I'm a traitor.

[Nomadicvar]

I haven't even started the build thread for my '85 745i (getting that done today), but I went out and bought a new daily. Previously, I had been driving a Subaru Outback XT that I did a full Legacy GT conversion on. Bigger turbo, all the goodies, about 300whp. While it was fun and reliable, it never truly felt like me and definitely lead to far too many aggressive overtakes and high speed corners within the Twin Cities metro. She had to go. After a little digging on CL, I found what seemed like a deal that was too good to be true. Meet Hugh (previous owners name; read Huge).

A 1991 Mercedes-Benz 420sel. 134k on the clock, a metric buttload of NOS parts, and important upgrades where it mattered. Unfortunately, the monoblocks are reps, and the paint has seen better days, but for a rust free Texas car, I think he looks great!
00R0R_lXJshTz8pp0_1200x900.jpg00j0j_4dk6q7fKNre_1200x900.jpg00y0y_uKPP3npdvt_1200x900.jpg00F0F_8ELBzsNqZgj_1200x900.jpg00b0b_grXDZttiImb_1200x900.jpg

[Hit Man X]

I own four W126s, have since around 2002 I think. I have rebuilt everything on them, so just ask. HVAC, trans, front ends, whatever. Just not a fan of the clear corners.

1991 is the last and best year, dual air bags make it a prick to R&R the vacuum pods that were behind the original glovebox location.

[dude99]

I really miss my w126. I've never really bonded with a car since I sold it... they are fantastic.

[Nomadicvar]

I own four W126s, have since around 2002 I think. I have rebuilt everything on them, so just ask. HVAC, trans, front ends, whatever. Just not a fan of the clear corners.

1991 is the last and best year, dual air bags make it a prick to R&R the vacuum pods that were behind the original glovebox location.

I thought that was you I saw on one of the Merc forums! Factory amber corners were included in the sale, and will be installed post haste! I'm indifferent in regards to the look of amber v clear, but the fit of the clear corners is horrible. Back to factory is a must. I've put on about 700 miles since purchase, and have found but two small issues.

1st: The driver window regulator is grumpy. Rolls down perfectly, and tries to roll up with as much enthusiasm but there is a massive repeated clicking sound and needs a helping hand. Assuming it's the window regulator, I started searching for a replacement. I found a yard near my house with plenty on hand, but they want to know which brand is installed in mine, to provide the best replacement.

2nd: The driver side high beam is stuck on. Passenger functions normally. For now, I have pulled the power to the high beam.

3rd (sort of): I have a rough idle. RPM seems good, just rough, and perfect on the highway. From the seller, and proven via receipts "What's New: Water pump, new brakes, rotors, pads and calipers, fuel tank refurbished, new fuel pumps and filters, new fuel injectors, new headlights, high end sound system by Focal, AMG replica wheels, lots and lots of gaskets and seals, Bilstien shocks, H&R sport springs (1.5 inch drop), new seat control modules" - With all the new fuel system components, I think I've safely narrowed the issue down to the fuel distributor in some capacity and have sourced a gasket kit for it. Mainly to replace the old, inevitably stiff and crunchy diaphragm. But I'm open to other ideas.

I really miss my w126. I've never really bonded with a car since I sold it... they are fantastic.

With nearly 700 miles behind the wheel, I am already thoroughly in love. This car will be mine for as long as it allows, or until it is taken under unforeseen circumstance. Such a big lovely dream boat!

[kojo96]

W126s are excellent long range cruisers! Loved mine while I had it, regret selling it but a good friend has it now, last drive in it was to Vegas from N CA, that car didn't miss a beat!

[Nomadicvar]

W126s are excellent long range cruisers! Loved mine while I had it, regret selling it but a good friend has it now, last drive in it was to Vegas from N CA, that car didn't miss a beat!

So far, that's exactly what I'm experiencing! Made a quick round trip from Minneapolis to Des Moines and the Merc didn't even blink. The 17-18 hwy mpg sucked but hey, I couldn't have been more comfortable, and the style is undeniable!

[Hit Man X]

The 17-18 hwy mpg sucked but hey, !

That is pretty good, the M116s and M117s cannot breathe. The crossover pipe on the 560 is a 1-5/8" OD pipe. No joke. Gutting that precat is a smart move, removes excessive heat from underhood. Euro dual logs add a good bump in power as well economy...plus they are not too expensive.

Also, replace the timing chain guides ASAP with OEM only. You can just pop in woodruff keys to time the cams. You need THREE.

[motohunter4]

I've been on the lookout for a nice 420sel.

[Hit Man X]

I've been on the lookout for a nice 420sel.

All the 116s/117s need head work after about 100-150k...something with the camshaft to rocker arm angle on the valve guide with the SOHC engines. This is an engine out job as the threads usually rip out upon reinstall of fasteners. This requires a torque plate looking device and Helicoils in all the holes. It also has six bolts per cylinder. Mind my warning about chain guides, if the upper driver one fails, the chain skips and adds something around 30* of cam timing from what I recall. This bends all the valves in the head.

Hey, at least the transmissions do not have any major issues! They always leak from the pump bushing with miles and reverse gets weaker and weaker due to clutch delamination. FWIW, I have 325k on a stock 722.3 trans. Mind the flex discs on the drive shaft, especially the front unit. SGF or Lemforder is what you want to use. Well of course, OEM but they were SGF.



Crap idle is almost certainly an indicator of intake leaks. It LOOKS super complex to do, it is easily a weekend job. The intake manifold is a two piece design, that is how the torque is so flat and wide on this engine. There are eight o-ring looking guys that seal the upper to the lower. IMO, while it is out TIG up all the emissions BS holes as they will just cause issues. AIR injection crap can fall off. Same with the hoses that all run to the throttle body, just counter sink and fill with epoxy. You really just need a vacuum signal to the FPR and EZL best I recall. EGR is always plugged up with age, can just TIG that hole in the plenum up too then figure out how you want to plug it on the exhaust manifold. Junking all that stuff just eliminates places to fail. The 560 pulls about 23" of vacuum at idle and needs a head job.

While that is apart, replace all the seals for the CIS-E system. You may want to speak with Larry at CIS Flowtech in Alabama and have them bench test your fuel distributor. They are pretty robust, but I think after 300k the one on my 300SEL is weeping internally as cold starts are poor. If the car sat a bunch, the Ethanol in the fuel will easily eat up the seals...just like on your EHA valve! FDs are very precise units, this is something even I do not build at home as they have to be tuned to flow the same volume per port.



Heed my warning and do timing chain guides ASAP.



https://epc.startekinfo.com/epc/home.jsp subscribe to that for every part number. It was free for years, now is $70 or so. Worth every cent.

[motohunter4]

Sounds like a headache compared to the m30.

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[Hit Man X]

That is why the car was significantly more expensive and a pile faster.

[motohunter4]

My friend's dad had a sweet 560sel when i was in school, I always liked the w126. His ran flawlessly.

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[Nomadicvar]

That is pretty good, the M116s and M117s cannot breathe. The crossover pipe on the 560 is a 1-5/8" OD pipe. No joke. Gutting that precat is a smart move, removes excessive heat from underhood. Euro dual logs add a good bump in power as well economy...plus they are not too expensive.

Also, replace the timing chain guides ASAP with OEM only. You can just pop in woodruff keys to time the cams. You need THREE.

Which vehicles might I find euro logs on? It sounds like my local import salvage yard has a few comparable vehicles right now. Precat will definitely get gutted as soon as I'm in there. Timing chain guides were done with the chain very recently and all OEM parts were sourced. I have some great service history from the PO.

[Nomadicvar]

Yesterday was an adventure. In the hopes of curing a rough idle, and with the entire fuel system being new with the exception of the fuel distributor, I pulled and rebuilt it. This seems like such a finicky and overly complex mechanism. A carb almost seems like an upgrade!

Here are most of the components in a mineral spirit bath inside the ultrasonic cleaner. Magic.
20181009_113742_HDR.jpg

Unfortunately, the rough idle didn't go away, though I can definitely tell everything is happier with a new diaphragm installed. The old one was crusty and hard.

@HitmanX - With all fuel system components now sorted, where would I look next to resolve the rough idle? Is there something in the vacuum system to diagnose, or some intake boot-like issue? Idle is between 600-900rpm depending on temperature, but choppy. Don't notice it at speed.

[Nomadicvar]

Placed a RockAuto order for a heap of small things. Non-resistor spark plugs (not sure when last replaced), intake seal set (rough idle), little antenna bezel (broken), and a trunk seal because I saw a tiny amount of moisture beaded on the trunk carpet after a car wash.

[dude99]

This is why I swore off gas powered Merc's from the era. I have never owned a CIS-E car and managed to get it to idle correctly. However a couple notes:

Intake boot equivalent on this is the big rubber boot under the fuel distributor. These can split and cause an air leak. The other common one is the injector seals and holders. Have you checked your lambda duty cycle yet?

Your trunk leak. I have never seen a bad trunk seal on these. What is far more common is leaky taillights. These fool you as they leak, then the trunk heats up and the water evaporated and condenses up in the trunk lid. Then it rains down inside the trunk, often running out when you open the lid. What I have done int he past with these is remove the tail light and the rubber seal. Clean both sealing surfaces (the tail light and the car), then put a small bead of clear silicone on the taillight surface and put the seal into it. The put a small bead on top of the seal so that when you install the taillight it will seal to the car.

[BONDOSPECIAL]

I don't understand how a 1985 Camaro had real EFI with a hot wire mass air flow sensor, but an early 1990s luxury car had this mechanical nightmare FI.

[dude99]

I don't understand how a 1985 Camaro had real EFI with a hot wire mass air flow sensor, but an early 1990s luxury car had this mechanical nightmare FI

Boggles my mind as well.... its just stupid...

[motohunter4]

How does the positraction in a Plymouth work?

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[youngbimmer]

While I would never own another CIS-E powered car again, I understand the 80s MB charm and appeal. I've fancied a W126 on more than one occasion. Off the bat, expect to replace all your fuel injectors, both seals (the o-ring around the fuel injector holder + the top gasket), and rebuild your fuel distributor. It's not that hard to do, if a dumbass like me could do it, so can you! My 190E could not hold an idle in the winter, would simply die and would randomly cut off in the summer. I replaced every vacuum line and injector and seal, except for the fuel distributor. I got a salvox kit off ebay, made to resist ethanol fuel degrading the seals. It was unbelievable how bad the old diaphragm was, full of pin-prick holes. After I replaced all the orings, diaphragm, and EHA valve o-rings, sparks, wires, distributor cap/rotor, ignition coil, and tuned the lambda to ~50% duty cycle, the car was much, much, much happier.

I gained a newfound appreciation for EFI after that nightmare. BMW was so far ahead of Mercedes in the 80s as far as fuel injection is concerned, its not even funny. Mercedes kept that garbage CIS-E system into the early 90s!

EDIT:

I see you rebuilt your fuel distributor. Make sure your plunger moves smoothly, I would have advised to mark the factory settings before taking it apart. You may also need a new EHA valve to correct idle, it could have an internal leak. CIS-E was such an overly complicated system to get right. From another user over on MBWorld, turns out his rough idle was actually a bad head gasket on a M103, which is fairly common on that engine. I do not know if the W126 V8s also suffered from bad head gaskets.

[Hit Man X]

CIS-E was evolved from CIS which was Kjet before was Djet.

MB did not want to reinvent the wheel when the W126 was on the market. This car was designed in the '70s and came out in '80 in Europe...it lasted until 1991 here in the USA. No reason to change EFI (massive cost) in '86 when the W126s facelifted to keep up with the upcoming E32s. Hell, Rolls and Bentley used it too. Ever seen a Ferrari V12 with dual fuel distributors???

W140s that came out around '91 has SEFI with MAF. This car was designed in the 1980s. BMW did not go SEFI on the M70 or B35, both were batch fire.



Why did Bosch and BMW use the barn door AFM? A simple Baro sensor would work fine.



In any event, the system is very sensitive to vacuum leaks. The V8s need the intake assembly pulled and resealed. The eight upper to lower donut o-ring things need to be replaced, they are about $10/ea for OEM. AFM plate to throttle body boot, IAC rubber, injector seals, etc. It looks hard, it is not. Just remove the fuel distributor and lines first. TIG up all the bullshit emission ports while in there, EGR is most likely plugged shut anyway. Time the camshafts. You will be surprised how much better it starts and drives.

[Nomadicvar]

Had a minor issue that seems to have turned into a larger issue and I'm looking for some advice @HitManX

The big 27mm bolt holding the harmonic balancer and pulley to the crank came loose (I have absolutely no idea how that is even possible) and everything decided to have a big fist fight, breaking the woodruff key and marring the crank snout and hub pretty badly. I sourced another running engine, but am trying to save myself some hassle in removing just the engine, leaving the transmission in place. I'm guessing it shouldn't be hard to do, but I'm not sure how to get to all the bellhousing bolts.

[Hit Man X]

I am not sure how I would approach that. You are positive it cannot be repaired with a sleeve kit or anything?

If not, and both engines out...you may want to just consider dropping a crank into yours since you know how the bottom end is on it. Finding a crank probably easy. Either way, I would jerk heads at this point on either engine and have a valve job done. Hardest part is pulling the engine to do Timeserts or Helicoils anyway. Believe me, all M116s and M117s need a head job. Head gaskets are cheap, guides are cheap, stock springs are usually good to reuse.

IMO, drop the trans and install fresh reverse clutches and reseal the case...including the leaking pump bushing. Loss of reverse is the failure point of the 722.3. This is really easy.

Hope it helps.

[dude99]

I seem to remember this coming up in the w126 forum over at benzworld at some point.... I think it may even have been a common issue in the day... I would ask there before replacing the engine...

[Nomadicvar]

I could go the route of a sleeve kit if I can find one that'll work. The bigger issue for me is probably trying to fish out the bit of sheared off woodruff key to replace it. If that was the goal, maybe I could accomplish the repair without pulling the engine at all. Unfortunately, the heads were gone through just before I purchased it, and I'm hoping I don't have to pull them. When the key snapped, the engine only revved to ~4800rpm or so and continued to run well, which was weird. The accessories just weren't spinning.