Free Automotive Repair Advice by Certified ASE Technicians
Repair Topics / Engine Misfire
Car Engine Misfires Poor Running - Tune Up Engine Miss Fire and Rough Running Condition
There are three kinds of gasoline engine misfire scenarios, first there is the
"under load" misfire and there is the "at engine idle" misfire,
and finally there is misfire continuously. All engine misfires exist because one
of three things has occurred. First, a cylinder has lost compression, a cylinder
needs a certain amount of compression to operate correctly. Second, the
ignition system has failed or is failing intermittently, spark is needed at the
time of compression to ignite the fuel air mixture. Third, the fuel air mixture
is incorrect, proper mixture is needed for the ignition system to ignite
fuel properly. If any of these conditions occur
in the engine, the engine will misfire.
1. Low or no compression can be caused by
a. burned or leaking intake or exhaust valves
b. worn or broken piston or piston rings
c. worn out camshaft
d. wrong weight motor oil was installed holding the cam followers from adjusting
e. broken valve spring
f. failed head gasket.
2. Ignition system has failed or is failing
a. spark plug has fouled or is worn out
b. ignition coil has failed
c. spark plug wires have shorted
e. engine control module coil driver has failed
3. Fuel/Air Mixture is incorrect
a. vacuum leak at the intake manifold
b. fuel injector has failed
c. EGR valve is stuck open
d. mass air flow sensor has failed
e. oxygen sensor has failed
f. air intake boot is cracked
Most vehicles can monitor the cylinder misfire condition and will illuminate
the "service engine soon" light if a cylinder misfire has been detected. A engine
code reader is used to read the trouble codes and can isolate the cylinder
malfunction. See
Checking Trouble Codes after the repair is complete the "service
engine soon" light must be reset with a code reader. The vehicle has to be
driven thoroughly (30 to 60 miles) to let all computer monitors and relearn their system to deem
the vehicle repaired.
common problems:
1. fuel injector has failed or is failing
2. spark plug wire has shorted
3. spark plug is worn out or is cracked
4. ignition coil has failed is failing
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Tune Up your engine
This
category contains featured questions as
examples. They relate to most vehicles.

Question:
2001 Mercury Sable_mileage: 34000. Hello, I have a
weird problem. When the outside temperature falls below
55 degrees approximately and I start the engine in the
morning, the check engine light turns on and a misfire
code is stored on the computer. The car misses a lot.
After I drive it for a while and the engine warms up,
it runs smooth again. I already tuned it up and changed
the coils module to try to deal with the misfire code.
Nevertheless, I still have the problem. Any suggestion
will be greatly appreciated. Thank you.
Answer:
First, have a compression check done on your engine.
If this checks out fine, you probably have a bad fuel
injector.
Question: 2003 Mercedes Benz C320
mileage: 60,000. This is my head-ach. It
started one day when I passed a car and the
engine started to miss. I tested the spark
and the #2 cyl had no spark. I then tested
for spark at the cap to eliminate the plug
and wire and had no spark coming out of the
#2 tower, it did. If I replace the plug
wires will my problem be fixed?
Answer: Good trouble shooting, yes
the plug wires is bad and the remaining plug wires are
right behind the failed one. We always replace plug
wires in a set.
Question: 2003 BMW M3,
miles: 45,000 Gentlemen, maybe you can help
me out. I seem to be having a "misfiring"
problem and the dealer and no one else can
help me out. It will misfire only when you
bring up the rpms. You notice the "surging,
misfiring or breaking up" more when you
drive the vehicle but it also does it when
the truck is in park and bringing it up out
of idle. When you are driving and floor the
pedal it does not break up, it only does it
when you are easy with the accelerator or
while driving at a steady speed. I have
checked out all fuel possibilities and this
is not the problem. The regulator, fuel
injectors, fuel pump, fuel filter, fuel
lines and fuel rail are good and are in
spec. I have new plugs, and throttle
position sensor replaced and checked. I'm at
a loss, please help.
Answer: It sounds like you have an
fuel injector or a ignition coil going out. Scan Pcm to
isolate the problem cylinder and replace as needed.
Question: 2003 Ford F-150 mileage:
46,000. Truck was running fine and then I changed my
plugs, and fuel and air filter . Now it misses very
badly. What made it start missing?
Answer: In tightening the
spark plugs you may have cracked one of the insulators,
or the spark plugs could have a closed gap. Remove spark
plugs to inspect. (BTW this is the number one thing that
goes wrong in a tune up)
Question: 2003 Ford Focus mileage:
67,000. Engine misses at speeds above 50 mph and
continually getting worse. Several repairs made, such as
Master Flow Sensor, new fuel pump, new fuel filters. It
has been put on computer at a garage. Starts good, runs
good thru the gears, but always misses at higher speeds,
as though it is not getting fuel. Tried everything, done
everything, but no results. Please help. Timing belt
replaced about a year ago. Engine light stays on all the
time.
Answer: Your ignition system
is breaking down at higher RPM, Try replacing the plug
wires and spark plugs that should do the trick.
Question: 2002 Chevrolet S10 Pick Up
mileage: 55,000. I've developed a dead miss in the no. 1
cyl. I know that a gas engine requires fuel, compression
and ignition to run, which it has. At idle the miss is
more prevalent than above an idle or while at driving
speeds. The compression in no.1 cyl is 125 psi & no. 2
cyl is 120. There is a blue spark equal to the rest of
the cyl. The resistance of the spark plug wire is well
within limits and the dist. cap and rotor show no signs
of arc tracks. Being a half decent shade tree mechanic I
presented this problem to the head mechanic, who
maintains the fleet of various vehicles at work, and he
went over all of the various diagnostic techniques again
with me and he says whatever the problem is that he's
never run across this one before. Can you shed some
light of this one? Gratefully appreciated.
Answer: No problem, it sounds
like you have an injector problem. Replace the failed
fuel injector to repair problem in #1 cylinder.
Question: 2001 Dodge 1500 Ram Truck
mileage: 68,000. It began missing in the mid range rpm's
(1800-2200). Of course, I noticed it and thought I could
figure it out. After replacing the fuel, filters and
having the fuel pump checked out they were ok. I had the
drive train checked with no affect on the missing. Are
there any procedures (especially in the EFI and/or EI)
that might have been missed and how do I get the
computer to give me its trouble codes.
Answer: It sounds like your
truck is ready for a simple tune up, replace spark
plugs, plug wires and service throttle bore and IAC
(idle air control) motor and passages.
Question: 2001 Toyota Camry, miles:
87,330. Engine floods, has an intermittent miss, and
idles rough. I have scanned the car with repair shop
scanner, have run a compression test, checked fuel
pressure (38 + pounds), checked fuel regulator, replaced
ECM, plug wires, plugs, MAP sensor, removed catalytic
converter for testing purposes, checked voltage at every
conceivable location, cleaned throttle bore, beat,
cursed, and replaced every thing possible that could
cause this problem. All tests performed within or above
specs. Any ideas?
Answer: Sounds like you may
have a shorted fuel injector that is wide open. Causing
the fuel to flood in the engine. Test ohm's across the
injector terminals, reading should be between 30 to 70
ohm's. What you are looking for is the injector that the
reading is way off on. Replace fuel injector as needed.
Reassemble to recheck system.
Question: 2002 Mazda MPV mileage:
55,000. What is causing the intermittent engine miss I
get driving at highway speeds? My mechanic cannot find
the problem. I have replaced spark plugs and wires, CO�
and temperature modules to no avail. During a 100-mile
trip, it may not miss at all or it could miss
sporadically several times. The misses may last 10
seconds or continue for several miles. The check engine
light has never come on. It was put on a scanner and
there were no trouble codes. Thank you for any help you
may have.
Answer: It sounds like your van is
ready for a simple tune up, replace spark plugs, plug
wires and service throttle bore and IAC (idle air
control) motor and passages.
Question: 2002
Toyota Avalon mileage: 45,000. At any and
all cruising speeds (not when pulling), the
car has a missing hesitation. Computer test
showed faulty oxygen sensor valve. I
installed a oxygen sensor but still have the
same missing effect. Spark plugs and are ok.
A friend suggested changing the MAF sensor.
Does this make sense? What could be some
other possibilities?
Answer: We would suggest trying
replacing the Mass Air Flow Sensor. If problems still
persist, rescan the computer.
Question:
2002 Dodge Neon mileage: 41,000. "Service engine
soon" light is on. Code is "misfire". From time to
time car may accelerate or slow down without any reason.
Tachometer readings are changing (500-3000 RPM) if on
parking or neutral. Smell of gas. It
happens 2-3 times a day during 20-30 minutes only.
No special conditions. (Any weather.
Car maybe cold or hot.) No problem other time.
Done: 1). Plugs were checked and replaced.
Engine was tuned. It did not help. 2).
Oxygen sensors were replaced. No effect.
Problem is still here. 3). No problems
found. What can it be? PCM?
Maybe something else?
Answer:
It sound like you have a secondary ignition failure.
Replace ignition coil and spark plug wires to recheck
system.
Question:
2004 Acura NSX mileage: 42,000. The third cylinder
is not firing, I replaced the spark plugs, and the third
cylinder did not fire still. I disconnected each
ignition coil one at a time with the engine running and
to see if it made a difference. It did all all but #3.
How can I fix the Problem? Thank you for your
help.
Answer:
The ignition coil for the third cylinder should be
replaced. Reassemble to recheck system.
Question:
1999 Pontiac Grand Am Quad 4 mileage: 73,578. My
1999 Pontiac Grand Am with a 2.3 liter Quad 4 engine is
running ruff. It is missing and won't idle. When
checked the #1 & #2 cylinders don't make any difference
in the motors idling when the fuel injectors were
disconnected only cylinders #3 & #4 make a difference.
The injectors are functioning. The plugs show signs of
weak spark the other cylinders are fine.
Compression tests show all cylinders good. The
coils have been checked. The ignition module
replaced. What could the problem be?
Answer:
Your reported symptoms would point to a breaking down of
the ignition coil housing. Replacing it should fix
your problem.
Question:
2002 Ford Focus mileage: 73,300. Hey guys.
My car has had what feels like a "missing" problem for
the past several months. Between the speeds
of 45-65 mph, the car will "miss" on gradual
acceleration. Additionally, the car sometimes
stutters on acceleration after a stop. Both
of these problems are erratic (some times it seems like
I'm not going to make it to where I'm going, and other
times I can go days without a problem). I have
taken the car to Ford several times, but each time they
insist that no codes have been set, and that they cannot
duplicate the problem. I took the mechanic on a
test drive myself, but (of course) the car ran fine.
Coincidentally, my extended warranty is almost up.
I get the feeling that Ford is putting me off until my
warranty is up. I have another appt. with Ford
because these problems are getting worse. I
realize that many things could probably cause the
symptoms I've described, but I'm completely without
options in the face of Ford's denial of any problem.
Either my car was assembled on an enchant burial ground
or it has a mystery problem that doesn't show up on
Ford's scanner. Any advice you could give me would
be greatly appreciated.
Answer:
Check the fuel pump pressure, your fuel pump may be
failing.
If a major tune up has not been done recently, this
could be the cause of your problem. Replace the
spark plugs, plug wires, fuel filter and air filters,
etc. Also, replace the primary oxygen sensor.
In addition, clean the carbon deposits from the throttle
bore and idle passages. Although some
manufacturers recommend 100,000 miles between tune-ups,
we have found that many cars need tune-ups before the
magic number.
Question:
1999 Toyota Camry, miles: I just took my car
in for a tune up, they guy seemed nice. They
replaced all the normal stuff in a tune up,
spark plugs, plug wires, distributor cap
ignition rotor, fuel filter. When I drive my
car and it comes down to an idle it
vibrates. My car had a vibration at idle
before but I thought a tune up would make
that go away. So I took it back to the
garage and now they are telling me the motor
is running fine and now I need motor mounts?
... can this be ! Answer:
Yes, engine have a certain vibration at idle,
especially four cylinders. If the engine mounts are
collapsed is will cause this condition. Replace engine
mounts with new, recheck. 
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