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 didnít' 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
I had the timing adjusted, it didnít 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
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 itís 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, Iíve 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.