w124 603 electronics, ECU, what's it for? - PeachParts Mercedes-Benz Forum

locry · #1 06-16-2007, 09:57 AM

i always thought 603s were all mechanical, so why do i have an ECU? and there's this AFM type thing under the airfilter... what does it compute and why, and what does it do mechanically? lessen fuel output, if yes, then how does it do this? i don't see any servos/solenoids on the IP.

jcyuhn · #2 06-16-2007, 10:14 AM

The ECU controls the idle speed and the two vacuum valves which regulate the EGR and the boost. The air flow meter in the airbox is an input the ECU uses in controlling the later two functions.

Other that idle speed none of this is really necessary. You can block off the vacuum source to the two vacuum valves located under the air cleaner and the car will run better.

- JimY

2.5Turbo · #3 06-16-2007, 03:43 PM

On the 87's, the EDS only controls the idle speed and the EGR. The boost is controlled by the pressure actuated wastegate. The EDS uses the AFM signal to decide when to open the EGR. On the 87 there are no ill effects to blocking off the vacuum line to the EGR.

justinperkins · #4 06-16-2007, 03:46 PM

Quote:

Originally Posted by jcyuhn

The ECU controls the idle speed and the two vacuum valves which regulate the EGR and the boost. The air flow meter in the airbox is an input the ECU uses in controlling the later two functions.

Other that idle speed none of this is really necessary. You can block off the vacuum source to the two vacuum valves located under the air cleaner and the car will run better.

- JimY

Do not block the vacuum line that goes to the turbo (just under the EGR). That would be bad.

locry · #5 06-18-2007, 04:13 AM

thanks for the reps guys! that cleared up a few things! just have to block off the EGR now.

Hit Man X · #6 06-18-2007, 05:59 AM

Only for idle.

Rest is emissions.

DslBnz · #7 06-24-2007, 04:29 PM

I just removed the AFM from my grey 300SDL and plumbed in a tubing section from an '84 SD air filter snorkel to replace it. I noticed correspondingly huge increase in blowby.

This has the same effect as plucking that breather hose away from the turbo compressor snorkel and venting it to the outside air. When I do so, there is no change in said emissions.

Why is this?

sixto · #8 06-24-2007, 04:44 PM

On an 87 EDS controls idle, EGR and ARV. EDS does not need a MAF signal to control idle. If you disabled EGR, disable ARV as well.

Sixto
93 300SD 3.0 - comatose

Hit Man X · #9 06-24-2007, 06:40 PM

Quote:

Originally Posted by DslBnz

I just removed the AFM from my grey 300SDL and plumbed in a tubing section from an '84 SD air filter snorkel to replace it. I noticed correspondingly huge increase in blowby.

This has the same effect as plucking that breather hose away from the turbo compressor snorkel and venting it to the outside air. When I do so, there is no change in said emissions.

Why is this?

Weird, I didn't have that occur.

Hatterasguy · #10 06-24-2007, 06:49 PM

They will run with no battery, just won't idle well.

DslBnz · #11 06-25-2007, 05:21 PM

Quote:

Originally Posted by Hit Man X

Weird, I didn't have that occur.

I reinstalled the AFM...No more blowby.

Apparently that AFM flapper creates a vacuum in the PCV system which draws the exhaust gasses back through the compressor and through the intake manifold.
You can even feel a slight vacuum at the filler cap.

Without the AFM, it is like the system is being vented to the atmosphere. With no vacuum sucking the gasses out of the valve cover.

Detach the AFM and place your hand over the turbo compressor snorkel as the engine is running. You should see a difference (thhhhhock, thhhhhock).

So,....The true test for OM60x blowby is to leave that AFM out of there, and then take note. Its cheating if you have suction, IMHO.

I did my blowby testing when the engine was very hot.