How to Diagnose an Engine Misfire- Fuel, Fire or Compression

A misfire can be a tough problem to trace. Many parts of the automobile can factor in causing it making for a very difficult time and aggravation. Mike and I give you a quick and simple way to find out whether one of the three components are missing thus causing a misfire.

The automobile consist of:
1. Engine:
• Fuel System: Purpose is to deliver fuel to the engine. It consists of the fuel tank, pump, gauge/sensor, filter, pressure regulator and injectors.
• Air Intake System: Purpose is to clean and direct outside air into the engine. It consist of air filter, ducts, air plenum and intake manifold.
• Exhaust System: Purpose is to direct exhaust gasses out of combustion out of engine. It consists of the exhaust manifold, converters, pipes and mufflers.
• Cooling System: Purpose is to remove excess heat from the engine. It consists of water pump, hoses, radiator, thermostat, cooling fan and coolant recovery tank. Also the oil system serves as a cooling system as well as a lubricating system. It consist of oil pump, pan, filter and cooler.
1. Clutch: Purpose is to connect the engine and transmission together. It consists of clutch drive disc, driven disc, release bearing, clutch fork, cable, slave cylinder, master cylinder. There are three types of clutch systems: mechanical, cable and hydraulic.

2. Transmission: Purpose is to match engine speed to road speed. Two types used are manual or automatic. These consist of gears, linkages, cables and converters for automatics. A manual is connected to the clutch by a flywheel and automatic by a flexplate.
3. Driveshaft: Purpose is to connect the transmission to the rear axle. It consists of a slip yoke, shaft and universal joints.
4. Rear axle differential: Purpose is to change the angle of motion from engine to the wheels. It also divides torque between the wheels. It consists of a ring and pinion gear, carrier, bearings, crush sleeve and axle shafts.
5. Wheels/Tires: Purpose is to provide traction to the road as well as carry the weight of the vehicle.
Vehicle Control Systems:
1. Brakes: Purpose is to slow and stop the vehicle. It consists of master cylinder, brake booster (vacuum or hydraulic), calipers, drums, pads and rotors.
2. Steering: Purpose is to direct vehicle in the required direction. Consists of steering gear (rack & pinion), steering wheel, column, inner/outer tie rods, pump, reservoir, hoses and pipes.
3. Suspension: Purpose is to provide stability and handling while also providing comfort to the ride. Consists of shocks, struts, sway bars, end links, springs, trailing arms and bushings.
Comfort System:
1: Heating Ventilation Air Conditioning (HVAC): Heats and cools interior air to passenger comfort. Also circulates outside and inside air.
• Air Conditioning: Consist of condenser, compressor, accumulator (receiver/dryer) orifice, expansion valve, hoses, evaporator, controls, actuators and modules.
• Heating: Consists of heater core, valves, hoses and switches.

Electrical Systems:
1. Power Generation: Creates electrical power to run all the electrical systems. Consists of the alternator.
2. Power storage: Stores unused power to start the car and supply voltage to the alternator to create more electricity.

• Both systems consist of wiring, harnesses, fuse, relays and modules.



49 thoughts on “How to Diagnose an Engine Misfire- Fuel, Fire or Compression

  1. Guy charged me 500 for tune up said couldnt test for misfire without it. Was i robbed? Now he want 2700 to fix heads. Is that neccerary?

  2. This idiot seriously just prodded every wire so we know this are shit now ..the material used to make the wire just got prodded and we know how fibrous and sensitive they make them. This vid is terrible he had to remove the boots and plugs anyway

  3. I learned that the chubby guy likes to flip his hands around when trying to remember his lines and the skinny guy likes to look at the chubby guy.

  4. Hello there. friends, when the engine is cold when I run, the muffled gas is not working, when I'm moving in a mischievous time, the vehicle goes like a hit, the engine is warmed up when the engine warms up, I get loaded to the gas, the smoke of black smoke is starting to improve, then it starts to improve,

  5. What did you do if you have a random misfire. I have that issue in my car but can't even figure out what is it. Change plugs, wires and still the same. Code P0300 any help. Thanks

  6. Why wouldn't you do a wet compression test after the dry test? It would rule out a valve issue if the compression doesn't shoot up.

  7. I guess you should have done Leak down test at the same time with compression test .And some batteries dies out after a few cranking , so we have to keep charging the battery While cranking it for the test or change the battery all together if it’s worn out .

  8. What the hell kinda Mickey Mouse hack shit is this? Piercing plug wires, pulling heads without doing a leak down test and for Christ sake, how are you gonna completely skip function testing the injector. “Oh we have pulsewidth” great. Does the injector open? You don’t know because you didn’t check it.

  9. Hi I have a LS 6.0 2006 Chevy carbureted MSD I added headers and a few other things and a cam I added is a 622 lift and I am getting blow back through the carburetor what can cause that someone told me I had to degree the camshaft thank you

  10. Videos of rhetorical questions are weird… it's like watching a bad porno flick from the 70s ….. ps… this is absolutely horrible diagnostic testing … YOU DON'T STAB HOLES IN THE PLUG WIRES, NOW THEY ARE TRASH… you also need to do a leak down test BEFORE you pull the head !!! YIKES !!!

  11. FYI, I found this article, describes the poor quality of condensers leading to arcing, they recommend a better capacitor -condenser, but I re-read it, gave it some thought, then I put a 2nd condenser on the coil -ve post, reason – the chance both condensers arcing at the same moment would be remote, and thus the non-arc condenser electrically kills the arc of the other, my long time problem in L20b Nissan engine is cured, so – on any engine with points and condenser, replace 1 old condenser with 2 new for great results

  12. Why are you taking the cylinder head off before you've proved whether you're dealing with a gasket, a piston or a valve issue?? Why didn't you test cylinder 7 as well? More to the point, why not run a cylinder leakage test to get a better idea of what to look for when you do dismantle the engine?
    You could have used a pressure transducer – such as the PIco PP939 kit – to see what was happenning under cranking, and with engine running. You'd have had a superbly clear and informative picture of what was going on in the engine. You'd have had a saved copy of your bad engine with the fault(s) and a printable report to show your customer.

    The PicoScope with the COP tester would have given you the answers to your fuel and fire on all cylinders in just seconds, again if required allowing a saved and printable document, before going onto the intetrnal engine issue. The pressure tranducer really is the ansewer to in-cyliner issues. You can see valve timing issues, valve operation or seating issues, as well as all the other possible internal problems. Of course the other test that could have been performed early on would been a relative compression test using the PicoScope and a high amp clamp without any dismantling, you have know you had a compression issue within seconds!

    The relative compression test is actually the quickest and easiest test to use as a starting point with all misfire or power loss issues! Again, you have recordable trace which clearly proves in just seconds that you have or haven't got a compression issue.

  13. "Hey BertPass me the triple overhead manifold sprocket, "er ye sure thing Erney. Could be the flux capacitor" ye could be! " but before I check I think I'll go jerk off cos I've posted a video on how to sound like a **nt. " I think those acting lessons have finally paid off. "er ye I think so, "let's go jerk off together.

  14. What about separate problem if is rings or valves before pulling head by squirting small amount of oil into cylinder combustion chamber and do comp. test again. If reading up is rings or… and if stays same is valves.

  15. Hi sir, I have a Honda Accord 1995 SV4 misfiring problem and I do check following:
    1. Distributor – replaced
    2. Plug cable – replaced
    3. Timing – realigned
    4. Compression test – normal

    1. Misfiring
    2. Intake manifold seem like having some leaking
    3. Cooling system water decrease without leaking (by visual check)

    Please kindly advise…

    Jeff Foo (Malaysian)

  16. can't you do a wet test to determine the rings, or a leak down tester to determine again rings or the valves , head gasket etc, without pulling the heads off

  17. I have a 1998 ford explorer sport 4.0 ,, check engine light is on,, I was told that # 3 injector was bad, and upper o2 sensor was bad, i check injectors with stethoscope , about half of injectors are opening and closing about 3 times faster than the others is this normal or should all run the same, i cleaned the o2 sensor and didn't help,

  18. You said two cylinders 7&8 were missing. a misfire on two cylinders next to each other with low compression and spark and fuel being okay means there is a gasket blown between cylinders and not a piston problem. and sticking plug wires with a test light is just plain backyard wrenching. use a timing light to test for spark it is safe and quick. you two need to go cut grass.

  19. Who taught you fools to check for spark !???? Poking (Probing) HOLES into perfectly good plug-wires is a SURE GD good way to ruin a good set of plug-wires, let alone create an opening for future moisture to get into the wires, and a sure way for a wire to "arc" outside of it's self ! The SMARTEST method to check which plug and/or wire is faulty, is to either use an "in-line" spark tester….AND/OR to unplug each individual wire, one at a time, at the distributor, while the motor is running ! That way you'll find which cylinder is not firing !  And secondly, you've wasted the customers $ by adding a step to your diagnostics, You should've used your "In-line" spark-tester at the VERY beginning like I mentioned, instead of poking holes in the perfectly good plug-wires !!! IDIOTS ! Also, the "Noid" light ONLY tests the ECM's pulse signals TO the injector plug ! It DOES NOT test the INJECTOR itself ! Like you said you were doing at the beginning. You have to remove the injector to determine if it is opening & atomizing correctly ! And finally BOYZ, you DO NOT have to REMOVE the head to find out why and where you're losing compression ! If you're experienced w/a Compression gage, it can tell you whether the valves are the culprit or the rings ! Also, have you ever heard of a "Leak-Down" test !???? A leak-down test will ALSO confirm what's losing compression, exactly. Also, just because the plug smells like gas doesn't confirm that it's getting ample fuel !!! So Good-luck to all of your customers, because w/you TWO working on their cars & trucks, they're going to need all the luck they can get ! And remember,  it takes a clown to know a clown ! Ha ! Ha ! Ha !

  20. Thanks for the good video. I followed how you checked for ignition and compression, but was a little hazy on your fuel check. Still very informative. – jwrit

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