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Discussion Starter #21
True, and I've seen some long-lived ones as well. But we've tried just about everything else at this point. The only other thing that comes to mind for causing misfires is a head gasket leak spewing coolant into all those cylinders at once. But I've had head gasket leaks before with other cars, and it's not acting like that.
 

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Discussion Starter #22
OK, the catalytic converter assemblies, both left and right, have arrived. I'm assuming they're remanufactured. They look like they're freshly re-welded and shined up all nice 'n' clean. These assemblies came with only the front cats, so we'll see how this fits on the car in a week and a half or so when I get a chance to jack up the car.

Let's hope this does it.
 

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Discussion Starter #24
OK, here's an update. The new cats are in as of last night--finally. No mufflers, just the cats wit the 1-metre of exhaust pipe that's attached to them. This is because I took the entire exhaust out due to some seriously rusted-up bolts that hold the cat pipes to the muffler/resonator pieces. I guess that's what happens when they're on there for almost 17 years. Essentially, I'm currently running open pipes after the cats. Sounds like I'd imagine an S65 AMG must sound, though the 2,000-RPM drone is definitely there. Once you get past 3,500 RPM, though, it sounds GREAT! It's not like that Japanese fellow with the naturally-aspirated V12's and that high-pitched Ferrari scream, but it's pretty neat, just the same. But that 2,000 RPM drone would get bothersome after a while.

All four O2/Lambda sensors have been reactivated in SDS Developer Mode, per stock settings; I had done that last month.

Started the car up this morning. Lots of steam for about the first two minutes, after which it cleared up. No wonder, since the car's been sitting for at least the last month. The goal here was to see if the misfires would come back. So, I let it idle until it warmed up to 85 deg. C., and...no misfires! Good sign. Then, I drove the car around today to see how things would go.

@Kraut56, it seems, was right.

My misfires seem to have gone away. The Check Engine Light (CEL) did come on after driving it around, shutting it down for about 20 minutes, and then driving it again. However, this is probably because it hadn't been driven in some time. Fortunately, I had the SDS setup with me. Cylinders 4 and 9 were listed, along with the P0300 code (misfire). So, I took a look with SDS and...no errors at all on Cylinder 9! Only three on Cylinder 4. All cylinders seemed to be actually firing just fine, so I cleared the code and repeated the experiment. Drove around, keeping everything up to temperature. Went into the local Walmart for about 5-10 minutes. Came out, started the car up, and ended up driving in some stop-and-go traffic. No CEL. No hiccups. The engine seemed to be perfectly happy.

It appears that those cats were indeed clogged up after 16 and a half years.

Since I took off the entire exhaust, it was a good time to inspect it, since normally I'd reuse the after-cat part of it. Turns out the resonators are rusting through. That means that in a couple of years, it'll need replacing anyway (it's an inspection item, too, so legally I'd have to at that point), so since the whole thing is off right now, I might as well do it all now and be done with it.

So, this evening, the rest of the exhaust piping is on the way, courtesy of MBOemParts.com and their free shipping code. Note that the shipping for the "cat-back" part of the exhaust is about US $270 and change. The BenzWorld free shipping code covers up to $75 of shipping costs. Fortunately, they have a pre-Black Friday free shipping code that covers EVERY-THANG! Yep, I just saved $270+ on shipping charges. Heck, yeah.

The upshot to all of this? This car should not need exhaust-, ignition-, or cooling system-related anything for quite a few years. Here's what was replaced as part of all this.

  • Ignition coil assemblies, both sides
  • Red silicone boots
  • Voltage transformer
  • O2/Lambda sensors, all four
  • A few more of those translucent vacuum hoses that I'd missed before
  • Upper radiator hose
  • M275-to-M279 intercooler mini-tank upgrade
  • Intercooler circuit pump, with the new upgraded Bosch pump
  • Throttle body intermediate pipe (the "Y" pipe from the intercoolers)
  • Air baffle/director that sits on the engine oil cooler
  • Intake manifold temperature sensor
  • That one-way-valve hose at the top of the engine, the one that comes out of the oil separator
 

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W220 Moderator
S500 W220 SLK320 R170 C200 CDI W203 Peugeot Expert Van
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Hi @cowboyt,

That is some well looked after baby you got there, should give you many years of trouble free motoring, as well as peace of mind on a long road trip :)

I'm glad you got it sorted, and what a great result on the shipping cost :D

Remember those Sports Mufflers I put on my V8 W220, that bloody Droning got on my nerves so much, when I bought the Parts Car and found it had a 6 month old genuine MB Exhaust system I ripped that off and put my S Class back to stock, (well just the AMG Quad Tailpipes fitted on otherwise stock back boxes), much much nicer !!

Hell I have an R170 SLK with an imminently incoming V8, that Car will be far more suitable for "Grumbly Growly" Exhaust System 👿

Nice one buddy !!
 

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Discussion Starter #26
Thanks, but it appears that I spoke too soon, because....

IT HAPPENED AGAIN! AUGH!! AAAUUUUUUUUUUUGGHH!!!

2610783


Yes, it's true. This time, I got some more data. At first, Cylinders 4-9 would take some errors. But then, Cylinders 1, 2, 3, 5, and 6 started shooting up with the misfire count, and...yep, cylinder shutdown resulted. As before, this happens only at idle; if I give it some gas, even a little bit, it doesn't happen.

Yet, after the engine got warmed up some, i. e. close to 80 deg. C, misfires stopped happening, even at idle. I let it run for about 20 minutes, idling, and the error count did not rise.

Pictures of diagnostic info from SDS to come. This is very frustrating.
 

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2007 E220CDI, 1990 300E-24V, 1987 W124 3.6 AMG build 1993 E500 W124, 94 320CE, 1997 W140 S280
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This video shows a great way of testing CATs or other exhaust components for restriction before replacing them:

 

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Discussion Starter #28
Thanks, and I'll have a look at that on the next car.

This one, though...it's got me perplexed.
 

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Discussion Starter #29
OK, here's pics, which hopefully will provide some clues.

From November 9th. Note that we're getting a few misfires on Cylinder Bank 1-6. Also recall that this happens only at idle. It's worse when the car is warming up, and that's when I now get the CEL and cylinder shutdown. Once it gets to temperature (currently 96 deg. C. here), things appear to get better. More pics from the following weekend to come as well.

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2611560
 

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Discussion Starter #30
Hmm...getting errors about "message is to long to process, please shorten it", yet the post that was going to be in this space had only 4 images, compared to the previous image's 6. Go figure.
 

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Discussion Starter #31
Next day, November 10th.

Cylinder #4 wants to misbehave...but only cylinder #4.

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Then, this happened. Cylinder bank 1 again.

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Clear the codes and try again.

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Didn't take long for the misfire count to start shootin' way up there. Note that Cylinder 4 is again considerably higher than the rest.

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As you can see, we're not up to operating temperature yet this morning.

2611567
 

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Discussion Starter #32
Interim post to keep the forum software happy.
 

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Discussion Starter #33
Here's what I mean about being at idle apparently mattering. RPM's here are 625, standard idle.

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Let's step on the gas some. We're at 2900 RPM. The 60-second timer cycles and clears out the previous minite's misfire statistics. Things are looking better now, with only Cylinder #4 showing any issues (15 misfires).

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Stay on the gas for a bit. Hey...no increases whatsoever! Even Cylinder #4 is staying at its previous level of 15. This is typical of the engine's behaviour when I'm actually driving, too; if I give it even a little gas, it stays smooth, I don't feel misfires, and no cylinder shut-off.

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OK, we just let off of the gas pedal, engine's now back down to idle (575 RPM). Look at those misfires rise....

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Just on a whim, I decided to have a look at the O2 (Lambda) sensors. I happened to catch it when the cylinder shutdown happened. See where the graph changes? Before the cats, red (right side) goes low, green (left side) goes high. Also note that after the cats, blue (right side) also goes low, while yellow (left side) goes a little higher.

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We're almost at operating temperature here. There's that Check Engine Light.

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More to come....
 

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FWIW I have read before that on the M275 there is no point in reading misfire events when the motor is cold or still warming up to operating temp. This is because they can and will misfire when cold - in an ideal world they shouldn't but they can.

Hence always take the car for a short drive to fully warm it up then proceed with plugging in DAS and monitoring misfire events.
 

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S500 W220 SLK320 R170 C200 CDI W203 Peugeot Expert Van
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Hi @cowboyt ,

OK so you got one Bear on your hands here, so lets go wrestle Bear !!

I hear what @JC220 is saying, certainly it won't record a Fault Code / CEL while the Engine is still in Open Loop mode, but at a certain point (temp) in the Warm Up period it will go into Closed Loop Mode, at which point Lambdas take over the Fuelling Control and then it can and will pop a code !!

That's a point, are you 100% Certain the Stat is not opening too early / quickly and also that the ECT Sensor is actually reading the correct Temperature !! ..............
Verify with IR Thermometer against Live Data ;)

Here's what I'd look for now...........
Have you tried ..........

2 NEW Spark plugs (and make certain the gaps are correct, (just in Cyl 4) ............... Yes I know you've replaced them but doesn't mean 1 isn't a dud or been knocked and closed up gap ;)

While your at it get a Compression Test with a "proper gauge" (not SDS Cranking Speed Comp Test) on that Cylinder, and perhaps also do same on one of the low miss count Cylinders on same Bank for comparison.

Other than that I'd be looking for a small Air Leak, is there anything like a Vac port near number 4 cylinder Intake Runner, perhaps spray some carb cleaner near where the manifold runner for Cyl # 4 joins the Head, maybe along a Plastic Seam if it's a Plastic Manifold ?? (IIRC they are ally, but just trying to cover all bases )

Swap # 4 Injector with another from low count Cyl ?? (see if fault migrates)

Final possibility that I can think of, does this Engine have Intake Runner Flaps ?? If so make certain that Cylinder # 4 hasn't got a bent or slightly broken piece of Flap !!

HTH, Cheers Dave
 

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Discussion Starter #36 (Edited)
Interesting idea about a leak, given some other things I saw in the diagnostic screens. We'll get to that in just a moment.

Same day, November 10th. Just got the CEL and cylinder shut-off. I let the O2/Lambda control graph go for a little bit longer. Seems that the left side O2 sensors, both green (before cat) and yellow (after cat) took a bit longer to head downward, but downward they did go. The engine didn't seem to change in the amount of "roughness" when that happened, at least not that I could tell.

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The key for the graph, again. I find this handy.

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Now, here's where we might be looking at a possible leak somewhere. Notice the reading from the MAP, after the throttle valve? There are four MAP's in this car. There's one on each air intake, there's one on the left intercooler before the throttle body, and finally the one after the intercooler. The other three are reading in tolerance. The post-throttle-body one, however, is reading suspiciously low, and out of tolerance. This is at idle, after clearing codes and starting the engine again. The engine is fully warmed up by now and is not misfiring.

Note that there are two specified values for this MAP. When the engine is off but ignition on, the reading is in the mid to high 990's. However, with the engine at idle, it hovers between 315 and 305 or so. Specified range is 313 to 513 at idle.

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Here's a look at the MAP sensor before the throttle body, just to show we're apparently getting enough air through the intercoolers and filters, at least at this point in the process.

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And what the O2/Lambda sensors look like when the engine's behaving. It's been about an hour, and the Sun is starting to set. I did notice that the post-cat O2 sensors are reading about 550 to 575 mV. Earlier, they were reading about 720 to 750 mV, and in a previous graph, above in Post #29, that was true not just during warm-up, but also when the engine was at 96 deg. C and at the same RPM (586 RPM here, vs. 590 RPM above).

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Not sure if it mattered, but I checked the self-adaptation values as well. Note that self-adaptation is not enabled. Should it be, and do we know what this actually does?

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And just for completeness, yep, we're at operating temperature, in this case, 96 deg. C.

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What I found especially curious here was the post-throttle-body MAP sensor reading. If the engine thinks it's not getting enough air, it's going to reduce fuel. However, if the sensor's giving wrong readings, then we're actually getting enough air...thus the reduction in fueling would give us a slightly lean mixture.

Again, this happens only at idle. It has not happened at any other RPM.

That's about it for pics, it turns out.
 

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Discussion Starter #37
I should note one improvement of this new forum software. Unlike before, I can upload/attach images to a post, while also being able to put text in between them! Yep, we can put images "in-line" now. That's a nice feature. This means that we no longer need to depend on external sites like imgur.com or pixhost.to...unless you just prefer to use thumbnails to keep posts from getting too much space on the Web page.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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I read the last few pages, and looking over your list of parts changed.....I don't see the transformers on it.

That's another source of misfire -- if the transformer is getting old or has one too many heat cycles, it'll degrade and not be able to deliver clean power....thus misfire.

EDIT: I just saw the transformer on the list. Not sure how I missed it.

Did you do a smoke check, by any chance?
 

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Yes I am leaning towards an Air Leak affecting that Cylinder 4 in particular, small enough leak not to affect it as the revs rise, but leaning that one out at Idle ;)

Thing about the MAP Sensor for that Bank is that it should affect all Cylinders on that Bank, not just one in particular !!
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Honestly, if I were OP I'd do leakdown test too. It's curious that only cylinder 4 has consistent misfire, makes me think that there might be some unusual/uncommon cause for it to miss.

Another cause would be the MAF. Maybe swap the MAF to see if problem follows the bank?
 
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