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· Registered
1979 280SL 1982 500SEL 1991 420SEL
3 Posts
Discussion Starter · #1 ·
First of all, I would like to thank everyone here for the wealth of information on this board.
My son acquired a 91 420SEL a month ago and we have already dug farther into it than I ever expected, armed with knowledge gained here.

I have a few questions:

1) This is a California vehicle, it has the X29 plug with the LED and the switch. In order to interrogate SRS and AirCon, do you still need the switch and LED tool, or do you just jumper pins 1 and 6 or 7 and read the code off the existing LED?

2) Is it advisable to change the duty cycle to 70% as opposed to Cali's 85%, or are there other factors to consider ?

3) When looking aft into the lower intake manifold, the EGR injection tube is plugged solid with carbon. I elected not to disturb this plug, as I am not removing the entire manifold at this time in order to remove the tube and flush it out. Should I remove and plug the vacuum line going to the EGR valve in order to prevent it from actuating, or will this trigger another fault ?

4) We have replaced cap, rotor, wires, plugs, timing chain, sliders, tc tensioner, injectors, injector bases and caps, most rubber parts and cleaned everything down to the throttle plate. The engine still idles just a little rough. Any suggestions ?

· Registered
'91 560SEC, '91 300SE (sold), '98 Yota, '02 S-10 Hauler, 1961 Albright Cabin Cruiser
9,569 Posts
Welcome to The Machine Hector, glad that you've already used some of the info here :wink

Be glad you have the LED fault code reader installed (California cars only from my understanding), no I don't think you'll need any other equipment nor pin jumping (I'm going from memory here of a car I sold over 2 years ago so you might need to research a little more but . . .) have the ignition on with engine NOT running, push the button next to LED for 2-3 seconds and release, count the flashes. There is a fault code chart (make sure you get the correct one) that will give you an idea of what caused the Check Engine Light (CEL). Push and hold the button again for about 8-10 seconds to delete that code, it'll have a long flash to verify. It will also hold multiple codes (if more than one fault) just push the button again for 2-3 seconds to read them. Again, this is from memory and I usually only had an O2 fault and just erased it.

I don't know about changing the duty cycle, I read something the other day and can't find it now, look up posts by member "HG" I think it was, he did an indepth write up on how these fuel distributors work and any adjustments, if needed, to do to them

In the EGR, I would try running some fuel system cleaner in a few tanks of gas to see if that would unstop it, I run a can of SeaFoam every few tanks to keep mine cleaned out (entire system, fuel, EGR, and where ever else gunk might collect)
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