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Old 04-02-2005, 10:21 AM
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Join Date: Jun 2001
Location: Northern Calif. (Fairfield Area)
Posts: 2,225
Originally Posted by bigblue1
I have been following this fix for a long time as many of the problems were familiar.

This time I was able to leave the car with them for a few days and they put the guages on and reset the upper and lower chamber pressure differential to .4bar as per spec. The intention was always to slightly richen the original setting to .45 bar.

Turns out that the original setting was way off. Perhaps done at a time before my ownership or perhaps it can change over time.

For all you out there it is worth the specialist investment and time to get this adjustment professionally calibrated in older M103 engines.

89 300CE
152k kms
What did they do to set the differential pressure to .4 bar?

Auto Zentral Ltd.
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Old 04-04-2005, 10:27 AM
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Join Date: Dec 2003
Location: Perth, Australia
Posts: 42
Checking EHA

There is a 10 page detailed description in the factory manuals.

It consists of connecting pressure guages into the fuel distributor system to measure fuel pressure and lower chamber pressure alternatively. The differential needing to be .4bar.

It obviously requires some setting up and the proper equipment.

Whilst my warm start problem is not completely resolved the car is otherwise transformed now I have this setting right.

If I want to go to the next step I believe I need to change the fuel injectors.
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Old 05-17-2006, 08:18 PM
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Join Date: Apr 2006
Posts: 30

you are my God!!! I followed exactly what you wrote in your thread, and the problem I had was fixed (well 98% of it) but none the less of you were standing in front of me right now I would kiss you thanks so much for posting!!!
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Old 05-19-2006, 12:26 PM
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Join Date: Apr 2006
Posts: 30

did the adjustment, which was simple as pie, but when I brought the car to get an inspection the NOx reading was thru the roof I am bringing the car in to a shop for, what I think he said, " 5 gas check?" it is supposed to tell you what exactly is going wrong and where. then we can make adjustments accordingly. does anyone have other suggestions? and has anyone adjusted their EHA and has had this happen as well? let me know. thanks!
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Old 08-10-2006, 12:34 PM
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Join Date: Sep 2004
Location: DFW / Collin County Texas
Posts: 1,882

My 300E has been transformed with 1/4 turn clockwise on the EHA adjustment screw.
Prior to Adjustment:
Very weak startup when cold, engine would stall unless I gave it gas. Having A/C on made it even worse, so A/C always had to be switched off when starting. Had to hold gas pedal for about 1 minute before putting car in gear, or it would stall. Once in gear, had to give it gas and get the car moving right away, otherwise it would stall. Not the greatest impression in a parking lot full of coworkers or friends. Once moving, I could finally turn on the A/C without fear of stalling. After driving for about 5 minutes, everything would level out. The car wouldn't stall, but it would come close at times. At stop lights the idle was very rough and erratic. The engine would stumble from a standstill and would hesitate and sputter when gas was applied while moving. The car used to idle perfectly but slowly degraded to this condition over the last 2 years and 30K miles.

After Adjustment:
When cold, engine will stall if I put car in gear immediately after starting. I either have to wait about 30 seconds or rev the engine a couple of times before putting in gear. But after that, everything is fine. No rough idle, no stalling, no stumble from standstill, no hesitation or sputtering. It's almost back to where it was a year ago.
I will test the coolant temp sensor, but I no longer suspect it. I tend to suspect the fuel pressure accumulator. Attempting to remedy these issues, I cleaned the ICV, looked for vacuum leaks, changed the sparkplugs, inspected the wires (which only had about 30K on them), and even replaced my cap and rotor. The cap/rotor also had only 30K on them and when inspected had only slight wear. I should have gone with my gut feeling, as replacing the cap/rotor didn't improve anything one bit.
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Last edited by gmercoleza; 08-10-2006 at 12:35 PM. Reason: Left out Info
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Old 09-05-2007, 03:13 AM
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Join Date: Sep 2007
Posts: 1
Similar results on my 190E, but...

It's amazing what a quarter turn can do. I've experienced the difference in both start-up and in acceleration from standstill. The thing that baffles me is I started down this path in experiencing sudden lack of power during starting from a light or when pressing the gas hard on a turn or braking hard on a turn (stalls). While I haven't experienced the same level of issues since the 1/4 turn exercise, I still need to artfully apply the throttle to get power as needed - can't just press the pedal down hard. Is this normal? Needless to say the symptoms are intermittent. I've cleaned out the choke plate, have clean air filter in place and adjusted the aforementioned 1/4 turn. Anyone have other ideas of what may be going on? Of particular concern is the tendency to stall during hard braking on a turn. Just for reference, the car has 207K miles and had the engine rebuilt around 150K.
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Old 10-20-2008, 03:58 PM
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Join Date: Jul 2006
Location: Tampa, FL
Posts: 814
Here's something interesting I found concerning EHA's.

"According to the web page maintained by Mercedes owner in Japan, he has disassembled several broken EHA's and found that there are two valve settings, one is 6 and 1/2 turns back from the end, and another is 5 and 3/4 turns. Just try both before buying new one."

1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible
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Old 10-30-2008, 12:29 AM
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Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
I'm troubleshooting a cold start issue with my 23 year old 190E 2.3L.

I've owned this car since 2002, and done things to it many professional mechanis are afraid of. I can't say I have total understanding of the fuel injection system used on these engines, it is probably one of the most difficult systems to diagnose and troubleshoot, and as many have probably seen before, some mechanics will simply refuse to touch the car, others think they know exactly what the problem is.

The idea of adjusting the EHA valve to improve a cold start problem feels a bit too easy to me, and I have reason to believe that although it might seem to correct the problem, there is another cause for the cold start issue. If I remember the documentation for this fuel injection system correctly, the electronic components on this fuel injection system have been put in to even out the A/F to meet specific standards. All those out there who had problems with hesitation, or lack of power which were fixed by replacing the OVP, or the fuses on it are proof of this. The OVP is the main fuse for the entire CFI system, without it, the electronics are dead, and they do nothing for the A/F mixture, yet in some cases, years go by before the owner of a car with a dead OVP comes to the conclusion that the car should be running better.

I must admit that I am tempted to try this fix, but the fact that it is just a cold start problem tells me to hold off on this. Adjusting the EHA will change the A/F across the board without the electronics knowing about it, and they were carefully calibrated with the proper equipment. I know that my car once the EHA correction kicks in drives like a rocket, I could not ask for more power out of an engine this old.

The possibilty of the upper and lower chamber pressure differences being off seems on the right track to me, I will have to look into obtaining some type of equipment to measure, and adjust to prove my theory, but you can be sure that if I do, I will post my findings.

Until then, I installed a remote starter to fire up the car and give it that minute or two to warm up before I have to head out on a cold morning, this so far did the trick for me. Only now that the temperatures started dropping did I notice this, last year it was not there, and the car was not used all that much over the past year, so I don't think it would be wear and tear, but I'm sure it is a factor.

1985 190E 2.3L - a constant project.
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Old 10-30-2008, 07:58 PM
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Join Date: Jan 2003
Location: London Ontario Canada
Posts: 382
Temp. sensor

I am not a mechanic nor am I familiar with your car. But I do have a 420SEL and the first 2 things I would check on a 420 with a similar problem is the engine coolant temperature sensor and the cold start injector.
1989 420 SEL
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Old 10-04-2009, 08:58 AM
Melbourne, Australia
Join Date: Aug 2009
Location: Melbourne, Australia
Posts: 10
I have been looking for a solution to cold running issues since I got my car. Would run fine at idle, but stumble and lose all power at part throttle when cold. WOT was fine. Would run fine at 80+ degrees.

Made a 1/4 turn CW adjustment on the EHA and the difference was immediately apparent. Pulls strongly when cold, no hot starting issues, idle smoothes out fast on cold start. I've been watching these threads with interest - and now wanted to let you all know THANKS!
1988 300CE 124.050 M103.983
1986 190E 201.024 M102.962
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Old 04-03-2010, 03:50 PM
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Join Date: Apr 2010
Location: Ensenada, Baja California, Mexico
Posts: 1
A 15 Minute Fix to Months of Headaches

This produced ASTONISHING results! I have been struggling for months with my '88 300CE that, once warmed up, sputtered and backfired every time I accelerated from a stop or at any time it was below 2,000 rpm. It would almost cut out unless I floored it and it often stalled as i was coming to a stop. It was not safe to drive in that condition.

I replaced the plugs, wires, vacuum lines, distributor cap, rotor, fuel filter and injectors. Plugs helped somewhat, nothing else impacted the problem. My next attempt was going to be to change the Overload Protection Relay, Coolant Temperature Sensor and O2 Sensor. I ran across this post and in 15 minutes I adjusted the EHA exactly as detailed above and had my fix. Smooth as silk acceleration once again! Thanks...

Last edited by tomgarcin; 04-03-2010 at 03:54 PM. Reason: Clarification
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