300SE hesitation solved. - PeachParts Mercedes-Benz Forum

fahrgewehr2 · #1 11-17-2003, 01:19 AM

Here is a link to my previous thread, which gives a run-down of the problem:

Hesitation again ('90 300SE)

Found car was running lean (flucuation around 75%). I watched the DMM as the car warmed up from dead cold. was around 50%, but then started to head upwards (leaning out) as temp gauge hit aprox. 60C. Enrichened the mixture so that it flucuated around 50% while in closed loop operation.

I also discovered that the air intake sensor was not attached. what happens if it is not functional? Anyways, obviously reattached it.

So, car runs like a raped ape now. Idles great too, can't even tell she's running.

Mike

John Plut · #2 11-17-2003, 11:10 PM

I'm chasing the same problem on my '88 260e. Do you think the mixture adjustment or the air temp sensor fixed your problem?

Unfortuately, my model doesn't have an air temp sensor and I have already set the mixture to spec's to no avail. I'm beginning to suspect either the EHA or the fuel injectors.

John

fahrgewehr2 · #3 11-18-2003, 01:21 AM

Hi john-

Well to be honest, I am not sure which fixed the problem, as I made both changes at the same time. I predict the lean running condition was the culprit, though.

How did you set your car's mixture? Did you watch what was happening as it warmed to operating temperature? Where do you have the mixture set (%)?

What are your exact running problems?

Lastly, the sensor I refer to- I am just guessing as to its name ("air intake temp sensor"?). But I would guess you have one as well as we share the m103 engine. Perhaps it is tucked away and out of view? Or maybe not?

Here is a pic of where I found my sensor disconnected (picture features a 260 engine bay, however.)

Hope I can help. Mike

John Plut · #4 11-18-2003, 09:40 PM

Mike, my hesitation problem only occurs when the temperature outside is below 40 degrees F. The car starts and runs fine, but as it begins to warm up it hesitates very badly when accelerating from a stop, like 0-60 in five minutes, which can be dangerous. When the car reaches normal operating temp it runs fine again. I'ts been doing this for three years now and I have not found the problem.

The car is an '88 260e which does not have an air intake temp sensor. They must have started using them in '89 or '90. My wife's '92 300e has one. For the air/fuel mixture adjustment I used a multimeter to measure MA through the EHA and adjusted to get approx. -2 MA. The reading before adjustment was -8 MA (too rich). All adjustments were made with the car warmed up and running closed-loop, (O2 sensor connected).

The EHA on my car had a very slight fuel leak, more like weepage that was noticable when it was hot out. I replaced the o-ring seals which seems to have cured it but I have also heard that a leaking EHA means it is no good. I am keeping an eye on it to see if it leaks at all and maybe needs to be replaced. I might try swapping it with my wifes car since the part numbers appear to be the same and see if that helps the hesitation.

John

fahrgewehr2 · #5 11-23-2003, 03:57 PM

John-

Any progress?

John Plut · #6 11-23-2003, 08:34 PM

I have not worked on my hesitation problem because my wife's car is out of commission right now and I don't want to do any experimenting on mine. The rear subframe bushings failed on her 300e and I am working on removing them while waiting on parts. Parts should arrive Tuesday. .. it's always something.