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Green '02 E320 Wagon
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Discussion Starter #1
What's a good way to diagnose fouled spark plugs? What could be causing them to foul?

My 2002 E320 4Matic wagon with 150k mi has been idling rough and finally threw a code for cylinder 2 misfire, in conjunction with notable loss of power. In Sept 2016 at 117k mi, I had rough idling and a code for cylinder 3 misfire which I fixed by replacing its plugs. In Aug 2013 at 105k mi, I replaced all of the spark plugs. So, different cylinders have had their plugs foul and misfire over the years.

I will use my compression tester on cylinders 2, 3, and others. I will also compare spark plugs in cylinder 2, 3, and others. Beyond that, I'm not sure what to check. I've attached a picture of cylinders 1-3 with the valve cover off from Oct 2017 if that helps at all.

IMG_20171001_200603.jpg
 

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2007 E320 Bluetec, 2008 320ML CDI
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Valve train looks very good.
That the spark plug fouling affects both plugs in a cylinder (guessing here), I’d confirm that the plugs are connected correctly (A-B) and that the leads are fairly matched in terms of resistance.
Might this also indicate the aging of the coils?


Sent from my iPad using Tapatalk
 

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1998 E320 base sedan @ 160kmiles
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Hello :).

Do you have a scanner ? If so, are there any other codes ?
Can you clear the codes and obtain freeze frame information which includes the fuel trims engine load, rpm, MAF, etc. etc. ?

Do have access to the SDS ? If so you can manually turn off one of the spark lines and observe the rough running cylinder value. It is equivalent to pulling off the spark plug line, and observe the engine behavior, as in the old days ,(but done with HHT-WIN commands for your car). You can then isolate if it is the particular circuit (spark plug cable, plug, or partial coil), or both sides.
 

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88 560SL - 01 C240 - 02 W210 4matic Wagon - W212 4matic wagon
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Check to make sure no oil one the wires .... the covers leak and wet the wires. Also -- if the wires are original .. replace the set. The first thing is to check the compression ...

All three of my v6's of this generation had a wire or two replaced prior to replacing the set with new plugs in the 120k range ... get a decent set online. $100
 

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Green '02 E320 Wagon
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Discussion Starter #5
and that the leads are fairly matched in terms of resistance.
By "leads", do you mean the wires? How can I test the resistance of the wire using a multimeter?

Check to make sure no oil one the wires .... the covers leak and wet the wires. Also -- if the wires are original .. replace the set. The first thing is to check the compression ...
My valve covers were leaking for years, so there probably is oil on the wires. In 2016, I proactively replaced the cylinder 3 wires when I replaced its plugs. I will buy replacement wires, but I need to drive the car long distance tomorrow, so must replace only the cylinder 2 plugs for now.

Do you have a scanner ? If so, are there any other codes ?
The codes in the system were P0300 (random misfire), pending P0302 (cyl 2 misfire), pending P0442 and P0432 (cat below efficiency, probably from burning coolant).
The freeze frame data on the P0300 was:
Fuel Sys 1 and 2 = CL
Calc Load = 27.84%
ETC = 140 F
STFT B1 = 3.91%
LTFT B1 = 6.25%
STFT B2 = 3.91%
LTFT B2 = 6.25%
MAP = 13.58 inHG
Engine RPM = 600
Vehicle speed = 0 MPH
Engine had warmed up, I had driven about 5 minutes, and the CEL came on while at a stop light.

I don't have an SDS. How can I perform the tests you mention with just a multimeter and a spark plug checking light?
 

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Green '02 E320 Wagon
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Discussion Starter #6
I just drove to the shop to replace the plugs and the car had full power. The misfire reduced back to the rough idle I've been experiencing all year. The check engine light, which I had cleared, did not come back. (the shop was in use, so I didn't get to check the plugs)

When I experienced the misfire, I had picked up the car when it was freezing cold outside, from valet parking where it had been for nine days.

How could a significant misfire happen during only one drive?
 

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1998 E320 base sedan @ 160kmiles
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Well you could measure the resistance at the input side of the ignition coil, with the ignition off cable pulled out. The resistance between pins 1 and 3 is between 0.9 to 1.6 ohms. Between pins 1 and 2, and pins 2 and 3 should be around 0.6 ohms. I think moisture can be the culprit. Once my son had a misfire on cylinder 3, after he traveled over a big puddle. You could remove the spark plug cables, clean the connectors with electronic contact cleaner, and let it dry. Then you could smear very small amount of dielectric grease on the rubber part (in which the plug porcelain goes into) of the cable boot connector.

You either have had a serious misfire (CEL flashing), or the car had a pending misfire with steady CEL.

Apart from slightly high long term fuel trims, nothing I could see out of ordinary.

How do you know that the car is burning coolant ? Have you tested it ? of is it a mysterious coolant loss case ?
 

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Discussion Starter #8
Thanks for the resistance measurement info. I will test it before replacing the wires.

I slightly smelled burning coolant when the car was seriously misfiring with loss of power. Today when it was driving normally (just rough idle), I didn't smell it at all.

I check my fluids every month and the coolant level has been dropping slowly all year. After five months, I had to add 0.4 quarts to bring it back to full. I missed my check this month, but it's probably down 0.2 quarts.

Eight or so years ago, when the E320 acted up, I would turn it off and back on again. The problem would go away and not come back, so I assumed the problem was a fluke. These days, I evaluate each problem in depth. The fact that the car misfired causing loss of power one day and not the next has me ready to dig in and diagnose until I find the problem, not just ignore it.
 

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W123 '83 200, W210 '98 E200K, W212 '13 E350
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By "leads", do you mean the wires? How can I test the resistance of the wire using a multimeter?



My valve covers were leaking for years, so there probably is oil on the wires. In 2016, I proactively replaced the cylinder 3 wires when I replaced its plugs. I will buy replacement wires, but I need to drive the car long distance tomorrow, so must replace only the cylinder 2 plugs for now.



The codes in the system were P0300 (random misfire), pending P0302 (cyl 2 misfire), pending P0442 and P0432 (cat below efficiency, probably from burning coolant).
The freeze frame data on the P0300 was:
Fuel Sys 1 and 2 = CL
Calc Load = 27.84%
ETC = 140 F
STFT B1 = 3.91%
LTFT B1 = 6.25%
STFT B2 = 3.91%
LTFT B2 = 6.25%
MAP = 13.58 inHG
Engine RPM = 600
Vehicle speed = 0 MPH
Engine had warmed up, I had driven about 5 minutes, and the CEL came on while at a stop light.

I don't have an SDS. How can I perform the tests you mention with just a multimeter and a spark plug checking light?
Before you posted data, I was thinking maybe leaking injectors or a dirty MAF sensor.

Reading the data above, a few things don't seem to add up:
Your Fuel Sys 1 and 2 show closed loop, but car is not fully warmed up - ETC 140F
Your engine load is at almost 28%, but you're at idle and stationary.

I don't know enough to say whether your MAF reading is reasonable.
 

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1998 E320 base sedan @ 160kmiles
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Before you posted data, I was thinking maybe leaking injectors or a dirty MAF sensor.

Reading the data above, a few things don't seem to add up:
Your Fuel Sys 1 and 2 show closed loop, but car is not fully warmed up - ETC 140F
Your engine load is at almost 28%, but you're at idle and stationary.

I don't know enough to say whether your MAF reading is reasonable.
The ME2.0 ECU has a timer, as well as it monitors the coolant temp. It goes into closed loop if a timeout occurs too (provided that the ECT sensor and MAF are not faulty).

There is no MAF information posted. With Torque Pro, the MAF info is part of the freeze frame data.

The car is stationary but the gear is in Drive (waiting at the stop sign).
 

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Discussion Starter #11 (Edited)
I pulled the cylinder 2 plugs and compared them to a cylinder 1 plug. They all looked the same, slightly white but otherwise clean (cylinder 2 are left and center, 1b is right) . The 17 year old wires looked a little gross on the inside terminals compared to my 3 year old cylinder 3 wires.

IMG_20191118_144516.jpg

I erased the check engine code and it came back after a short drive. This time it says cylinder 2 and 5 are misfiring. The data is:
Fuel Sys 1 and 2 = CL
Calc Load = 24.71%
ETC = 102 F
STFT B1 = 0.00%
LTFT B1 = 6.25%
STFT B2 = 4.69%
LTFT B2 = 6.25%
MAP = 11.52 inHG
Engine RPM = 800
Vehicle speed = 0 MPH

That STFT B1 doesn't look good at 0%. The car seems to drive fine but idles quite rough.

I suspect the coils, wires, and plugs are fine and the problem is elsewhere. I also have an engine whine which I'm trying to diagnose, and I'm worried it may be related. And there's a whirring sound when I drive which has been there for over a year. And a clicking sound when I'm driving at 30 mph. So many problems that I'm worried about, but never the time to fix them, and since it drives ok, I keep driving it because I have to.
 

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1998 E320 base sedan @ 160kmiles
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The whining noise seems to be related to a bad idler pulley. Easy to check. Remove the belt and run for few minutes to see if the engine still whines. Also you can spin the pulley with the belt off and listen. It is worth replacing it with an INA brand. Mine cost only $10 few years ago.

Spark plug tips look fine, but did you use anti-seize on the threads ?

Of significance, the coolant temp seems to be low. I don't know how long the drive was, and what the ambient temp is, it seems to be low to me. have you ever serviced the cooling system, and checked the ECT sensor condition ? Sometimes it is covered in crud, and takes sometime to show the correct temperature.

Don't worry about the STFT at this point. They are dynamic, based on O2 sensor readings.

It is hard to diagnose the misfire related issues without a proper scanner that allows you to see the live misfire data from all cylinders, at different engine loads. It is possible that maybe more cylinders are misfiring (which points to a different problem) but only one or two of them exceed the threshold to raise pending or stored code. You never indicated whether the CEL is flashing or steady. I do not think that a steady CEL will come in one drive cycle. Are there any other codes that came on, or any other freeze frame data (if more than one code). ?
 

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Discussion Starter #13
Can you recommend a proper scanner which will show live misfire data? I am interested in buying a more advanced scanner which can provide detailed active diagnostics about the vehicle systems as its running. I can spend maybe $400 on one, so not a $10,000 MB Star diagnostic kit. All I have is a decent quality OBD2 scanner.

Is it possible that the car only misfires at idle? It idles really rough but drives just fine. It only drove rough one time after it was sitting for nine days. I've cleared the stored codes and they've come back a few times. Each time, the freeze frame data shows vehicle speed of zero.

I replaced the coolant two years ago when I replaced the water pump, idler pulley, belt tensioner, and belt. It's cold here in NH, so that could be why the temp is low. I'll look into the ECT temp sensor.
 

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1998 E320 base sedan @ 160kmiles
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Obviously the first choice would be the SDS Clone from China / EBay. Which one to choose (C3/C4 or compact C3) is discussed in R129 forum in detail, and also recommended vendors and models. It takes time to do the setup in the laptop and get it working, and moreover understanding what is what. So it has a relatively long learning curve.

Few forum members recommend Foxwell :

https://www.amazon.com/FOXWELL-Diagnostic-Mercedes-Multiplexer-connector/dp/B07CJY4V6X/ref=sr_1_5?keywords=foxwell+mercedes&qid=1574644776&sr=8-5

I do not own one, so I do not have any knowledge if it can display the extended live data from the ECU (misfires, smooth cylinder running, etc, etc.). You can go to the spec sheet and find out.

I have a scanner that can access most of the modules (few body control modules) and it can display the misfire data on per cylinder basis.
https://www.ebay.com/itm/2018-Bluetooth-TCS-CDP-Pro-Plus-OBD2-OBDII-Scanner-Diagnostic-Tool-for-Car-Truck/142913023465?hash=item214647ade9:g:FiIAAOSwyohbfN1n

Some bought this and could not get it working, but very likely due to a problem with the car diagnostic access, rather than the unit itself. You would need to follow the instructions carefully.

Have you checked the throttle ? Dirty throttle can cause rough idle, as well as dirty fuel injectors.

Have you used a good quality fuel injector cleaner ?

Could be a marginal MAF sensor.

My son's car had recently developed rough idle (at least he recently told me :).) No codes, no CEL, accelerated fine but some vibration at 40 to 50 mph. Replaced the flex discs, and the transmission mount which was totally destroyed. Idles smooth now.
 

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1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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How long does it take for the engine to get up to operating temp?
 

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Discussion Starter #16
Thanks for all of the info. I will be diving in to this today.

How long does it take for the engine to get up to operating temp?
Today, at 55 degrees and sunny, I started and immediately drove no more than 50 mph, it took 6.5 minutes for the needle to be horizontal. I feel like that's the same as it's been for at least five years.
 

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Discussion Starter #17
The car is running hotter than it should. While stuck at traffic lights for five minutes, the engine temp climbed to 200 (according to climate control code #6). When idling, it rose to 188. When I resumed driving on the highway (with 35 degree outside temp), it cooled to 175.

Today is the first time I've driven it more than 20 minutes in a day. I smelled a faint scent of coolant a few times today. I have to check the coolant level again when it's light out.

Misfire. That's what the title should say. The car is misfiring and the plugs are fine. Why can't I get this car to run correctly? It's just a machine, it should be possible to make it run reasonably well.
 

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Have you swapped plugs to a different cylinder? How about the coils?
 

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Discussion Starter #19
Can I test a coil by running the engine with one plug wire going to a voltmeter instead of the plug? Would that allow unburnt fuel to fill the cylinder and pass into the catalytic converter? The compression test sticky recommends cranking the engine off the K40, so does that avoid sending fuel to the cylinders?

I tested the resistance on the wires for cylinders 1, 2, 4, 5. Wire 2b had a resistance of 30k ohms instead of 2k ohms. I moved that wire to cylinder 1b to see if the cylinder 2 misfire moved with it. I will replace that wire and may do them all since they're rather stiff.

The cylinder 5 misfire was reported less frequently than that of cylinder 2. Its wires had the correct resistance. I swapped its coil with cylinder 4, leaving the wires in place. The cylinder 5 plugs looked slightly ashy, just like those in cylinder 2 and 1, which appears normal for 50k miles of use.
 

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Can I test a coil by running the engine with one plug wire going to a voltmeter instead of the plug?
I do not recommend that. The coils go up to 10kv sometimes, so you may end up getting some nasty shocks, nevermind destroying your DMM.

Good idea on swapping the wires and coils, that's a start to see if misfire moves or not. It's a cheap and quick way to see.
 
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