2G Random misfire/other concerns

[GSTjordan831]

Hi guys I've got a few problems I've been trying to diagnose for months now I've read countless threads chased many leads but haven't found a definitive resolution to any of my problems. I have a 98 gst a/t, I've had a

#1 misfire problem for a while now, when I bought the car it ran amazing and one day on the freeway I'll admit it was really stupid of me but at the time I didn't know what the overdrive button did. So when i was on the freeway i let off of the gas and i pressed it and didn't notice a difference so i pressed it a few more times in a row and than (I wanna say, i might be wrong due to this happening a while ago but I'm pretty sure there was a clunk) the engine made a small clunk and the check engine light turned on. So immediately upon getting into town I did a obd2 diagnostic check and the code P0300=random misfire came up so I've changed the spark plugs and wires I checked the voltage on the coils I did the lazy test of unplugging the injectors to see of anything changed and everything seemed to be fine, but everytime I hit 70mph it starts misfiring until I come to a stop and when I continue from the stop it drives normal until I hit 70 again and when I drive a few days with out ever hitting 70 or full throttling it the check engine light clears itself and only comes back on when I go full throttle or hit 70mph. Upon changing to new spark plugs it ran like no problem ever occurred and I was able to go 125mph with out any issue and slowly it's back to whenever I hit 70mph or full throttle it. Also everytime upon initial startup a

#2 puff of white smoke comes out and smells kinda like burning plastic but it only happens once a day even of I let the motor completely cool down or doesn't happen again until the next day even if its morning or night or in the middle of the day on a hot summer day it does the white smoke always on the first start up of every day. And every time I start it up my

#3 turbo starts dry even if I turn off the car and immediately turn it back on again if I go to hit boost it sounds like the turbine or bearing scraping like it has no oil but after a few times of hitting boost to basically "prime or pump it" it doesn't make that sound again until I turn it off and back on and the

#4 blow off has slowly gotten almost completely quiet when I first got it and I hit boost and let off the bov was really noticeable it wasn't LOUD but u can definitely hear it and I loved it but over time it's almost silent now i can hardly hear it, it sounds the loudest when I drive it for the first time for the day but once i turn it off and back on and I hit boost and let off its actually completely silent and u can not hear it blow off.

I just don't know what to do about these problems

I know its an incredibly long post but PLEASE HELP ME

 

[jpmxrider489]

#1 misfire problem for a while now, when I bought the car it ran amazing and one day on the freeway I'll admit it was really stupid of me but at the time I didn't know what the overdrive button did. So when i was on the freeway i let off of the gas and i pressed it and didn't notice a difference so i pressed it a few more times in a row and than (I wanna say, i might be wrong due to this happening a while ago but I'm pretty sure there was a clunk) the engine made a small clunk and the check engine light turned on. So immediately upon getting into town I did a obd2 diagnostic check and the code P0300=random misfire came up so I've changed the spark plugs and wires I checked the voltage on the coils I did the lazy test of unplugging the injectors to see of anything changed and everything seemed to be fine, but everytime I hit 70mph it starts misfiring until I come to a stop and when I continue from the stop it drives normal until I hit 70 again and when I drive a few days with out ever hitting 70 or full throttling it the check engine light clears itself and only comes back on when I go full throttle or hit 70mph. Upon changing to new spark plugs it ran like no problem ever occurred and I was able to go 125mph with out any issue and slowly it's back to whenever I hit 70mph or full throttle it. Also everytime upon initial startup a

#2 puff of white smoke comes out and smells kinda like burning plastic but it only happens once a day even of I let the motor completely cool down or doesn't happen again until the next day even if its morning or night or in the middle of the day on a hot summer day it does the white smoke always on the first start up of every day. And every time I start it up my

#3 turbo starts dry even if I turn off the car and immediately turn it back on again if I go to hit boost it sounds like the turbine or bearing scraping like it has no oil but after a few times of hitting boost to basically "prime or pump it" it doesn't make that sound again until I turn it off and back on and the

#4 blow off has slowly gotten almost completely quiet when I first got it and I hit boost and let off the bov was really noticeable it wasn't LOUD but u can definitely hear it and I loved it but over time it's almost silent now i can hardly hear it, it sounds the loudest when I drive it for the first time for the day but once i turn it off and back on and I hit boost and let off its actually completely silent and u can not hear it blow off.

I just don't know what to do about these problems

I know its an incredibly long post but PLEASE HELP ME

#1 What plugs did you install? Also what wires did you go with. Only run NGK plugs. Nice wires will also help. I attached a photo where you can test your coil pack. Another thing you can try is stress testing your plugs but if you get NGK shouldn't be a issue. You can check this link on how to test the transistor pack as well. I was chasing a misfire for the longest time and it ended up being my coil even though it tested good. I believe it failed the stress test. I only recommend OEM coils but others will work.
https://www.dsmtuners.com/threads/how-to-test-the-power-transistors.229419/

#2 Do you have a oil pressure guage? I would Make sure there is no issue there. Take your intake pipe off and see if you see oil or damage in you turbo. Wiggle the wheel to see if it has play. If for some reason you broke the wheel and that piece got in your motor that wont be good. How do you know the turbo starts dry? Are you feeding from the head still? I would drain the oil and see if anything is wrong. Also see if there is oil in your coolant. It sounds like your turbo is dying. The white smoke could be from starving turbo from oil and burning coolant. Maybe do a compression check if you can.

#3 If your turbo is damaged and you not making as much boost, the BOV doesn't have much air to blow off. What BOV do you have? They are simple setup. Make sure your vac line is good and your recirc tube is good.

Check your trans fluid as well. Does it smell burnt? I hope this helps. Please keep me informed.

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[ShadyDoins]

It sounds like your turbo is going, as far as the misfire code. I have never once found any problem by trying to track down a check engine code that had anything to do with misfire, I honestly think they programed the ecu to throw a misfire code for any problem when the ecu knows something is wrong but has no idea what.

You might have 2 problems but it is hard to diagnose that unless you fix them one at a time. I think if you test and figure out if the turbo is bad like recommended above, and replace it then it will be much easier to pinpoint other problems if they still exist

 

[GSTjordan831]

#1 What plugs did you install? Also what wires did you go with. Only run NGK plugs. Nice wires will also help. I attached a photo where you can test your coil pack. Another thing you can try is stress testing your plugs but if you get NGK shouldn't be a issue. You can check this link on how to test the transistor pack as well. I was chasing a misfire for the longest time and it ended up being my coil even though it tested good. I believe it failed the stress test. I only recommend OEM coils but others will work.
https://www.dsmtuners.com/threads/how-to-test-the-power-transistors.229419/

#2 Do you have a oil pressure guage? I would Make sure there is no issue there. Take your intake pipe off and see if you see oil or damage in you turbo. Wiggle the wheel to see if it has play. If for some reason you broke the wheel and that piece got in your motor that wont be good. How do you know the turbo starts dry? Are you feeding from the head still? I would drain the oil and see if anything is wrong. Also see if there is oil in your coolant. It sounds like your turbo is dying. The white smoke could be from starving turbo from oil and burning coolant. Maybe do a compression check if you can.

#3 If your turbo is damaged and you not making as much boost, the BOV doesn't have much air to blow off. What BOV do you have? They are simple setup. Make sure your vac line is good and your recirc tube is good.

Check your trans fluid as well. Does it smell burnt? I hope this helps. Please keep me informed.

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#1 I installed NGK plugs and NGK wires

#2 I do not have an oil pressure gauge and I have taken off my intake and didn't notice any physical damage to the turbine but I can't remember if i checked for shaft play and I could tell it starts dry because everytime I turn the car on and i hit boost it sounds like metal on metal scraping but it goes away after a couple boost hits and it blows off fine Except for when I turn the car off than on and the bov completely goes away and its completely stock 100% stock only thing aftermarket is the muffler because the one it had was cracked and leaking air and made a horrible high pitch whistle

#3 I still have the OEM BOV and I've recently checked all lines and they seem perfectly fine

 

[GSTjordan831]

It sounds like your turbo is going, as far as the misfire code. I have never once found any problem by trying to track down a check engine code that had anything to do with misfire, I honestly think they programed the ecu to throw a misfire code for any problem when the ecu knows something is wrong but has no idea what.

You might have 2 problems but it is hard to diagnose that unless you fix them one at a time. I think if you test and figure out if the turbo is bad like recommended above, and replace it then it will be much easier to pinpoint other problems if they still exist

That's what I've believed this whole time that the t25 is going out and it is a random misfire code but I can physically tell that once I hit 70mph it starts misfiring

 

[jpmxrider489]

#1 I installed NGK plugs and NGK wires

#2 I do not have an oil pressure gauge and I have taken off my intake and didn't notice any physical damage to the turbine but I can't remember if i checked for shaft play and I could tell it starts dry because everytime I turn the car on and i hit boost it sounds like metal on metal scraping but it goes away after a couple boost hits and it blows off fine Except for when I turn the car off than on and the bov completely goes away and its completely stock 100% stock only thing aftermarket is the muffler because the one it had was cracked and leaking air and made a horrible high pitch whistle

#3 I still have the OEM BOV and I've recently checked all lines and they seem perfectly fine

What NGK plugs are they and what did you gap them to? I would stress test them as I said. I would function test the bov alone. Definitely wiggle the wheel to see if there is shaftplay. If its blown, then there's a reason for smoke. But you mentioned about oiling and how the turbo is dry. Are you saying this because of the noise? If you can put a T in the feed line for the turbo to find out pressure or test it at the OFH. I'm still unsure if this is the cause for the misfire or not though. Do you notice the misfire happening at a certain RPM or with a certain boost amount? You need to do more test for me to provide more help.

That's what I've believed this whole time that the t25 is going out and it is a random misfire code but I can physically tell that once I hit 70mph it starts misfiring

I think there may be a bigger issue here. Defiantly stress test the plugs.

Something like this would help. Have you changed oil and looked for metal since this?

https://www.autozone.com/test-scan-and-specialty-tools/ignition-tester/p/oemtools-adjustable-ignition-spark-tester/10257_0_0