bad news 16v - PeachParts Mercedes-Benz Forum

jasondew · #1 09-18-2002, 07:57 PM

i've been fighting with my car lately with a variety of problems. something's causing the ABS to fail and shut off and something is causing a horrible idle. today i rechecked my wheel speed sensors for metal or debris stuck to the magnet (nothing). a few days ago i found a crack in my exhaust just before the 2 downpipes collect to one pipe under the car (i haven't been able to weld the crack yet). i replaced the overvoltage relay because when the ANITLOCK light flickers on and off the voltage meter spikes and drops wildly and the engine hesitates--no improvement. here's the bad news: i pulled my spark plugs to look at them and found that the ceramic on 3 of the 4 had cracked. trying to solve this idle problem, i just replaced all the plugs about a week ago. at that time i noticed that 2 of the 4 plugs were cracked. also, the two electrodes are clean but the metal portion around the electrodes (the bottom of the threaded part of the plug) was covered in black soot. the plugs are gapped correctly and the wires are in good shape. what does this mean?

please help--my 16v sucks.

thanks

#2 09-18-2002, 08:28 PM

Cracked insulators are often signs of DETONATION, a bad thing. Garbage gas or funky timing are the most common issues. For timing issues, use two different lights or magnetic sensor to insure the one used originally is at least reasonably close. One national agency did a study a few years ago and found these instruments varied as much as 10 degrees among those tested.

Leaving detonation go on very long will put you in position to buy new pistons.

Benzmac · #3 09-18-2002, 08:31 PM

Replace the overvoltage relay. It has control over both systems mentioned.

jasondew · #4 09-18-2002, 09:41 PM

i just changed the overvoltage relay and it didn't change the idle. i noticed the spark plugs being cracked so i didn't get a chance to test the brakes.

also, this rough idle came on suddenly. when i was driving around my local test loop checking out the brakes the idle was fine. when i came to a stop at a light the idle was rough. what could have happened all of a sudden while driving that would make the idle rough?

i hope i didn't mess anything up, but i did adjust the EHA about 1/10th turn clockwise to richen the mixture and provide a little more power. the engine seemed to have a little more torque after i did it and i drove it with no problems for about a week before the idle problem popped up suddenly. i've heard of many people doing this with no problem so i don't think this is the cause but i wanted to mention it.

i mentioned earlier that the ceramic has cracked. i was referring to the ceramic on the outside of the plug where the wire goes, not the ceramic on the cyclinder side. the ceramic on the cylinder side has frosty appearance.

my mechanic said that he couldn't hook his diagnostics computer up to the ABS. don't all the diagnostics for all the systems just come through the one diagnostics harness?

should i even drive the car the 50 miles to my mechanic to have him check it out?

thanks

Robby Ackerman · #5 09-18-2002, 10:41 PM

Three times during the past 18 months I had rough idle problems start out of nowhere. Each time I fixed it by unpluging and plug the various ignition and fuel sensors. I didn't replace any parts.

Tinker · #6 09-21-2002, 07:53 PM

Jason,

You over tightened the plugs, that is why they cracked. You ARE using a torque wrench to install? I am speaking from experience..been there and cracked that.

Maybe the cracked plugs are causing a ground problem or are shorting/arching?

Sometimes it is hard to keep the 16V faith. If I could sell mine and get a decent price.....I`d buy a Lexus.

Tinker

jasondew · #7 09-21-2002, 10:01 PM

i have to admit that i'm not using a torque wrench. i've never had a problem with just estimating the torque before but then again i've never owned an engine that runs like this one. what is the appropriate torque for the plugs?

thanks

Tinker · #8 09-22-2002, 10:24 AM

Not much, 14 to 16 ft/lbs.

If I am not mistaken, the plug is not like a typical spark plug in that it sits in a V shaped port and has no crushable washer (???, can`t recall). Anyways, once they seat, its a slight turn and thats it.

Tinker

jasondew · #9 09-22-2002, 01:37 PM

you're right, it has no washer; the plug sits in a tapered hole. i guess i have been tightening too much. i've been using about 18-20 ft*lbs (estimated). thanks for all the help.

meek · #10 09-22-2002, 07:16 PM

That's funny. Those are two of the things my car is doing. Do you get the occasional loss of pedal firmness and grinding along with the Antilock lighting up while coming to a stop? My car idle sometimes goes from 800 to 1400 and back down. I am trying to sort it out as well. Good luck.

190dee · #11 09-23-2002, 03:32 AM

One thing to check if the abs lights up is definetly the ovp. You check it by applying voltage to some of the pins on it. Do a search on the forum because somebody did already post how to test it for functionality.

The ovp IS a very common failure when you get bad perfomance AND abs light on.

Robby Ackerman · #12 09-23-2002, 07:07 AM

Was it the idle control switch you disconnected?

Si.

... This weekend a fellow 16V driver mentioned to me that he cured his erratic idle problems by permenantly disconnecting the idle control switch.

#13 09-25-2002, 08:26 PM

Diconnecting helps for warm starts; not good for cold starts. At least that's what I experienced on my 16V. So far (fingers crossed), my idle has been fine. The last thing I did to make it so was install new plugs (Bosch Copper), torqued to 15 ft-lbs

Prior to that:

new Fuel Pump Relay
new OVP
new Idle Control Valve
new cap
new rotor
new injectors and seals

Waiting to be installed: new Deceleration Microswitch and Dual Coolant Temperature Sender

Brian16V

#14 09-25-2002, 09:51 PM

For what its worth, my son's 89 Mustang 5.0L used to get a rough idle and I would disconnect the rubber/plastic air supply at the throttle body and use a rag wrapped around my finger sprayed with carb cleaner to clean inside of throttle body after rotating throttle plate 90 degrees. His throttle body and sometimes plate accumalated a sooty residue that apparently would cause the throttle plate to stick when it was in the almost closed position with small movements, i.e. idle. Takes about 20 minutes and doesn't cost anything - give it a try - and good luck.

Hilton Smith

#15 09-26-2002, 03:01 PM

I dislike saying this, but disconnecting idle controls to get a better idle and hot start is a jury rig for emergencies. Wholesale replacement of the fuel and electrical controls will cause you to spend more on parts than a good diagnostic session. Put the meters and gauges on the systems and see what is happening. Some of the stuff Brian replaced is routine, maintainence-type stuff. Others, like the injectors, should only be replaced after testing.

What if your erratic idle is the result of a worn valve guide causing combustion leaks? What if it's a worn throttle body or a sticking control piston in the fuel distributor? As Hilton noted, accumulated crud, especially in the airflow sensor box and throttle body are candidates for service.

How erratic is the idle? +/- 50 rpm, 100, 200? An occasional miss followed by a brief surge?

Finally, since warm idle mixture is controlled primarily by the lambda unit, an exhaust leak in front of the O2 sensor can have an amazing amount of influence on the sensor. Essentially, the unit sees an entirely incorrect version of the exhaust gasses as the leak changes back pressure and (depending on the size of the leak) actual makeup of the gas passing by the sensor. Fix the big, obvious problems first, then go to the analysis and test procedures.