08/27/2020
Pastor brings 1986 420SEL to me in running order, smooth idle, great power.
- New plugs ( incorrect Bosch Resistors)
- Valve Cover Gasket replaced
No more valve cover leaks, but after a few miles the engine shakes violently at idle, no loss of power or hard start yet….
09/15/2020
- Pastor brings 420 to back, rough idle, engine shakes, neighbor installed cheap rotor and distributor cap
- I replace spark plugs again (unknowing that the 420 has resistor wires from factory and needs resistor less plugs) rough idle consists, no change
- Oil Light and check engine light on…. Oil level and pressure is great, I assume faulty sensor but negligible considering performance and no leak, still running strong both in city and highway.
10/15/2020
- 420 becomes increasingly worse following one can of BGK44, Rough idle is worse, loss of power, hard start now, Engine finally stops running Will start but dies within seconds, very very carbon fouled on all plugs, strong smell of fuel from exhaust, running rich!!
- I get the 420 back, this time we do full system back, both pumps, filter, accumulator
- This time we do the correct BP5ES Resistor less plugs, verify good spark, still no start
12/30/2020
- Begin diagnosing fuel leak, pressure is good to the Distributor, EHA valve leaking, lots of fuel in the AFM housing and all my brand new spark plugs are Carbon Fouled, likely from cranking for so long?
- Distributor rebuilt, internals were toast…. New EHA valve, injector seals and housing, injectors soaked and ultrasonically cleaned.
- 420 starts again, rough idle and have to floor it to keep it alive but it runs, once warmed up it will drive around the block but still smells extremely rich and low power under acceleration, once warmed up, excellent power and take off.
- Clean and check function of Coldstart valve, works well, suddenly temp gauge doesn’t work? No broken wires, connections are good… great more problems
Current date
- Vacuum check last night, my economy gauge pins left during operation, but why the hell not, identify big leak on AFM housing, but I don’t have high idle and I’m running rich? No adjustments to A/F on my behalf but tamper ball is missing.
- *Rotor arm has left the building…* cheap Italian part looks like, ordered MB OEM arm and Ignition coil ($20 why the hell not)


My next steps…..
- Replace Distributor rotor
- Replace ignition coil
- Get my good spark back again
- Clogged cat or O2?
- Get it running rough again, verify Duty Cycle and make adjustments to A/F ratio with new and rebuilt parts?

I just went through this with my 560. Who rebuilt the fuel distributor? If it wasn't CIS flowtech, it needs to go to them. Was the new EHA valve adjusted at all?

Cleaning injectors is an exercise in futility on these cars. Hit the trash with them and get new ones. The cheaper steel ones work just fine, they don't have to be the expensive all-brass ones.

New O2 sensor will be required at this point. After being that rich for that long, it's dead Jim.

Only after fixing the fuel distributor, replacing the injectors (don't waste your time cleaning), and replacing the O2 sensor should you go after adjusting the A/F ratio.
An excellent writeup: https://www.landiss.com/mixture.htm

You've introduced a considerable number of variables into the equation here by throwing parts at this car and done yourself a huge disservice. You need to take a step back, go in with a calm and focused approach, and fix what's wrong.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Check for vacuum leaks. The best way is to do a smoke test. If the rubber vacuum lines haven't been replaced yet they need to.

Check the resistance of plug wires with a multimeter.

Verify that the plug wires go to correct cylinders.

The hex socket adjuster thru the air filter cover. very small adjustments, take notes. Use masking tape to mark your starting position. Forget any dweeb that tells you not to monkey with it. This is the fuel air ratio adjustment to die for. It holds open the plenum to the adjusted amount.


You must depress the spring and feel that you are engaged before twisting or you won't have a clue how much you are adjusting.

Are you familiar with this or do I need to dig up diagrams?