560SL tuneup - Page 2 - PeachParts Mercedes-Benz Forum

ctaylor738 · #16 08-21-2007, 09:41 PM

OK, so you have eliminated the sensor as a problem.

My next suggested step would be to replace the O2 sensor, and re-set the mixture with the on-off ratio. This procdure is on the CD.

The theory is that the sensor is old and reading low, telling the ECU that the mixture is lean, and the ECU is enriching to compensate.

sgaar · #17 08-22-2007, 06:27 PM

I ordered a new O2 sensor and should have it mid next week. I also looked at the lambda duty cycle as described here http://www.landiss.com/mixture.htm.

The values should be:
Key on, engine off: 70% = 4volt
Operating temperature: 45%=7.5volt

I found that I got 3.65volt = 74% and 13.5volt = 1% at operating temp. Either the O2 sensor is failing (we'll see next week) or I just need to adjust the mixture per the above article. The lower % the riched the engine is running (if I am reading the article correct). There is also a thread here: '86 300E rich mixture - Duty cycle help. The fact that the duty cycle % does change leads me to think that the O2 sensor is working correctly. Would you agree?

ctaylor738 · #18 08-22-2007, 08:09 PM

The fact that you got the reference value means that the brain is working, which is good news.

I don't know your car's history, but it would be unusual to get such a low reading without something failing, so I would hold off on a serious adjustment until you get the new sensor. But you can try going leaner (turn CCW), no more than 1/4 turn at a time, and giving the system at least 10 seconds to react. Keep track of your 1/4 turns so you can get back to where the car was at least running.

ElectricElf · #19 08-25-2007, 04:39 PM

I'm not certain about the Benz 560SL - but a little smoke in the exhaust for the first couple of minutes is common on many older cars or those with a few miles on 'em - depending on the setup in the top end, after a car is turned off, a small amount of oil in the top end may seep through the valve stem sleeves overnight and wind up on the tops of the valves - so when the engine is started again, you get a little bit of oil smoke for a little while as the oil burns off. Of course I could be completely wrong.

However, on another note, I happen to have a 1987 560SL that may have a similar issue to your car - initially when the car was "cold" it started fine, and then after driving it for a while, it simply wouldn't start - a shot of engine starting fluid usually got it running pretty quick however. I've checked the resistance on the coolant temperature sensor and it seems to be correct, and I've even put a 10k ohm resistor across the temperature sensor cables, which should ensure that the "cold start valve" ie extra fuel injector is spraying like it should. No go (well it the car still wouldn't start, and I know that the cold start valve is working) - So tomorrow (since I've went and bought the CD manual set) I'll go and check out the next most likely culprit, the fuel pump relay - I've been told that it's not uncommon for the fuel pump relay to flake out, and fortunately it's not an incredibly expensive part (or difficult one) to replace. I'll post further and let you know what my automotive spelunking reveals.

Of course, if anyone has any insight as to my issue - please let me know.

-Kevin

ctaylor738 · #20 08-25-2007, 05:23 PM

I suggest two quick tests. Put your hand on the fuel pumps while someone cranks the starter to see if they are running. Then an easy way to check for spark is to buy/borrow an inductive timing light, clip it on a spark plug wire and see if it flashes while cranking.

Figuring out if it's fuel or spark is a big step forward in troubleshooting.

sgaar · #21 08-31-2007, 05:14 PM

Quote:

Originally Posted by ctaylor738

The fact that you got the reference value means that the brain is working, which is good news.

I don't know your car's history, but it would be unusual to get such a low reading without something failing, so I would hold off on a serious adjustment until you get the new sensor. But you can try going leaner (turn CCW), no more than 1/4 turn at a time, and giving the system at least 10 seconds to react. Keep track of your 1/4 turns so you can get back to where the car was at least running.

I got the new O2 sensor and got it installed. It was VERY black from sod but otherwise looked fairly new. Well, I got the new one installed, started the motor with not change in the amount of smoke or how the engine idled. I measure the duty cycle and it was still very <1% so I deceided to let it get to operating temp and them I adjusted the mixture. I got the pin 2-3 voltage to about 7.5 vold and it was like a new car. Idled much better, easier to start (and cold start this morning). I took it for a quick drive and it had much more pick-up and go than before. Overall a great outcome to my smoke problem.

I moved on to my steering wheel slack. I looked at the tierods and drag rod and the ball joints looked very worn and one of them had some play. I figured that it was my problem and ordered some new rods. Got them installed this morning but I found that some of the slack also comes from the power steering box. Now, I would like to avoid paying $500 for a new one some my question is if ther is anything that cam be done to eliminate the slack other then getting a new one?

Also, are there any tourque values for the tie and center rod? For now I just tightened them as much as I though safe.

ctaylor738 · #22 08-31-2007, 09:38 PM

Nice wrench on the mixture/O2 sensor. But what got it so off-base in the first place?

On the steering, see if the slop is coming from the steering coupler. Several posts on this. You need to look up behind the box while someone wiggles the wheel.

sgaar · #23 08-31-2007, 11:10 PM

Quote:

Originally Posted by ctaylor738

Nice wrench on the mixture/O2 sensor. But what got it so off-base in the first place?

On the steering, see if the slop is coming from the steering coupler. Several posts on this. You need to look up behind the box while someone wiggles the wheel.

I don't know what got it so bad but the seal for the mixture screw was missing so I am guessing that someone fiddeled with it before I got the car. I am guessing that it was a while back since the tip of the exhaust was completely black and very sooty.

On the steering; when I had the tie and drag rods off today I could feel the slop in the steering arm connected to the power steering box. I moved it back and forth but didn't see the steering collumn move. I was looking to see it it was just a loose nut but it didn't seem like it.