# Misfire puts the Emergency Fund in action



## KaeJS (Sep 28, 2010)

Pulled into work this morning and the car starting idling real rough. I figured maybe it was the cooler weather, moisture in the air, who knows. I let it be and hoped that it would fix itself.

Nope.

Get in my car after work - still rough. I diagnose my engine light (engine light is always on due to my exhaust) so I would not notice if there was something else wrong. And sure enough, I have a new code. P0300, Random Misfire.

Ugh.

Will be taking the car to the shop tomorrow. Not sure whats wrong with it. The spark plugs have been replaced about 2 months ago, I couldn't find any vacuum leaks. I'm guessing the coil packs are ruined or an injector is fudged.

Sucks that this had to happen 3 weeks before I put the car away for winter!


----------



## slacker (Mar 8, 2010)

I put away about $100 a month for possible car repairs/maintenance. I don't really consider car repairs to be part of my emergency fund, as it's an expected expense.


----------



## mind_business (Sep 24, 2011)

I also budget for the 'expected' repair costs. I budget for $150 per month on maintenance / repairs. I have a 2005 Toyota Matrix. 

Cars wear out and need to be maintained.

I have a total of $470 per month budgetted for transportation (fuel, insurance 
& repairs). Definitely not cheap owning a car.


----------



## carverman (Nov 8, 2010)

KaeJS said:


> Get in my car after work - still rough. I diagnose my engine light (engine light is always on due to my exhaust) so I would not notice if there was something else wrong. And sure enough, I have a new code. P0300, Random Misfire.


Permit me? I do electrical diagnostics online for the dodge dakota forum.
I have my own fuel pressure guages.OBDII code reader, Haynes manual
for electrical diagrams etc. 
You didn't mention what kind of vehicle it is, but perhaps I can help
you with general "check engine" light codes.

Random misfire generally means a high tension spark not occuring at 
proper time, in relation to engine timing crankshaft/camshaft timing.

The only way the ECM knows that the engine is "missing" or random misfiring
on a particular cylinder, is if the crank sensor and cam sensor are providing timing pulses at the correct sequence for that particular cylinder, and the ECM pulsed
coil primary is not being "staged" correctly at so many degrees before TDC.

The ECM is low voltage 12volts and 5 volts, so the only feedback is the 12v primary winding of the coil being pulsed by the ECM coil driver(s) providing a feedback. 

Yes, a coil can do that, and you will get a "miss" on the cylinder but since
the ECM CAN'T CHECK to see if there is a 30K volt spark at the spark plug,
it has to go by timing pulses coming in from the two most critical sensors
the crankshaft sensor ( which indicates piston position on the crankshaft) and
the camshaft sensor (which indicates when the spark should be delivered)
to the cylinder on the compression stroke, and just a few degrees before TDC,
and perhaps coil's primary winding feedback.

Here in a nutshell is how a 4 cycle engine works:
For every single rotation of the crankshaft, the camshaft has to rotate TWICE. The two are connected by the timing chain or timing belt on
smaller cars.

On a sequential port FI (fuel injector) engine:
1. the INTAKE CYCLE, the intake valve opens via the camshaft, draws air from the air intake throttle body.

2. On the piston upstroke, COMPRESSION CYLE of that air occurs and at the
correct point of the piston compressing the air, the fuel injector mists
in some fuel determined by the ECM, and around that point a spark occurs.

3. Power cycle. As the 14.7:1 fuel air mixture expands in combustion, the
pressures push down the piston..to turn the crankshaft

4. On the upcoming stroke of the piston, the exhaust valve opens via the
camshaft, and the exhaust is scavenged out by the piston pushing it out and the next cycle begins. 

I apologize if you know the theory already.

More than likely your previous steady "check engine" light would point to
a code that indicated that the oxygen sensors (O2) needed replacing.

The ECM uses the input from each O2 sensor to determine the fuel-air
mixture setting. If the O2 sensor isn't functioning anymore, most ECMs
will ignore it, running with an internally stored program of 14:7 to 1.
So more than likely, your gas mileage will go down a bit when that happens.


> Will be taking the car to the shop tomorrow. Not sure whats wrong with it. The spark plugs have been replaced about 2 months ago, I couldn't find any vacuum leaks. I'm guessing the coil packs are ruined or an injector is fudged.


Random misfire would be more of a spark issue, I would think, as generally
for injector malfunction there are individual codes for each injector. 
On my Dakota V8, #1 cylinder injector malfunctioned for a while. I had to get to
get the injectors cleaned and the fuel rail purged, and it went away. 
I bought a spare injector, just in case, but the injector code has not come
back in 10 years, so it may have been a speck of dirt blocking it..or
something to do with the ECM, since the ECM pulses the solenoids on
each individual injector, it knows about each injector and gives the code for each injector separately.


----------



## KaeJS (Sep 28, 2010)

carverman said:


> I apologize if you know the theory already.
> 
> More than likely your previous steady "check engine" light would point to
> a code that indicated that the oxygen sensors (O2) needed replacing.
> ...


The car is a 2003 MazdaSpeed Protege.

I know the theory, but thanks for taking the initiative.

My previous check engline light was not steady. I have an aftermarket exhaust with a "hi-flow" cat. Basically, there is no cat, so the check engine reads that there is a "Catalytic Converter Warm Up on Bank 1/1", but it comes and goes and is off more often than it is on.

You are right. Random Misfires are more of a spark issue as it affects all of the cylinders. My vacuum pressure is also really low at idle, which leads me to believe that maybe there is a vacuum leak somewhere. Which, could very well make sense because the car is turbocharged.

Anyway, it is at the shop now and will be fixed at the expense of my wallet. Thank you for your insight, though. Hopefully I'll be able to post an update on what the issue actually was later on tonight.


----------



## HaroldCrump (Jun 10, 2009)

carverman, your varied knowledge about a wide range of technologies, matter and issues never ceases to amaze me.
You are quite a walking encyclopedia.
Always interesting to read your posts.

Cheers


----------



## KaeJS (Sep 28, 2010)

Still at the shop. They did a few tests and couldn't find anything wrong.

Right now its leading to the EGR Valve. They are going to try to clean it tomorrow and then replace it if that does not help.

Spark plugs and coils checked out fine. No vacuum leaks that they (or I) could find. However, the vacuum pressure is definitely low at idle.

EGR???

It's the only thing I can think of as well.

It makes sense, though. Its getting cooler outside and I do have holes in my hood. Some moisture could have gotten into the valve somehow due to condensation and changing weather.


----------



## mind_business (Sep 24, 2011)

Ugh, I can't stand waiting at the repair shop ... especially when they can't quickly find the issue. Just glad it's you and not me


----------



## KaeJS (Sep 28, 2010)

Lol. I'm not waiting. I'm at home.

What I should have said is "The car is still at the shop."

Sorry.


----------



## carverman (Nov 8, 2010)

KaeJS said:


> The car is a 2003 MazdaSpeed Protege.
> 
> I know the theory, but thanks for taking the initiative.
> 
> My previous check engline light was not steady. I have an aftermarket exhaust with a "hi-flow" cat. Basically, there is no cat, so the check engine reads that there is a "Catalytic Converter Warm Up on Bank 1/1", but it comes and goes and is off more often than it is on.


Are you still using the original factory 02 sensors with aftermarket exhaust
and no original cat?
If so, then it is possible that the 02 readout, does not agree with the ECM stored program range with the original cat working with the 02 sensors. 

O2 sensors have a built in heater to pre-warm them so the O2 readings can
be done at the correct exhaust temperatures. On mine, the ECM ignores
the 02 reading and goes "open loop" until the 02 heaters bring the 02
sensors into the correct temperature for reading.

On mine there are two 02 sensors since I have a crossover pipe and one
cat/exhaust pipe/muffler. The precat 02 provides the exhaust reading
on the fuel-air program settings determined by the ECM and the post-cat
O2 reads any changes in emissions . 

It could be that the output from the O2 sensors now doesn't always correspond to the acceptable program range of the factory emissions program on the ECM.


----------



## KaeJS (Sep 28, 2010)

I'm using the factory O2's without the cat. There are no pre-cats on my exhaust either, but there was on the original one.

I don't know how this would affect my vacuum pressure being so low, though. The O2 is just a sensor, so it wouldn't affect the amount of air going into the throttle body if the O2 is on the exhaust...

Plus, the car works fine when it is given some gas. Even under boost, the car works great (yeah, I don't know why I was boosting with a misfire. That was dumb)

I don't think its the O2. And I also don't think an O2 would throw a misfire on all cylinders. a bad O2 reading would just screw with the AFR maps on the ECU, but it wouldnt torture the AFR's enough to stall the car.

The car feels like its not getting enough air at idle. It feels exactly like a vacuum leak, or like you are letting the clutch out a little too late and the engine drops down to low RPMS before you manage to hit the gas pedal. Feels like the engine is on life support, but as soon as you open the throttle even the slightest bit, all problems are solved (minus the barely noticeable misfire).

Misfire is most pronounced at idle and almost indecipherable with throttle in neutral or in gear. It's definitely an air issue.

If it is the EGR, it could actually be choking out the engine with too much CO2 and not enough O2, as exhaust gasses would be flowing into the combustion chamber, suffocating the engine and depriving it of O2, causing rough idle and sporadic combustion (aka misfire).

And i really hope that's the case. Because if I buy a new EGR, and its not the EGR....


: MAD :


----------



## jamesbe (May 8, 2010)

O2 could affect the AFR enough to cause loss of power, rough idle and stalling. I've had it happen to me.


----------



## m3s (Apr 3, 2010)

KaeJS said:


> And i really hope that's the case. Because if I buy a new EGR, and its not the EGR....
> 
> 
> : MAD :


I had a hi flow exhaust on my Honda as well. The biggest PITA was those OBDII codes. That system is basically only concerned with emissions as far as I can tell.

EGR is a very common issue. There is rarely a reason to replace it, however 99% of mechanics will just buy a new one. If you clean it, and it doesn't stop the codes, you need to clean the hoses and random ports. I use Seafoam and wire brushes etc. It was a huge PITA to get rid of those codes. I learned afterwards there are EGR delete kits however that won't work in Ontario

My new car comes stock with none of this emissions stuff. Ironically, it gets seriously better MPG especially when driving hard than its American counterparts. That emmission equipment just chokes the engines with carbon especially as they get older. The computer will also tell mechanics waaay more than OBDII however only "authorized" BMW mechanics can read those 

With today's technology, we should have all these diagnostics available in realtime on smartphones, or heck a screen on the dash


----------



## carverman (Nov 8, 2010)

KaeJS said:


> I'm using the factory O2's without the cat. There are no pre-cats on my exhaust either, but there was on the original one.


Then you are in effect using the factory preset emissions data inside the
ECM. While you can physically swap out exhaust components, you can't
change the data in the emission part of the ECM flash memory, unless
you reprogram the emission portion to update accurately what the sensors
are reporting. Presumption here is that your exhaust mods are still within the acceptable emission/AFR limits for the ECM. 



> I don't know how this would affect my vacuum pressure being so low, though. The O2 is just a sensor, so it wouldn't affect the amount of air going into the throttle body if the O2 is on the exhaust...


The 02 sensors feed back a voltage depending on the amount of chemical
reaction in the exhaust gases...here is a explanation of how it works..
http://www.howstuffworks.com/question257.htm



> Plus, the car works fine when it is given some gas. Even under boost, the car works great (yeah, I don't know why I was boosting with a misfire. That was dumb)


When you give it more gas, the rpm goes up and any misfire or idling issues
are "masked" because the engine develops more horsepower. 



> I don't think its the O2. And I also don't think an O2 would throw a misfire on all cylinders. a bad O2 reading would just screw with the AFR maps on the ECU, but it wouldnt torture the AFR's enough to stall the car.


No, I agree. The O2 sensors just tell the ECM to change the fuel-air mixture
to richen the mixture during idle... or lean it out..to improve fuel economy.
If the ECM choose to ignore the O2 sensors, it will go into what they call
an "open loop" part of its emission program and set the mixture at
14:7 (air/oxygen) to 1 (part fuel), the stoichiometric AFR. 



> The car feels like its not getting enough air at idle. It feels exactly like a vacuum leak, or like you are letting the clutch out a little too late and the engine drops down to low RPMS before you manage to hit the gas pedal. Feels like the engine is on life support, but as soon as you open the throttle even the slightest bit, all problems are solved (minus the barely noticeable misfire).


Most ECM controlled cars use what they call a IAC, Idle Air valve (motor)
which adjusts the amount of air coming into the throttle body at idle
based on engine load. This is controlled entirely by the ECM based on
input from various sensors..IAT (intake air temp) MAP sensor, etc or
operating a load like the A/C compressor..anything that will drop down
the idle. The ECM will adjust the amount of idle air coming in to keep
the idle rpms steady. 
http://www.ehow.com/how-does_4969915_idle-air-valve-work.html

However, (and I've had this problem with mine), the IAC valve "Pintle" and
the throttle body can get dirty..carboned up and that will affect the
amount of idle air coming in. In most cases the IAC can be removed and
cleaned with carb cleaner, along with the inside of the throttle body,
where it varies the air passage (at idle) when the throttle plates are closed. 



> Misfire is most pronounced at idle and almost indecipherable with throttle in neutral or in gear. It's definitely an air issue.


I would be examining the IAC then. I'm sure yours must have one. 



> If it is the EGR, it could actually be choking out the engine with too much CO2 and not enough O2, as exhaust gasses would be flowing into the combustion chamber, suffocating the engine and depriving it of O2, causing rough idle and sporadic combustion (aka misfire).


I don't think so, the EGR is not that sophisticated a device, it is just a one way valve.
A faulty EGR will affect your emission test though. 

As I mentioned before, random cylinder misfire IS an ignition (spark)issue.
You just haven't found the cause yet.


----------



## KaeJS (Sep 28, 2010)

mode3sour said:


> With today's technology, we should have all these diagnostics available in realtime on smartphones, or heck a screen on the dash


Let's go into business.

As for the car, it is all fixed. It was the EGR valve. I'm not sure if the mechanics actually tried to clean it. I mean, they let me hold the old one and it looked like they tried to clean it, but who knows.

They put a new EGR in and it works great.


----------



## carverman (Nov 8, 2010)

KaeJS said:


> Let's go into business.
> 
> As for the car, it is all fixed. It was the EGR valve. I'm not sure if the mechanics actually tried to clean it. I mean, they let me hold the old one and it looked like they tried to clean it, but who knows.
> 
> They put a new EGR in and it works great.


Well, I'm glad they found the rough idle problem. Usually, it's not worth
the mechanics time to clean it because if starts to idle rough (again) with 
a month or so, and you bring it back again complaining about the exact same problem, they would then have to replace it under any garage workmanship guarantee. 
You would still have to pay for the part, but they have to eat the labour cost.

However, even though it would solve the rough idle, I'm not still sure at this
point that it *caused* the misfire symptom..I just can't see that relationship
to the EGR.


----------



## m3s (Apr 3, 2010)

To clean my EGR I just soaked it in Seafoam (or any carbon eater) for awhile. carverman's reason makes sense for them to replace it. Cleaning the EGR was not enough for me, the codes came back later because the hoses and ports that connect to the system were clogged with carbon as well

All this carbon is from the crap gasoline in NA. Look up how to prevent it in your car with seafoam, just don't use seafoam on an old engine that has been neglected (could loosen big chunks of carbon etc)


----------



## KaeJS (Sep 28, 2010)

carver, I will get my engine light checked to make sure the misfire code is gone. But I think if I understand how EGR's work correctly... it could hinder the available oxygen which would result in no combustion for multiple cylinders at random time frames. I'll check it though.

mode, I've heard of Seafoam. Never used it. I've heard some mixed reviews. I may try it, but generally I like to go by the "if it ain't broke, don't fix it" rule.


----------



## crazyjackcsa (Aug 8, 2010)

Seafoam can cause a because it works too well. It happened to my car. It cleaned out everything in the fuel system and deposited it directly into my injectors. Had to get them flushed after that. Then it ran well.


----------



## m3s (Apr 3, 2010)

KaeJS said:


> generally I like to go by the "if it ain't broke, don't fix it" rule.


I'm a big fan of preventative maint. I thought my car was working perfectly fine. Just changed all the fluids, filters and spark plugs and DAMN I will not call this car a pig at low RPMs anymore. It was always fast on the highway but now it's torquey and lively in town as well.

The thing with Seafoam is you have to use it correctly. I know it works from working on small engines and seeing the difference, but it can do damage used the wrong way


----------



## m3s (Apr 3, 2010)

crazyjackcsa said:


> Seafoam can cause a because it works too well. It happened to my car. It cleaned out everything in the fuel system and deposited it directly into my injectors. Had to get them flushed after that. Then it ran well.


Yea it's true. It's better to use it regularly from the start, and it is dangerous to use on an old engine that gunked up


----------



## KaeJS (Sep 28, 2010)

Many times when I've tried to do preventative maintenance, something else goes wrong.

Not sure if maybe I don't know what I'm doing, or if I've just been unlucky.

It seems like my car is picky. 
My truck, on the other hand, can take anything. 

Maybe it's just a mental stigma I have


----------



## m3s (Apr 3, 2010)

Mazda's and Japanese cars are pretty tolerant to abuse and neglect, I swear you could put water in the engines. I'm seeing how German vehicles are engineered with much less tolerance, but it's less of an issue here as Germans tend to do maintenance strictly by the book.


----------



## carverman (Nov 8, 2010)

KaeJS said:


> It seems like my car is picky.
> *My truck, on the other hand, can take anything. *Maybe it's just a mental stigma I have


I've had some issues this year with my 13 year old Dakota v8..mostly
suspension problems because Chrysler didn't include grease fittings on
the suspension, so I had to replace all 4 ball joints. How stupid of them
not to do that, but then, they don't want people keeping their vehicles
for 10 years or more these days..bad for dealers, even if it's good for
the repair shops.


----------

