nubby

hi i have the 4 pin style tempature sensor which i believe is the one for the cold start icv etc but the question i have is that there is no index on the sensor the round plug can plug into the sensor in any direction which seems odd since i have 4 volts on one of the pins of the plug if anyone knows anything about this please let me know
thanks

its a 1991 300e

hineywineries

The 4 pin temp sensor is actually two identical sensors wired across from each other. The plug can go either way. Ohming the pins diagnally should show the same resistance.

nubby

thanks do you know what the resistance should read as i am having cold start problems and no power at icv i have changed icv cold start injector overload relay and now i am waiting for the mas relay i have not bought the sensor for the simple fact that the place i was looking has it for 2 different engine series and i dont know which i have or how to find out these are my options 10-016764- and a 12-082792-
thanks
fred

hineywineries

Fred,
Since it is a 91, it would be the 12- which means left hand drive and automatic if you live in the U.S. If you live somewhere else, it could be 10- which means left hand drive and stick shift. I'm at home right now so I don't have any manuals here. I'll try to remember to look up th resistance chart tomorrow.
Peter

nubby

thanks alot at least i know what to buy now i just got the mas relay tonight i put it in no change still no power to the idle control and cold starts are the same sometimes i have to try 5 to 6 times to start it in the mornings then it runs rough and smooths out once it warms up then runs perfect its making me crazy lol
thanks
fred

hineywineries

It sounds to me that the EHA isn't getting the signal to adjust pressure in the lower chamber to richen the mixture when cold. If this were a carburetor, the choke is not closing to the pre throttle gap position. It is difficult to explain EHA control current. The test procedure is laid out in the Mercedes diadnostic manual if you can get your hands on one.
Peter

nubby

well i checked my eha current nothing there seems i have no electronic control whatsoever i guess this means the engine is running open loop i would not have noticed the performance loss as it has been this way since purchase could it be a bad 02 sensor causing this open loop mode or a bad ecu also noticed the check engine light is on someone pulled the bulb is it possible to jump the 02 sensor lines with a resistor to make it go into closed loop just for test purpose
thanks
fred

hineywineries

When I was an electronics tech, we were tought to be sure the test equip is working. If you get no current readings, check the fuse in your DVM. They are usually blown. Also buy or borrow a top quality DVM. I use a Fluke. They cost over $300, but they are worth it. Diagnosing with a cheap meter is like trying to jump start a diesel with a set of $9.99 cables from Slam Auto.

You can't put a resistor across an o2 sensor, because they generate a voltage. You can check the voltage output with a good meter and read somethig between .1 and .9 volts.

Now you tell me the CEL is on. I'm assuming this is a 49 state car which means you will need to get a CHEAP scanner to pull the codes. Yes, I said cheap. You can get away with it here. You can pull the codes for the ECU from pin #3 at the plug by the battery, but to pull codes from the MAS unit, you will need to back probe pin #16 on the MAS unit. I'm assuming your car has a MAS unit and not a fuel pump relay. 91 was a cross over year.
Peter

nubby

hi yes it does have a mas instead of a fuel pump relay i already replaced that along with the icv and the ovp relay plugs wires cap rotor i am pretty familiar with volt meters it is not a fluke im using a mac tools meter but i think its made by fluke anyways i will try another one and see what i get i rember there was a way to get the codes with and led and a switch ill have to see what i can get out of it if anything as of now it seems like nothing electronic in the engine area has any power accept 4 volts on one of the 4 pin temp sensor lines
thanks
fred

nubby

well i just checked the eha again with another meter i still get no current and on the volt setting i get .004 off the line to the eha if i unplug eha while running or starting it makes no change whatsoever the only thing in the whole engin bay that seems to do anything is on the front of the plate housing i dont know what it is it seems maybe to be the potentiometer it has three pins when i pull it the idle climbs to about 1500 other then that ive unpluged almost everything in there and nothing seems to happen i think i might be beating a dead horse at this point unless you have any other suggestions
thanks
fred

hineywineries

Fred,
Been there done that. Just because you tried a second meter doesn't mean the fuse is good on that one either. You need to determine that you can measure a current on your meter. Yes, the Mac meter is probably a good meter. The U.S. Navy sent me to a solid year of electronics school for 8 hours a day. Trust me I know these things. I see you are willing to listen which is why I will continue to assist you as best I can. Did I mention that I've been a factory trained MB mechanic for 30 years?

Unplugging the EHA probably won't change much at idle, because its purpose is to trim fuel under driving conditions. You need to pull codes and find the source of the codes. You need to determine if the CEL condition is being generated by the ECU or the MAS. Remember you can't pull codrs from the MAS at the box by the battery. You will need to back probe pin #16 at the MAS.
Peter

nubby

thanks i really appreciate the help i will open one of the meters tomorrow and check the fuse i also found a small schematic to make the led code reader so maybe i can get you some codes tomorrow night i see now why they call you mb techs bechause i can do anything with a chevy or ford dodge etc i love this german car since i bought it but its a whole new world lol
thanks
fred

nubby

i have tried again wih reading the eha wit no success i have built an led code reader i have read pin 14 of the 16 pin connector near the batery and i got a code 11 and a code 12 i have read also somewhere to read pin 8 but the is not even a wire on pin 8 i also tried to read pin 3 and i get constant led and idle control valve opens and idle climbs when i push the button
thanks
fred

nubby

for anyone following this thread i still have not got the car 100% on cold start but it only takes 2 trys now at 35 degrees rather then 15 trys
what i did was give the eha adjustment about 1 turn clockwise it drives like a different car much more power all this time i just thought these cars were dogs i am amazed at what a difference this made feels like 50 60 more horsepower although i still have the codes so once i take care of those maybe it will all be ok then