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1990 Mercedes Benz 190E 2.6
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Discussion Starter #1 (Edited)
Well my 1990 190E ran beautifully for two weeks after the O2 sensor was changed and the duty cycle seemed about right in the 50% range but that all changed yesterday. The previous cold start problem has returned. It seems to take about 6 tries before it will keep running. The CSV seems Ok since the car fires right away but then quits and quits and quits until the engine stumbles at about 500 rpm and then begins to settle into a normal state.
This afternoon I checked the duty cycle and its back to about 10% from what was - 50% + but wavering a bit. The fuel pressure Is normal with a 0.4 differential of 5.8 and 5.4 bars but maybe a wee bit less. The EHA shows about 18 ohms between the pins.
I am wondering if the 10% is actually a code rather than the actual duty cycle? According to the H.D. posting on W124 forum the steady 10% would mean a faulty TPS if I not mistaken. Would a faulty TPS cause a hard cold start? The cra runs fine once under way and engine warm. Warm starts are OK. Where is the engine to chassis ground so I can check that. Tomorrow I want to check the O2 sensor reading again also. No snow and no cold weather yet either.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Too Bad.

If it is a steady 10% and not moving at all and it may well be a code. Just make sure it is 10% not 90%,
And if it is the TPS, you will have to check the switch itself by using the ohm meter.
I'm struggling with why the TPS would only cause trouble when engine is cold. But you should check it, easy enough.

This is a time in which being able to read the EHA current directly would help. This will tell you if this is a fueling control issue (EHA) or an air control issue ( IACV)

BTW, when the engine is cold the O2 sensor output is ignored, so even if you had a bad O2 sensor my suspicion is that it will not effect your cold run behavior..

- Cheers!
 

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1990 Mercedes Benz 190E 2.6
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Discussion Starter #3 (Edited)
OK thanks, I have the duty cycle wires + to 3 and - to 2 on the X11 plug. Can you provide specs for the TPS plug Ohms. There are 3 plugs. I am going to try to make a harness for the EHA valve and will test it as well. The 10% duty cycle reading is cold or hot. I checked it with another multimeter to be sure and the voltage of 1.4 or so seems to jive with the 10% with the alternator showing 13.6 volts.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I believe 1.4V would be 90%, the way Mercedes defines it (the backwards way)

What is 90% on the list?

TPS is just a switch. It has 3 positions. Closed, wide open and in the middle.
 

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1990 Mercedes Benz 190E 2.6
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Discussion Starter #5
There is no 90%. 85% is IATS which checked and is OK and 95% is the micro switch on the throttle linkage which I have checked and its also fine. If a code shows on the X11 does does it have to be cleared before the duty cycle is displayed?
 

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1990 Mercedes Benz 190E 2.6
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Discussion Starter #6
My problem is the cold start. Once running it works as good as it ever has. Can the two prong temp sensor be a factor?
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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3,896 Posts
There is no 90%. 85% is IATS which checked and is OK and 95% is the micro switch on the throttle linkage which I have checked and its also fine. If a code shows on the X11 does does it have to be cleared before the duty cycle is displayed?
What is IATS?
I do not know the answer to that question as I have never gotten an error code from the X11 port
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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3,896 Posts
My problem is the cold start. Once running it works as good as it ever has. Can the two prong temp sensor be a factor?
Which 2 prong sensor? The aux fan switch? If that one, no that can not be a factor.

If you have doubts, the best measurement is the EHA current. That is definitive on the fuel enrichment side and it eliminates a whole bunch of suspicious sensors all at once.
If that is messed up than the reverse, there are a few sensors that are suspicious.
 

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1990 Mercedes Benz 190E 2.6
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Discussion Starter #9
Intake Air Temperature Sensor at ths air intake hose. I'll try to make a EHA test harness. I did notice that when I reved the engine to about 2500 the fuel pressure differential did not change. Should it?
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I have never tested the fuel differential at 2500 rpm, so I can not comment.

Remember we still suspect some rodent activity, so sensors being OK may not be sufficient.

Measure the EHA current. If that checks out you can pretty much eliminate all fueling issues and related sensors and concentrate on air.
 

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Discussion Starter #11
No rodent damage that I can detect. The EHA harness will be the next project. What fuel pressure should the pump put out when the ignition is first turned on? I noticed that it went to about 3bar before I cranked the starter.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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My behavior is such:

Jumps to 5bars (or so) for 1-2 seconds while the pump is running(priming), when it shuts off drops back down to 3bars.
Then when I crank it goes very quickly back to 5bars.

But the expected behavior is your pressure should hit 5bars in a fraction of a second after you start cranking.

Does your pressure not go to 5 bars when you first turn the key to ignition on? Mine does.

You should probably make note of what happens to your pressure during rough starting and running when cold.
 

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Discussion Starter #13 (Edited)
I checked the fuel,pressure again this morning. Pressure jumps to 5 + bars when key turned to ignition on then drops back to 3bar.
I fabricated a harness for the EHA using fittings from an old broken 450SL cruise switch.
Duty cycle still at 10 but fluctatiing. EHA cold -3.4mA and then tapers to -2.1mA when warm. With key on to ignition engine not running and the engine fully warm it seems to sit a 3.5mA. I I tried the harness using another multimeter and the warm reading was 0. The car is running very rich and difficult to start. Black soot in the tailpipe and idle is erratic. I wonder if the ECU is defective. Is there a way to test this?
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Hi Laura great job with creating the harness.!

Let us ignore your fuel readings, they are matching mine exactly. And my car has a super cold start and running condition. I assume after you start it jumps back to 5+ bar instantly.

Now on the EHA:

(1) Most likely your polarity is backwards. Meaning -3.4mA is actually +3.4mA.
(2) So do me a favor and turn your ignition on , engine off. Measure the current. You Should read +20mA. If it is -20mA then reverse the leads to your meter so that all the rest of the readings have the correct polarity.
(3) When you are cranking you should see your EHA jump to +64mA as you are cranking. Report on this
(4) Ignore the duty cycle for now, we'll deal with that later.

Nothing in those readings suggests you have a defective ECU. You can tell that the EHA current is near the middle, so your ECU is not doing anything abnormal.
It just seems to be missing the initial "choke" function of increased enrichment.
BTW, When your car finally catches and starts (even if poorly) running and the engine is stone cold I expect the EHA current should be +10mA to +30mA, depending on coolant temp.

If you want a pictorial on this check out my post on "EHA current, how does it behave anyway". The first graph will show you how the EHA current should behave when cold.
Just look in the first minute or two.

- Cheers!
 

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Discussion Starter #15 (Edited)
I did read 20mA at one point when the engine was stopped. Maybe I need a new battery in the Multimeter! I will check things over again tomorrow and report back. Interesting graph! Thank you.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Great! Thanks. Just make sure your answers are itemized like the questions are when you are ready.

- Cheers!
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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One more thing Laura. Please take a picture of your set-up showing the multimeter and post here.
 

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Discussion Starter #18 (Edited)
dolucasi, -20C this morning BUT I did get to try the EHA harness once again. Findings are as follows:
Key on not engine not started 20.1mA
Starter Engaged 64mA ( hard to read from inside car)
Engine running COLD 3.28
". ". Warm. 2.12

I tried testing the Duty Cycle also but I am certain the meter is reading code "10 " almost constantly which is the faulty throttle position switch code. I disconnected the battery for more than two hours hoping to get the X11 to clear the code so I can read the duty cycle but it still isnt cleared. There must be a way. When the O 2 sensor failed the install of a new one cleared that code so maybe if I disconnect the TPS it will clear the X11 until I source another. I will try that tomorrow.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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So you are getting hardly any fuel enrichment during a cold running compared to mine. 3mA is hardly any. You can compare against my readings.
I'm going to assume this is not a normal behavior for a car with (yours) or without(mine) EGR.

So at least we know why your car is struggling at cold. And the colder the temp the worse your car will run
You can now put fuel pressure issues to bed for good.

TPS should not have much to do with the cold temp enrichment but perhaps a faulty TPS causes the ECU to return to default mode (no enrichment)?
So the logic inside the ECU could have been designed this way for some reason.

Best to check your TPS next when it gets a bit warmer in your garage.
TPS is buried deep down in the throttle body.
Also check the wiring to the ECU when you get your chance.

- Cheers!
 

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Discussion Starter #20 (Edited)
dolucasi, Thanks, it does seem to be a fuel enrichment issue but would that not be a faulty temp sensor signal that the ECU receives that determines that? There is the 4 plug one which tested OK and the one two plug beside it on the cylinder head. Is that the one that the ECU gets its signal from? The 4 plug one seems to be wired to the CSV and that works fine as the car starts instantly at -20C so it might be the wire to the ECU. I will check that but see no problem at the socket.
My car is my daily driver not a weekend drive collector car so I will have to get in with the TPS removal if that is the cause of the issue. It's a blessing that once running it seems to run well. I seem to be able to reach the plug to the TPS for testing so that will be the next project if I can find the test procedure. Thanks again for all the help!
 
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