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Today's adventure took a bit of an unexpected turn. Drive to work no issues. Coming home I figured I'd let the car warm up first before leaving and doing a longer drive home. That plan fell apart right away. Turning the car on it started with rough idle, voltage was 14.7 but amps were 40+ and check engine light was on, I don't recall seeing that before. I let it run for a bit and then turned it off. Restarted and no rough idle but engine light was still on. It was running for a few minutes and then went into rough idle and current started to slide around, engine light is now flashing so I turned it off. Third time started fine but light was on but eventually moved to rough idle with amps all over the place, 50+ to -30 and engine light flashing again. Fourth time it started fine and ran fine all the way home though voltage was lower and amps were moving around. Scan gave me another code:
Now it's saying coil 4 has an issue, so maybe something to work with.
Thanks.
I wouldn’t be concerned about voltage output just yet. The misfire is the more pressing concern. Check all the wires to the number 4 coil, check connector, unplug and insure pins and terminals look sound. Another thing could be terminal fretting. That is where a terminal has lost tension on the associated pin leading to intermittent open in circuit. It requires a sized terminal pin to test pin drag. Do not stick anything into terminals as it could deform it. But wiggling while engine running may isolate the issue.
If that doesn’t show any difference, you can swap number 4 coil with another cylinder and see if misfire moves with coil. If it does, replace coil, if not, then move number 4 spark plug to another cylinder, if it moves with spark plug replace all plugs, if no change, most likely wiring issue, but can be the driver in the PCM acting up, if that’s the case may be associated with funky voltage readings as PCM controls voltage regulator too. But tests need be run to confirm.
Thanks Rick. I need to decide if I'm going to attempt this or just take it to a local shop.
Sure, smart thinking. If you decide to attempt, you have here several good people willing to help. I did this for a living but I always considered myself as a student rather than an expert, simply put someone always finds a better way to fix something. Just keep in mind things we try to share, and hopefully if you choose you can either find success in fixing yourself or success in finding a reliable shop.
As some would tell you, I have issues with dealers service departments, so I would advise a reputable independent shop that specializes in Mercedes or German cars. If you have a local German car club, they can tell you who they like.
Good luck, and keep us posted on your progress, my friend.
Stick one of these in the cig socket to monitor the battery voltage all the time
Shows what voltage you have before you crank
and charging voltage while you are driving
Sure, smart thinking. If you decide to attempt, you have here several good people willing to help. I did this for a living but I always considered myself as a student rather than an expert, simply put someone always finds a better way to fix something. Just keep in mind things we try to share, and hopefully if you choose you can either find success in fixing yourself or success in finding a reliable shop.
As some would tell you, I have issues with dealers service departments, so I would advise a reputable independent shop that specializes in Mercedes or German cars. If you have a local German car club, they can tell you who they like.
Good luck, and keep us posted on your progress, my friend.
Thanks!
A friend told me who he used and there is a gentlemen down the street with an S and CLS so I'll pick his brain.
I'll definitely keep you posted.
Stick one of these in the cig socket to monitor the battery voltage all the time
Shows what voltage you have before you crank
and charging voltage while you are driving
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
