300E hesitating after repairs..HELP - PeachParts Mercedes-Benz Forum

mike690003 · #1 08-19-2003, 05:06 PM

Hello Board,

My 300E was going through its little bugs for a while. So I recently had my fuel mixture adjusted, my 02 sensor replaced(with the Ford Mustang sensor). Well after that, my car now hesitates badly. I feel the hesitation when coming off a stoplight, all the way to freeway speeds. My idle is more steady, but it hesitates badly when I am on the gas. What now could be wrong with my car??? I have replaced :
injector seals
02 sensor
fuel filter
used 2 bottles of techron ia 1/4 tank of gas
new gas cap
new plugs and wires
new cap and rotor

Should I disconnect the battery so the ECU restes??

What else could be causing my car to hesitate???

#2 08-20-2003, 08:03 AM

Perhaps you have messed up the A/F. What symptoms did it have to make you think it needed adjustment?

ctaylor738 · #3 08-20-2003, 09:38 AM

I suspect a worn-out airflow meter. It is a little black box on the front of the air intake. Remove the air cleaner. Pull the connector off a bit so that you can get a problem on the middle pin. Measure the voltage between it and ground with the engine idling. You should see a stable .7 volts.

If you do a search, you will find an excellent post by sbourg on the subject. I also did one on its replacement on my 300E.

#4 08-20-2003, 10:41 AM

I did a search for all your posts Mike,you have had so much trouble and done so much with this vehicle that basically it is impossible to diagnose. An accurate diagnosis depends on having what is called a baseline, that is, to know what state a vehicle is in or was in prior to a drivability problem occuring.
Performance depends on the whole system working together correctly, too much has been done to this engine.

This may seem blunt, but I see similiar scenarios everyday.
Oh yeah, just my opinion, and opinions are like anus's, everybodies got one.

mike690003 · #5 08-20-2003, 02:40 PM

Quote:

I did a search for all your posts Mike,you have had so much trouble and done so much with this vehicle that basically it is impossible to diagnose. An accurate diagnosis depends on having what is called a baseline, that is, to know what state a vehicle is in or was in prior to a drivability problem occuring.

I find it very hard to believe that me replacing parts could be a BAD thing. I have replaced everything that was bad on my car. I do not replace unnecessary parts. Sure I have replaced a lot of parts, but none were replaced for kicks.

Does anyone have even a slight idea of what could be wrong with my car??

1991300SEL · #6 08-20-2003, 07:09 PM

I agree with inspector1. I too have read alot of your posts and am of the belief that you most likely have shot yourself in the foot - possibly many times.

You've made numerous "adjustments" and had work done in shop(s).

I'm not sure I follow your comments about changing parts. If you don't know what you are doing, changing parts can indeed cause problems.

The questions you've asked and the comments you've made lead me to believe you should let someone else fix your car.

If my comments bother you - so be it. I call it the way I see it.

psfred · #7 08-20-2003, 08:10 PM

Make a harness so that you can monitor the duty cycle, and better yet (if possible) the EHA current while driving. This will allow you to see what is happening.

If you set the mixture with the O2 sensor cold, it may not be on the correct mixture while driving. You should be getting a little enrichment on acceleration (lower duty cycle, I think), going back to 50%.

EHA current should be near zero at idle, go positive on acceleration, then go to -20 or so on closed throttle deceleration (shuts off the fuel). If you have no change on acceleration, you aren't getting acceleration enrichement.

That is usually the result of a bad potentiometer -- it "tells" the computer you are moving the throttle and airflow is going up.

You should also check the base position of the flap in the mass air flow sensor -- must be at the base of the cylindrical section at idle -- and your base fuel mixture. You can unplug the EHA and see where the duty cycle goes -- without the EAH plugged in, there will be no feedback, so the O2 sensor just sees the current mixture, doesn't change it. If the duty cycle changes off scale with the EHA unplugged, try to set it to 50% and see how it drives.

Peter