Arthur,

I checked the voltage on the heater circuit, it reads 12.6 volts. I checked the resistance on the two white wires leading from the O2 Sensor, it read 3.3 Ohms with the meter set to 200 Ohms setting. What do you think?

Thanks again,

John Bjork

Well, you have heater, but the sensor may be getting weak..
The true heater test is to see if it draws 1.2-2.2 Amps
The sensor has to be kept at 600 degrees to work, so sometimes the exhaust can't maintain that at idle , so the heater is an aid for that, plus it gets the sensors into closed loop fast at cold start.
But , it is not uncommon to see a drop of 02 readings after 20 secs or so at idle as a sensor ages. Some new sensors even have a low reading at idle . You want to do my rich/lean test after a 1 or 2 min/2500 rpm run to be sure the sesor is good and hot. Then do both rich/lean right away. That will tell for sure.
Then an actual in-situ test is 02 monitor at a 2K rpm and watch for sensor to cross count the 4.5 v line at least 1 htz when ECU is hooked back up.

You may also want to clean the MAF. MAFS get dirty film on them and tend to run rich, specially at lower rpms.. MAF cleaner aeresol at any parts place.

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A Dalton

On the later engines I would agree, but the early hfm cars tend to not throw codes that readily. I have seen timing off on a 104 without any cam position codes present, just similar symptoms as described in this scenario.

Maybe ...
The problem I find here is he does not have the problem once the car has warmed up to temp..........

quote:

<<>

My specs show a currect draw of 1.2-2.2 amps for heater, so that would equate to an R factor of from 6 to 10 ohms.. Your 3.3 ohm would be almost twice the spec. amp draw.
so, if your ohm readings/values are correct, you may have a shorted heater element. Try to redo that ohm test on a lower range setting, if your meter has one.... a better reading would be current b/c most low end meters have a hard time with accurate low ohm readings.
Amp draw will require meter in series with circuit..........

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A Dalton

Arthur,

I've got two things I'm going to try. First, I'm going to go to the parts shop and check how many Ohms the resistance is on a new O2 Sensor to check if the old one and a new sensor have similar resistances.

Second, I've been reading about the resistor spark plug problem. I replaced the plugs about a year ago with whatever Bosch was recommended by my local parts store. I pulled one out today and sure enough, it was a resistor plug: FR8DC. I think the proper plug for my car is an F8DC4. I'm going to order some of the F8DC4's and see if there is a difference in performance. I'll post what I find.

Thanks again,

John Bjork

Must have missed that Arthur, I thought it was a problem all the time, not just cold.

FR8DC's are Bosch's replacement for the F8DC4, which is on the way out. We havn't had any real issues running them. I wouldn't be surprised if the spark plug connectors go out a little sooner due to the resistance but other factors influence their life too so it would be hard to quantify.

Yes , no more F8's...my concern with R plugs on that engine is it is both a waste spark system , and they are known for weak plug connectors from the get-go, plus he has the early version which had the Blue coils..they were not the best and the later ones seem a lot better. The real prob seems to be when they use palts, and I think that is b/c the second plug has to fire from ground back to electode ..and the plats electrode is quite small..but that is just my theory.
Might want to have a look at both MAF and IAT sensor......

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A Dalton

OK so heres where I'm at now. After testing the O2 Sensor, I cleared any faults with my code reader. I ordered a compression tester and a new set of the correct F8DC4 spark plugs. I drove the car for about a week to check for any fault codes, and then when the plugs and compression tester arrived, I changed the plugs and tested the compression. Here is what I found:

1.) I retested the O2 Sensor heater by putting the Meter in series with the heating circuit. It started at about 2.0 Amps then fell to a constant 1.4 Amps. The O2 Sensor seems to within its operating specifications.

2.) I checked for fault codes after driving the car for a week. No faults at all, on any system. All came back with 1 flash.

3.) The spark plugs that I removed look very good. Nice clean look, a little bit of white and very minimal carbon buildup after about 1 year in the car. All plugs looked alike.

4.) The compression test results as follows, done with all plugs removed, the throttle full open, and the engine hot:
- Cylinder #1 = 82 PSI
- Cylinder #2 = 80 PSI
- Cylinder #3 = 80 PSI
- Cylinder #4 = 80 PSI
- Cylinder #5 = 77 PSI
- Cylinder #6 = 77 PSI

5.) New Bosch F8DC4's installed. The car runs better with these plugs but the problem is not completely solved.

6.) Note on the current performance, when I first started this post, it was late winter here in Minnesota. Now its summer time and the car has been running a bit different. Basically the car is very sluggish at low RPM's then at about 2800 RPM, it seems to really kick-in and take-off. In the summer heat, the engine seems to run better just before it completely warms up. On hot days the car is at its sluggish worst and when the AC is turned on the car accelerates at a snails pace. When I hit the accelerator, the engine sound reminds of an old Chevy V8 with the ignition timing too retarded. Not snappy but rather fighting to increase RPM's.

7.) Also while working on these problems, I've noticed that I am leaking a little oil from what looks to be the head gasket. The leak is at the back of the engine on the drivers side. I do not have any milkiness in my coolant nor do I have any smoke coming from the tailpipe.

Any ideas? Thanks in advance for the help.

John Bjork

Yep, it does indeed look as if the cam timing is off.

To check the cam timing you have to pull the valve cover and set the engine at TDC. If your cam lobes on #1 aren't pointing somewhat upwards and towards each other then rotate the engine another revolution.

Once you are sure you are at TDC then take a pair of channel locks and grab the intake cam 1/2 way down it's legnth and turn it towards the exhaust cam until you feel it stop. If it doesn't move at all then all the slack is already out but pull it a bit clockwise and then back counterclockwise to make sure you feel the stop. This takes out any slack from the variable cam timing.

Now you need to locate the timing marks, the marks are actually small holes in the back side of the camshaft gear flanges. The holes are approx. 3mm and will be located toward the outside of which ever cam you are looking at when the engine is near TDC. There are several holes visable on the back side of the gears but the timing hole is the only little one. To check the timing you insert a 3mm rod a few inches long (I use a 3mm allen wrench) into the hole. The allen wrench should lay close to flush with the top of the head if the cam is in time. Don't fret if it isn't completely flush as chain wear will have the intake a little above flush and the exhaust a little below flush. If you have one that is a lot less than flush (I seriously suspect you do) you need to eyeball it and determine if moving it one tooth will put it back nearer to flush with the top of the head.

Once you have found which cam is out, (most likely the intake) you will need to re-time the eninge. That isn't any fun as the front upper timing cover has to come off. Trust me, although it looks as if you can slip the chain over the gear with the tension off, I assure you that you can not. But you can worry about re-timing the engine after you know it is out.

You may want to unplug the cam advance solinoid at idle and see if there is a change.....could possibly be getting an sig input for cam advance when it should not..

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A Dalton

Arthur and Dux,

Thanks for the replies. I think the cam timing is a little out of my league, I'm going to look for an independent mechanic in the Minneapolis/Saint Paul area and get a quote.

I am unfamiliar with the Cam Advance Solenoid. Can you give me a rough idea of where and what to look for?

Thanks again for all the help,

John Bjork

As Dux has stated , you have low compression all the way across...so...
that would point to a jump in cam/valve timing..most likely chain.

But...
This car has a variable cam timing feature and that is done by The ECU sending an electrical sig down to the cam advance magnet [ solinoid] That is at the front of the head .. round device w3 cap screws... two wire plug goes to it.
I have never seen one stick, but I have read about them failing right here on this forum. There shoud be NO sig to this actuator unit until a certain RPM [ 3K in N or P..] at which time the intake cam advances valve timing for more power. However... If this gets a sig at idle, the cam will advance when it is not supposed to, or the mechanism inside could be stuck..
The test for cam advance magnet is to unplug the connector and bring a 12V battery jumper over to the solinoid at idle ... that will cause the cars idle to be adversely effected b/c you are advancing the cam manually at too low a RPM .. it will run like crap, but that will confirm the mechanism is working. Or, if one suspects a sig to it at idle [ causing the same complaint, unplugging it would see that difference...if it is working as it should [ electrically] there should be no change at idle. In other words, there should be NO 12 V at those wires at idle.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2EI1B4MYE2EN1CY8CT&year=1993&make=MB&model=300-E-003&category=A&part=Camshaft+Adjuster+Magnet


But again, this is just a quick test to rule that possible out before going in there for possible chain jump....

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A Dalton

One quick question.

When doing comp test...did you let the engine crank several turns for each
test..

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A Dalton

Arthur,

Thanks for the response. I tested each cylinder twice and I rolled the engine several times on each test.

I found the cam advance solenoid. I pulled off the 2-wire connector and I tested each lead for voltage. At idle, one lead had 13.5 Volts, and the other had 0.5 Volts. I know you said there should be no volts at idle, so I left the unit disconnected and test drove the car and it ran very poorly, no power.

I'm not really sure what to think now. Maybe a prior owner "hot-wired" the lead to compensate for a valve timing issue. I don't know. I haven't found any splices and all the wires in the car look good, no cracking or flaking that I can see.

I will test the solenoid itself with a 12 Volt lead from the battery tomorrow and see if I can hear the solenoid activating. Also I will see if it affects idling.

Thanks again,

John Bjork