You don't test each lead to ground ..you test across the leads b/c the ECU does the switching on the ground side.

The best test is the 12v jumper test b/c that also checks the inner mechanical workings of the advance mechanism. As you switch that jumper power on/off , you will see if it is working by engine response.
I am not eliminating the possibility of a jumped chain and that is a very likely cause, [although rare on a 104]....I am just telling you that a jumped chain one tooth off is an 18 degree valve timing change and the advance feature on that chassis is a 20 degree change...so my common sense tells me that I would do a simple advance solinoid test before ripping anything apart...just a simple test ..hate to see you take it all apart and then see the problem was not a jumped chain.
Kinda like taking out your starter before turning on the headlamps to test for a dead battery..............

OK, so I tested the Cam Advance Solenoid today with a hot lead wire connected to the battery terminals. With the engine off, I connected a positive and a negative lead to the two prongs of the solenoid. I could hear a click-clack sound inside the head.

When I started the engine and connected these hot leads again to the solenoid, the engine idled down a little. I could definitely tell that engine experienced a change when the solenoid was manually activated.

The strange part of this is that even though I had current in the connector plug that I had previously disconnected, I could not hear a change in the engine idle when I reconnected the connector plug to the solenoid.

I tested for fault codes and I found that I had fault #38 on pin 8. This is the fault for the Cam Solenoid. It looks like the car knew the solenoid was unhooked.

I figured that maybe the 13.5 Volts that I had measured from the solenoid connector plug could be the engine diagnostic trying to read a response from the solenoid. So I reconnected the solenoid plug but I left a sliver of room to test the prongs on the solenoid when the connector plug was reconnected. With the car running and the solenoid connected, I could not measure any volts across the two leads connected to the solenoid.

Any idea what this means? Maybe I should try to wire in a hot lead to the solenoid so that I can test not only the idle, but how well the car drives when the solenoid has been artificially activated?

Thanks again for all the help,

John Bjork

Like I said....There is always 12 pos at the cam solinoid. The switching to activate the solinoid is done on the neg side by the ECU..it is a SWITCHED GROUND circuit.
In a S/G circuit, the switching to complete the circuit is done on the ground side of the circuit, so just cuz you have battery voltage on the pos side of the solinoid does not mean the solinoid has a complete circuit..it does not have a complete circuit until the ECU grounds the other leg. Only then will the solinoid activate. This is quite common on ECU switching..same as your blower or ign, etc..they are SWitched Ground circuits , not switched positve circuits.

The criteria of the cam advance on that chassis is:

No Load/ N or P
3000 RPM activation/advance /20 degrees/intake valve cam

Under Load :
1500 RPM to 4200RPM/Load Dependant Advance Range - advance 20 degrees
4200 and above RPM.- Cam Advance Retard

When those criteria/demands are met , the ECU will ground the return leg of the solinoid circuit and you will have cam advance b/c you now have a completed circuit. [ pos to sol.> thru sol coil >back to ECU> ECU to ground/ neg]

If you are testing the solinoid for activation in N or P , you can hook up your meter to your 2 wires at the plug [ back-probe] , but you must meet criteria of 3K RPM. When the engine reachs 3K, you should read 12v on meter.
The reason that I have you jumper 12 v to the cam solinoid when it is at idle is b/c there is no criteria for cam advance at that RPM, so if we manually induce some, we will see an idle change IF the cam solinoid AND mechanism are activating..it is just a test that we trick the engine with...just like when you want to test your EGR valve ..the egr is designed to NEVER opens at idle, but if we MANUALLY open it at idle with a hand vac pump, the engine will run very rough..that tells us that the EGR is in fact OPENING and the passages are clear..it is just a test that is out of the NORMAL engine running condition and it's results tells us what is working inside w/o taking stuff apart.
That's all.... the cam should not advance at idle , so we make it advance just to see if it works...the engines responce to our cam input tells us if it is working..if it did NOT work, the engine would do NOTHING different, even though we have brought 12v directly to the solinoid, thereby eliminating all controls..you are the ECU and you are looking for the engine to respond....the ECU is out of the picture b/c you do not have it plugged in.

So, if you have a definate change in RPMs with a jumper to cam sol. from battery [ pos and neg] at idle , the advance is working and the test has passed...so, suspect is now timing chain. If your car did not have this advance feature, I would have gone with the timing chain right from the start, but you can see why this test is performed with cam advanced engines. When one notices that surge of power that the 104 HFM engines are so well know for, it is the cam advance along with the intake variable runner length kicking in...it's like a whole new power-plant....kinda cool..........

Arthur,

Thanks for the reply. It makes a lot more sense now that I know how Mercedes set of the pos and neg to the sensor. I would not have guessed that.

I'm going to start looking for a good MB tech here in the Minneapolis/St Paul area. Do you think I should look at replacing the timing chain along with the adjustment job? I was thinking about what else would be an easy, accessible job since the engine going to be opened up for valve timing adjustment.

Thanks again,

John Bjork

If the timing chain has jumped . it is definately going to have to be replaced.
So, any rails and chain tensioner should be looked at then too.
And make sure whoever does the job is aware that the tensioner is a ratchet design and has to be reset when re-installed or the new chain will break the cams right in half.
Many guys [ even Techs] do not know about that until they learn the first time.
I might add that I am almost surprised that the engine runs at all with comp that low...those engine are high comp and usually run close to 200psi.
[ Although that spec would be on the 3.2 version, so maybe on the 2.8 the comp is much lower ]

Also, The code for cam advance was b/c you had unplugged the sensor, so that diagnostics module is working nicely.


Might want to read this article by SB ..Kinda covers the ins and outs of 104 top end well..

http://www.peachparts.com/Wikka/M104HeadGasket

Might even be a good idea to print that article out to show whoever..........................if ya know what I mean.

One more possible..
If this car was purchased used and you have had this problem since you owned it, it is possible that it had a head gasket repair b/c of the common leak they all incurred, and possibly the repair person never did adjust the valve timing correctly when doing the head gasket..

Just a thought.

Did you ever do the head gasket and was this car bought used and if so, did it have this complaint since you have owned it??

I bought the car used and I didn't get any info from the previous owner because I purchased the car through a third party. The car has performed this way since I've owned it. I thought it may be normal since it was my first MB but I had someone familiar with these cars drive my car and commented that mine was very sluggish at low RPM's.

It is possible that head work was done on the car, but I'm not sure. First, the EGR/Secondary Air Injection module has been taken on and off at some point. I know this because whoever removed it broke off the mounting bolts from the head. I'm not sure why this module would need to be taken off unless someone was removing the head.

Second, there are old oil deposits/buildups near the front end of the engine which suspect may have come from oil leak that has been repaired. The oil leak would be the characteristic front end oil leak that I read about for this car. If the head gasket was changed, then this would have fixed that oil leak. Its strange because now I have the usual oil leak near the rear of the engine.

When I first purchased the car, I found lots of plugs disconnected under the hood. It seems like the prior owner was trying to troubleshoot the car by disconnected all the sensors. I've spent a lot of time tracing wires and checking error codes until I've found and reconnected everything that will create an error code. Any anything that I can visually see disconnected. Believe me, the car runs a lot better with everything hooked up and working!

Thoughts?

Thanks again,

John Bjork

Sounds to me that the head gasket had been done and it would not be far fetched to find they did not time the cam correctly upon re-assembly.
These cars are not sluggish at all, even the 2.8...they are a high pereformance engine, as some of the performance features demonstrate. A variable valve timing and variable intake runner engine with DIS ignition is not a snail. [ even though most of the performance power is after 3K]
You have poor compression, [ you are sure on these readings ?], so all of this fits incorrect valve timing..could be a jumped chain or someone got in there before you bought the car and did not know how to set up the timing [ b.c it is a little tricky on cam advance system].... now that we know it has been like that since you bought it and lots off other stuff was fooled with, I would go with the later possible b/c 104 valve train and chains are know for durability way beyond earlier engines..they are known to go 250K with no chain problems at all..not even valve seals.
Not to say it is not a jumped chain either....it is going to have to come apart and at least see if everything lines up as it should. Just make sure who does look at it is familiar with that engine b/c it is not like the old TDC /Cam index mark line up simplicity of the previous IL-6 engines ...anyone could time them.
Now that you have read a little about the dowel pins alignment, you may want to take the cover off yourself and take a peek...can't hurt just lookin............
I would also go back to Dux's Post # 40 and print it out. [ along w/SB article] Then, give it to the guy that is going to check it and ask him if he is familiar with that procedure..he will give you a definate YES if he has " Been there/Done that" before.
.....otherwise, move on.
Like I say, read it a couple of times and you may want to take a look yourself.

http://www.lmvindmercedes.com/smpl-commoninstruct.htm