help please - PeachParts Mercedes-Benz Forum

mhingram · #1 04-14-2003, 09:08 AM

Okay having finally got my idle right and almost perfect a new and more troubling issue showed up yesteday.
The car now has a really hard start cold or hot, and more troubling she stumbles on acceleration from stop. I can floor it, do it slowly, all with the same impact no power. Then she will suddenly catch and it is like nothing is wrong.
She has new injectors and rubber, new plugs, wires, cap and rotor. No vacuum leaks.
Any ideas?

mhingram · #2 04-14-2003, 01:33 PM

On further research this looks like a coil issue. Am I off base and is there an easy way to test this? I also found some discussions about the air mass potentiometer, please tell me it is not this!

mhingram · #3 04-17-2003, 12:41 PM

Okay so setting the duty cycle back to 70 seemed to fix my stumble. Now to find out why I need to have it so rich. Any ideas, I am going to start with the O2 sensor, unless anyone thinks I should try elsewhere.
m

mhingram · #4 04-17-2003, 08:50 PM

Well I thought I would check my chain stretch as this is an easy painless one, got a 10 degree stretch so putting in a new chain and tensioner tomorrow. Rails are all still in good shape very light shade of tan. The PO must have used the old chain when he changed the rails.
See if that helps the old girl out, I hope it at least relieves some of the burden and lets me lean it up a bit not going to hold my breath though, I still think it is electronic and am going to use Steve's O2 sensor test after the chain is in.
m

mhingram · #5 04-19-2003, 02:04 AM

Okay my O2 sensor was bad based on my test stolen from a previous steve post,and the ovp was a bit flaky, I replaced them. Took the car in to get adjusted for fuel mixture based on gas and lambda. It was in deed very rich. So she was adjusted to factory spec (av 50%). However, my lambda was very flaky according to my mechanic and would fluctuate at idle. But was giving a very good reading at 2500 rpm. I also still have a horrible hesitation on acceletration from stop and a hard start. He recommended a new eha or throttle switch and to check the temperature sensor. I am at a loss, pretty much everything has been replaced now, and since the hesitation last week started I seem no closer. The only way to get rid of the stumble is to over rich the mixture. I am going to use steves test for the EHA but does anyone know what I should do to test the throttle switch and temp sensor. Please help.

haasman · #6 04-19-2003, 04:56 AM

Martin

I have been following your postings. Interesting. Have you cleaned the air sensor plate? Is it dirty at all? Someone with a 190 had posted a similar complaint and was amazed after cleaning it.

I had to bleed the injector lines at the fuel distributor, which I had never ever done on any car before to get the 190e to run right.

I was amazed at the amount of crap that came out. Right after that, oh and the double-dose of Techron, it started running extremely well.

I never had thought about anything clogging at that end. You might want to give that a try. Be careful, raw fuel and a running engine.

Keep us posted,

Haasman

mhingram · #7 04-19-2003, 08:14 AM

Air sensor Plate is spotless I cleaned it last week good catch. I had my lines purged 4 months ago when I put a new filter on. Also had the distributor cleaned out to. I think it is definately something electrical. Either the throttle switch, eha or idle potentimeter as the lamda control (x11) is very intermittant at idle. The car was running great until I cleaned the engine, I was pretty careful but a day and a half later this hesitation showed up on acceleration, it also starts hard have to give it some gas. It does improve when the car is overly rich, but when adjusted to spec it is pretty bad. Outside of the hesitation on acceleration the idle is okay not perfect but solid. Power once moving over 10 miles and hour is amazing and very clean all the way through the power curve.

pentoman · #8 04-19-2003, 09:53 AM

Quote:

Originally posted by mhingram
However, my lambda was very flaky according to my mechanic and would fluctuate at idle.

Umm, on the Bosch lambda sensor training course I tagged along to recently, they showed how the lambda sensor works - at idle, it is supposed to fluctuate regularly between high and low. Was this what it was doing? Or something else? I'm probably misinterpreting what you say..!

Also, check my steps for seeing if your throttle switch is working:

I'm chuggin' again!!

good luck!

mhingram · #9 04-19-2003, 10:01 AM

No good question,
I fluctuates well at 2500 like it should. However, at idle it will either not fluctuate just stay at max no fluctuation or read correctly. If I can find out what is causing that I think I can remove my stumble on acceleration.

stevebfl · #10 04-19-2003, 12:34 PM

There are a lot of tricky relationships here and I believe you are focused too closely.

I would recommend looking at this system by viewing the EHA current. Although eventually you will see the same sort of closed loop evaluation for making adjustments, but tthe EHA current is what really matters, so viewing it is the window to seeing whats going on.

In other words if you thought that some form of constant or imtermittant signal was taking place with the coolant temp sensor then you would see the results of this in the EHA current.

The other thing about the EHA current is that it is real easy to achieve the default limp home state of zero milliamps; just unplug the EHA.

The system works properly when the mixture is set to 0.5 - 1.0% CO by exhaust gas analyzer and then the electrical correction is engaged. If the mixture is such the system will read it from the O2 sensor and keep lambda control through closed loop correction above and below 0.0 milliamps EHA current.

This is why one can adjust the system electronically without an exhaust gas analyser. but if things aren't in closed loop control the EHA current will tell more about whats wrong than the dutycycle at the diagnostic port.

mhingram · #11 04-19-2003, 12:47 PM

Thanks steve, Will post the eha test results tonight. I did notice that the car does not hesitate when the eha was disconnected as you summized. This was in the garage test though, the hesitation is easier to confirm when under load. So will test this afternoon. By the way my CO is .6 per the gas analyzer although it does fluctuate up and down as expected on rpm change.
m

stevebfl · #12 04-19-2003, 01:02 PM

If you are looking at current, here are some things to look for:

Closed loop operation will be a changing current going up and down about 2-3ma. it should be centered about 0.0ma but can occur anywhere between -12ma and +12ma. In other words a ranging from +5ma to 8ma and back and forth is still closed loop. It will represent a rich correction (positive current is rich correction) of a lean mixture as determined by the O2 sensor.

Key on engine off should look like +20ma in most cars. Starting enrichment will be over 50ma and cold running will get up to 20ma correction. While running you should not see corrections above +12ma when warm. Lambda correction stops at +12.

Whatever range of correction you find yourself when in closed loop, you should see basically the same range at any steady rpm. In other words if you adjust it like I like: to a range of -3ma to 0,0ma at idle, it should be within ten percent of that at 2000rpms.

mhingram · #13 04-19-2003, 02:37 PM

My x11 socket 3 - key on engine off was 30%duty cycle. (thought it should read 70%) The eha - key on engine off is 210ma.

Will try the rest when I have the kid in his nap.
m

mhingram · #14 04-19-2003, 03:40 PM

during warm up while air pump is on -6.41to -6.42ma The lambda was pegged at 99.8 no movement the so something is flaky as my mech said
At operating temp and idle - x11 duty cycle is at 50.8% at idle no fluctuation at all, unless it goes to 99.8 where it sits. Then suddenly it will read good and give 50% plus a fluctuation between 48 and 56%. So it is very flaky.
the EHA is still at -6.41ma no fluctuation at all
At operating temp and 2500 rpm my x11 duty is a nice fluctuation around 56%. The EHA does not move nor fluctuate from -6.4 ma

Thanks steve does this mean I have a bad eha or is it just getting a bad message.?
m

mhingram · #15 04-19-2003, 11:22 PM

Okay ignore my last post I am a dumbass. I did not read the doc very well and missed the section on an eha harness. I will order it Monday. Will let you know the correct reading when it arrives. In the mean time, my hesitation/stall is almost completely gone when I disconnect the EHA. I assume this lets the car run rich. Or if the car is correctly adjusted will it be okay once it reaches operating temp. Sorry for the stupid questions but I have to drive it daily and the hesitation/stall will kill me when I pull out.

Now the confusing thing to me is I get no reading from the x11 #3 socket when idling but it works like a charm at 2500rpm. Actually as soon as it is off idle.

thanks and sorry for the silly mistake.
m