PLEASE HELP!!!PO300 random misfire

[PC 2015]

Denso ITV-24 gapped 24
Lund tuned
Stage 2 whipple 3.5 pulley 14psi
Fore level 2 triple pump
Id1300
I fired the car up for the first time Friday after the motor rebuild/install. Took it to the dyno Friday after noon first pull 2500 to 5500 WOT. Second pull 2500 to 7000 when the car hit 6100 or so pulled timing and random misfire or deceleration. Lund changed a couple things happen again. So I stop. Yesterday Filled her up with new E85. Did two pulles 3rd to 4th ran great. Did a third pull 3rd to 5th ran great but random misfire again but. So today I did a crank relearn. Did Two 6th gear pulls one just over 6000 and the other to 7000 just like on the dyno. No problems. Did some other pulls car was fine. I did not baby it all. was doing pulls WOT pulls at diffrent RPM in diffrent gears no problems . But did one last pull 4th to 7th had to hit the break pretty hard right before the car comes to a complete stop check engine light flashes PO300. So again on the declaration. Didnt do plugs yet as I didnt think plugs would matter on the decel. Anyone have this same issue? If so what was the fix. All pulled we're WOT
Thank Joe

Sponsored

 

[Bioni007]

I’m having the same problem with my car but I think it’s my rxt clutch

 

[Tommy V]

What are you doing the crank relearn with?

 

[PC 2015]

What are you doing the crank relearn with?

The Ngauge. Why Is that no good?

 

[Tommy V]

Not sure about nguage but i did a relearn with sct and it said relearn completed when at the time it was impossible for my car to complete a crank relearn because my tuner had code po315 turned off.Not sure why the sct kept saying it was complete when it was not.I def would not keep doing wot passes until you make sure your not getting real misfires,in the end that was what took my first motor out.

 

[PC 2015]

Not sure about nguage but i did a relearn with sct and it said relearn completed when at the time it was impossible for my car to complete a crank relearn because my tuner had code po315 turned off.Not sure why the sct kept saying it was complete when it was not.I def would not keep doing wot passes until you make sure your not getting real misfires,in the end that was what took my first motor out.

No I'm done car is getting ready for AM show now. Next Monday swapping plugs. Lund just got back to me and said all my logs look great even the one that the misfire popped up on the decel. So I'm gonna start with plugs and compression test witch I'm 99.9% positive is good. Smoke test just in case. Coil pack check. This motor just cost me 14000 I cant afford a major problem. The thing that sucks tho is you can 10 pulls no problems 11 pull random misfire on decel. WTF LOL

 

[Tommy V]

Yea man race cars problems lol.I just put my built trans in only to find out that my passenger head gasket is leaking a small amount of coolant into the header.Now i have to pull the motor and do head studs and new gaskets.

 

[PC 2015]

Yea man race cars problems lol.I just put my built trans in only to find out that my passenger head gasket is leaking a small amount of coolant into the header.Now i have to pull the motor and do head studs and new gaskets.

When we are old we will look back and say was all the money and time worth it. I hope I say yes lmao

 

[Tommy V]

When we are old we will look back and say was all the money and time worth it. I hope I say yes lmao

Lol i am already getting their at 51 and after long days of working on this damm car and feeling like ive been hit buy a truck,i start to wonder lol.But i dont trust anyone but my two 2 buddies and me too work on mine,so i just suck it up.Would love to be in my 20's again with a car this fast!!

 

[Bioni007]

I know I had this problem right after I installed the RXT
But I’m on e85 and 72mm pulley on a Roush Supercharger

 

[Ponderthis]

check porcelain on spark plugs...

 

[PC 2015]

New plugs coming. Ngk 6510

 

[Bioni007]

Regap to .025 and did a crank relearn
Let’s hope it works

 

[Burkey]

Cats or no cats?

 

[olaosunt]

Lol i am already getting their at 51 and after long days of working on this damm car and feeling like ive been hit buy a truck,i start to wonder lol.But i dont trust anyone but my two 2 buddies and me too work on mine,so i just suck it up.Would love to be in my 20's again with a car this fast!!

Think of all the money you are saving on labor ...that should help with the aches .
I am turning 50 next year and planning to “retire “ from this modding business . I need to accelerate my real retirement plan and this cars are not helping. Lol

I know I had this problem right after I installed the RXT
But I’m on e85 and 72mm pulley on a Roush Supercharger

Hmm . Could it be related to the clutches/steels just installed ? I was getting what felt a misfire also before I swapped mine (no code )

Regap to .025 and did a crank relearn
Let’s hope it works

I was still getting what felt like a misfire after the swap but new plugs(looked grreyish I assume from all the octane booster I had been running )and gaping to 0.025 seemed to have helped . I did not do crank relearn yet .

Sponsored