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1994 s600 coupe
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359 Posts
Discussion Starter #1
I have read that the earlier S600 V12 engines, had high speed fuel enrichment.
that was accomplished with the LH or Egas module.
can't remember which one.
the modules were later changed, removing the high speed enrichment.
can the early modules be substituted for later,
to get the high speed enrichment back ?
it was removed after model year 1993 ?
any input much appreciated.
 

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1994 S600 Coupe, 1995 S600 Coupe
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You should be able to substitute one for the other. I searched for someone who's actually done it, with no luck.

Jon
 

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1994 s600 coupe
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359 Posts
Discussion Starter #3
which modules would control the high speed enrichment, the egas, or the 2 LH modules ?
 

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1994 s600 coupe
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Discussion Starter #6
update- I obtained (2) early LH modules from a private seller in Oregon, off Ebay, when they arrived by FedEx, I simply pulled the old modules out of the coffin box, and plugged the early modules in. car started right up and ran better and different right from the get go. noticeably richer fuel mixture, better throttle response, the car is now EXHILARATING to drive. amazing. I highly recommend doing the permanent pin block on the ASR module, to delete the ASR, and replace the LH modules with the pre-September 1992 modules. the original ASR system and LH modules were simply starving this engine for fuel ! as an engine wears it demands more fuel to keep it running, and I'm starting to think the original programming in these modules is just too lean for long term use past 100,000 miles in some cases. it's not rich enough. I noticed a pattern where many 1993-up W140's would run to about 100,000 -110,000 miles then develop odd running problems that could not be tracked down. these factors may be a contributor to the problem.
the car is a real bear now. thrilling acceleration. it's a V12 that runs and sounds like a V12, no excuses. the ASR delete and early modules turned it into a real 12 cylinder sports car, rather than a V12 in name only.
 

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1994 s600 coupe
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359 Posts
Discussion Starter #8
s-l1600.jpg


date coded 04/92 april 1992, p/n 0125456332
these work really well and were plug and play,
I did not do the ECM replacement procedure in the Snap-On scan tool,
there is a function for that, but wanted to investigate if they would just work as is.
they do.
I may proceed to reset them to base settings with the scan tool.
there are a few other varieties of pre-9/92 LH modules,
quite a few for sale in Europe but very pricey $250 each and up.
I picked these up in the USA for $135 shipped for pair of modules,
took a chance, it paid off.
 

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Mercedes w140 S500 1997
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156 Posts
update- I obtained (2) early LH modules from a private seller in Oregon, off Ebay, when they arrived by FedEx, I simply pulled the old modules out of the coffin box, and plugged the early modules in. car started right up and ran better and different right from the get go. noticeably richer fuel mixture, better throttle response, the car is now EXHILARATING to drive. amazing. I highly recommend doing the permanent pin block on the ASR module, to delete the ASR, and replace the LH modules with the pre-September 1992 modules. the original ASR system and LH modules were simply starving this engine for fuel ! as an engine wears it demands more fuel to keep it running, and I'm starting to think the original programming in these modules is just too lean for long term use past 100,000 miles in some cases. it's not rich enough. I noticed a pattern where many 1993-up W140's would run to about 100,000 -110,000 miles then develop odd running problems that could not be tracked down. these factors may be a contributor to the problem.
the car is a real bear now. thrilling acceleration. it's a V12 that runs and sounds like a V12, no excuses. the ASR delete and early modules turned it into a real 12 cylinder sports car, rather than a V12 in name only.
[/QUOTE
Can you show with a pic where is that pin who should be blocked?
 

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1994 s600 coupe
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359 Posts
Discussion Starter #11
no pins get blocked on the LH modules, you replace both modules with early modules, that must be dated before September, 1992 on the module green tag. if they are dated 9/92 or later they will not have high speed enrichment.

the pins that get blocked are on the single ASR module, you must pull out and tape off pins 25, 29, 35, 37
I posted a thread about it here in this forum. it is not an original idea of my own, I found it online in archives elsewhere on the net. essentially it's copying the Renntech ASR defeat module add-on, that sells for like $800. with the addition of shutting off pin #29 which shuts off the ASR dash light.
the Renntech module defeats the ASR with a flick of a switch, but the ASR light remains on. I don't want that pesky light glaring in my eyes. also the Renntech mod requires cutting and splicing into the harness, a laborious tricky task that may lead to other problems, it's just too cumbersome. and taping off 4 pins is free, not $800.

if you have other problems with the car, defeating ASR will NOT fix it. all you will do is shut off the indicator light in the dash. so the car has to be running tip top shape first beforehand, then you can shut the ASR off and get more low end power out of the engine, without the ASR limiting it.
 

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1994 s600 coupe
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Discussion Starter #12
here is the thread about shutting off ASR by taping off 4 pins

 

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1994 S320, S 600 1994 , SL 600 1999
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We need to change both the modules? Can the modules be from 2 different months but before 92 /04?

Would be great if you had a before /after video .

I would like to do this if it really makes a difference.
 

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1994 s600 coupe
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Discussion Starter #15 (Edited)
I've been working on cars for 40 years now. after that much time, one develops a method.
each design has its own good and bad points, and its own maintenance and repair issues.
what happens is, you develop a standard approach to each make, once you encounter them to repair/service.
you develop a standard approach that enhances the strong points of the vehicle/engine/drivetrain,
because they're all different, especially depending on what era they're mfd. in.
when you start in on a car that you have not encountered before, the waters are muddy,
because your knowledge base is limited, so you go for the basics all cars share,
ignition system, fuel delivery, etc.
then delve into the model specifics, in this case the ECM's, ASR, etc.
eventually the waters clear, and you understand the system, it takes time.
I've been on this car since March 2019. 7 months.
now that a clearer picture has emerged of the design....
I'd change those ECM's as a matter of course, based on my experience.
the difference is DRAMATIC.
you notice it as soon as you start the car, and drive it 300 feet, it responds to the throttle much better. an experienced mechanic can hear an improvement in how an engine idles, and also how the exhaust smells, and the amount of heat emitted from the engine when he opens the hood. a lean, sick engine is usually very hot in your face. a well fueled engine runs cooler.
a rich engine smells like unburned gas out the exhaust and all around, a proper mixture smells cleaner, but too lean it's backfiring into the airbox air cleaner. too rich backfires into the exhaust.
these things happen and are understood quickly in real time, after 40 years experience.
you find yourself going to the problem area just like an MD with a patient,
the car is talking to you with its symptoms.
all the little mods and tune up tricks I've done have improved the car to some extent along the way.
changing out the ECM's has improved it the most, along with shutting off the ASR system, by taping off the 4 pins on the ASR module. blocking the EGR also was measurable improvement.
epiphany struck- these cars are extremely de-tuned, emasculated, and basically castrated as issued from the factory.
they take a 183mph top end car, and choke it down to 155mph. in doing so, they also diminished the low-midrange characteristics of the engine as well. the car being nearly 5000 lbs. needs every bit of power it can muster.
so you gain a few HP here, a few HP there,
after shutting off EGR, air pump, ASR, canister purge system, removing cats (previous owner) and mufflers, installing early ECM's, it has definitely gained a LOT of rear wheel horsepower. it went from driving like a tired old elephant,
to being a thrill to drive, and sounding like a piped V12 Ferrari.
it amazes and blows away anyone who hears or sees it.
on the winding back roads, I can't even get it out of 2nd gear, it's going too fast.
so I use 3rd and 4th to just putt around and quiet it down.
I'll get a video up soon enough, issue is I have 10 cars to maintain for 5 different family members, it's becoming a full time duty. to do a video with the W140, requires setting up a tripod in the back seat, for a digital camera, then taking it for my weekly ride. just don't have the time for that now, I've been repairing and wrenching on other commuters and trucks for my family, mom, and mother in law.
suffice to say, if you can find the modules for a good price, buy them. I may buy other versions of the early modules and do further comparisons. there are 2 or 3 different pre-9/92 modules to choose from.
doing all of the above, I didn't have to replace the harnesses, just repaired them as best I could.
also did not replace or repair the throttle bodies, or MAF sensors. original ones with 103,000 miles still on car.
which made me think, a lot of this harness, throttle body, MAF sensor changeout/rebuilding, is unnecessary.
it's really the design of the ASR, ECM's, and emissions, that are holding these cars back.
and in my car's case, defective original worn out parts-
from the get go, I had to replace both fuel pumps, fuel filter, both caps/rotors, spark plugs, and one ignition coil. they were shot or very worn, barely functioning. I also replaced the fuel regulator for good measure. start there, the basics.
then remove the emission controls, and shut off the ASR, and change the modules. as a matter of course.
my gut tells me, rebuilding the throttle bodies, and installing new MAF sensors, would sharpen it up even more. it would remove whatever lag or wear exists in those parts input/output from the system. being it's also the most expensive I'd leave that to last.
cracks in wiring harnesses doesn't mean they're not functioning. all the wires on all the powerline poles to your house are bare by design. if they aren't touching ground or each other, there is no short or open circuit. if your car is 100% otherwise, and you have a heated/AC garage to work in, and nothing better to do, sure buy all new harnesses and install them. who knows if I have the car long enough I may do that. not now.
 

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1994 s600 coupe
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Discussion Starter #16
ps- another thing I noticed, the engine sounds healthier while idling with the early ECM's, and it revs through the rpm range quicker. it's obviously fueling better. and the early modules removed the 4500 rpm rev limiter point in park, it will free rev past 5000 rpm now in park.
I don't know where the automatic rev limiter is at now with these early modules, but I did bounce off the limiter twice during a full throttle blast down the back road straightaway in 2nd gear. I didn't look down to see where that point was, my eyes were on the road.
with the original modules, the car wouldn't even rpm that high, that quickly in gear while driving, on that same short 1500 foot straightaway. it's a lot faster now.
 

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'95 S600
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419 Posts
Certainly add it to one of the potential benefits of owning a pre-facelift model.

I imagine a well made set of exhaust headers would give these things a very good mid-high range power increase.
 

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1994 s600 coupe
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Discussion Starter #18
headers would add more power, but they already have a very good exhaust system on them. 2 manifolds each side 3 into 1, then those two pipes go down into a single pipe. basically they have a hybrid of a V8 type tri-y pipe already on the M120 V12 from the factory as oem.
the engine was pretty damned amazing for its time. the early LS V8 engines were 5.7 liter and made only 305HP in 1998. the M120 was a 6 liter and made 390-410HP range ? that was really cooking with an OBDII compliant engine in the early-mid 1990's. using 10:1 compression in the M120 at the time was unheard of too. amazing.
 
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