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2G Missfire on Highway Restart fixes

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mx3baker

Proven Member
101
25
Apr 27, 2017
Topeka, Kansas
I recently purchased a 96 GSX which may have been a mistake with the issues im having.. If i drive the car on the highway 60mph+ it will throw the P0300 misfire code and act like its running on 2 cylinders. I shut the car off while on highway and start it and the cylinders come back for a short while. I do have the stock CAS.

I have captured some ECMlink logs. The Highway pull shows the missfire towards the end then i shut off the car and turn it back on. The cylinders come back.
 

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Here's out of the FSM, you can "band-aid" the fix by going to the DTC's tab in ECMLink and uncheck the "cylinder misfire" box.

  • Crankshaft position sensor
  • Fuel Injector Resistor Pack (test)
  • Ignition system related parts (see attached to test)
    • Ignition coil
    • Ignition power transistor (IPT)
    • Plug wires
  • Low compression (compression test)
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Gofer, Thanks for the informative reply. I had a picture of what my plugs look like. Just as a start. I will start some of these tests after work.
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Dont jump straight to this but sounds like a bad coil. Heat causes everything to expand and sounds like when the engine heats up you have a arching spark somewhere. But, everything he sent you check first. Is this car 6 bolt swap? I seen you said you had a stock cas.
 
Its the stock engine that came with the car as far as i know. I say i have a stock CAS because someone asked if i was running a 1G CAS in which im not.
I was going to mention the car has a manual boost controller and is running 17-20 lbs boost could this be too much and cause this?
 
So i tested voltage on the Crankshaft position sensor plug from the wiring harness i followed this tutorial: http://www.checkenginetroublecode.c...-0l-how-to-test-a-crankshaft-position-sensor/
The voltage is 4.89v on blue and 12V on Red... Also while i was pulling these plugs apart this came loose ... Anyone have an idea where this goes? Didnt look easy to get to...
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Oh not to mention the new wireless technology i cant find the harness that would have ran back to this.

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When you're linking images you copy the image address and click the square "image" icon above the text that you're posting that looks like a picture of a mountain range, there you'll paste the image url. I edited your previous posts but if you need to post more photos that's how you'd do it...

That spark plug looks fine, don't just pull one though and expect them all to look like that. If you haven't already, be sure to pull the other 3 and verify that they all look like that one.

That 1st picture is hard to tell what you're looking at, since a lot of the connectors look similar (or are even the exact same for that matter) the only way to tell them apart is by looking at the color of the wiring going into the back of them to identify the plug. If you really want to know where that connector you broke off goes you'll need to look at the part of the harness that goes to the back of it and see what color each wire is.

The bottom sensor that has busted off wiring is the rear o2 sensor, the wiring for it runs under the driver seat and out the bottom of the floor board. There's a hole in the bottom of the car right there, typically if there's a harness going to that sensor there's a built in rubber grommet on the rear o2 sensor's wiring that plugs this hole and keeps out the elements. Hopefully that's still there at least?
Typically having the rear o2 sensor wiring cut like that you'd throw a CEL however, since you have ECMLink it looks like you unchecked the "o2/cat efficiency" box under the DTC tab it will prevent the ECU from throwing the code. You don't necessarily need that sensor to be functioning since it's for emissions and nothing else, don't expect to pass a SMOG test if your state requires them though.

The concern isn't that your crank position sensor (CPS) isn't functioning, although testing it like you did isn't a bad idea and your results appear that it's working fine, it's that the ECU is losing a signal when you're doing 60mph+ and experiencing a random misfire. The issue with OBD misfire codes is that there are so many things that can cause them and even after testing all the sensors (and the test fine) you still find the car throwing the code and shutting off a cylinder because it's impossible to test the sensor's under the circumstances that are causing your issue. Unless of course you throw the car up on the dyno and bust out the multimeter... LOL

Next time you're out driving and this happens pull off the road (don't shut the car off, keep it idling on 2 or 3 cylinders) and try to figure out which cylinder the ECU's shutting off if you can. If it truly is "random" like the DTC suggests the cylinder the ECU shuts off shouldn't be consistent so you may have to do this a few times, recording your results and see if it's always the same cylinder or not. A quick and easy way to tell what cylinder isn't firing is by pulling the spark plug wires off one at a time, listening for a change in idle speed.
 
Gofer, Thank you again for the knowledgeable post. I Looked through snowboarder714's post showing all harnesses and found the one thats attached to this broken part is for the A/C http://www.dsmtuners.com/forums/151542271-post37.html

Ill see if that hole has been plugged. I found later that the ECMLink has been unchecked... Our state emissions are non existent so im ok there.

The idea of pulling over to check the random misfire is a great idea. I will do this today.
Thank you again
 
I had a similar problem. Don't know what the fix really was but did seem to help having the ECU inspected and a few things fixed by ECM tuning. The only other things that were done was plugs. Hasn't happened in a long time now.
 
Ok I just ran it down the highway and got it to miss. I pulled over and pulled each spark plug wire out individually i could hear the spark clicking in each. The only thing i really noticed a difference in was on plug 1 (Closest to timing belt) was arcing at the coil when i removed the plug wire.

Also i took the car down to the local import shop and he said he thinks my main ground is in the wrong spot and could be causing this? I have one running to the firewall and the other was attached to the starter bolt. Does this seem correct?
 
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I did the ignition power transistor check using this method http://www.dsmtuners.com/threads/how-to-test-the-power-transistors.229419/
I checked the cam shaft position sensor voltage i was not able to check if its voltage changed when the motor turns though i need an extra hand to move the car..
plug wires are fine.
Im not sure there the coil is with the 3 ports on it. and also the secondary coils do i test them while the back part of it is still plugged in? I dont see an easy way to get to them to unplug if so.. Any tips on checking the coil resistance is appreciated.
 
The coil pack primary and secondary coils are all on the bracket sitting on top of your intake manifold. The plug wires plug into the secondary coils, just unplug them, and the primary plugs into the engine harness (see connector in image below). Both the primary and secondary coils can be tested sitting on a shelf...

Remember you're checking the coil pack so don't ohm out the engine wiring harness connector when testing the primary.

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As far as testing goes, that's good to hear you've got spark which means the ECU is shutting off an injector. Next time it does it you'll want to do the same thing, pull over and pop the hood while it's still running rough but this time pull the injector connectors off the injectors one at a time and figure out what cylinder it is.
 
The coil pack primary and secondary coils are all on the bracket sitting on top of your intake manifold. The plug wires plug into the secondary coils, just unplug them, and the primary plugs into the engine harness (see connector in image below). Both the primary and secondary coils can be tested sitting on a shelf...

Remember you're checking the coil pack so don't ohm out the engine wiring harness connector when testing the primary.

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As far as testing goes, that's good to hear you've got spark which means the ECU is shutting off an injector. Next time it does it you'll want to do the same thing, pull over and pop the hood while it's still running rough but this time pull the injector connectors off the injectors one at a time and figure out what cylinder it is.

Im not too familiar with the ECMLink software but when the car was stuttering i pulled over and selected to turn on the injector one by one to see if it would manually kick on and fire all on 4. It had no change in the motor. Didnt know if this was a good way of testing this idea.
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I left my question off at the end of my last post, so I missed the point I was trying to make. While it's good you had spark on all 4 cylinders, pulling your plug wires wasn't to check for spark necessarily, it was to see which one of the four you pulled had no effect on the idle. If the cylinder(s) are firing then by pulling the plug wire you're effectively "shutting off" that cylinder, which will have a noticeable change in engine idle speed and sound. In your case, however, the ECU is already shutting one of the cylinders down so you're looking for the plug wire that, when you pull it, it has no effect on the idle/sound of the motor. 3 of the 4 should cause the motor to drop another cylinder until you plug them back in... Unplugging the injectors from the harness will have the same effect.

When the ECU experiences a cylinder misfire is shuts-off the fuel injector going to that cylinder to prevent from flooding the motor. This is why when you shut the car off and turn it back on the motor comes back, the ECU powers off/on and starts firing whatever injector it decided to shutoff.

As far as the injector switches go in ECMLink, they're enabled (dark gray) by default so when you select them they disable (shutoff) that injector. You have the right idea, you can do this (if you have a laptop) instead of jumping out of the car and popping the hood to see what cylinder isn't firing too. Disable each injector, one at a time, and see which one DOES NOT effect engine RPM when it's disabled. That's the cylinder that isn't firing...
 
I left my question off at the end of my last post, so I missed the point I was trying to make. While it's good you had spark on all 4 cylinders, pulling your plug wires wasn't to check for spark necessarily, it was to see which one of the four you pulled had no effect on the idle. If the cylinder(s) are firing then by pulling the plug wire you're effectively "shutting off" that cylinder, which will have a noticeable change in engine idle speed and sound. In your case, however, the ECU is already shutting one of the cylinders down so you're looking for the plug wire that, when you pull it, it has no effect on the idle/sound of the motor. 3 of the 4 should cause the motor to drop another cylinder until you plug them back in... Unplugging the injectors from the harness will have the same effect.

When the ECU experiences a cylinder misfire is shuts-off the fuel injector going to that cylinder to prevent from flooding the motor. This is why when you shut the car off and turn it back on the motor comes back, the ECU powers off/on and starts firing whatever injector it decided to shutoff.

As far as the injector switches go in ECMLink, they're enabled (dark gray) by default so when you select them they disable (shutoff) that injector. You have the right idea, you can do this (if you have a laptop) instead of jumping out of the car and popping the hood to see what cylinder isn't firing too. Disable each injector, one at a time, and see which one DOES NOT effect engine RPM when it's disabled. That's the cylinder that isn't firing...

Im guessing when i tried pulling the spark plug wires i did not pull them out far enough and it was still arcing to the plug... When i initially tried the software i didnt notice a big difference in RPM i guess it would be easier to go to the live live showing the true RPM numbers.. I will try this again using the ECMlink software.
 
Something else worth mentioning too is you won't be able to "re-enable" the injector that the ECU disabled from the misfire it detected by deselecting/reselecting the swithc in ECMLink. Only killing power to the ECU (shutting on off the car) will do it.
 
Something else worth mentioning too is you won't be able to "re-enable" the injector that the ECU disabled from the misfire it detected by deselecting/reselecting the swithc in ECMLink. Only killing power to the ECU (shutting on off the car) will do it.
Hmmm... I wonder how it stayed running when i disabled them all when i was trying to troubleshoot this...
Well i disabled 1 at a time but i thought it reactivated them to keep the car running?
 
Corey, can't he just clear his DTC code and it will re-enable it? I had to move my oil cooler so I pulled all the injector plugs off so I could prime the new line and when I started it, of course it had thrown a code, so I just cleared it, knowing it was me that caused it. Just trying to make it as easy for the OP as possible, and you are doing a damn fine job too!!
 
Hmmm... I wonder how it stayed running when i disabled them all when i was trying to troubleshoot this...
Well i disabled 1 at a time but i thought it reactivated them to keep the car running?
You can disable/enable them through the software but IIRC once the ECU shuts off an injector the switch in ECMLink won't "reactivate" the injector the ECU deactivated until you cycle power.
Corey, can't he just clear his DTC code and it will re-enable it? I had to move my oil cooler so I pulled all the injector plugs off so I could prime the new line and when I started it, of course it had thrown a code, so I just cleared it, knowing it was me that caused it. Just trying to make it as easy for the OP as possible, and you are doing a damn fine job too!!
That I don't know the answer to.

I had this P0300 misfire code years ago after I swapped to a '95 wiring harness (long story) but I was 100% certain it was the engine harness that I just installed because everything was working just fine prior. If I remember correctly though, the only fix was to cycle power to the ECU to get the cylinder that shutoff back. I'm fairly certain I tried reactivating the injectors using those switches to try to get the cylinder back before shutting off the car but I don't remember if I tried clearing the DTC too and see if it started firing again.

My fix was to go to the DTC tab in ECMLink and disable the cylinder misfire check from the ECU, then replace the harness with something that was in better shape in the future to see if the problem returned.
 
Ok just got done testing the coils and after i found something better to sting down in there to get a good reading they came out reading at 12.4k and 12.6k (good) i took it for another spin to set off the misfire and i shut off each injector in ECMLink with no changes im guessing when the P0300 triggers it will not let you change the injector state. So i pulled ea spark plug cable 4, 3, 2 all made the car sputter worse and i noticed sparking still happening on the spark plug end of the cable. Plug 1 on the other hand when i pull the plug out it arcs AT the coil and does not change the sputtering of the engine. Also if i unplug the injector for 1 it does not sputter any worse like the others do. Now to figure out which part is bad?
 
Something to try that has not been mention. Start the car and take a spray bottle and spray some water on the wires and around the coil. Pretty much all of the connection and routing on the ignition wires. If they are arking you should catch when it will ground out. For some reason I don't think it's your problem.

If you disconnect the injector and the idle don't change then that's the cylinder not working. So drive it and make it misfire and the disconnect injectors one at a time to see when it will not change the idle. If you can catch it like that then you have identify cylinder. Mark injector and move to differant spot. Test again and see if the problem follows. If not move the spark plug, cables. If it don't move check compression. Might have internal problem. Also your fuel trims have to be in check.

P0300 just simply means that the PCM can not identify which cylinder is misfiring. It knows I can assure you of that but it won't tell you. I am assuming you don't have a scanner but on some cars you have mode6 in global OBD2 and you can see exactly how many times a cylinder has misfired.
 
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