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97 SL600 Pano, ex: 96 (late 95) SL320
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Discussion Starter #1 (Edited)
Hi all!

Like I mentioned in another another thread, I’m working on resealing the valve covers of my 97 SL600, and while at it, doing all the “while I’m there” preventive maintenance jobs. Wouldn’t want to do the same job twice in short succession.

A short recap on what’s been done before this is probably in order. Soon after I got the car in summer 2018 I realized there was a slight idle fluctuation that could be felt inside the car as an annoying vibration a V12 shouldn’t have. Initially the engine was also lacking a lot of power at high RPM. It didn’t feel much quicker than my old SL320. I replaced the ignition coils and spark plug boots, but the real issue turned out to be that the cats were clogged. After replacing them I finally got to meet the power reserve of the engine properly.

The vibration got worse, though, and last spring I had the engine and trans mounts replaced. Much better, but after a while I realized the problem was still there, just not as obvious. A while ago I replaced the fuel pressure regulator because the vacuum hose smelled of fuel. Still no change. New spark plugs (Bosch F8DC4). Nothing. But I did notice some oil in the spark plug wells, and being the perfectionist I am, I decided the next step was going to be pulling the intake manifold and valve covers. Maybe I’d stumble across the idle issue while at it.

I started this project last week. The first 2 hours went into removing everything from around the manifold: Throttle bodies, MAFs, air cleaners, vacuum hoses, ignition coils, wiring harness, and finally the fuel rail. The only thing that caused a little head scratching was the wire that goes to the AC compressor. But nothing special really.

harness-off.jpeg

The following day I took the injectors to be tested and cleaned if necessary. They all checked out, which was kind of disappointing because I hoped they might be the cause of my idle problem. The first column in the report below means leak test while pressurized, and the second one is the spray pattern.
injector-report.jpg

All that was left was to unbolt the manifold itself, and the left brake booster vacuum line. It was a bit tough to get to but nothing too bad. The bolts were all easy to get to and gave in after spraying a little WD-40. You need to be very careful with the Allen bolts though as they strip easily.

In addition to the manifold bolts, you also need to remove the upper bolt of the right bank engine hoist bracket at the back of the engine. It’s a trivial detail but it almost made me shed a tear of joy to see how that bit was designed: On the left bank bracket, and that one only, there’s a slot that’s designed for reaching the bolt on the other side easily. You could reach it otherwise too, but it makes it a little easier. As an engineer, I found that a beautiful detail. After removing that bolt, the bracket bends just a little which makes it easier to wiggle the manifold out.

access-to-hoist-bolt.jpeg manifold-off.jpeg

Speaking of the manifold, the WIS says something to the tune of “lift it to the side”, but I found that it came out by wiggling it up from the front. Once you get it past the power steering fluid reservoir, it comes right out.

After the manifold was out, the next step was to undo a couple of dozen bolts to get the valve covers out. I took them and the manifold to be glass bead blasted and powder coated, and I’m still waiting to get them back. Fingers crossed they’ll look nice.
covers-off.jpeg

The next step was to remove the flanges between the heads and the intake manifold. Nothing special there except some more unbolting, which was easy as this time I sprayed WD-40 the day before. As a result, the crankcase breather pipe on the bottom of the valley was exposed. To get to the knock sensors it needed to be removed, and I wanted to check it out anyway. It’s bolted to the head at the front and middle of the engine.

Flanges off and crankcase breather pipe visible

Once I got the breather pipe out, it seemed pretty clear what my idle problem was about. The wide plastic center part of the breather, the pressure damper, was cracked. And not by time or wear, but quite obviously because someone has been there before and forced it in place. I have no idea why, especially as all date stamped parts I’ve found down there seem to be originals, so it doesn’t seem like anyone has actually replaced anything before. Gaskets don’t have date stamps so I don’t know about them. In any case, the damper was leaking and it’s quite certainly a source of unmetered air and therefore the (or at least a) cause of my idle issue.

Cracked pipe

The bad news is that now I have to wait a couple of more weeks to get the replacement part. The pipe costs around 100-150 EUR depending on the seller. While at it, I also ordered the small coolant hose that connects the heads through the hoist brackets, and the hose that goes from the same place to the firewall (towards the heater core). And the O rings on the hoist brackets that act as pipe fittings.

Now that the breather was out, I was able to replace the knock sensors down in the valley. Nothing special there either. I had also decided to deal with the crankshaft position sensors while I had the access. The right bank sensor was readily accessible from above after the intake was off, but there’s no way you can reach the left one. It’s too tight between the firewall and head. However, after removing the upper firewall portion and the heater hose that goes from the back of the V to the firewall, the bolt is easily accessible with an extension.

Knock sensors visible Left crank sensor

The trick to removing and installing the sensor is to wiggle it by the cable through the back of the V valley with the plug connected. Before I figured that out I feared I couldn't do it at all, but in the end it was surprisingly easy. Careful with the cables with both the knock and crank sensors though - I’m told their insulation deteriorates and they’re unobtainium. I didn’t see any damage on mine though and the cables were flexible.

The last thing I did so far was to replace the two hoses between the tandem pump and power steering reservoir. Having done it, I think it would be possible to do even without removing the manifold, but it was certainly easier this way.

Here’s the list of parts I’ve ordered so far:
  • Valve cover seals: A1200101430 & A1200101530
  • Power steering reservoir hoses A1409975782 & A1409975682
  • Throttle body gaskets, 2x A1041410780
  • Knock sensors, 4x A0031538628
  • Seals between intake manifold and intermediate flange, 12x A1041411080
  • Gaskets between intermediate flange and heads, 2x A1201410280
  • Plastic holders in rear corners of valve covers that hold the crankcase breather pipes that go to the throttle bodies, 2x A1200160338
  • Crankcase breather pipe gasket A1200180180
  • Coolant hose between hoist brackets in the rear of the V A1202030382
  • Hoist bracket O rings, 2x A0129975148
  • Heater hose from rear of V to firewall A1298300796
  • Crankshaft position sensors, 2x A0031537228 or A0031537428 (interchangeable, not sure what the difference is)
  • Bunch of vacuum bits and pieces as well as some mounting bits such as MAP bracket mounting buffers A6019880111 and air cleaner mounting buffers A1029880111 that were broken
Many of the parts are available directly from OE manufacturers for a fraction of the MB price, so I got e.g. Bosch knock sensors and crankshaft position sensors, and Elring valve cover, throttle body and intake manifold seals.

At this point I’m about 7-8 hours into the job, excluding all the studying online and with Alldata/WIS, figuring out what parts I need and getting them, and of course taking the parts to be painted and injectors to be tested. I’m working in a public parking facility where I have a permanent spot, so the time includes setting up before and cleaning up afterwards. The trunk is my toolbox and storage…

To be continued when I get the valve covers and/or the remaining parts I’ve ordered. Below is a teaser of the color options I was considering. I went with RR41. The color chart is that of some Finnish industrial company so you probably won't find the exact same color pretty much anywhere. It's called metallic dark silver and has some metal flakes. I'm an OEM kind of guy, but I don't mind a little refresh here, especially as I couldn't find an exact match to the original colors.
colors.jpg
 

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96 SL600, 07 BMW M5 ,04 545i sold, 2013 C300 Sport (for wifey) 03 CL55 s/Chg sold,91 500SL, sold
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112 Posts
Wow! Great write up! Glad you were able to get to the root cause of your problem. Such documentation will undoubtedly help us all moving forward.
Question, did you experience the idle issue in only park or was is also obvious in Drive but with say foot in the brake at a standstill?
Mine is silky smooth in drive but sometimes in park I can experience a little fluctuation in rpms especially when the AC is on. I'm not referring to when the compressor kicks in..It's an ever so slight roughness occasionally, so will keep an eye on mine.Thanks again. Send some more pics when job is completed. (y)
 

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97 SL600 Pano, ex: 96 (late 95) SL320
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257 Posts
Discussion Starter #3
Thanks! Yeah, I figured there aren't too many writeups on this stuff so posting should help others down the line, like so many similar threads have helped me with other things.

The idle issue was there in D too. The RPM fluctuation wasn't as significant though. Even in P/N we're talking max +-50 or maybe occasionally 100. Sometimes it barely registered on then needle but I could still feel the vibration.

I'll keep posting as the project progresses.
 

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97 SL600 Pano, ex: 96 (late 95) SL320
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257 Posts
Discussion Starter #5
Hey Juuso, are you painting both the manifold and valve covers with the same RR41 color?
Yeah. I was considering RR40 for the manifold alone but decided that a dual tone setup was too risky with my aesthetic skills. It could end up looking awful.
 

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97 SL600 Pano, ex: 96 (late 95) SL320
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257 Posts
Discussion Starter #6
I got the covers and manifold back today. Installing the valve covers is easy and I did it right away after making sure there wasn't sand left on the insides of the covers. The only thing you kind of have to look out for is that the half moons at the rear of the covers seat properly. On the M104 the half moons are separate parts but on this one, luckily they're part of the gasket so it's harder to screw things up.

The torque spec for the bolts is only 9Nm so you have to be quite careful not to strip the threads on the heads.

IMG_1931.jpg

The color looks a bit darker in real life than in the photos. I'm not sure yet if I like it but let's see when everything is back together. And I'm stuck with it anyway so better get used to it ;)

IMG_1936.jpeg

This was as far as I could go with reassembly as I'm waiting for the (hopefully) final parts order. I should get it tomorrow but let's see when I have time to actually do something.

Next up is figuring out how to get all the sand out of the intake manifold. I guess I'll have to take it to a self car wash as I don't and can't have a pressure washer at home.

The corgi is confused.
 

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'82 500sec euro, '95 Ford F150
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1,562 Posts
Great job, and writeup.
yes, the color is darker than factory, but almost passes for Renntech color. Just add two period stickers and you’re done!
9D18CC6D-2553-431B-A9F5-8E2CEC09176C.jpeg
 

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97 SL600 Pano, ex: 96 (late 95) SL320
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257 Posts
Discussion Starter #8
Yesterday I pressure washed the intake manifold, and today I took it to a friend who has an air compressor. Nothing came out with the air but I'm still kind of worried in case there's some lump of sand hidden in some corner of the plenum. I wish I had an endoscope, but I guess I'll just have to hope for the best.

Anyway. I got the last set of parts yesterday and today I had a little time to continue reassembly. The first part was replacing the O rings on the rear hoist brackets. I didn't drain the block or radiator beforehand, so there was coolant in the heads. I just removed one bracket at a time, stuffed a shop towel in the hole and then replaced the O ring. The original O rings were in fact just fine. But now they're new.

IMG_1960.jpeg

Next up, the heater hose from the left hoist bracket to the left side of the firewall, by the brake booster. Nothing special about the job as such, but I wanted to show how the outer insulation layer of the hose had given in. It seems to have chafed against the engine over the years. Certainly didn't hurt to replace it.

IMG_1969.jpeg

Before installing the short hose between the two rear hoist brackets, it made sense to install the crankcase breather hose on the bottom of the V. It wasn't quite obvious how you can wiggle it down there past the heads, so in order to avoid damaging the plastic part of the pipe like someone before me did, I disassembled the pipe and reassembled it in place. It's made up of 3 parts and there are rubber fittings in between.

IMG_1967.jpeg

Before bolting the breather back on I realized that the old gasket between the pipe and the block was still there and simply wouldn't budge. After trying to get it out of that tight spot for a while, I decided to let it be and just install the new gasket on top of the old one. I figured it's only air and other gases and the pressure isn't huge so it's probably going to be ok.

IMG_1964.jpeg
IMG_1966.jpeg

To be continued tomorrow. The rest of this job should be fairly straightforward reassembly. It'll take time though and I'll try to take it easy and not rush things.
 

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97 SL600 Pano, ex: 96 (late 95) SL320
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Discussion Starter #9
So, next up on Sunday was installing the intermediate flanges between the heads and intake manifold, and then the manifold itself. No problems there, except that it wasn't a good idea to bolt on the manifold before the final rear hoist bracket bolt. I had to unbolt the manifold in order to slide it forward those precious few millimeters. The extra clearance was enough to get the hoist bolt in the correct angle.

Installing the fuel rail was no problem at all after I sprayed a little silicone oil on the new O rings.

IMG_1977.jpeg IMG_1984.jpeg

Tuesday's goal was to install all the remaining mandatory bits to get the engine running again. Routing the wiring harnesses and vacuum lines, installing throttle bodies, ignition coils, MAPs, MAFs and air boxes. It was all quite straghtforward, but I really thanked myself for taking a lot of photos and videos before disassembly. It would have been a bit more painful otherwise.

IMG_2021.jpeg

Finally it was time to start the engine. To my disappointment, it cranked but that was it, didn't even seem to try to fire up. Tried a few times before hooking up the SDS, only to find nothing interesting in terms of faults codes. I decided to try resetting the right ECU crank position sensor adaptations, and after that it started. Maybe on the second try, I don't quite remember as I was a bit freaked out about possibly having screwed up something.

Next I took a little test drive in the parking garage. Throttle had a weird lag and after I stopped and popped the hood, the left side of the engine was hissing like crazy. Luckily it just turned out that the bolt holes of the air pump switchover valve go all the way through the intake manifold's side, so there was a major vacuum leak. I left the switchover valve out because I've bypassed the air pump with a shorter belt (EU instrument cluster => no CEL and no problem). Bolts back on and everything was fine again.

IMG_2023.jpeg

Today I drove to work and in the process took the first proper test drive. Things seem to be working fine. Unfortunately though, the idle issue doesn't seem to have gone anywhere, at least not completely. Still, I'm happy to have completed the job. I like how it turned out and at least the oil leak should be sorted out.
 

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1994 SL500 1998 SL600
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Nice job! I'm having a idle issue too that seems to be disappeared once I inverted the throttle valves. I was having fault P1580 and P0170 constantly. Just in case I got another throttle valve and hopefully I can pass the smog test by the end of the week.
 
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