1995 SL600 Engine issues - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 04-17-2019, 08:42 PM Thread Starter
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1995 SL600 Engine issues

I recently purchased a 95 SL600 and it only has 74k miles.

I was curious if anyone might have any ideas on why the exhaust has a very heavy gas smell, and it does blow smoke. It also has slow acceleration response sometimes (kind of mushy).

When I replaced spark plugs, they were heavily carbon fouled.

So far I have replaced main wiring harness, 12 spark plugs, 2 ignition coils, cabin filter, 2 air filters, all fuses, fuel cap... also I was pleased to see that both throttle bodies had been rewired by previous owner.

Greatly appreciate any advice or ideas you might have on items to check or replace.

What the fouled spark plugs looked like on left, and new one for comparison on right in picture below.
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post #2 of 10 (permalink) Old 04-17-2019, 10:32 PM
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Does it blow white black or blue smoke? The best way is to check the engine with a HHT tester for error codes to get clear information.
I would also suggest to change the oxygen sensors. But first do a HHT test. There you can see the readings of the o2 sensors.
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post #3 of 10 (permalink) Old 04-18-2019, 06:53 AM
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STOP DRIVING THE CAR!!!!
Almost certainly you have degraded wire harness to the Mass Air Flow sensors, that sends bad information to the ECUs which in turn floods the engine with fuel. The overfueling can be so bad that it keeps washing down the cylinder walls, scoring the cylinders.
The MAF harness is available from the dealer around 140-ish.
The overfueling can show up as hesitation to bellowing white putrid smelling smoke. Btw, you’ll also fry your Kats in the process.
So again, DO NOT start the car again until you verified the condition of the harness by slicing it open right about where it’s closest to the exhaust manifold. It degrades the fastest where it’s the hot.
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post #4 of 10 (permalink) Old 04-18-2019, 06:59 AM
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People replace the upper engine harness, but often overlook the MAF harness. It’s just as important.
“While you’re in there” also open the cover to your throttle actuators and check the condition of those wires. If those haven’t been replaced, you may want to address those as well.
If you can do the work yourself, none of these are are very costly projects, but rather piddly, time consuming.
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post #5 of 10 (permalink) Old 04-19-2019, 03:52 PM Thread Starter
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Thank you! Definitely issues with both sides of the MAF Harness (pictures)...

I found GUSMB’s post where he did the replacement, but his site is not working. Any other recommendations for walk throughs, since his site is down?

You also mentioned checking the wires on the throttle actuators? Forgive the ignorance, but where is that?

Thanks again
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post #6 of 10 (permalink) Old 04-19-2019, 07:57 PM
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post #7 of 10 (permalink) Old 04-29-2019, 11:59 PM Thread Starter
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Couple questions if you wouldn’t mind helping me a bit more.

1. Dealer was not confident and was having a hard time finding part, however I found at ECS tuning for $136 per side (part 1405400081). Does that sound correct, I assume the $140 you mentioned was per side, correct?

2. I noticed the wires are connected in with lots of other wires. Is it advisable to cut those all the way out, or better to just lay new wires and leave the old ones in, just not connected? I am concerned as I am going between the air box and engine and jiggling other wires I could mess something else up... yeah that is the luck I have sometimes lol (although looks like other wires in engine wrapping are looking great!).

3. Any idea what would be a reasonable price for a shop to do this job? (Replace the MAF wiring on both sides) Little concerned I might be out of my league, so was thinking about calling a couple shops and see if they were familiar with the problem.

Thanks again for the help and advice.
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post #8 of 10 (permalink) Old 04-30-2019, 04:41 AM
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The best thing to do is to go directly into the plug of the ECU by unpinning the old wires and pinning the new ones in their place. I would not recommend cutting and splicing, as the the entire length of the insulation is deteriorating, even inside the coffin box, where it’s relatively cool. The insulation is just past it’s lifespan.
You can just lay the new bundle over the original, in a proper sheath. Once the new one is installed, you can just cut back the old, and leave it where it is.
The instructions I posted are very clear, for determining the pins and the corresponding numbers on the plug to the MAF. I still verify my work with an ohmmeter as I go.

Surprised the dealer could not help you, as the p/n posted is accurate, and I have just done the job recently. You can of course buy it from ECS tuning, it is the same part.

It does require some patience and concentration, but quite straightforward with the provided instructions. Shouldn’t take you more than a day from start to finish.
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post #9 of 10 (permalink) Old 04-30-2019, 06:18 AM Thread Starter
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Thanks @roadhouse !
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post #10 of 10 (permalink) Old 04-30-2019, 06:20 AM Thread Starter
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And thanks to everyone else also!

This is a great forum, and we are very lucky to have a strong group here!
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