Random Miss

[marcman804]

my car was sitting in the shop for about 2 weeks while i was waiting for ACT to send me a new clutch. well i finally got my car back and now it has a random missfire at idle and i noticed it when i kept a constant rev as well. i replaced the plugs and wires but it still has the missfire. i was thinking it may be my injectors but im not sure. i have some new pte 680cc injectors that i would like to put in but right now all i have is the stock fuel system. would it be ok to put in the injectors or will my car run like shit? what else could be the problem? im so sick of repairing things when i could be making it faster and better.

 

[Speed_RacerGSX]

The random mis code can cover a pretty broad spectrum of issues. Plugs and wires is a good start, if you can look at the freeze frame data, and see if anything is out of usual range, look for intake leaks(between the MAF and turbo) as that will give you a lean mix and a mis, our o2 sensors aren't that great, and generally wont throw codes too often, you can have a way lean or rich mix, and the sensor wont do shit, especially if they are old and crappy.
Take a can of carb clean and check for vac. leaks, pull your plugs and take a good light and look at the tops of the pistons for carbon, if they are black and mountainous, run some BG 44K through it... hell do that anyhow, it kicks ass.
But again, I stress the freeze frame data, it will tell you if the crank sensor is off, or MAF, or IAC, EGR etc... If you have access to a good scan tool( like the modis or genysis) test the egr and the IAC, if you miss is ONLY at idle, especially look at those two. The EGR can usually just be cleaned out... the IAC usually needs to be replaced...
Hope that helps a bit

 

[marcman804]

thanks man thats some good info. i dont believe any of those things have ever been done to my car. where can i find the BG 44k and what exactly is it? ive never heard of it. and at first i thought the mis was only at idle but when i revved the engine to a constant 2500 it still did it.

 

[marcman804]

I finally found some bg44k and ive used it but it still has a random drop in idle when the car is sitting still. its really quick and i dont even see the rpms drop when it happens. its really hard to explain. its kinda like its idling smooth and then it hits a bump

 

[MrBoxx]

What plugs and wires are you using? What gap?

 

[dSmgs-T]

^
look into to new plugs and wires. NGK bpr7es and some magnecores!

 

[MrBoxx]

^
look into to new plugs and wires. NGK bpr7es and some magnecores!

BPR6ES, unless boosting above 18psi.

 

[marcman804]

I have ngk bpr7es gapped to .028 and the guy at advanced autoparts told me that these magstar 8.5mm wires are better than ngk's and like a dumbass i believed him and took his words for it, has anybody else tried these?

 

[MrBoxx]

As I mentioned in the post above, unless you're running fairly high boost, you don't really have a need for the colder 7ES plug. Switch to 6ES's and see if your problem is fixed.

 

[e36bmer]

I would reccommend either checking the gap on the plugs or just getting some new plugs and gap them correctly. That is always where I start when finding a slight misfire.

 

[marcman804]

I have used those plugs since i got the car and never had a problem and i just replaced the plugs. what gap should i use? has anyone used the magstar wires im using? and i know i have some boost leaks and i havent had a chance to boost leak test it. I just made a tester being that i work at a hardware store, but my question is do i have to use a compressor to test it or could i use a regular bike tire pump?