Would a bad MAS give misfire?

[Eurosport]

ty

[98_Benzo]

Technically YES, but more then likely NO. I would check your plugs and maybe see if your timing is right on (highly doubt you jumped the chain, but you never know). I would start at your plugs though!!

Also, are you sure you put the right type of fuel (92 octane)?

try throwing some fuel dryer down your gas tank, might help out a little bit.

[kodiak]

Originally posted by Eurosport
ty

I doubt it is the MAS, but if you tell us the engine type and year, we might be able to help you more.

~dnm

[Eurosport]

MAS is the only thing left
engine wire harness=new
spark plugs=new
plug wires=new
supressors(between coil packs and plugs)=new
coil packs=new
gas=always run on 92 from same gas station which is about 1 year old so new tanks not much of a chance of bad residue on the bottom of their tanks

gave me P0300 code today, which is random misfire
while doing a 0-100mph sprint, went in limp mode of course
pulled over, restarted car, limpmode resets
cleared my code, tried to duplicate and no luck
pushing the car hard, and runs like a champ

i'm just thinking is MAS worth changing if this happens so random and rare?

and from what i've heard sometimes a bad MAS won't necessarly give you a bad code pointing you to MAS as being the problem
but as you can tell that's pretty much only thing left on the list that hasn't been replaced

98_Benzo,
you coming tomorrow? email me your cell

[CKlasse]

YES! Your ECM reads MAS and O2 sensor to control timing and fuel ratio during close loop cycle.

BAD MAS READING will throw your fuel ratio off balance therefore causing misfiring. Most likely you would go RICH!

You said when you run hard, the car runs like a champ. This is a good hint. As you go Wide Open Throttle, the ECM switches to OPEN LOOP - It doesn't read MAS or O2 sensors and your car runs fine.

When you cold start the car in the morning, pay attention to the idle. Does your RPM stay steady at approx. 1200RPM and then 800RPM after awhile. Do you smell gas fume from the exhaust?

Now, when you scan the OBDII port, try to write down the A/F ratio. Another possibility of the prob. would be DIRTY FUEL INJECTORS! Good luck. :)

[Eurosport]

sometimes i do smell gas from the exhaust fumes when it's cold,
i'll write down the A/F ratios and keep an eye on what the exact rpm is when starting cold and when it warms up what it goes to, i know warmed up is about 680-700 rpm idle can't remember

thanks for the tips btw

[98_Benzo]

as Lynyrd Skynyrd once said "ooh ooh that smell"

[C280 JR]

why are the spark plugs such problems on mercedes..ive had my car for about 14 months, and i had to replace them 3 times..

Elvir

[Eurosport]

here's some data
cold start
idle
rpm 928
airflow rate from maf 0.88
throtle position 31%
engine coolant temp 122F
ignition timing advance 8.5 deg.
intake manifold 10.4 inhg

now after letting it warm up to normal
idle
rpm 672 with sometimes jumping to 704
airflow rate from maf 0.44 and jumping to 0.59 (and back and forth)
throttle position 2.7
engine coolant temp 185F
ignition timing advance 6.5
intake manifold 10.1


seems like the jumping in AF from 0.44 to 0.59 makes the rpm switch as well from 672 to 704 (or backwards)
could that be the MAS?
this is all at idle remember
misfire was not at idle but at high rpm
ty

[J Irwan]

Eurosport

If you have a buddy with W202 6 Cyl you could try to swap the MAS to see if that fix it

If it does then it's time to get a new MAS


PS: Elvir, what kind of plug you have (i found it weird you have to change the plug 3 times in a year time frame) just stay away form platinum sparkplug (plat +4 or splitfire)


Regardz,

[JRE320]

If you've change almost every single part that you think that's causing the mis fire then one last thing and hoping not the
"ACTUATOR"... actually the throttle body itself. This will cost you like $1200 for parts alone. This is based on my experienced on my C-class. No code is coming up and just got a major tune up done. Then finally replaced the actuator and it rans like a brand new engine again.

[J Irwan]

Originally posted by JRE320
If you've change almost every single part that you think that's causing the mis fire then one last thing and hoping not the
"ACTUATOR"... actually the throttle body itself. This will cost you like $1200 for parts alone. This is based on my experienced on my C-class. No code is coming up and just got a major tune up done. Then finally replaced the actuator and it rans like a brand new engine again.


Jun, what is the sympton for bad Actuator..??


Regardz,

[C280 JR]

Then finally replaced the actuator and it rans like a brand new engine again.

Well after spending $1200, id be pi$$ed if it did not!

Elvir

[JRE320]

First the idling. After you warm up the car it won't idle like it's suppose to be. 2nd check engine light would come on no matter
how many times you have it reset. 3rd you can feel that it's hesitating to pick up even when you try to floor the gaspedal down. I'm glad I replaced the actuator after looking at the old one. There's so much dirt in it w/c you can't even reach in to clean.

[98c43amg]

My car was sputtering and even (if only rarely when cold) backfiring due to a filth clogged airbox.

EDIT: I also use fuel injector cleaner every few months now. I understand the adatives in newer "lower emission" fuel has us going backwards to the times when the injectors may clog more.

[Denlasoul]

Is there a diagnostic tool that can read the voltage of the MAS sensor? Does it have to be connected to the car, or can I pull it out and use the testing equipment?

Today, I pulled out my MAS and tried to clean it out. I didnt have the proper "torx star" piece to take out the wire, but I was able to slightly clean the wire by using Q-tips. I havent taken my car for a spin yet, so I cannot determine if the cleaning helped. I was hoping to test the voltage running through the wire to see if it is heating up properly. I dont want to buy a new one, if I dont know 100% it is not working properly.

DLS

[714guy]

Originally posted by Eurosport
here's some data
cold start
idle
rpm 928
airflow rate from maf 0.88
throtle position 31%
engine coolant temp 122F
ignition timing advance 8.5 deg.
intake manifold 10.4 inhg

now after letting it warm up to normal
idle
rpm 672 with sometimes jumping to 704
airflow rate from maf 0.44 and jumping to 0.59 (and back and forth)
throttle position 2.7
engine coolant temp 185F
ignition timing advance 6.5
intake manifold 10.1


seems like the jumping in AF from 0.44 to 0.59 makes the rpm switch as well from 672 to 704 (or backwards)
could that be the MAS?
this is all at idle remember
misfire was not at idle but at high rpm
ty

Kindaa of topic but what kinda of Diagnosic tool do you have, was it pricey, i am looking for one but can't seem to find one for benz in my price range.

Thanls

[98c43amg]

Originally posted by 714guy
Kindaa of topic but what kinda of Diagnosic tool do you have, was it pricey, i am looking for one but can't seem to find one for benz in my price range.

Just thought I'd jump in here. I bought two PC based OBD-II readers. Of the two, I recommend the Car Code:
http://www.carcode.com/

I was disappointed to find out how slow the MB OBD-2 bus runs, at about 10Hz. Between that and the mandatory delays required per code request, scan a half dozen codes at a time and the scan rate is well under 1 per second.
:(

[Eurosport]

this is the one that i have
http://www.auterraweb.com/

it works on any US car 96+ since odbII

it has already paid for itself at least double by not going to the shop to read codes, not to mention doing the work myself

[714guy]

cool thanks, but i was looking for something with out the palm, i hate using the palm. i always forget to charge its batteries and it dies on me.

[CKlasse]

Go to your local part stores. A generic scanner is about $150. A great one such as GENESIS works on both OBDII and pre OBDII is about $1200. Ebay has a bunch of GENESIS scanner for much less.