I own an 03 H2 with a dreaded misfire that doesn’t seem to want to leave. The misfire is on cylinders 1, 5, 6, 8.
i have just replaced the coils , all plugs, all wires, yet the misfire is still present. The engine has 320km or 80k miles on it. It starts up good, great throttle response of the rpm’s.


The only engine code that I keep getting other then an evap vent issue is p0300–random misfire.

I’ve replaced my ignition system with no repair, is there another common component I haven’t covered that could rectify this problem. I have yet to do a compression test, really hoping that’ she doesn’t need a new motor.

thanks in advance for any suggestions what else I could check.

i have an in depth scan tool that allows me to monitor almost anything, that said it doesn’t tell me what the values should be reading, it just tells me the current values you select to monitor—Which all seem to be consistent with one another.

 

maybe an intake air leak.
check to see if your intake plenum bolts need to be re torqued or if the intake gaskets need replacing.
clogged cats can also cause random misfires.

 

Thanks for the reply, I saw online that the plastic intakes can crack and cause leaks. I tried the spray bottle trick and sprayed all around the intake to check for vacuum leak but didn’t find anything.

wouldn’t cats being clogged trigger my 02 sensors engine light?

 

Knock sensor replacement with OEM parts and crankshaft relearn, would be a next step.

 

my knock sensor is reading zero degrees, at idle, and with throttle. My spark is around 14 degrees at idle.
camshaft L-H and H-L both read around 1996.

my MAP is around 5psi with only 1.43 v and psi dropped with acceleration as well as voltage drop too.

im not sure what these values should be reading, I can only relay what I’m seeing on my scanner. The 02 sensors all seemed to be in sync with each bank as well.

while running these test I did get a flashing engine light, but the only codes still were evap, fuel level high circuit and p0300 still

 

well i mentioned the intake gaskets because there was a TSB on them and your being an o3 with 80k miles on it maybe it was never performed. if i recall if they are orange colored then they needed replacement. here is a video that shows them at about 17 minutes in
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as for partial clogged cats they do not always throw a code. they tend to throw inefficiency codes when you have lost parts of the honeycomb matrix. you can check them for backpressure at the first o2 bung with a pressure gauge. if it's more then 2 psi there may be restriction in your exhaust could even be mouse nest in the muffler.
you can also use a temperature gun before and after the cats and then before and after the muffler to have an idea.

what is the MAF reading it should be around 600 ish at idile since is a 6.0 liter if not them maybe try cleaning it.

 

I do appreciate the suggestions and knowledge. I guess it wouldn’t hurt to pull the intake, and check/replace the gasket, and replace knock sensors while I’m there regardless.

here’s maf reading at idle

 

I checked out my ignition timing advance for cylinder 1, range says between 5-30

at only 2000-2500 rpm I’m reaching high 40s. Shouldn’t the knock sensor retard the timing if it gets high enough to spark knock? Or does the crank sensor control the timing for these?

 

 

thanks for the correction, I must have made a typo/mistake clearly when I did a quick km-mile conversion online.

I wish you could help me figure out the problem I’m having with my truck with how quickly you found the problem with my conversion lol