Hi all, newbie here. Hope somebody can help me cause i'm lost. I have a 1988 420 sel that had a very bad hesitation right off idle. I replaced the fuel filter and air mass meter and the hesitation is now gone. However, it's flooding out something terrible at idle now. Any help would be greatly appreciated.

Exactly what part are you referring to as the air mass meter? The fuel distributor?

Have you checked the fuel pressure and the differential pressure in the fuel distributor? They can go bad from corrosion in the diaphram between the upper and lower halves, causes the engine to run way rich.

Did you re-set the fuel mixture?

More details, please!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

The air mass meter is the part the fuel distibutor is attached to. It's like the upper half of the intake. The actual meter is mounted on the right side of it but you have to buy the whole part. As far as resetting the fuel mixture, I dont know how to do that. If it is the fuel distributor can you repair them or do you just have to replace them?

You need to reset the mixture, I'm sure -- you have to adjust the flow sensor when replacing it if you don't replace the fuel distributor.

You will need to set the flap of the flow sensor to sit just very slightly below the venturi at idle, then adjust the mixture screw (3mm allen through the small hole between the venturi and the fuel distributor.

EHA needs to be plugged in (back side of the fuel distributor) and you need to check the fuel pressure, too, although unless the fuel distribultor went south while you were working on it, it should be fine.

Pin #3 of the diagnostics connector (round plug with a screw cover) has the duty cycle, get a digital voltmeter with duty cycle function, connect the red lead to #3 and the black lead to #2, set the mixture screw slowly, waiting 20 sec or more between changes, to get 50% or so on the duty cycle.

You need to engage the 3mm allen in the socket, then press down to engage the actual adjuster. Don't push down very hard, it goes rich when you do.

If the duty cycle won't change no matter what you set the mixture screw, something else is wrong.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

ok I'll try that tonight and let you know how it works. Thank you very much.

Thanks bud, you da man. I guess if we're going to own this car I better find a manual for it. I'm almost ashamed to admit I'm a tech at a GM dealership! lol These Mecerdes are a whole new ballgame for me. Anyway, got the idle set and it runs like a top now.Thanks a bunch.