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94SL600, 76MGB, 99Suzuki Bandit 1200, 05Yamaha Warrior, 72Triumph Bonnie
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14 Posts
Discussion Starter #1
I've read every topic on this subject but haven't found what is happening to me:(

My 94 has 115K miles on her. I've had her since August and put about 1,000 miles on her myself.. All was well up until a week ago.

I changed the oil & filter myself (Mobile 1 5w30 as that is what the previous owner used) about 1 month ago. All was well.

Once warmed up, she began "missing" and plumes of smoke shot out of the exhaust. Smelled of raw fuel as well as the dark gray oil were present. My local indy discovered a broken vacuum at the brake booster check valve and I also had the right side MAS, socket and wire replaced (I knew that needed to be done, so I did it while the car was there). He replaced the bank of spark plugs on that side as well.

I took the car back and she was running great! Unfortunately, the smoke started up again (WITHOUT the gas smell present. I assume the vacuum fix cured that) once up to operating temperature.

NOTE: I DID NOT replace the main harness (I know, I know..it's the FIRST thing to do). Through my inspection, all individual wires appear to be in excellent condition, so I am not certain if they've been replaced already...That will be next on my list once this problem is resolved!

Anyway, the new plugs still look good, the codes all check out and the compression tests are being done today to see if this locates the cause.

Would a head gasket or valve cover gasket issue cause this condition? I would think that would cause external leaking and not an exhaust issue...
Would any issue with the main harness affect only ONE SIDE of the cylinders?
Can the throttle body be a cause?

There is no evidence of oil in the coolant reservoir and the trans is tight and fine.

The right side (passenger) cat needs to be replaced (rattling), but the problem obviously is before the cat. The exhaust system is completely stock.

My apology for the questions, but I have tried for several days to find my situation on the site to no avail...

Short of replacing the harness, any suggestions??

Much appreciated and love the site!!! (wish I joined prior to jumping into an old 600!!!:eek:)
 

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MB SL600, MB 380SE, Suzuki Grand Vitara, 38' Chris-Craft, Volvo V70XC, and my own two feet...
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4,131 Posts
The head gasket and rings are not weak points on this motor. I have heard of ring failures in the very early M120s, but those were related to cylinder-wall washdown issues caused by programming flaws in the original (1992-1993) fuel injection system, not to any inherent design flaw.

I would guess your motor is structurally sound and you have some other kind of running issue going on.
 

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94SL600, 76MGB, 99Suzuki Bandit 1200, 05Yamaha Warrior, 72Triumph Bonnie
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14 Posts
Discussion Starter #3
Thanks chris!

I picked the car back up.. Report is Cylinder #2 had 45lbs of pressure (cold) while the others were around 195lbs... That went up to 150lbs or so when a little bit of oil was added and the engine was started hot.. Also cylinder #6 was the only one which the valve was slightly wet (he used his scope to check them all).
I know the rings do not need an overhaul (big $$$'s!!), so I am wondering if I should spring for the main harness replacement and, possible, change out the cats to the free-flow variety as well....
I do not want to do ring, head & valve gasket replacement if it is not the actual cause of my issues!!!
Aaah, the joys of owning the 600 (during the cheap wire insulation years!!)
 
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