Hesitation = History!
 

As some of you might have already known my 1985 190E has been suffering
from quite a terrible case of hesitation that I have been fighting since I
have bought the car back in April 2002.

Yesterday morning January 13 2003, I have fixed the problem.

A huge Thank you goes to Steve Brotherton who shed all the light I needed
on the problem to solve it.

From the beginning, I was stubborn enough not to throw money a the problem
but take the time to see how the car works and why it's not working right.

My first step was to obtain the Service Manual from which I have followed
every diagnostic step that was outlined there, even ones I didn’t' have to,
to try and find the problem. Unfortunately since I do not have all the
equipment necessary to do everything right away, not all test were conclusive, however, I was fortunate enough to be able to invest in a Digital Multimeter.

Of course, a few parts I did replace to maintain the car in proper shape,
but what I found was a huge mess overall.

The car had a jumped fuel pump which means the fuel pump relay was just
sitting in the car not doing anything at all. Just about anything that
could have been adjusted was adjusted way out of its range. Slowly and
piece by piece I got everything back to where it should be, I had to go as
far as re-soldering joints on the fuel pump, Cruse Control Computer, CFI
computer, and a bunch of other things, but the car still ran, there was not
ONE day since I got the car that it would be just sitting since it was out
of commission, well one day maybe when I was getting the timing chain
changed, which I had to do since it was 3cm longer then it should have
been.

I had the timing adjusted, it didn’t change anything, new spark plugs,
wires, idle control valve, nothing... car hesitated every time.

In the process, I hooked up a whole bunch of wires to the engine controls
to see how they work while I drive, so my car still looks like a big
experiment on wheels, but it paid off.

The main step to fixing this problem was the current going through the all
so famous EHA valve, which I almost dished out $400 for, but managed to
stop myself in the last moment.

Since my car is pre 1986, the current in the valve ranges from 0ma-12ma.
The higher the current is, the more the fuel mixture is enriched.

My problem was that the engine was running very rich, and the mixture was
not being enriched on acceleration which cause it to hesitate. So it runs
rich, but it misses cause the mixture is too lean when accelerating? What
the...

Since I'm only a student right now and can't afford to take the car to the
dealer to simply get it fixed, I had to do most things myself, and with
the help of MercedesShop and 190 revolution, both have been a huge help the
car now runs like a charm.


What really happened, is that the fuel mixture was tampered with so much that the computers adjustments had absolutely no effect on the way the engine was running, sure it did it’s job as it should, but the huge amounts of fuel just cancelled everything out.

Here is what I did. From what Steve told me, the current in the EHA should be 8ma when the system is in closed loop (meaning everything works right once the car is warmed up) system gets feedback , makes adjustments, car runs really well and is economical. My current was at 8ma when I disconnected the 02 sensor, good way to see if everything works as it should, but once I hooked it back up, within a few seconds the EHA current was right back to 0 causing all the problems. Now that I have done all the tests and I knew that all the subsystems are working fine, I asked Steve if he thinks it would be a good idea to adjust the mixture using the screw which is on top of the fuel distributor, Steve told me that I should try it and see what results I get. If engine runs good, keep going, if not, stop and re-test all components cause something is wrong. With the Multimeter hooked up to the EHA valve, I slowly, very slowly started turning the adjustment screw counter clockwise to lean out the mixture all while watching the current. At first I thought that it has no effect, because nothing was changing, but since the engine still ran good, I kept going, eventually after about 180 degrees, things started happening, current went up to 3ma, I stopped gave it some gas and let it level off and watched, sure enough there it was 3ma, I kept going until I got up to 7-8ma, I went over to 8-9ma the car still ran perfectly, but I pushed the allen key in a bit too far and I killed the engine, I tried starting it but it refused to turn over, I turned the mixture back a bit, it started right up, this time I was right in the zone, 7-8ma, so I crossed my fingers and went for a ride and believe me, it was like driving a new car, the moment that I have been waiting for so long, at time thinking that it might never come.

To finish off the job, since the same day (coincidence) my new proper spark plugs arrived along with the distributor cap and rotor arm, I replaced them all, got a can of fuel system cleaner and will run it through next time I fill up to clean up after running rich for so long, I know the fuel injectors need it, I’ve seen them, they will thank me.

Now I just have to adjust the idle mixture to get the car running emission free and enjoy the ride that I already love so much.

Cheers everyone and happy fixing, I hope this helps someone.

xp

Thanks for the info.
I had actually planned to call the local MB shop today, to get my fuel/air mixture adjusted. (running way too rich!) But this sounds like a good way to do it myself.

Could you please shed some light on exactly where you connect the multimeter to measure the mA? -And will this be the same on a w124 300E?

Freestyler

Mixture Adjustment on Fuel Distributor 103/104
 

I have made numerous adjustments to the mixture screw on both my 89 and 92 300CE and the results have been quite dramatic. This adhustment effects a lot more than just the idle. It seems that you have to find just the right spot to get the best combination of idle and accelaration. In both cases, the best accelaration setting was not the best for the idle but I prefered the improved throttle responce in any case. Unless I have missed it, I have not seen a lot of correspondence on this site regarding how this adjustment REALLY effects this type ot fuel injection. I did not have any analyzers - it was many trial adjustments to get it right. Getting the little steel ball out of the housing on my 92 was a *****! I had to drill 2 1/16" holes on the sides of the housing (make sure everything is covered so the chips won't end up in the wrong place) just below the center of the ball and pry it out with a long pointed punch. I had to let penetrating oil soak in for a couple out hours also. Not for the faint of heart but there was no harm done and it goes like hell now. Got to do it to my wifes 1990 300SL next.
Futher fellow owners experiences with this adjustment would be appreciated. Craig

idle?
 

I never really had any problems with my idle after I cleaned the valve and all the air hoses going to and out of it, it's stable as a rock, what I did I did to fix the overall mixture and get the car back to specs and propper performance, it had nothing to do with the idle speed, but now that I have the running mixture figured out I can fine tune the idle which I plan on doing as well.

xp

Re: Hesitation = History!
 

I'm fairly new to DIY on MB's, so bare with me.. -Where is this EHA valve located? (preferrably on a w124 300E)

Freestyler

I'm not sure about 300E but I'm guessing in the same place as on a 190E, you'rs is just a bigger brother.

It should be on the fuel distributor, it is a plastic box, with two wires going into it, and is on the side of the fuel distributor most likely in the back. You can see a pic of it on FastLane for comparison.

If you want to get the current, you have to either get a harness from MB for it, or simplay cut one of the wires and put in your MM in it's place.

Remember basic electronics here, current is measure differently then voltage.

-------(A)-------- Current

----(V)-----
---|------------|------- Voltage


xp

Got it!

Thanks xp190! :)

Freestyler

Remove your air cleaner and look just behind the fuel distributor, in front of the throttle linkage. It's circled in the picture below.

you got it, that's the EHA, I had problems finding it the first time too, now I can do it with my eyes closed :)

xp

Hi xp190,
great information.
Thanks
Reinhard Kreutzer

skeletons in the closet
 

seems my older friend hesitation is back and he's back with a vengance.

He showed his ugly head a week ago when I was going down the road, but went away quickly. Now my car bearly starts and when it does it runs fine for a few seconds and then starts to miss and miss and miss accelerating on not it stands in idle and shakes as if only half the engine is working.

I have no idea what it could be, new spark plugs, wires, rotor cap, the works...

also does not look like it's some electronic control since I see the computer trying to keep the engine going by dumping fuel in to the cylinders that do work, economy gauge goes 1/2 way up....

I need help with this. bad....

xp

Air mass sensor?
:confused:

not in this case, I don't think so, wouldn't cause cylinders to miss and the engine is struggling even in idle

here we go again....
 

figured it out partly.

engine was missing overall cause of bad plug wires, and it's a new set too... weird....

now I'm back to hesitation like originally, but I'm not sure wher it's originating from... gotta do some testing...

xp

any word, do you still have the hesitation. I am in the same boat new O2 sensor and OVP. Mixture is fine but still have the hesitation.
m