Mercedes-Benz Forum banner

1 - 15 of 15 Posts

·
Registered
Green '02 E320 Wagon
Joined
·
570 Posts
Discussion Starter #1
This is a more appropriately titled thread than my first thread about this. I have more work to do from that thread, so I'm not abandoning all the good info there. I just want the proper thread title.

My 2002 E320 4Matic wagon has had a rough idle for over a year, but it always drove fine. Recently after sitting for nine days, it misfired while driving, causing a rough ride and loss of power. That triggered diagnostic trouble codes P0300 "random misfire", P0302 "cylinder 2 misfire", and P0305 "cylinder 5 misfire". Since then, the car hasn't driven rough but still has the rough idle, and erasing the codes allows them to keep coming back. The freeze frame data always shows the codes triggering at idle with a moderate to fully warm engine.

I created a checklist for diagnosing misfires by searching the forum. It's still not complete and I can't edit the original post to clean it up.

So far I've visually confirmed that the spark plugs look normal and added injector cleaner to my gas tank. When testing the resistance on the plug wires, I found cylinder 2 had a wire with 30k ohm resistance instead of 2k ohm. I moved it to a new cylinder but it has not triggered a DTC there. I swapped the cylinder 5 coil with cylinder 4, but cylinder 5 still reports misfires (its plugs and wires are fine). I have yet to check the injectors, coil inputs, catalytic converter, vacuum leak, and more.

Tonight, the car was misfiring while driving for the first time in two weeks. I pulled in to a gas station, turned the car off, and waited 20 minutes. When I turned it back on, it only had a rough idle and drove smoothly. How could the problem go away by simply waiting 20 minutes?
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,015 Posts
Have you ever replaced the crankcase position sensor ? I am not saying this is the problem but a worn and failing sensor, senor wiring and / or connectors, a defective or dirty ring gear (where the CPS senses the timing from the tips of the wheel), can cause problems like this. The ECU may be missing some timing pulses needed for firing the cylinders exactly when needed. If the missed pulses are excessive, the engine stalls, and will not re-start till it gets cooler. The firing order is 1,4,3,6,2,5.

If you have the tools (E8 socket I think) and a a long extension for the wrench, you can remove the CPS and check it out. Also you can clean the connectors (CPS and the harness) with electronic contact cleaner spray, and see if it makes any difference. You might as well replacing it if you have not done so.
 

·
Registered
Joined
·
262 Posts
I had a similar issue which turned out to be deteriorated/collapsing vacuum hoses.
For misfire, pull leads to find the culprit. Sometimes it was a matter of removing corrosion from wire connectors.


Sent from my iPhone using Tapatalk
 

·
Registered
Green '02 E320 Wagon
Joined
·
570 Posts
Discussion Starter #4
I had a similar issue which turned out to be deteriorated/collapsing vacuum hoses.
How does engine firing depend on vacuum hoses? Which hoses did you find had deteriorated?

When I resealed my breather covers, I replaced its large rubber hoses on the left and back of the engine. Are those the vacuum lines?
 

·
Registered
Dallas, Texas
Joined
·
6,990 Posts
How does engine firing depend on vacuum hoses? Which hoses did you find had deteriorated?

When I resealed my breather covers, I replaced its large rubber hoses on the left and back of the engine. Are those the vacuum lines?
Vacuum leak creates lean mixture that may cause misfire at idle. Look in freeze frame data of misfire code. LTFT of more that 10% is a problem with vacuum leak.
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,015 Posts
His LTFTs were around +6. No problem there. Plus it would be an engine-wide issue, not one cylinder or two.
 

·
Registered
Joined
·
262 Posts
My misfire was due to a bad coil pack.
Low/rough idle was due to a collapsed vacuum hose running from the valve cover breather.


Sent from my iPhone using Tapatalk
 

·
Registered
Dallas, Texas
Joined
·
6,990 Posts
His LTFTs were around +6. No problem there. Plus it would be an engine-wide issue, not one cylinder or two.
Not if vacuum leak is at injector seal or right at the port leading to it. If small enough it will not trigger P0170, P0173 but it will make it run with the lope at idle.

OP has scattered his query among several unconnected posts making it difficult to follow.
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,015 Posts
Not if vacuum leak is at injector seal or right at the port leading to it. If small enough it will not trigger P0170, P0173 but it will make it run with the lope at idle.

OP has scattered his query among several unconnected posts making it difficult to follow.
Leaky injector seals would certainly be an issue, but he also reports coolant loss, and few non-misfire codes. Yes it would have been much better to have the problem in one thread.
 

·
Registered
Green '02 E320 Wagon
Joined
·
570 Posts
Discussion Starter #10
I replaced the plugs and wires for cylinder 5 and the rough idle is gone. The old wires had the same correct 2k ohm resistance as the others and the plugs looked only slightly grey like the others. But I snapped one of the plugs while trying to do a compression test, so I installed the new parts. I will be installing the remaining wires soon.

Maybe these plugs had a problem because of dielectric grease I put on the metal electrical contact when I changed the plugs 50k miles ago. I only put it on cylinder 4-6. I'm reading now that grease should go on the ceramic to keep water out, not on the metal contact. I will correct this when replacing the other wires.

I am still going to try an exhaust leak test on the coolant or a compression test if I can find parts which fit. I am loosing coolant, so I'd like to rule out a leaking head gasket.

I got an OBDLink MX and Torque Pro for Android to closer examine the misfire information. I don't see how it can access the misfire rate for individual cylinders. It appears to only have access to a basic set of sensors, not much different from the freeze frame data on my code reader.

Thanks to everyone for their detailed help. Sorry I went to so much depth when I should have just thrown wires at the problem (or just cleaned the ones that I had). I just wanted to know the root cause.
 

·
Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
Joined
·
3,405 Posts
It's probably the plugs, not the wires. Day 1 I told you to swap spark plugs to see what's up, and seems that you made this out to be far more complicated and expensive than it needed to be.

But yes, now you do need to figure out the coolant loss, a coolant pressure tester would be a good place to start.
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,015 Posts
I got an OBDLink MX and Torque Pro for Android to closer examine the misfire information. I don't see how it can access the misfire rate for individual cylinders. It appears to only have access to a basic set of sensors, not much different from the freeze frame data on my code reade
TorquePro is a general purpose OBD2 scan / access program, not specific to a particular brand to obtain brand/model/year specific live data from the ECM. You need a different scanner from Autel, Foxwell, Autocom/Delphi, MB Star, Carsoft and others.

It is correct that you put very little amount of dielectric grease on the ceramic part (or smear inside the rubber part of the connector). This will help prevent stray electrical paths over the ceramic, between the tip and the metal grounding nut. Also my NGK plugs have anti-seize properties on the threads, so use of anti-seize is strongly discouraged (it increases the grounding resistance).
 

·
Registered
Green '02 E320 Wagon
Joined
·
570 Posts
Discussion Starter #13
It's probably the plugs, not the wires.
I just checked the maintenance manual and saw that the plugs have a lifespan of 5 years or 100k miles. I'm at 6 years and 50k miles. Maybe they are starting to fail from age, though they looked good to me. I'm sorry I didn't try your solution sooner. If the rough idle or misfire comes back, I'll replace them all.

But yes, now you do need to figure out the coolant loss, a coolant pressure tester would be a good place to start.
Can anyone recommend a pressure tester with the correct cap to fit a W210 coolant tank? I've tried generic ones and they either wouldn't seal or popped off. I'm also looking for a combustion leak detector with the W210 coolant tank cap.
 

·
Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
Joined
·
3,405 Posts
Rent one from AutoZone or orielly, unless you don't mind plopping $70-100 for one.
 

·
Registered
Green '02 E320 Wagon
Joined
·
570 Posts
Discussion Starter #15
Some of the my plug electrodes have turned brown while others remain silver. For instance, plugs 1A and 2A are silver while 1B and 2B are brown. Plugs 5A and 5B which had the misfire were also brown. Why would some turn brown after 6 years, 50k miles?

I finished replacing all of the wires (though only one failed the resistance test). There are no more misfire codes and the car idles and runs great. Thanks again for all of your help.
 

Attachments

1 - 15 of 15 Posts
Top