84 500 air sensor plate adj - Page 2 - PeachParts Mercedes-Benz Forum

dloveless · #16 03-29-2004, 09:49 AM

Had some time this weekend and kept getting erratic running / idle/ start. Would be fine for awhile then different. I think I found the majority of the problem in loose Idle Control Module plug fittings. They did not look bad but with the ICM dismounted but plugged in and engine running the rpms would change significantly just by moving box around. Looked at this previously many times but did not look bad and continuity always tested good. The back of the plug comes off with prying screwdriver but when you do that the wires are loose so kept my thumb on them while writing down the color code and position. Further inspection revealed spread sockets on most of them and somewhat grungy. gently squeezed the sockets back together with a small needle nose and cleaning with connector cleaner-[ did not want to replace as it would be soldering and that plug does not come out from between the firewalls- helps if you use three hands- take the hood off and hang suspended in midair above the back of the engine compartment. An engine crane/hoist hooked to the back of your belt works well for this but you will need the remote control model unless you have a helper. A further side note here: don't ever drop the remote unless you have close neighbors that can hear you or you have your cell phone with you.]

Seriously, the plug sockets were spread enough and/or grungy enough to make a big difference. After reconditioning the plug sockets at least I'm always the same now. I'm understanding more clearly now the concepts written by Steve. I don't know why this is so hard to understand but it is. I think I still have an ICM issue but it is running much, much better. I even drove it to church yesterday.

Right now have idle around 1000. otherwise runs well. But will take Steve's words to heart and try the EHA current. When I try the lambda - using sockets 2 and 3 on the diagnostic socket- drivers inside fender- I am using a dwell meter- it goes to 30% and stays. revving to 1500-2500 it will change to 25% over several seconds. My DMM does not have % on it. Should I just get a DMM with % on it? Is lambda, eha current and duty cycle all discussing the same procedure?

Again, thank you.

stevebfl · #17 03-29-2004, 06:16 PM

The values on pin #3 are for a duty cycle of a pulsed input. It is related to control but actual control is done by the eHA current. That is why I like to view control there as it is the bottom line.

If you are idling at 1000rpms or more you are stiil not in control of the air volume at idle. You are either not closing the valve enough or you are leaking air somewhere unaccounted for. One way of telling is to pull the idle valve and shove a cork in either of the hose connections with a 4-5mm hole in it. This is about the amount of air that runs through at idle.

Untill you have the idle air straightened out I wouldn't worry about the mixture. Set it by ear to the best running (highest speed). If its is in control the idle speed will not change only the smoothness will.

dloveless · #18 03-29-2004, 07:08 PM

does a 1984 model year 500 SEL have an EHA ?

stevebfl · #19 03-29-2004, 07:34 PM

Ooops!

No EHA on pre 1986 v8s. You will in this case need to view the duty cycle of the frequency valve. This is the same as pin#3.

dloveless · #20 04-13-2004, 04:55 PM

new fuel injectors... don't ask me why I thought I did not have to replace them when I had the heads all off and apart... hey they "looked OK". I feel like an idiot but am really happy with how it is running now. Lots of new parts I bought that I probably did not have to. The digital multimeter with the duty cycle [%] on it was helpful in getting the air/fuel mixture corrected after all my monkeying around with it prior to the new injectors. My year and motor is DMM red probe in #3 in the analysis plug and black probe grounded because 1984 still has the frequency valve instead of the newer models' EHA.

Thanks everyone !!