87' 300E power loss
 

Since you people helped me out with my defroster problem I though I would throw another one out there. Once my car is warmed up and I stop at a stop sign or just slow down in traffic and try to accelerate again my engine seems to bog down or not respond to gas pedel. It usually picks up power again slowly. runs great at high speeds and idle fine. The rpm's seem to stay up and the car doesn't stall. Is there any vacuum problems associated with the transmission perhaps Any Ideas out there.
Thanks
Vinnie Laraia:confused:

Vin:

You have a vacuum leak, most likely at the idle control valve. Those big rubber hoses get hard, shrink, and fit loose with age. All the rubber vac hoses on the engine are likely to be bad by now, I'd replace them all. The plastic lines are probably OK. If you have harsh tranny shifts and the defrost comes on when you accelerate, you definitely have a vac leak.

The vac leak means that when you open the throttle, no air goes down the fuel metering flap for a second, so there is no throttle response. If it then suddenly roars off, this is even more likely.

It's also possible that the throttle posistion sensor "pot" on the side of the throttle body is bad, too, so that you dont' get good enrichement on throttle opening. It can be replaced.

Peter

87' 300E power loss
 

Thanks Peter I will check it out as soon as I get a chance. I figured it must be a vacuum problem but didn't really know where to start. where is the idle control valve located.
Thanks Vinnie

Hesitation Problem
 

I had a hesitation problem with my '88 260e that turned out to be the EHA. My car would run fine when first started and after it was warmed up but during warm-up would hesitate badly. I suggest checking simple things, such as vacuum leaks and adjusting the fuel mixture to specs with the engine warmed up first before replacing the EHA.

Vin:

Idle control valve is under the air filter housing, held down with a strap. Single two-wire connector and two large hoses. Check the hoses -- mine were actually loose on the barbs. They are a pain to replace, but it cured the stagger at takeoff!

Peter

Similar 87' 300 power loss
 

Hi,

I have a 1987 300E, completed tuned up and replaced two fuel pumps last months because the car has been neglected excepting adding water and oil. The car starts fine however when the speed is gradually increased 20-25 mph the car would hesitate then pick up the speed, the engine rpm would increase from 2000 rpm to 3000 rpm then drop down to 2000 rpm, after that it seems fine without any problems. When returning home, I have to drive up a slightly steep hill, the car would, sometimes, behaviors the same and hiccup 3-4 times when I press the accelerator along the climb. Do I have the similar problems, as posted this thread #16215 and I should check vacuum leaks and adjusting the fuel mixture and EHA?

Approximately how much would it be costing me if I let a mechanic, specializing in Mercedes but not from dealers, to do the work? Certainly I hope my problems have nothing to do with the transmission.

DL

Getting closer
 

I think I am getting closer to my problem. I hope.
I finally got to check out vacuum hoses and idle air control and they seem fine. For some reason when the temp. gets up to 80-90 C the mass air flow I guess you call it a butterfly does not open all the way when the throttle is opened it only opens a little and you can hear the engine bog down but the engines rpm's still stay up to 7-10k but the mass air sensor doesn't open enough to let more air in. If I open it by hand the engine revs up.What controls when it opens and closes. Is there a cold start valve that controls this. My car idles fine. Only seems to lose power once engine gets up to operating temp.
Thanks Vinnie

It's not supposed to open all the way. If you rev the engine with no load it will only open a small amount.

What controls it is the air passing through it into the engine. In fact, its function is to measure how much air is passing through and report to the KE Computer.

87' 300E power loss
 

But when the engine is running OK the butterfly seems to open about double the amount as when it isn't runnig well. Is there an air flow sensor that tells it when to open or close.
Thanks
Vinnie

Probably a sticky control plunger or bad seals. Also can be dirt in the ventrui causing the plate to bind. With the engine off, press it down and take a paper towel wetted down with carb cleaner and wipe it all clean. May fix it.

Otherwise, you will have to remove the fuel distributor and remove the plunger, inspect it, and clean it. If it is scored or has ridges, it will cause the symptoms you have, but replacement of the plunger may also not fix it. May need a new fuel distributor ($$$).

Peter

Re: 87' 300E power loss
 

The butterfly IS the airflow sensor. It's entirely mechanical and is moved by the air going into the engine. As it moves down it enriches the mixture mechanically and sends an electrcal signal to the computer. Does it move smoothly when you push it down with your finger (engine off)?

i'm trying
 

The air flow sensor doesn't seem to hang up when i push it down slowly with my finger with the engine off and the rim is clean. It will open about an inch when the engine reaches operating temp. and I give it some throttle the plate stays where it is and it seems like engine is getting to much gas (poor gas milage too) and not enough air flow. Peter how hard is it for me to replace seals or clean the plunger. If I let up on throttle air flow closes and car idles fine. The Temp. it only seems to happen as the car reaches operating temp. 80-90C this has me a little frustrated.
Thanks

Vin:

you need to get a digital VOM that does duty cycle and test the fuel control system. Described many times on this forum, but the basics are that with the red lead connected to pin #3 of the round diagnostics connector and the black lead in #2 (or another ground), the duty cycle reading shoudl be around 50% and fluctuating on a warm engine. Should to low (I believe, check the DIY engine controls post) as the throttle is opened and drop back to 50% or so quickly. Should go way high on coast (fuel shutoff), returning to 50% when idle is achieved.

Check the idle switch on the linkage -- if it is failed, you would be in idle condition all the time, this will goof up the running mixture. So will a bad engine temp sensor.

Peter

Re: i'm trying
 

That plate should be barely cracked open at idle. It's open an inch??

I see you have 2 300Es. Have you looked at the other one to see how far it opens?

We ARE talking about the round metal plate right under the air filter, right?

87' 300E power loss
 

Right.... Yes it only opens a crack at idle. When I give it throttle it opens further. If I really rev it up the plate drops down about another 3 inches. However during the transition from cold to warm there is a point when it is almost to full operating temp. that plate will only open about an inch or two even when I rev the engine. And when I do its almost like its choking for air. if I push the plate down by hand as I give it gas it seems to run ok. I have never had this happen twice while driving. It happens once just as the engine warms up to operating temp. I have a multimeter without a duty control (below) and I hooked it up and set it on 20 DC as shown. I put in in #3 and grounded it with just key on. Got 6.6 reading. I started it and as engine warmed up it dropped. When fully warm it stayed steady at 1.07. Does this help or do I need one with duty cycle.
Any help to you guys. I also tested the engine temp sensor when fully warm and it reads .52 ohm 's.
Thanks Again for trying to help a benz newbie out
Vinnie

A meter with duty cycle will read the error codes, if any. You want the reading to VARY somewhere near 50%. If it's a fixed reading, it's a fault code.

It's only about $30 at Sears and looks a lot like the one you have.

Vin:

You are running either too rich or too lean (don't remember at the moment - dyslexia is like that...).

You can set the idle mixture with a standard digital VOM, but one with a duty cylce is MUCH easier to use, even the cheapest one there is.

What you want to do is set the idle mix to give a reading of about 50% duty cycle warm.

However, there are some things you must do first:

Find and fix any vac leaks. Just because a hose LOOKS OK doesn't mean it doesn't leak. My idle control valve hoses looked fine, but were very hard and floating around on the barb, and leaking. I replaced all the hoses in the vac systems except a couple connectors, and I will do those when I remember to order them.

You must also verify that the O2 sensor is working correctly -- if it is bad, the mixture will be off.

Peter

Duty Cycle results
 

First I want to thank you guys for your help.
Key on engine off 68%
engine running cold constant 49%
As engine reaches 80c the car starts to idle rough for about a minute and the duty cycle raises. to 92% and idle smoothes out.
Now what do I do. Should I check it the same way with O2 sensor out and see what readings I get.
What do my numbers mean. I have read alot of posts related to this but am still confused. Whats my next step.
Thanks Again
Vinnie

The simple answer:

Looks like you're running rich. Turn the adjusting screw counterclockwise a bit and aim for 50-55%.

Has anyone been tampering with that adjustment? Seems pretty far off.

Vin:

Read the DIY post on electronic engine controls and test your O2 sensor -- if it is whacked, you are going to have trouble with the mixture! If it's OK, re-set the mixture and see what happens.

Don't turn very far, and wait at least 20 sec for the reading to stabilize, or you will just swing from way lean to way rich and back -- took me a while to get the hang of it.

Peter

Duty cycle test
 

I don't know if the adjustment has been tampered with I bought the car in Nov. and just got it on the road a month ago.
I will try to check the O2 sensor today if I get a chance.
Thanks again
Vinnie

O2 sensor
 

Wasan't able to get under the car today so I looked for the connections for the o2 sensor under passenger carpet. Remember I'm new:-) There wasn't one plug but 2. One round one and 1 double rectangular one. Are these the connections for o2 sensor.
Thanks Again
Vinnie

Yes, there are 2 connectors. One is for the O2 heater. I believe the single one is the O2 output, if I remember right.

Thanks
 

Now thats what I call a QUICK answer.
Thanks

duty cycl test
 

I went out and dsconnected the o2 sensor and did a duty cycle test.
Key on Engine off 69%
engine cold 49%
Engine warm 80c 49%
Only difference with o2 sensor connected was warm engine duty cycle was 92% the other numbers were the same.
Again the only time I have power loss is when the engine temp. reaches 80c. is this the transition time when O2 sensor starts sending info to the fuel system. Do we think it is the o2 sensor. Notice I said we lol.
OH yea can anyone help with the file 07.3-0121 Testing electrical components of the KE injection system from the CD. Mine seems to be missing or is that not possible to do.

Thanks Vinnie

That 92% number; is it a fixed value or does it vary? If it's fixed, it's an error code but I don't remember what 90% error code means.

The 49% reading when the O2 sensor was disconnected was because the KE system was not operating.

Check and see what the O2 sensor is putting out. It should vary .5 to 1 volt.

The O2 sensor should be operating and sending info well before 80c.

OK, 90% says, "Current to electrohydraulic actuator implausible."

Sounds like something is wrong here -- mixture is OK until you hit operating temp.

Check the resistance of the engine controls coolant sensor (don't remember which one it is, will have to look it up). If that is flaky, you will get a goofy mixture correction or ECU error due to impossible temp. Obviously, this one fails the ECU to max rich.

Make sure the air inlet temp sensor is connected, too -- this often gets pulled loose when the air filter housing is removed and someone yanks on the hose to the grille vent -- the temp sensor is in that area.

Peter

O2 sensor readings
 

Peter my 87' doesn't have an air inlet temp sensor on the intake horn like my 91. The resistance on the engine control coolant sensor was .48 ohms. I think it was the furthest sensor on the rear left of the engine near the valve cover right.

Brewtoo the voltage from the o2 sensor started at .36v I reved the engine for about 2 min and it dropped to .30v
Does the constant 92% duty cycle mean my EHA is bad or could it be that my o2 sensor at .36v is not sending a strong enough signal for it to work properly.

I wish the file 07.3-0121 Testing electrical components of the KE injection system from the CD worked for me. It seems to be missing on my CD.
Help with the numbers is appreciated.
Thanks Again Vinnie

Again, the 92% fixed reading would be an error code.

That is a low output for the O2 sensor. Should VARY, up to 1 volt.

Send me your email address. You've blocked emails thru the forum.

O2 sensor in
 

Put a new o2 sensor in today. Don't know yet if that will fix my problem but I am now getting some variation in my duty cycle readings. Ranging from 35-39% engine warm and running. Also Tested o2 sensor getting .3-.8V the old one was getting only .3-.34V so now I drive it and see if the problem comes up again. Keep our fingers crossed.
Vinnie

Vin:

Get a 3 mm allen wrench. The mixture adjustment is at the bottom of the "tower" that lines up with the hole in the air cleaner. If you get a long enough allen, you can set the mixture with the air cleaner on, otherwise remove it.

Insert the wrench (you may have to remove the original pressed in cover if no one has adjusted the mixture before), fit it into the socket, then press down and turn slightly CW (I think) while watching the duty cycle meter, engine warm and running.

You want about 50% -- 35% is too low, you are out of control range rich. If I'm wrong on the direction, turn CCW. Don't turn very much at a time, and pull the allen back up and wait at least 20 sec after each adjustement before deciding to adjust more -- at idle, it takes a while for the exhaust gasses to get to the O2 sensor, and you will go rich every time you push down on the keyed adjuster!

Shouldn't take more than a quarter turn to get you set right.

This will make a BIG difference on performance and milage.

Peter