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
 
Visit - How to 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.

Repair Topics / Engine Misfire

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