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1997 E420
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12 Posts
Discussion Starter #1
Hi guys, and happy new year! One of my resolutions was to get my two Mercs back on the road, they've just sat on the driveway for a few months now...

Anyway, the main issue on my 1997 E420 is that cylinders 5, 6, 7, and 8 are misfiring. She was used for a bit in that condition out of necessity, but took the keys away when she couldn't go past 30 or even 20 miles per hour.

I tried tapping with a closed fist to see if the catalytic converters were clogged, but I didn't hear anything. Maybe I'll try with a rubber mallet lol

I need guidance on how to proceed...

1) The only faults that appear now are the misfires, but before that, and for a very long time two faults, one with "O2 Sensor Circuit Malfunction" and the other with "O2 Sensor Heater Circuit" both on (Bank 2 Sensor 2) persisted even after replacing or swapping the O2 sensor.

Are these two issues possibly related or even on the same side of the engine?

I'd hate to replace the pricy California rated catalytic converters, if they are indeed "clogged", only to have the new ones also go bad, because I didn't fix the O2 sensor issue.

2) I'm about to replace the spark plugs myself this afternoon, which side of the engine and exhaust system is the problem area? The side with the air filter, or the side with the washer fluid container?

3) When I first bought the car I replaced all of the visible breather hoses, plastic, and rubber connectors for the hoses and vacuum lines on top of the engine. The old ones were brittle, cracked, slightly sludgy, or completely snapped off.

It ran fine after that for a year, but today as I prepared to change the spark plugs I noticed that a lot of the breather hoses came loose very easily, then I realized that they had a bit of oil on them...

Did this happen as a result of the problems I'm having?

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My hope is that maybe by replacing the spark plugs maybe that allow me to at least limp her to shop, that can straight pipe or replace the catalytic converter, unless you guys think it's something else...

Below are some pictures,


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1997 E420
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12 Posts
Discussion Starter #3
@Kajtek1 Sorry if my I didn't make myself clear, I wanted to share my observations and concerns, to see what you guys think.

To be concise then,

1) Is half of the engine misfiring a result of me ignoring the O2 sensor problem since I bought the car?

2) Did that potentially cause the catalytic converters to go bad?

3) Is the "Bank 2 Sensor 2" even in line with the misfiring cylinders 5, 6, 7, and 8?

4) Will replacing the spark plugs offer any clues?

5) There's some oil in my breather hoses, what does that mean, is it related?

6) besides bad catalytic converters, what else can cause half the engine to progressively worsen with misfires?

I'm actively trying to educate myself, but I'd appreciate your and anyone else's input.

I can't afford a mechanic, and I definitely can't pay someone to buy and replace all FOUR catalytic converters, and have them charge me an arm and leg here in California.

Especially if the cause isn't identified or addressed.

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2002 E55 AMG Sedan
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1,165 Posts
The car could be misfiring because of the O2 sensor issue but it's hard to say for sure. Pull the spark plugs and see how they look.

I have a feeling it's the cats causing the problem because the O2 sensor issue was ignored for so long. Which cat converts did you bang on? The ones monitored by the O2 sensors or the ones that are not monitored?
 

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E320/E250 Bluetec Ford F350 6.7l
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36,372 Posts
1. O2 sensor sends signal to ECU to adjust the fuel mix for the bank it is on. When it malfunction, you will have wrong fuel mix and misfires
2. if the wrong fuel mix is rich, it can burn cat, but that takes long time
3. bank 2 is driver side and cylinders 5,6,7,8 are driver side
4. not likely you have 8 spark plugs failed at the same time. Get known problems fixed before going farther.
5 breather hose carries oil fumes, so oil residue is normal
6. about million things.
Once again, fix what you have clearly showing and go from there.
 

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w163 02 ML500 W210 97 E50Amg w202 99 C230K w124 - need more space, time to build again
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2,230 Posts
Invest in a temp gun. Im with illstplaya, the cats.
Read the temps before and after the cats. SImple procedure.

 

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1997 E420
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12 Posts
Discussion Starter #7
The car could be misfiring because of the O2 sensor issue but it's hard to say for sure. Pull the spark plugs and see how they look.

I have a feeling it's the cats causing the problem because the O2 sensor issue was ignored for so long. Which cat converts did you bang on? The ones monitored by the O2 sensors or the ones that are not monitored?
I checked all four, two going up to the engine, and two that are side by side further down... I even used my rubber mallet, but I didn't hear anything but pipe...

I also replaced the spark plugs. They were well passed their prime as you can see, but didn't solve the issue. Though the car did seem to start right up, idle smoothly, and want to run better than ever, but things get rough as soon as I try to drive it.

I reset the codes did a really slow and rough lap around the block, and the codes returned as you can see, though instead of the usual P0156 and P0161 for the Bank 2 Sensor 2, I now get P0150 for Bank 2 Sensor 1... All I did was change the spark plugs, spray clean the mass airflow sensor, and wipe the oil off the breather hoses... Not sure why P0150 is showing up now for the first time...

I also, took a picture of one of the cylinders on the driver's side, I can't make sense of it though, I guess that's part of the cylinder and piston head.

1. O2 sensor sends signal to ECU to adjust the fuel mix for the bank it is on. When it malfunction, you will have wrong fuel mix and misfires
2. if the wrong fuel mix is rich, it can burn cat, but that takes long time
3. bank 2 is driver side and cylinders 5,6,7,8 are driver side
4. not likely you have 8 spark plugs failed at the same time. Get known problems fixed before going farther.
5 breather hose carries oil fumes, so oil residue is normal
6. about million things.
Once again, fix what you have clearly showing and go from there.
I also got P0150 Bank 2 Sensor 1 today for the first time...

If I swap the Bank 2 sensors with those of Bank 1 and it still shows Bank 2 as having faults, what would that mean? Could it be faulty wiring? I did notice a clump wrapped in brittle electrical tape on one part of the wiring harness over the engine... Doesn't look like something Mercedes-Benz would do...

Invest in a temp gun. Im with illstplaya, the cats.
Read the temps before and after the cats. SImple procedure.

I do have a temp gun somewhere... I'll get the car up to temperature, and try to test them, do I test all four? Can you even test "before" on the two cats that going upward towards the engine?

I should make a video of the locations and readings, so you guys can tell me if did them right.

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Something I noticed tonight was the smell of exhaust surrounding the car just after parking it, perhaps even coming into the cabin from the vents slightly...

Thank you guys, I really appreciate your responses!


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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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3,544 Posts
I remember your old thread. Did you ever remove the B2S1 O2 sensor and then going for a drive around the block?
 

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1997 E420
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12 Posts
Discussion Starter #9
I remember your old thread. Did you ever remove the B2S1 O2 sensor and then going for a drive around the block?
I really don't remember anyone ever mentioning it... Sorry if it was you, but it's very interesting! Are you saying to physically remove it to allow the exhaust to escape? Is it safe to do?

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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3,544 Posts
Well it's not exactly safe to do long term, but just as a test to verify clogged cat? Perfectly reasonable. Just around a block or two.
 

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Premium Member
97 E-420 (180K miles), 97 SL500, (93K miles) 2015 GMC Sierra Denali 2500HD CC/SB/4x4 Duramax(55K)
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4,220 Posts
I'm pretty late to the conversation, but how many miles on the car? If it's over or near 100K your at the point of having the coil packs start to fail. Between 90K and 120K my E420 had 7 of the 8 coil packs fail. symptom is misfire codes. And the E420 plug change interval is 25K miles, NOT the common today 100K miles. And if water ever gets under the hood onto the plastic cover over the plugs you WILL in almost all cases start gettiing misfires due to water accumulation in the plug wells. So, first thing I'd do is start pulling the plug cover, blow them out to see if there is any water in them. then change the plugs on all 8 cylinders. Then take #5 coil pack and swap it with #1 coil pack. Once you get it going again if the #1 cylinder has a misfire you've found the issue Bad coil pack. If your lucky, you will find it was only moisture in the plug wells and old plugs. And my experience is that water in the plug wells is it gets in ALL the wells on a bank, not just one.
 
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