In this video I revisit the MAP sensor during cranking and address some of your questions from part 2 Here is Part 1 of this series http://youtu.be/tZWsOupUz…
In this video I revisit the MAP sensor during cranking and address some of your questions from part 2 Here is Part 1 of this series http://youtu.be/tZWsOupUz…
You must be logged in to post a comment.
')){kind=link}
As promised, your questions and comment dictated my next steps in this
series. I revisit the MAP sensor waveforms during a crank and compare it to
two other cars.
Hi Paul. When you’re comparing a reference waveform to another where the
voltage, time base, etc. are different, you can put each waveform into a
scope view. You can find this function under the menu “Views>Add
View>Scope”. In other words each waveform would have it’s own separate
window. Then you can zoom, change scale factor, etc. of one waveform to
match the other for comparison. Good series on using the MAP sensor to try
and isolate valve issues. Keep up the good work!
Have you thought about contacting Tom Roberts from auto nerdz and asking
for advice I am a subscriber to his you tube channel and he figured out
some crazy problems
In addition to my other note, MAP will contribute the vaccum / pressure
across all 5 cylinders across 720 degree. looking for just one cylinder
within MAP waveform just for one cyclinder might not be correct because of
other variables other cylinders are contributing at the same time, example,
intake event of one cylinder, leads to exhaust even of someother cylinder
and both that intake and exhaust event wil be reflected at same time in MAP
wave form.
i may be wrong, if some one knows please reply..
I’m going to have to stand in the corner because I do seem to have the
cylinder stroke and firing order baffling me. Between the coil firing
events is 720 deg, and during this time all 5 cylinders have fired. It
does look like at the 5 min area where you label the 4 cycles of an engine
it is between the two coil firing events and 720 deg. I guess I did not
see you zoom into just one cylinder and the wave form looks like its level
across the page and not on a slope as shown for each cylinder. Ok so the
single cylinder wave form shown does not show the red coil firing lines
and it is the degree coursers on the left and right I see. This is tough
stuff – and loving it.
Wow this is a good one. I would’ve never thought the injector would be
firing that far before intake valve opening. I guess I always thought it
would fire on the intake stroke, thought that helped with atomization
rather than having the fuel more or less sitting on top of the valve, guess
it’s pretty violent when the valve opens which would cause plenty of
turbulence and atomization by itself. Still, dang, good to keep in mind.
Really curious if this map testing like this can be used for valve issues
or not. Now I want to grab my pico and go trace the map on my impala’s
3.8L cranking! I’m not sure how much time you have on your hands, I’m sure
you’re very busy, but if you guys do wind up replacing the cylinder head on
this vehicle I’d be very interested to see the map crank/idle trace
repeated with some known good valves in there. Really enjoying this one,
thank you.
Was that 300C a V6?
Would a gm fuel tank pressure sensor work only for the cranking test or
would this still be to much vacuum for this sensor.
Hi Paul, great pioneering work. Just a thought from a novice like me.
Would pulling out or loosening a spark plug in varying degrees from an an
easily accessible cylinder to introduce a massive or partial
vacuum/compression leak help you to definitely identify a particular
cylinder and also see when and what effect it has on the waveform? Keep up
the good work. Joe
Great series. One test using the Pico Ive used is using a pressure
transducer in the suspect bad cylinder, set the scope up with 50sec. per
division giving you about 8 mins of viewing to check for compression loss.
Should be perfect on the hummer since the vehicle runs good then bad
depending on engine temp. Learned this from auto nerdz. Watch wrangler from
hell part 1 at the 7 min mark.
@ Paul , nice video as all other , would you be able to take some capture
after the Hummer is fixed??
I am wondering how will look the map sensor on Honda’s when they have
misfire for valve issue clearance??
If you do pull the cylinder head off and you can not visibly see a valve or
seat issue then you could use some type of liquid like water and poor it in
the combustion chamber on all of the valves and see witch one leaks the
most and compare it or them to a known good valve correct me if im wrong
but it should work.
We could easily wire up our own GM 1 bar MAP sensor or fuel tank pressure
sensor for cars that don’t have MAP.
I notice that cars with valve sealing issues tend to have random (and
cold!) pressure puffs out the tailpipe. Perhaps we need to try rigging a
MAP sensor vacuum line laying into the tailpipe, or better yet use an
exhaust back pressure O2 sensor adapter and a MAP sensor.
Just don’t use a MAP on a running exhaust. You will overheat and kill the
sensor.
Really, you could’ve gotten to the #4 injector control wire with a back
probe without taking anything apart. There’s a 6 pin connector on the back
of the cylinder head on the drivers side that has the injector power wire
and all the injector control wires on it. I know this because I’ve played
around with this connector on my own truck measuring injector waveform
patterns.
looking at data from right to left the injector is on compression fire coil
at tdc and exhaust is to the left of coil fire kind of makes me think of
mirror effect as it happens. try writing compression on right of coil fire
and power on the left of coil fire.im not for sure.
that one that you call good is when number 4 is near TDC meaning number 4
is at it’s highest pressure and leaking the most
hence the sharp rise in pressure
when cranking you only look near TDC
when running you should look right after the spark when the pressure shoots
up
also there is no need to look at the strokes of cylinder 1 just find where
number 4 spark is and look for abnormal pressure rise or spikes there
you have a wsp500 that takes good vacuum waveforms
Hey Paul, great follow up video! The cranking MAP waveform on the Hummer is
definitely more telling than the one at idle. Comments:
1) At 18:30 where you point out the low spots, you can clearly see a trend
for each subsequent hump to be lower than the preceding one (decreasing
overall pressure), until it JUMPS BACK UP around the #1cyl intake hump,
which is precisely when the #4 compression/power stroke is occurring! My
theory is that the little burp of air back through the leaky #4 intake
valve is causing a slight increase in overall manifold pressure (average
MAP voltage rises slightly). So in this case, it looks like the MAP signal
agrees with the conclusions from the compression/ leakdown tests. Cool!
2) This also brings up the issue with AC-coupling a scope: in this
particular case, the slight overall rise in voltage over the five humps is
key in telling us when the leak is occurring. If we AC-coupled this signal,
would the scope not try to remove the slight DC change over 720deg and
exclude some important info? The question is how long a sample the scope
needs to determine if there is a DC bias and reset the zero line. The raw
DC-coupled data is always more telling, even though it may not be as
convenient to observe.
3) As for MAP waveforms on other engines: The Neon 4-cyl waveform looks
even and clean. The intake manifold is very simple, and there is no overlap
between the intake strokes. Therefore each cylinder’s intake stroke is
clearly visible on the MAP signal.
However, the signal on the V6 Chrysler looks messy. I just scoped the MAP
on my 2002 V6 Suzuki XL-7 with a very intricate intake manifold; the MAP
sits above the right bank. I counted about ~20 little uneven humps in
720deg! First issue: the intake strokes overlap by 60deg (or 90deg on a
V8), so most of the time there is more than one set of intake valves open.
Second issue: path from the MAP sensor to any one cylinder varies greatly,
and the dynamics inside the manifold are much more complicated than on a
simple inline setup; the MAP reads a mess of superimposed pressure waves
and resonances only at that particular location…not very valuable info.
Looks like the MAP waveform test for intake valve issues is not as valuable
on engines with more than 4 cylinders, especially V-engines with
complicated intake manifolds!
Thank you for sharing these case studies; love the critical thinking and
feedback. It feels like we are attending your class!
Hi Paul your not going to see the leaking valve what your going to see is
the next cylinder in intake, the pressure of the compression stroke of the
bad valve in cylinder 3&4 are going to affect the intake stoke of the next
cylinder that’s way you see lower voltage that mins more pressure in that
cylinder you have to go bake and look for the compression stroke of the
cylinder before that’s your liking cylinder for example valve siting
problem in cylinder 4 when is in compression is going to put more pressure
in the intake when and you will see more pressure in intake 2&1 #2 is
finishing the intake stroke wile #1 is big inning the intake stroke that’s
were you will see more pressure hope this will help.
I just posted the pictures of my intake, turbo intake, and crankcase
pressure waveforms on google plus. They were taken with the engine running
at idle. I’ll try to get some cranking captures later.
thanks
Hi paul all your video,s are brill but in this series it’s even better to
wach your thought proses on a new test procedure ( this is proper learning
) and not to forget all the comments and idears put forward from the
veiw’ers. . Like a lot of guys out there I will be doing some tests of my
own . Keep up the good work . Cheers
Paul I was wondering if you are looking at the right waveform, and if I’m
wrong I apologize. I’m wondering if the first dipping wave form is in fact
the power stroke and not the second one as you state. The one that the coil
is firing on. Then the cursor that you say is the first 180, would be on
the exhaust valve opening, then the third dipping waveform would be the
intake valve opening, which would be the waveform before the one you say is
the intake stroke.
Great video!
Paul, My understanding is within 720 degree, intake compression, power and
exhuast for all 5 cylinders will take place. but you are splitting 720
degree with 180 degree part and looking for the 4 strokes just for one
cylinder, will not other events from rest of 5 cylinders contributes to ur
wave form that u split within 180 degree apart.
Hey paul, you know Mazda mpv video that it misfire with no check engine
light? Would you suggest that it would have been easier to use mode 6 data
to find the issue.
Also when is it possible that you can make a video about mode 6 data. Will
they ever be possibility in one of ur videos?