EHA mA readings?

[Philbask]

Hi forum.... as per an earlier post, I have been having bad hesitation issues (W124 230CE (M102.982)). Problem went away after disconnecting the EHA, so I have wired in a mA meter, results are mixed:

Ign on, pre start - +20 mA (seems ok)
Startup - (cold) start at > +20mA, slowly reducing as engine warms (seems ok)
Over-run - engine >1500 rpm, throttle to fully off -66 to -69 mA (fuel shut off, until rpm< 1300 then back to 0mA (seems ok)
Throttle fully open (or quick blip) fleeting +mA reading (enriching? seems ok)
General driving when warm, 0mA........ but, occasionally reading will slowly ramp down to -10mA without any change in running conditions. This is when the problem occurs, leaning out the mixture. This is more often when up to normal temp. Very occasionally the reading will ramp the other way to +10mA.

What device / condition would cause a steady and bang-on -10mA signal to the EHA? Far too repeatable to be connections etc.

Cheers,

 

[Philbask]

??? Now know that the constant ramp to either plus or minus 10mA is stopped and the ramp in mA restarted by either full throttle or zero throttle. If there is no particular set of circumstances that create an output of +/- 10mA am I looking at electronic component failure? I.e. Ecu failing?

Any help / advice much appreciated

 

[chrisd87]

Sorry I can't offer any help, but can I ask how you wired in your ammeter to the EHA? Did you use the Y-shaped Bosch test lead as depicted in the manuals, and if so, where did you get it from? If not, how did you manage to connect the meter with the EHA still connected? I'd quite like to run a similar test on my car.

 

[grober]

Try this article PeachPartsWiki: Mercedes-Benz Driveability

Other thing to check is the OVP relay. Sometimes if they are faulty they can cause lots of weird electrical problems. They may check out nominally but if you draw conspicuous current through them they start to breakdown.

 

[Philbask]

Hi Chrisd87, That's OK mate, seems you are not alone ! haha... I used a length of twin cable (actually heavy speaker cable), to the two pins on the EHA I fitted two single bits of electrical "chocolate block" I had to trim excess plastic from the choc blocs but they slid over the pins just right, and enabled me to nip them on by tightening the screws (not too tight though!!) I ran the cable from inside the car to the bay (inside the car, terminated into choc bloc too, which also happens to be the right size for the meter probes ) So one side of the choc bloc on the EHA connected to one of the wires going into the car choc bloc, the other side of the choc bloc on the EHA connect with a short piece of wire to the corresponding side of the original car connector (i.e. bottom pin on EHA to bottom socket of connector. (again I found the wire when stripped and twisted, a good tight fit in the socket connector) Then the other side of the socket connector is connected to the other wire going into the choc bloc in the car. All cables secured with cable-ties. Meter setup for 0 - 200 mA and plugged into the car choc block, job done! Polarity is a guess but don't worry, when you turn ign on, you should get a +20mA reading, if it's minus, just swap the meter probes around in the choc bloc... To clarify (seems this "quick reply" is not so.... haha) you are effectively creating a loop, bottom pin of EHA to bottom socket of car connector, top socket of car connector to meter lead, other meter lead to top pin of EHA.
Hope you have good results!! I have deffo learned a lot about the car/system looking at this

 

[Philbask]

Thanks Grober, I replaced the OVP some months ago, as I had the sudden rough idle / ABS light on! This difference here is I can watch the current ramp from 0 to 10mA over a 10 second ish period.... Interestingly today when I got in (engine warm) I left it on tickover and watched the meter, ramp to -10mA then after a while reset to zero mA and start ramping again, a while later reset to 0 and so-on.... I disconnected the Temp Sensor (4-pin one) and the ramp - reset cycle stopped !! I'm out later so will see what happens (If it will start without it now it's cooled down !! haha)

 

[grober]

190e running rich with eha on/off.Bad mpg.Help! - PeachParts Mercedes ShopForum