Solved, see https://www.evolutionm.net/forums/ev...l#post11468563 .

Hi guys, I figured I'd see what you all can come up with, as I am almost out of ideas.
'03 Evo 8, mods are in signature. Car ran great on 93 octane and FIC 1250's and a wally 255. I decided i wanted more, so i put in FIC 2150's, Skunk2 intake manifold, and a wally 450 E-85 pump and moved to E-85. car starts and runs, but cyl #4 does not fire. unplugging #4 injectors changes nothing in the idle, all the other injectors affect it. I read a couple threads of similar problems but the thread goes cold and no resolutions.

Ever since then, cylinder 4 doesnt fire, things tuner, myself, and a friend have done so far:
injectors cleaned and flowed perfect
noid tested, injector is getting pulses
swapped coil packs from the 2-3 pack and 1-4 pack
swapped #3 cylinder and #4 cylinder spark plugs
compression test - 150psi stock block 116k miles
swapped pigtail for 2150's from cyl #3 and cyl #4
resoldered resistor box delete and tested continuity - good
checked lifters for anything collapsed - good
Can hear the injector firing
swapped #1 and #4 injectors
Checked in fuel rail, no clogs
Tried a spare coil
installed new wideband sensor

No matter what I try, it is isolated to cylinder 4. i know there is no combustion because AFR is reading fresh air and throwing my AFR into a 15+ afr every 4th cylinder exhaust cycle.

I dont want to say its the harness because the noid light gets a pulse and injector fires fine. Does this also rule out the ECU being bad since signal comes from ECU? I have a spare ECU i can try.

Please help, this is driving me insane!

 

Cannot see signature while on the mobile site. Have you tried your old injectors?

 

i'm thinking 4and1 fire simultaneously. so could you extend the shorter circuit to the long one? this should cause number 1 cylinder not to fire. then i would relate your issue closer to the ecu instead of the devices....

test resistor box delete for ohms. should be 0.0-+0.5

 

leak down test?

 

the 15s you are seeing is probably natural oscillation of the wideband. i'm pretty sure you can't see a single cylinder's AFR effects.
may as well try the ECU. you have done everything i'd do to find the issue other than that. if it's not the ECU, then i'm not sure. that's weird. hopefully you are able to post a solution for anyone else having the same issue.
keep us posted

 

no need. his compression is good and it wouldn't affect the cylinder firing.





OP: out of curiosity, how do you know the cylinder isn't firing? is the plug wet and smells like fuel?

 

Can anyone tell me what this red/black wire is that comes into the resistor box? or have a diagram for it?

 

unfortunately the plug looks pretty much the same as all the other plugs, no wetness on it.

If anyone can get me an answer on that red wire in the above picture that i found cut, i might be on to something.

 

if the plug is dry, then it's firing, unless that cylinder isn't getting fuel.

again: how do you know it's not firing?

 

there is no change in idle when unplugging the injector and plugging it back in, no stumble, no rpm change. all the other cylinders cause fluctuation in the idle, this one does literally nothing, and it sounds like its always missing.

Here is what i mean by the AFR issue, it looks to me like "fresh" air is being exhausted and causing it.

 

also a video of it:

 

that graph shows the AFR dipping to 12s if i'm reading that right? that would be added fuel, not air. assuming that's what you mean? i can see why you are thinking no spark.
it seems intermittent, which is weird.. unless that's the ECU trying to adjust trims to get to stoich.
hm... so hard to diag over the internet LOL.

now i'm curious, though.

 

it is the ECU reacting to the fresh air hitting the wideband from cyl 4 is how i read it. that blip going to 12 AFR is my bad, i was getting out of the car and bumped the throttle a bit.

From the ECU i see the injector 4 is a red wire from a pinout i found, is that the same red wire as the one that is cut in my picture? I still cant find what it is.

 

NVM. my post was confusing LOL

 

i guess i should have made it a question. Do 1 and 4 fire at the same time? if so you could plug injector 4 circuit into injector 1 and injector 1 circuit into number 4 injector. then injector 1 would not fire and you can work your way back from the plug to the ecu to find your issue.