systematic testing of fuel components - Page 3 - PeachParts Mercedes-Benz Forum

lsmalley · #31 04-25-2014, 08:47 PM

Quote:

Originally Posted by JamesDean

This makes me wonder...

If the EHA is unplugged:
1) Is CIS-E aware of this fact?
2) Does CIS-E fault out?
3) When it fault out does it return to open loop control?

If 1,2,3 are true then you are presented with the following:
1) Is the EHA really bad?
2) Or did reverting to open loop control resolve the problem?

Of course if it stalls out again..then none of the above matters..

I'm not sure what open or closed loop mean. I did read somewhere in another post, maybe on this forum or another, that the CIS-E is an electronically controlled injection system, however if the electronic component is taken out or in this case unplugged, then it would just be CIS, or a mechanical fuel injection. JD, I know your knowledge is extensive when it comes to the elctronics of these cars as you have helped me in the past and I am aware that you often dissect bad electronic components to see what makes them tick and if there are parts that can be fixed or resoldered to make them work again. Someone posted something with the analogy of the EHA being like a tennis raquet or something, but I was not following what they were saying. The EHA valve - in the inside of it, is there a part that can become loose or stuck in a certain position to cut off the fuel supply to the injectors and cause the car to stall? Seeing that the car would only stall when decelerating or coming to a stop, but never while accelerating or already stopped. My reasoning was that if there is a part that moves via electric current to control fuel output was in a position where fuel was not being cut off, then unpluggin the EHA would cut the power supply to that part and it would be stuck in that postion where fuel was being supplied, but if I were to unplug it after it has stalled then the part would remain in the position that does not allow fuel to go to the injectors at the proper force and the car would never start. But I am sure that when I stalled a few days ago and sprayed carb cleaner on the plate it would run as long as I kept spraying bursts of cleaner, but once I stopped, so did the engine. Tapping on the EHA may have been a coincidence that the engine fired right up without spraying carb cleaner on the plate.

JamesDean · #32 04-25-2014, 10:56 PM

Quote:

Originally Posted by lsmalley

I'm not sure what open or closed loop mean. I did read somewhere in another post, maybe on this forum or another, that the CIS-E is an electronically controlled injection system, however if the electronic component is taken out or in this case unplugged, then it would just be CIS, or a mechanical fuel injection.

Basically:

Open loop means w/o feedback. The system uses only the current state and tries to achieve the desired output. It knows nothing of errors.

Closed loop means the system uses sensors and error correction devices to achieve the proper output. Sensors being temp sensors, oxygen, air/throttle position. Error correction devices in this case being the EHA,etc.

Quote:

JD, I know your knowledge is extensive when it comes to the elctronics of these cars as you have helped me in the past and I am aware that you often dissect bad electronic components to see what makes them tick and if there are parts that can be fixed or resoldered to make them work again.

To be honest I've never worked on any of the CIS-E components. I've never had reason to. Would certainly be an interesting endeavor.

Quote:

Someone posted something with the analogy of the EHA being like a tennis raquet or something, but I was not following what they were
saying. The EHA valve - in the inside of it, is there a part that can become loose or stuck in a certain position to cut off the fuel supply to the injectors and cause the car to stall?

I'm not sure of the analogy but here is a good article and drawing of the EHA that you might find useful.
http://www.boschautoparts.co.uk/pdf/3-934584-28-4.pdf

Quote:

Seeing that the car would only stall when decelerating or coming to a stop, but never while accelerating or already stopped. My reasoning was that if there is a part that moves via electric current to control fuel output was in a position where fuel was not being cut off, then unpluggin the EHA would cut the power supply to that part and it would be stuck in that postion where fuel was being supplied, but if I were to unplug it after it has stalled then the part would remain in the position that does not allow fuel to go to the injectors at the proper force and the car would never start. But I am sure that when I stalled a few days ago and sprayed carb cleaner on the plate it would run as long as I kept spraying bursts of cleaner, but once I stopped, so did the engine. Tapping on the EHA may have been a coincidence that the engine fired right up without spraying carb cleaner on the plate.

You might be entirely right that the EHA is the problem. My main point was that before you go spending $300 on a new one, I would see if someone on here would be willing to lend you a good EHA so you can double check that it is the EHA. If the known good EHA does the same stalling thing then there is a good chance that the problem is not the EHA.

From what I can gleam from the document above the EHA has a "limp home mode" where if control current is removed it will default to a lamda of 1. What I'm not sure of is if there is EHA failure can a blockage/seizure of pressure can kill the engine...

Hope this helps in someway !

lsmalley · #33 05-06-2014, 03:11 AM

Well I bought an EHA and installed it and I have not stalled for a week since putting it on. I am glad on that front, however my car is still running very rough and it does not matter whether the car is warm or cold. Need some help with reoslving this. Will go update the original post to that issue.