Only firing on 3 cylinders

5.7L
no code told, why skip the most important fact?
P03xx (what is the XX)

code 300 is means all cylinders misfire,
301,to 308
my wild wild guess is P030x code
this misfire, means, this. in TRUTH
that cylinder has bad combustion. (means weak only or dead)
caused by 3 things.
1: bad spark plug. or wires to it. or cop coil if is.
2: bad injector.
3: bad compression this cylinder or water or oil landing here.
3b: bad cam lob on X
3c bad piston on X cracked,.
3d, valves burned, X
and more, even cracks in X. all things inside X

the service manual is online
https://eautorepair.net/Marketing/Default.asp


the injectors all have a 12vdc power rail to a fuse. 5.7L/4.7
as do all 8 COP coils. (i bet one is bad or just boots to it bad))
all 8 injectors use that one 12vcd fused feed line
these are called PnP injectors. 12v, 0v, 12v, 0= fire.
the coil on X unstated injector is about 12 OHMs , no not zero nor infinity a super basic test that
moving the injector if bad, (side swaps) the TDC error moves with it.one more basic test.
a simple NOID lamp test shows if the PCM is firing it.
here is the schematic in part.




now all tests a short list
All fuses good , not guessing testing./
spark plug good on X
spark COP boot replaced, $15 cost, cheap on X
compression on X passes
spark tip not soaked in OIL or ANTIFREEZE on X
Injector ohms out good and NOID lamp passes on X

the injector and COps run off fuse #10- 30amps.
if blown the ASD relay is dead, so fuse 10 is not dead
because ASD is closed now and engine runs. (no stated be inferred)

bad engine, bad spark or bad injector, on cylinder X
X not told.
there are other possibles. like cylinder X has a vacuum leak
in Intake X port, gasket cracked, lean burn misfire.
leaking injector
we do the FSM (SM) book injector leakdown test and balance test to find that.
and more. ask for more tell what X is?

Check for the computer codes. It can point to the cylinder that is miss firing. Could be a bad injector. Do a cylinder balance.

If you know for a fact the injectors are not opening, you would need to check for voltage and a ground signal from the computer. The computer grounds the injectors to open them based on the crank and cam sensors.

its faulty coil.

Get the compression test done on each coil.these will let you know if its faulty coil or not.

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It can be issue with spark plugs or faulty spark plugs. Also get the compression test done for cylinders. If any of cylinder shows low compression then required, then that particular cylinder will cause misfire.

Also get obd codes scanned, the error code will let you know which cylinder is misfiring or all cylinders are misfiring.

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For your trouble shooting I suggest you to refer the help oinks below. It has step by step details for many engine misfire issues.

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Click the link below:-----

Ford Explorer Cylinder Misfire?

http://whoisbyme.blogspot.in/2012/06/ford-explorer-cylinder-misfire.html

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Engine Misfire codes on Chevrolet Malibu?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

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Cylinder 6 Misfire?

http://howtobyme.blogspot.com/2011/12/cylinder-6-misfire.html

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Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Ford Explorer 5.0L: Engine Miss?

http://whoisbyme.blogspot.in/2012/06/ford-explorer-50l-engine-miss.html

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Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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Can cylinder misfire Damage the Catalytic converter?

http://schematicsdiagram.blogspot.in/2012/02/can-cylinder-misfire-damage-catalytic.html

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Car misfires and error code P0306 and P0303 is shown?

http://technoanswers.blogspot.com/2012/01/car-misfires-and-error-code-p0306-and.html

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Chevrolet K1500 No spark, random misfire

http://repairhelpcenter.blogspot.com/2012/11/chevrolet-k1500-no-sparkrandom-misfire.html

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2004 Ford F150: Engine Misfire and Lean Code?

http://whatisbyme.blogspot.in/2012/05/2004-ford-f150-engine-misfire-and-lean.html

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1995 Toyota LS: Misfire at idle or low RPM

http://whatisbyme.blogspot.in/2012/04/1995-toyota-ls-misfire-at-idle-or-low.html

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Toyota Corolla: Random Misfire?

http://technoanswers.blogspot.in/2012/04/toyota-corolla-random-misfire.html

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2006 Ford Freestar: Misfire on Cylinder Number 2?

http://whatisbyme.blogspot.in/2012/06/2006-ford-freestar-misfire-on-cylinder.html

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This will help.

Thanks.

first code means random/multiple misfire cylinder (s) detected
second code means misfire detected number 1 cylinder, third code, miss=fire number 3 cylinder fourth code misfire number 4 cylinder
causes can be spark plugs, HT leads, ignition coils, injector, wiring fault, low compression/ engine mechanical fault

Random cylinder misfire, you will need an OBDII Scanner with MODE 6 to see what the miss count is to help find the offending cylinder.

You may get lucky and get a P0301 though P0304 code to tell you which cyling but then you may not...

Then after you find the offending cylinder you will have to figure out why its running bad... Plug, coil, injector, compression or vavle problem.

The firing order is a sequence of ignition time when the engine cylinders deliver their power-strokes starting with the number-one cylinder. If this sequence is faulty or arranged disorderly, the engine may not start at all, and if it does start, it may does so hesitatingly, or not run enough well to enable it to drive-or simply lacks the power to move. A waste of gas, and unecessary tear and wear on the engine and its critical components ultimately result. Once the firing oder is correc and in proper sequence, the engine should starts easily and promtly, running as quietly as posiible.

For Dodge 2004 Durango firing-order:
All 6-cylinder K 3.7L MFI SOHC distributorless ignition:
1-6-5-4-3-2 (front 2-4-6) (back 1-3-5)

All 8-cylinder N 4.7L SFI (including HEMI 4-WD)
1-8-4-3-6-5-7-2 (front 2.4.6.8) (back 1.3.5.7)
(distributorless ignition)
It is also a good thing to try and compare the thread lenghts of the old spark-plugs being replaced with the new.

I was wrong about the distributor being round (I was thinking about my other car). I found variations about the firing order but after troubbleshooting, varified the plug wiring order from the front of the car is 1 - 4 - 5 - 2 - 3 - 6 not 1 - 4 - 5 - 2 - 6 - 3 found on several web sites. From the front of the car looking at the engine, the back three cylinders by the firewall going from left to right are 1, 3, 5. The front three are 2, 4 & 6.

check your firing sequence.

Ok since you did all that if you want to swap around fuel injectors taking note where you put cylinder 1 injector. Lets say you swapped it with cylinder 4 . Now if you get a different code say P0304 which is for cylinder 4 misfire then you know it is your injector at fault. These are wear items and should be replaced every 100,000 miles.
Also i would suggest if you dont want to do that is get some good high octane gas when you are completely empty and fill to 1/4 tank now put in Lucas Oil fuel injector cleaner and run the car till empty. Now fill up tank with high octane gas in see if this helps. Clear code after your second tank of gas and see if the code comes back. if code does pop back up then i would do the swapping of injectors as i stated earlier. I hope this helps and good luck with the diagnosis.