miss fire on cylinder #4

Jim Fairbanks

wrench
Joined
Nov 17, 2006
Messages
4,508
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38
Location
Portland,Oregon
Make
Mazda
Model
speed6
Year
2006
Miles
154,000
Engine
2.3 turbo
I have another problem...lol....2006 Mazdaspeed6,2.3 turbo,was showing a miss fire on #4...I put new plugs in it and swapped #4 coil with #1 to see if the miss would follow....no luck...the miss stayed on #4...compression seems ok...I'm thinking maybe an injector but #4 plug looks really wet...and I don't really want to pull the intake unless I have to...anybody have any ideas what I can look for?...thanks Jim
 

billr

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Swap the injector.
 

Mobile Dan

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Location
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I can't say I've ever changed an injector because it was "stuck open", but if the engine runs better with #4 injector disconnected (electrically) leakage might be the problem (over-fueling at idle).
Another guess would be camshaft lobe wear.
 

Jim Fairbanks

wrench
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Location
Portland,Oregon
thanks Bill....problem is I have to pull the intake on this one to get to the injectors....Dan...I don't know if it will run better with it unplugged....I just know it keeps throwing a miss fire code for cylinder #4 ...I can clear it and it comes right back..Jim
 

NickD

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Aug 28, 2007
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Did you actually do a compression check on that misfiring cylinder? Did on my daughter-in-law's Ford, it was zero.

Use to be real easy to remove a head for a valve job, with these OHC engines, all that stuff on the front and sides has to be removed too.

This thing used a shunt valve EGR system, vacuum was applied all the time, but the shunt kept on leaking if off. With no EGR exhaust valve was toast.

With misfires find it quickest to do both a compression and vacuum test first. One car, the MAP sensor gasket was bad low vacuum told me that instantly. Also used an engine oil tester gauge, nowadays, just get a light that goes off if the pressure is greater than 2 psi.
 

billr

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Even if you did do a real compression check, check vacuum too with an old analog gauge.
 

grcauto

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Here's what a simple vacuum gauge can do. It may very well show you your problem.

Evaluating engine operation and pinpointing specific problems requires a comprehensive testing
routine. Here's how to do it.
There's nothing more basic than the fact that an engine is just a big air pump. It draws in air by creating
a low-pressure area in the intake manifold and cylinders, compresses the air, mixes in a little gasoline,
lights a fire, generates heat and pressure and finally pumps out the spent exhaust. Our preoccupation
today with things electronic sometimes makes us overlook old-fashioned mechanical symptoms of
problems and the mechanical test equipment used to troubleshoot them. Vacuum gauges are often in
this category, but the insight that a vacuum gauge can provide is as valuable today as it was 30, 40 or
50 years ago.
Remember that engine vacuum is just air pressure lower than atmospheric pressure. The starting point
to evaluate engine vacuum is the intake manifold. When you connect a gauge to a tap on the intake,
you're measuring manifold vacuum. Note that vacuum will vary in different areas of the engine, such as
above or below the throttle valve and right at the intake and exhaust ports.
Vacuum drawn from an opening ahead of the throttle is called ported vacuum. Throttle opening affects
ported vacuum opposite to the way it affects manifold vacuum. For example, at closed throttle,
manifold vacuum is at its peak. But there is no significant vacuum at a port ahead of the throttle plate
when the throttle is closed. Vacuum appears at such a port only when the throttle opens.
It's important to remember that manifold vacuum is used to power vehicle systems that need a steady
supply of low-pressure air under all engine operating conditions. These systems include power brake
boosters, a/c vacuum motors and some emissions controls.
Ported vacuum is used to control vehicle systems in relation to engine load. These include old fashioned
distributor vacuum advance diaphragms and carburetor assist devices. They also include
many emissions control devices and transmission shift points. Under some engine load conditions,
ported vacuum may equal manifold vacuum, but it can never exceed it.
Get Out the Gauge
Most vacuum gauges are graduated in inches of mercury (in.-Hg) and millimeters of mercury (mm-
Hg). Some also show the modern metric scale of kilopascals (kPa). For comparison, 1 in.-Hg equals
25.4mm-Hg, or about 3.4 kPa. For this review, we'll stick to in.-Hg, or simply inches of vacuum.
Because engine vacuum is based on comparison with atmospheric pressure, it varies with altitude just
as atmospheric (barometric) pressure does. The following table shows that as altitude increases,
vacuum decreases about 1 inch for every 1000 feet above sea level.
Inches of Altitude Vacuum
Sea level-1000 ft. 18-22
1000-2000 ft. 17-21
2000-3000 ft. 16-20
3000-4000 ft. 15-19
4000-5000 ft. 14-18
5000-6000 ft. 13-17
Normal manifold vacuum at idle for an engine in good condition is about 18 to 22 in.-Hg.
Manufacturers used to publish vacuum specs in service manuals, but this isn't as common as it was
years ago. Still, the physics of internal combustion haven't changed in a hundred years, so the
guidelines given here are a good starting point for vacuum gauge troubleshooting. Your best analysis
based on vacuum readings will come from your own experience, however. As you use a vacuum gauge
on different engines, you'll learn what's typical for one model compared to another. Some engines have
reputations as low-vacuum motors; others are unusually higher than average. Experience is your best
teacher.
Cranking Vacuum & Speed Tests
You can get a quick basic appraisal of engine condition by connecting a vacuum gauge to the manifold
and a tachometer to the ignition to check vacuum and rpm at cranking speed. Warm up the engine first,
then shut it down and connect your test equipment. Close the throttle and disable the ignition, or use a
remote starter so the engine won't start. Crank the engine for 10 to 15 seconds and observe the vacuum
and tach readings.
Note that different engines produce different cranking vacuum readings. Some carmakers publish
specifications; others don't. Again, experience will be your best guide. What you're looking for, most
importantly, is steady vacuum and cranking speed.
If the cranking speed is steady (about 200 rpm) and vacuum also is steady (around 5 inches), the engine
most likely is in good mechanical condition. If rpm and vacuum are uneven, the cylinders aren't
pumping equally. The engine probably has leakage past the valves, rings or head gasket. If the vacuum
reading is pretty steady but cranking speed is not, you're probably looking at a damaged flywheel ring
gear or starter. If the cranking speed is normal or high but vacuum is low and slightly uneven, the
engine probably has low compression or retarded valve timing. A jumped timing chain or belt is a
common cause here.
The cranking vacuum test also can provide a quick test for PCV restrictions. Perform the test and note
the average vacuum reading. Then pinch the hose to the PCV valve closed with your pliers and repeat
the test. If the PCV system is clear, vacuum should increase. If it doesn't, check the PCV system closer
for restrictions.
What Idle Tests Can Reveal
You can zero in on several basic mechanical problems by taking a quick look at manifold vacuum.
Warm the engine to normal temperature-get it really warm-and connect your vacuum gauge. Make sure
you connect to a manifold vacuum tap and not to ported vacuum. Connecting a tachometer also is a
good idea.
Just to be sure that the evaporative emissions system doesn't interfere with vacuum testing, disconnect
and plug the canister purge hose and its manifold port. If you're testing an OBD II car, check for evap related
DTCs when you finish testing to be sure none set.
Run the engine at idle, low cruise (1800 to 2200 rpm) and high cruise (2500 to 3000 rpm). Note the
vacuum readings, and any fluctuations, at each speed. Next, hold engine speed steady at about 2500
rpm for 15 seconds and read the gauge. Now release the throttle and watch the gauge as the speed
drops. The vacuum reading should jump as the throttle closes, then drop back to its normal idle reading.
If vacuum doesn't increase at least a couple of inches when you release the throttle, you may be looking
at worn rings, cylinders or valves.
Idle vacuum for most engines is about 18 to 22 in.-Hg, but some may produce only 15 to 17 inches at
idle. (Remember what we said about experience.) If vacuum is steady and within these ranges, the
engine and fuel and ignition systems are operating normally.
If vacuum is steady at idle but lower than normal, the ignition or valve timing may be retarded. Low
compression, an intake leak or tight valves also can cause low vacuum at idle.
If the vacuum reading fluctuates within the normal range-the gauge needle bounces around a lot uneven
compression (broken rings or leaking valves or head gasket in one or two cylinders) is a likely
culprit. An uneven air/fuel mix, erratic ignition timing, a misfire, mis adjusted valves or a manifold leak
near one or two cylinders also are possible causes.
If vacuum drops intermittently at idle, one or more valves may be sticking open or dragging. Higher than-
normal vacuum at idle is a common clue to overly advanced ignition timing, while low vacuum
can indicate retarded timing.
Low vacuum also can be an immediate clue to a plugged exhaust. To check further, run the engine at
about 2500 rpm for about 15 seconds. If vacuum drops during this period and does not increase when
you close the throttle, you're almost certainly looking at a restricted exhaust.
Vacuum Fluctuations & Power Balance
Several of the guidelines in this article have distinguished between steady vacuum gauge readings and
fluctuating readings, where the gauge needle bounces up and down erratically. This may seem
secondary-almost inconsequential-but it's an important distinction. A steady but abnormal vacuum
reading indicates a problem common to all cylinders. Things like incorrect ignition timing or an old,
tired, high-mileage engine affect vacuum equally for all cylinders. A bouncing needle, however, usually
indicates that the problem is localized to one or just a few cylinders. Here's where power balance
testing enters the picture.
Compression testing on many late-model engines is flatly impractical from a labor standpoint for a
quick engine evaluation. That's especially true on some of the weird vans for which removing and
reinstalling spark plugs is a two-hour job. It's relatively quick and easy, however, to connect a vacuum
gauge to the manifold and your engine analyzer to the ignition system.
If your initial vacuum tests produce gauge fluctuations, you have a definite indication that the problem
is limited to just one or a few cylinders. In these instances, a power balance test can help you pinpoint
those cylinders and the condition they're in. Does the engine need a valve job (fluctuating vacuum) or a
complete engine exchange due to universally worn rings and cylinders (steadily low vacuum)?
Combine modern power balance testing with traditional vacuum analysis and you'll have the answer.
 

Jim Fairbanks

wrench
Joined
Nov 17, 2006
Messages
4,508
Points
38
Location
Portland,Oregon
I did a compression test on it and it was about 170 on cyl 1,3,4, #2 was only about 130...but #4 is the one I am having trouble with...I did put a vacuum gauge on it and it was about 18-20 in. lbs....everything seems ok...I might just have to replace the injector to see if it is the problem...alldata shows an injector driver module on this thing....I can't find it...I was just wondering if the wire to the injector might be the problem....thing is everything is so buried on here I can't even see the injectors or find the wiring harness for it...thanks again for the help....I know I am old....I just wish cars were as easy to find crap on like they used to be..lol....Jim
 

billr

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Joined
Mar 12, 2007
Messages
6,915
Points
48
Does the #4 plug look really "wet", or only black like it is running rich? Can you get to the wiring to the #4 injector anywhere to disconnect it? Maybe slipping out the pin that drives it at the PCM connector would be easiest. If that plug is still wet with the wiring disconnected it would seem the injector is leaking.
 

Jim Fairbanks

wrench
Joined
Nov 17, 2006
Messages
4,508
Points
38
Location
Portland,Oregon
#4 plug did look really wet......I can't get to the wiring for the injector....I wish I could...lol....I'll see if I can find it in the wiring diagram...thanks Bill....Jim
 

Mobile Dan

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Joined
Mar 1, 2002
Messages
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Points
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Location
Kentucky
Revisiting this concern....Can you remove #4 coil, then reconnect to harness to verify that good spark is actually happening? (bad PCM or harness problem)
Also...don't be fooled by possible software issue that scanner says #4, but the actual problem cylinder is a different one.
How many coils on this engine? If there are only two, the diagnosis is different than a four coil setup.
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
11,416
Points
63
Location
St-Hyacinthe, Quebec, Canada
Here's what a simple vacuum gauge can do. It may very well show you your problem.

Evaluating engine operation and pinpointing specific problems requires a comprehensive testing
routine. Here's how to do it.
There's nothing more basic than the fact that an engine is just a big air pump. It draws in air by creating
a low-pressure area in the intake manifold and cylinders, compresses the air, mixes in a little gasoline,
lights a fire, generates heat and pressure and finally pumps out the spent exhaust. Our preoccupation
today with things electronic sometimes makes us overlook old-fashioned mechanical symptoms of
problems and the mechanical test equipment used to troubleshoot them. Vacuum gauges are often in
this category, but the insight that a vacuum gauge can provide is as valuable today as it was 30, 40 or
50 years ago.
Remember that engine vacuum is just air pressure lower than atmospheric pressure. The starting point
to evaluate engine vacuum is the intake manifold. When you connect a gauge to a tap on the intake,
you're measuring manifold vacuum. Note that vacuum will vary in different areas of the engine, such as
above or below the throttle valve and right at the intake and exhaust ports.
Vacuum drawn from an opening ahead of the throttle is called ported vacuum. Throttle opening affects
ported vacuum opposite to the way it affects manifold vacuum. For example, at closed throttle,
manifold vacuum is at its peak. But there is no significant vacuum at a port ahead of the throttle plate
when the throttle is closed. Vacuum appears at such a port only when the throttle opens.
It's important to remember that manifold vacuum is used to power vehicle systems that need a steady
supply of low-pressure air under all engine operating conditions. These systems include power brake
boosters, a/c vacuum motors and some emissions controls.
Ported vacuum is used to control vehicle systems in relation to engine load. These include old fashioned
distributor vacuum advance diaphragms and carburetor assist devices. They also include
many emissions control devices and transmission shift points. Under some engine load conditions,
ported vacuum may equal manifold vacuum, but it can never exceed it.
Get Out the Gauge
Most vacuum gauges are graduated in inches of mercury (in.-Hg) and millimeters of mercury (mm-
Hg). Some also show the modern metric scale of kilopascals (kPa). For comparison, 1 in.-Hg equals
25.4mm-Hg, or about 3.4 kPa. For this review, we'll stick to in.-Hg, or simply inches of vacuum.
Because engine vacuum is based on comparison with atmospheric pressure, it varies with altitude just
as atmospheric (barometric) pressure does. The following table shows that as altitude increases,
vacuum decreases about 1 inch for every 1000 feet above sea level.
Inches of Altitude Vacuum
Sea level-1000 ft. 18-22
1000-2000 ft. 17-21
2000-3000 ft. 16-20
3000-4000 ft. 15-19
4000-5000 ft. 14-18
5000-6000 ft. 13-17
Normal manifold vacuum at idle for an engine in good condition is about 18 to 22 in.-Hg.
Manufacturers used to publish vacuum specs in service manuals, but this isn't as common as it was
years ago. Still, the physics of internal combustion haven't changed in a hundred years, so the
guidelines given here are a good starting point for vacuum gauge troubleshooting. Your best analysis
based on vacuum readings will come from your own experience, however. As you use a vacuum gauge
on different engines, you'll learn what's typical for one model compared to another. Some engines have
reputations as low-vacuum motors; others are unusually higher than average. Experience is your best
teacher.
Cranking Vacuum & Speed Tests
You can get a quick basic appraisal of engine condition by connecting a vacuum gauge to the manifold
and a tachometer to the ignition to check vacuum and rpm at cranking speed. Warm up the engine first,
then shut it down and connect your test equipment. Close the throttle and disable the ignition, or use a
remote starter so the engine won't start. Crank the engine for 10 to 15 seconds and observe the vacuum
and tach readings.
Note that different engines produce different cranking vacuum readings. Some carmakers publish
specifications; others don't. Again, experience will be your best guide. What you're looking for, most
importantly, is steady vacuum and cranking speed.
If the cranking speed is steady (about 200 rpm) and vacuum also is steady (around 5 inches), the engine
most likely is in good mechanical condition. If rpm and vacuum are uneven, the cylinders aren't
pumping equally. The engine probably has leakage past the valves, rings or head gasket. If the vacuum
reading is pretty steady but cranking speed is not, you're probably looking at a damaged flywheel ring
gear or starter. If the cranking speed is normal or high but vacuum is low and slightly uneven, the
engine probably has low compression or retarded valve timing. A jumped timing chain or belt is a
common cause here.
The cranking vacuum test also can provide a quick test for PCV restrictions. Perform the test and note
the average vacuum reading. Then pinch the hose to the PCV valve closed with your pliers and repeat
the test. If the PCV system is clear, vacuum should increase. If it doesn't, check the PCV system closer
for restrictions.
What Idle Tests Can Reveal
You can zero in on several basic mechanical problems by taking a quick look at manifold vacuum.
Warm the engine to normal temperature-get it really warm-and connect your vacuum gauge. Make sure
you connect to a manifold vacuum tap and not to ported vacuum. Connecting a tachometer also is a
good idea.
Just to be sure that the evaporative emissions system doesn't interfere with vacuum testing, disconnect
and plug the canister purge hose and its manifold port. If you're testing an OBD II car, check for evap related
DTCs when you finish testing to be sure none set.
Run the engine at idle, low cruise (1800 to 2200 rpm) and high cruise (2500 to 3000 rpm). Note the
vacuum readings, and any fluctuations, at each speed. Next, hold engine speed steady at about 2500
rpm for 15 seconds and read the gauge. Now release the throttle and watch the gauge as the speed
drops. The vacuum reading should jump as the throttle closes, then drop back to its normal idle reading.
If vacuum doesn't increase at least a couple of inches when you release the throttle, you may be looking
at worn rings, cylinders or valves.
Idle vacuum for most engines is about 18 to 22 in.-Hg, but some may produce only 15 to 17 inches at
idle. (Remember what we said about experience.) If vacuum is steady and within these ranges, the
engine and fuel and ignition systems are operating normally.
If vacuum is steady at idle but lower than normal, the ignition or valve timing may be retarded. Low
compression, an intake leak or tight valves also can cause low vacuum at idle.
If the vacuum reading fluctuates within the normal range-the gauge needle bounces around a lot uneven
compression (broken rings or leaking valves or head gasket in one or two cylinders) is a likely
culprit. An uneven air/fuel mix, erratic ignition timing, a misfire, mis adjusted valves or a manifold leak
near one or two cylinders also are possible causes.
If vacuum drops intermittently at idle, one or more valves may be sticking open or dragging. Higher than-
normal vacuum at idle is a common clue to overly advanced ignition timing, while low vacuum
can indicate retarded timing.
Low vacuum also can be an immediate clue to a plugged exhaust. To check further, run the engine at
about 2500 rpm for about 15 seconds. If vacuum drops during this period and does not increase when
you close the throttle, you're almost certainly looking at a restricted exhaust.
Vacuum Fluctuations & Power Balance
Several of the guidelines in this article have distinguished between steady vacuum gauge readings and
fluctuating readings, where the gauge needle bounces up and down erratically. This may seem
secondary-almost inconsequential-but it's an important distinction. A steady but abnormal vacuum
reading indicates a problem common to all cylinders. Things like incorrect ignition timing or an old,
tired, high-mileage engine affect vacuum equally for all cylinders. A bouncing needle, however, usually
indicates that the problem is localized to one or just a few cylinders. Here's where power balance
testing enters the picture.
Compression testing on many late-model engines is flatly impractical from a labor standpoint for a
quick engine evaluation. That's especially true on some of the weird vans for which removing and
reinstalling spark plugs is a two-hour job. It's relatively quick and easy, however, to connect a vacuum
gauge to the manifold and your engine analyzer to the ignition system.
If your initial vacuum tests produce gauge fluctuations, you have a definite indication that the problem
is limited to just one or a few cylinders. In these instances, a power balance test can help you pinpoint
those cylinders and the condition they're in. Does the engine need a valve job (fluctuating vacuum) or a
complete engine exchange due to universally worn rings and cylinders (steadily low vacuum)?
Combine modern power balance testing with traditional vacuum analysis and you'll have the answer.
yes, and yes again


 

Jim Fairbanks

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Messages
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Location
Portland,Oregon
Hey Dan.....it does have 4 coils....I can pull the intercooler again and check for spark...I thought I already did but I will do it again and let you know...I have swapped the coils to different ones and it still shows miss fire on #4...Hey Nick...hope all is well with you....Jim
 

billr

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Joined
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Messages
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Does that one plug come out "wet" after the engine is fully warmed and running for a while? I don't think a misfiring cylinder, on a fully warmed and running engine, will have visible fuel wetting a plug unless there is way more fuel than normal getting to the cylinder. There is enough heat in the head/block and air flow through the combustion chamber to vaporize the fuel and blow it out the exhaust; even if the cylinder doesn't fire.

Try this: disconnect spark from another cylinder, so it misfires, and check for wetness on that plug; see if it "wets" similarly to #4.

Is this a 4-valve per cylinder engine?
 
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