'91 300CE (M104) - EHA measurement results - PeachParts Mercedes-Benz Forum

rgnprof · #1 08-26-2010, 03:28 PM

I have been fiddling with this car and the mixture for a while chasing 3 primary concerns - declining gas mileage, hesitation upon acceleration, and a hard warm start problem. I finally adjusted the mixture to 47% - 54% at idle (at 2500 rpm it is about 39% - 46%), and car definitely runs better, with no more warm start problem (not sure why this issue was resolved).

Received my EHA harness from Mercedes and went about testing the EHA current this afternoon with the following results: KOEO - 20 ma's, engine idling and warm, current fluctuates around 0 ma (from -1.2 ma to +.8 ma), and current at 2500 rpm fluctuates from +1.3 ma to +2.6 ma.

Does this sound right? Should my EHA current - and duty cycle % - change that much at 2500 rpm?

ryan

rgnprof · #2 08-29-2010, 08:16 PM

bump

Anyone help here? I'm still struggling with a poor gas mileage issue...
ryan

sptt · #3 09-03-2010, 12:40 AM

Well...I haven't done the measurement stuff with electronic equipment but I have manually adjusted and replaced everything in mine and after a year, it now idles like new and starts on the first crank (it's a 1991 with 185K now). I did the EHA adjustment and turned the screw 1/4 turn CW which helped my warm start issue but caused bogging down problems on acceleration and a strong gas smell coming from the engine area. I turned this adjustment back 1/8th of a turn (shouldn't have messed with it at all in the first place), put new copper plugs (1.99 from Autozone), lreplaced the air temp sensor, leaned up the air mixture, and replaced the fuel accumulator (which was causing the hard warm starts and long cranking issues in the first place). It has ran like a dream and getting 20-22 mpg last 3 tank fulls. If you haven't changed your O2 Sensor...do it! Noticed much better idling and power when I first did this. Then, I replaced the Water Temp sensor and more improvement. I put a new rotor in (nothing), new coil (nothing), spark plug wires (nothing). I also took off and cleaned the IAC Valve which wasn't as hard as some made it out to seem. I did find a cracked hose coming from the fuel distributor to the IACV. It was at the neck so I used a hose clamp on it to keep it sealed. This may have helped idle (don't know about mpg).

rgnprof · #4 09-11-2010, 11:22 AM

BUMP!

Can anyone confirm my EHA measurements in the first post? Thanks!

ryan

cheeseraid · #5 09-11-2010, 12:18 PM

Well I don't know about the twin can version (I'm at work tech docs at home) but my car didn't like the correct spec of 50 at idle and 2500 with the eha hovering around 0 mha fluctuating +-2ma. Its a 91 2.6. Mines at 40 at idle and 45 at 2500. Starts great runs great. Weird part is I lost the fluctuating on the eha after getting it running right. It stays at 0 now. I know its working though cause it goes to zero resistance. Ma is just voltage divided by resistance (if I remember right). Good luck.

david s poole · #6 09-11-2010, 01:41 PM

as far as i know those measurements are in the ballpark.you might check drag on the wheels from the brakes not fully releasing for the mpg issue.sometimes when there is a lip worn on the rotors it causes the edge of the brake pad to drag.

cheeseraid · #7 09-11-2010, 01:45 PM

I get around 24 MPG where the car is set at right now. How bad is yours? I think your setting are right. Its not going excessively rich so I'm thinking that's not causing it. I have found that these motors m103 and early m104 like it a bit rich at idle and little leaner on the top end. Mine will smack 6500 before I realize it. Sometimes she's a bit fussy and 2500 to 4000 will be a bit soft.

cheeseraid · #8 09-11-2010, 01:47 PM

Also check your wheel bearings. If they are too tight your mileage will drop.

rgnprof · #9 09-11-2010, 08:48 PM

Mileage is actually getting better after checking it for a coupe of tanks - but, I haven't had it on the highway lately. I was getting 24-25 on the highway and I'm assuming that's where you are getting 24 as well...I don't think this thing likes the short commute that I have to work each day - my city mileage was usually around 17-18 mpg, but had dropped to 14ish...

Just noticed that the IAT sensor was left unhooked from the air filter for the last 250 miles or so - still plugged in to the connector, but not connected to the air intake hose leading to the air filter. Don't know if that would make a difference or not...starting checking the resistance on the IAT per a previous post and my ohms don't match up - so I'm thinking I may have a bad IAT sensor anyway...Would this make much difference?

Brakes and bearings have not been checked - I need to do that!

ryan

sptt · #10 09-11-2010, 11:16 PM

If you have one of those on your car, it can definitely make a difference on what the computer is telling the air/fuel mixture to do. I replaced mine even though it looked good but voila, my idle sweetened up and so did the start and idle quality, Not sure what it does when you are under way though.

cheeseraid · #11 09-11-2010, 11:18 PM

I get 24 MPG if I drive like a grama or beat the hell out of it. City and highway are the same. With that unplugged your mileage might drop. Idk how that part works yet (it's taking 3 years to get to this point and mostly without forums), but from the many docs I've seen it controls timing on certain models and second it controls fuel enrichment metering to atmosphere temp. Don't know for sure but its a reverse metering gauge with the same values as the water temp sensor. I tried sticking mine outside the engine bay, attaching it to the AC drier but my MPG and power fell on its face. Its a possibility so maybe someone with more knowledge of the sensor will chime in. I actually hope they do cause I wanna run a solid value if possible. How old is your water temp sensor?