From: Tomes on
Jeff Strickland wrote:
> "Tomes" <Tomes(a)ask.me> wrote in message
>> Hiya Hachi,
>> So it turned out to be easy. The rear panel just popped off once I took
>> off the pull-down handle, then there are 4 nuts holding it on, np. Now to
>> time inspection for when the check engine light is not on (occasional
>> cylinder misfire codes even after new plugs and wires).
>>
>> Other than that, the life of the Tomes has been good lately. Been playing
>> _a lot_ of rock and roll hammered dulcimer lately.
>>
>> Thanks for the help.
>> Tomes
>
>
> That misfire, particularly on random cylinders, can be the result of a bad
> MAF sensor or an intake (vacuum) leak.
>
> The job of the MAF (mass air flow sensor) is to detect air temp and density.
> The result of this detection is used to map the fuel delivery so that the
> desired blend of air and fuel is 14.7 to 1. If the MAF is lying, and the
> fuel map goes lean because of this, then a cylinder misfire can result.
>
> You can get O2 sensor errors too. Normally you want your O2 Sensors to
> report that the fuel mixture in the exhaust is rich or lean, but the error
> you get from this sensor if the MAF is on the fritz is simply Fuel Control
> Error, or something to that effect. This error means that the fuel is all
> over the place instead of usually one way or the other. A vac leak should
> push the Fuel Trim to the lean side, and lean can be detected as a misfire.
>
> One thing to consider is that a misfire is detected by watching the crank
> sensor. If a cylinder fires properly then the crank sensor expects to see a
> certain amount of work that contributes to the rotation of the crank. If
> that work is not detected then a misfire has occurred. When the plug fires,
> the next crank position sensor reading should come in a specific amount of
> time. If it comes slow, then the work was not done and a misfire is
> recorded. The point of this is that a misfire does not mean the spark plug
> or wire is bad. It can mean that, but it doesn't have to mean that. If the
> MAF is leaning out the fuel map, then it could be picked up as a misfire
> because the work that is expected isn't seen. Does that make sense?
>
> I'm not saying that it is your problem, I'm just pointing you to
> possibilities for the misfire that continues even after you supposedly fixed
> it.
>
Jeff - this does make sense. Thanks. Now, what might I be able to do
about this? Is there a diagnostic that I can do on my own? I just
cleared out the codes and will see when they come back again. I had 5
codes in there this time, all various misfires. It makes sense to me
that it could be something more global than individual wires/plugs now.
Tomes
From: Jeff Strickland on

"Tomes" <Tomes(a)ask.me> wrote in message
news:hrt2so$4tp$1(a)news.eternal-september.org...
> Jeff Strickland wrote:
>> "Tomes" <Tomes(a)ask.me> wrote in message
>>> Hiya Hachi,
>>> So it turned out to be easy. The rear panel just popped off once I took
>>> off the pull-down handle, then there are 4 nuts holding it on, np. Now
>>> to time inspection for when the check engine light is not on (occasional
>>> cylinder misfire codes even after new plugs and wires).
>>>
>>> Other than that, the life of the Tomes has been good lately. Been
>>> playing _a lot_ of rock and roll hammered dulcimer lately.
>>>
>>> Thanks for the help.
>>> Tomes
>>
>>
>> That misfire, particularly on random cylinders, can be the result of a
>> bad MAF sensor or an intake (vacuum) leak.
>>
>> The job of the MAF (mass air flow sensor) is to detect air temp and
>> density. The result of this detection is used to map the fuel delivery so
>> that the desired blend of air and fuel is 14.7 to 1. If the MAF is lying,
>> and the fuel map goes lean because of this, then a cylinder misfire can
>> result.
>>
>> You can get O2 sensor errors too. Normally you want your O2 Sensors to
>> report that the fuel mixture in the exhaust is rich or lean, but the
>> error you get from this sensor if the MAF is on the fritz is simply Fuel
>> Control Error, or something to that effect. This error means that the
>> fuel is all over the place instead of usually one way or the other. A vac
>> leak should push the Fuel Trim to the lean side, and lean can be detected
>> as a misfire.
>>
>> One thing to consider is that a misfire is detected by watching the crank
>> sensor. If a cylinder fires properly then the crank sensor expects to see
>> a certain amount of work that contributes to the rotation of the crank.
>> If that work is not detected then a misfire has occurred. When the plug
>> fires, the next crank position sensor reading should come in a specific
>> amount of time. If it comes slow, then the work was not done and a
>> misfire is recorded. The point of this is that a misfire does not mean
>> the spark plug or wire is bad. It can mean that, but it doesn't have to
>> mean that. If the MAF is leaning out the fuel map, then it could be
>> picked up as a misfire because the work that is expected isn't seen. Does
>> that make sense?
>>
>> I'm not saying that it is your problem, I'm just pointing you to
>> possibilities for the misfire that continues even after you supposedly
>> fixed it.
>>
> Jeff - this does make sense. Thanks. Now, what might I be able to do
> about this? Is there a diagnostic that I can do on my own? I just
> cleared out the codes and will see when they come back again. I had 5
> codes in there this time, all various misfires. It makes sense to me that
> it could be something more global than individual wires/plugs now.
> Tomes


I learned of all of this when we bought a '00 BMW 323i for my kid. We got
the car for a few grand because the CEL was on, and the seller was told by
somebody that he needed a new transmission. The transmission only needed to
be flushed, so we scored a nice car for my daughter to drive.

We had a host of issues with the Check Engine Light that all had to do with
Fuel Trim, Fuel Control, misfires, and generic O2 sensor malfunction. There
was no report of rich or lean, just that the fuel control and fuel trim (I
think these are the same thing, but one of them makes a Unique BMW code
while the other one is a common OBD II code).

If you have a scan tool that can read live data, then you should be able to
see what's going on. But when I began studying up on Misfire, I discovered
that the definition was that the cylinder was not doing its work, not
necessarily that there was no spark.

Since the fuel trim/control codes did not specify lean or rich, and I had
misfires, I started looking for stuff that my scan tool was not telling me.
I would expect a vac leak -- if you have a plastic intake manifold, this is
a very real possibility -- would cause a consistant lean condition. With
expansion of the plastic, the leak might come and go, which would make the
fuel lean or right, but never rich. But myj codes were just that the
trim/control was not right, which means to me that it could be either rich
or lean, or both. Turns out, it was both. The fuel mixture was all over the
place. BMWs have a diagnostic port in the engine bay that the good
diagnostic scanner plugs into and can display active real-time data.

My problem was the MAF was telling blatant lies about the weather
conditions, and the computer was chasing the fuel map all over the place. I
don't know why, but my car only threw one MAF error all of the time I was
working. It once threw all six misfire codes, but not in any order. Then it
would throw random misfires. The MAF can get dirty and this will confuse it,
but it also has complicated circuits inside that can fail. My MAF costed
$400. Ouch. It fixed all of the codes though.

I don't know that your Sienna has a data port for the Toyota Diagnostics or
not, and I also don't know if OBD II scanners will read live data from a car
that's not storing codes. My scan tool told me once that the MAF was bad,
but my mechanic's tool told him immediatetly that it was bad. He advised
that since we didn't really know what was happening since I had just bought
the car, then he cleared the codes and all of the data that was in the
computer and sent mme ho,e to drive for a few days until the CEL came back
on. Since we could not feel anything wrong, I was okay with driving the car
around town waiting for the sky to fall.






From: supraman_88 on
On Wed, 05 May 2010 18:09:09 -0700, Jeff Strickland wrote:

>
> I don't know that your Sienna has a data port for the Toyota Diagnostics
> or not, and I also don't know if OBD II scanners will read live data from
> a car that's not storing codes.

I think the data ports on all Toyotas, at least from the 90's is located
behind the fuse panal. Some models had a separate cover for the scan port.