Does a DI ignition system in a W201/W124 hold vacuum? - PeachParts Mercedes-Benz Forum

Stretch · #1 04-19-2015, 06:03 AM

G'day Folks,

I'm chasing down what I think is a vacuum related problem on my W201 - M102.910 engine

As all vacuum comes from the intake manifold I've been testing from the two points where it originates (there are actually three but because I don't have an automatic transmission the third is blanked and is being ignored).

At the back of the intake manifold on the upper side there's a Y splitter that sucks to two places =>

1) the cabin blower motor controls (seems to be a some sort of semi-automatic blower motor system that has a vacuum switch to activate the flow of coolant through the heater matrix) and the adjustable headlights

2) the vacuum sensor on the ignition control module

The vacuum line is the only non numbered part on the module (#14) shown in this picture!

When I apply a vacuum to the line it doesn't hold.

I've only done this with the ignition off - I'm guessing there isn't any mechanical movement within that little box...

...so the question is =>

"Should this little bugger hold vacuum or not?"

I'm guessing it should.

I can't find anything in the FSM about this though (other than references to the vacuum line helping the module determine engine load)

lsmalley · #2 04-19-2015, 06:45 AM

Mine is an M103, slightly different ezl, but mine does not hold vacuum either. I'm guessing it's just an internal sensor of some sort within that adjusts or reads according to vacuum. What you can do is unplug the vacuum line and run the engine for a bit. If it's functioning correctly you should get an error code.

lsmalley · #3 04-19-2015, 06:45 AM

By the way, you never really explained the symptoms your car is having.

Stretch · #4 04-19-2015, 07:16 AM

Quote:

Originally Posted by lsmalley

By the way, you never really explained the symptoms your car is having.

Nope I didn't because I didn't really want to confuse.

I'm quite surprised it doesn't hold vacuum because this suggests it does

EZL & Vacuum?? - Mercedes-Benz Forum

Anyway (just in case) problems are two fold

1) The semi-automatic blower motor always runs but occasionally when there is a sudden change of engine revs the fan switches itself off - I'm guessing this is vacuum related (engine load)

2) Real problem - I don't really care about problem #1(!) - is an unwillingness to idle during use.

Start the engine - idles fine

After driving the car the engine will more often than not idle fine too

However when driving the car - change from low gear to high (say) or change down from higher gear to lower the engine revs fluctuate wildly about idle until they "find themselves" - sometimes during this process the engine will stall.

(It might be the fuel pressure accumulator - pretty sure it isn't external electrical to the EZL as I've checked that side quite extensively previously)

Stretch · #5 04-19-2015, 07:54 AM

UPDATE =>

Suffering from finger trouble I found that the EZL / Ignition module does indeed hold vacuum - I just had trouble sealing a vacuum line on my tester

(For the record my ignition module has the following MB part number 010 545 53 32 just in case other versions don't behave in the same way)

lsmalley · #6 04-19-2015, 03:39 PM

I'm a genius....when I read your post I came out to the garage and grabbed my mityvac and disconnected the vac line and plugged that into the vac.....it did not hold vacuum because the other end was going into the manifold :-\ I just read your post again and thought, oooops something is wrong. So I'm in my garage now and yes, it does hold vacuum. I connected to the wrong end last night. Sorry.

lsmalley · #7 04-19-2015, 03:56 PM

Check fuel/air mixture.....I think this has happened to me when the mixture was off. Also check the O2 sensor

Stretch · #8 04-20-2015, 01:23 PM

Thanks I'm starting off with new crankcase breathing hoses and the connection to the fuel regulator