88 300E with stumbling/stalling problem - help
 

I'm trying to help a buddy of mind figure out a problem with his 300E. I'm somewhat familiar with the basics of the injection from my 88 VW 16V days but what's on the benz has a few more bits and pieces and it's been 15 years since I had the VW.

The problem is intermittent to a point but consistent enough that I hope to be able to find a solution. Car starts fine and idles fine. But usually within a minute or so idle goes to stumbling badly and the throttle is like a light switch. You can put the throttle down 1/2 way and if you leave it there eventually the car kicks in and takes off for a few seconds then loses all power then back on again. Literally like someone cycling a cutout switch to the coil

after a period of time things usually settle out and the car runs normally. At least for him. The little I drove it I would consider the car not safe to drive but he has a lifetime of driving through problems.

When the car runs it runs very smooth and strong. Cap, Rotor and plugs have been done. With the car running smoothly and past it's problem period I took off the air cleaner and started pulling connectors off of various electrical bits. Every connection I pulled had an immediate effect except for what I believe is the EHA. When I pull the plug to that gizmo there is no change in the way the engine runs.

??? How do I diagnose if the EHA is working or not? I did do some searching and found dozens of threads about how to set the EHA and some magic idle CO adjustment but no simple test came to mind for a simple yes this part still works or no it's no longer responding to voltage?

EHA is my best guess but it's a poor one. I would assume a temp sensor is cheap and probably worth changing but the fact that the car works perfectly fine some days and not driveable the next in my limited experience means the sensor is still functional.

Not looking to start throwing parts at this car to make it perfect. Just make it work!

Thanks in advance. I know how hard it can be to diagnose these things via an internet thread but all help is appreciated.

I would start with the coolant sensor if you already done the plugs and other tune up stuff...the coolant temp sensor is large in its' influence on engine performance. They are like $35 and not hard to replace...

Not a bad suggestion, but I would also do a fuel pressure test and watch the readings during the problem period.

When my fuel pump started going, it would do similar things to what you are describing.

OVP almost certainly for your problem. Check the fuse first before replacing it. It resides behind the battery and is red. It will have a fuse/two fuses on top. With any type of stumbling/stalling/light problems....OVP should be the #1 thing to check on the M103's.

EHA cannot be tested for working condition....In my 260E, it would bog down at low speeds then suddenly pick up. Fuel pressure on the lower chamber was dead on spec....I swapped the EHA and it was a completely different car. The EHA would not cause stumbling or stalling...only a loss of power at the bottom end.

Older/original OVP's are black on top and only have 1 fuse.

still going
 

I sort of hoped this would go away but he still hasn't found a resolution. Thanks for the replies. We did change the temp sensor and no change in performance. I've found lots of bits of info but is there a thread or writeup that covers where to check pressures? I saw a link at one point to a cheap harbor freight gauge but now I can't find it again. Anyone buy one and have a part#? We found a comment in the service manual that describes the condition of the car to a T. The recommendation is to raise the pressure. I believe it was to raiser the lower chamber .5 bar higher but I could be way off on that. Don't have the numbers in front of me.

You check pressures at the upper and lower chamber ports on the fuel distributor. You'll need to buy a CIS pressure tester, or a tester with the correct CIS adapters.

Here is the FSM PDF on it
http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/07.3-1603.pdf

Adjust the EHA
 

http://www.peachparts.com/shopforum/tech-help/104289-adjusting-eha-possible.html

Check it out! I had the SAME problem and made this adjustment and the difference is night and day. I thought it would be too good to be true, but it worked a charm.

It's baaaack. never checked pressures. A new upper pump from a yard was put in as that seemed to be malfunctioning based on what he was describing. Car ran well for a few months and seemed to be fixed. Now it's back to running poorly and the ABS sensor light is now on steady while the engine runs poorly? Please tell me there isn't some crazy interconnection between ABS computer and engine running? My vote is the yard pump failed or the lower pump failed. But right now it's simply not starting so hopefully it's a something permanent that can be found.

Thanks for the link to the pressure test - I printed that out for him

check ovp

Classic OVP symptoms, should have been the first thing you checked.

Thanks for pointing to OVP. That was the first conclusion I came to a few years ago. I understand his side of it too. Starts to get very expensive if you just start throwing parts at a problem. At one point he paid the long time Mercedes specialist down in town for a full diagnostic. $200 later the guy never checked full pressures just said there were still too many variables and his best guess was dirt in the gas tank.

Just to let you know, that fixed it! Thanks for the patience

update please .
thanks