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misfiring on idle and when going from coasting to light acceleration

285 Views 2 Replies 2 Participants Last post by  Kbake99
made quick threads about this before but didn't really get into details.

I have recently swapped my stock 2013 focus st engine to mountunes 2.3 mrx long block they make for the focus st. have had issues with it like a friend accidentally swapped the vac lines for bov and wastegate, cracked intercooler and charge pipe. I have since sorted all of that but it has left me with one thing i cannot seem to solve, when turning the car on it sometimes starts, sometimes doesn't. none the less the car when it starts will sit between 1300-1400rpm till it warms and drops to 1100rpm. This is where the issue comes in, once the car is normally idling and warm every few seconds I will hear a pop/misfire, I've smoke tested the system and charged it with a compressor and no boost leaks have been found.

I had turned on misfire count on my AP and it got up to 100 misfire in a span of 10 or so minutes. the other issue I have as well is that when I am going from coasting to light throttle the engine starts to sputter for 2-4 seconds and misfire anywhere from 5-20 times. The car is fine as long as I stay in a low enough gear to keep the revs above 2200rpm, won't misfire wont bog at all, also when doing WOT pulls it doesn't misfire under boost. NO CEL!?!?!

new motor came with all new gaskets

processes of elimination that I've done are
swap to new NGK step 1 colder spark plugs LTR7IX-11 gapped at .026
swapped from MSD coils back to stock
tested for boost leaks (none)
new pcv valve
clean MAP sensors
new air filter
ECU reset
KAM reset

modifications are
COBB AP
stock turbo
stock injectors
stock fuel pump
stock map sensor
COBB intake
COBB intercooler
COBB charge pipe
COBB downpipe
COBB cat back exhaust
Jones throttle spacer
GFB BOV
symposer delete
MSD coil packs
NGK LTR7IX-11 plugs
I am JSTUNED and they cant find any anomalies and also just a basic tune atm to get the car running

Below I will include the latest WOT 3rd gear data log I have done

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I know the stock motor doesn't play well with MSD coils.

I'm no expert by any means but I see no anomalies on that log either. You might try logging at startup since that's where your problems lie.

Some have had misfire problems solved by refreshing their grounds.

I know the stock motor doesn't play well with MSD coils.

I'm no expert by any means but I see no anomalies on that log either. You might try logging at startup since that's where your problems lie.

Some have had misfire problems solved by refreshing their grounds.

Just tried that, made no difference :(
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