Spyder Misfire under high boost, code P0300 random misfire

[Junzu]

Stock 97 GST, Have been chasing this code for little over a week, let me give some backstory.

- Only modification is a clutch job I did recently with ACT 2100 and ACT streetlight flywheel.

- Fresh NGK plugs and wires with less than 5k miles.

- Proper timing done 5k miles ago.

- Boost leak symptoms but I smoke tested it at work today. Nothing came up! However, PSI on smoke machine showed signs of a large leak.

- When code is cleared, only comes back on under heavy boost when I hit redline.

- Tested for spark which is good and injectors are firing.

Misfire is pretty obvious under boost now. Idle steady and otherwise runs fine. Electrical connections and harness around injectors fine.

Any ideas?

 

[Boomdeeze]

So what did you boost leak test it to? Smoke machines are cool but you still have to pressurize the system to know if it’s leaking. Since you’re on the stock MAF, a boost leak can make a big difference.

Do a boost leak test to your target boost and fix any leaks, we can go from there.

 

[DSMPT]

Maybe this is not your case but in case if you don't find any leak while you are doing a boost leak test but you still have a boost leak-ish symptom while you are driving, try to move the throttle plate while pressurizing the system (open/close/push-pull side to side while it's hot and cold). You may start to see/hear a leak from the shaft seals. Sometimes you have a leak only when the throttle shaft is moving or at WOT. If so, that's a sign to replace the shaft seals.

 

[Junzu]

So what did you boost leak test it to? Smoke machines are cool but you still have to pressurize the system to know if it’s leaking. Since you’re on the stock MAF, a boost leak can make a big difference.

Do a boost leak test to your target boost and fix any leaks, we can go from there.

Tested it thru a hose that connects to the intake manifold and plugged the upper intercooler pipe.

Sorry, first time actually doing a boost leak test but I assumed that would be enough to find leaks thru that area first off. Thinking about buying an actual tester that connects to the turbo, may need it down the road

 

[jpmxrider489]

If your misfiring under high boost only, you can tighten up your plug gap. Also what plugs are you running with what fuel?

As everyone else said, boost leaks are important. Those need to be fixed.

 

[Junzu]

If your misfiring under high boost only, you can tighten up your plug gap. Also what plugs are you running with what fuel?

As everyone else said, boost leaks are important. Those need to be fixed.

Copper NGKs with 91 premium, fresh NGK wires

 

[T bags]

Lower the gap on the plugs to .28 and go from their.

 

[Junzu]

Lower the gap on the plugs to .28 and go from their.

When I did them 3k miles ago I gapped them at .28

 

[T bags]

Remove and recheck
Could be bad. Look at the wires and ignition coil as well

 

[jpmxrider489]

Copper NGKs with 91 premium, fresh NGK wires

Your running bpr7es? Also pick up a spark stress tester from the parts store. Under 10 bucks. This will hopefully show where the weak spark is. You could try swapping the coil pack out.

 

[ZubUchiha]

Maybe this is not your case but in case if you don't find any leak while you are doing a boost leak test but you still have a boost leak-ish symptom while you are driving, try to move the throttle plate while pressurizing the system (open/close/push-pull side to side while it's hot and cold). You may start to see/hear a leak from the shaft seals. Sometimes you have a leak only when the throttle shaft is moving or at WOT. If so, that's a sign to replace the shaft seals.

Dude you're a genius. I want to try this out. My car also has a P0300 and on 10% > throttle, the rpm needle is jumping/dancing around. Can you explain this method to me a little more?

Where are these shaft seals you're speaking of? Thanks. I also have my own post too, if you go to it and reading all the things I have commented on, it might help you to help me diagnose and fix my issue, this issue has been ongoing for over a year now and making me go crazy.

Here is the link to my thread, please check it out when you can. https://www.dsmtuners.com/threads/random-misfire.542534/page-2#post-153887662