tested. I cannot see the missfire on the scope. No
codes set during the short misfire period. What can be
happening during this period when the engine compartment is
so hot with no air moving that corrects itself after 2
minutes of driving???


___________________ TEST AND REPAIR DATA ___________________

Checked for codes and none were found.

TESTING AND RESULTS

fuel pressure - ok
coil output - good

RELATED REPAIR HISTORY

New O2 sensor. New spark plugs. 1 new injector #5. New
hydraulic pressure regulator..was leaking. Wires 7k old.

Start by using some BG 44k fuel system and injector cleaner. Best to do the whole intake cleaning procedure at a shop that handles BG products. Call around.

We charge $130 for this service.

thanks but already used BG 44k fuel system and injector cleaner a few months ago.
I appreciate the suggestion.

Andy, if you have access to another set of good coils I'd install them and see if the problem persists.

Crank Position Sensor is common heat soak complaint ..

mechanic replaced both caps, rotors, seals, and crank sensor..problem remains...

Update:

My indy replaced 8 plugs, both caps & rotors, wires, both coils,
all 8 injectors and three days trying to isolate/correct the problem but no luck-
he is referring me to Mercedes. We're both frustrated and disappointed.

Mechanic is excellent and a great guy, no charge for time and parts-
all returned back to stock.

I could really use some expert advise.

thanks in advance!

-andy

Right after the condition exist, I would go into the modules and get the codes .
A simple LED tool works on that chassis [ 129.066]