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#141931 - 08/14/07 12:07 PM Re: P0300 misfire problem!
Emilee Offline
Junior Member
Registered: 08/09/07
Posts: 10
Loc: Ada, Ohio
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Alright I don't believe that it is the intake gaskets because A: I had this problem before I changed them and still have it after B: It would be running badly all the time, not just when I make boost.

okay update: I cleaned the MAF. its fine. I'm trying a MAP sensor soon.
my plugs are fine. I don't have a scanner but I have since replaced the wires and coils, tried a new ignition module checked my fuel pump and its none of that stuff. It only does it when I make boost. When I first start the car up and go down the road when its cold it won't really do it, but after a few minutes it will start missing again even if its only 1 lb of boost.
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#141932 - 08/14/07 12:44 PM Re: P0300 misfire problem!
SlickGTP Offline
Member
Registered: 03/26/07
Posts: 1399
Loc: Houston, TX
Do you have access to a scanner? At this point I have a feeling it could be a few things, but you won't be able to figure it out without a scanner.

For example: I was having an issue where under different engine loads, the engine would stutter and fall all over itself. Scanning the car revealed the the MAF sensor was intermintently dropping off to zero and freaking the pcm out. Replaced sensor and the car's been good ever since.

So, instead of guessing for a predictable but intermintent problem... I'd get a scanner on there and see if any of the sensors are acting weird.
_________________________

Kinda sorta, yeah, no?

'02 Black GTP - RIP 03/03/08 ||| '06 Black G35 MT6 - Stock ||| '73 Chevy half ton(resurrected)
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#141933 - 08/14/07 02:19 PM Re: P0300 misfire problem!
Emilee Offline
Junior Member
Registered: 08/09/07
Posts: 10
Loc: Ada, Ohio
ok... I just don't know where to find someone who has one... Ahhhhh this problem is killing me frown
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#141934 - 08/14/07 02:21 PM Re: P0300 misfire problem!
drummerboy1307 Offline
Member
Registered: 04/30/06
Posts: 3201
Loc: Groton, CT
The MAP is a good possibility. When you go into boost, you should be over 100 kPa MAP readings, maybe something weird is happening and your MAP sensor is not registering that you are into boost?
_________________________

'97 SE with alot of mods
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#141935 - 08/14/07 03:18 PM Re: P0300 misfire problem!
Emilee Offline
Junior Member
Registered: 08/09/07
Posts: 10
Loc: Ada, Ohio
I have one on the way from ZZP... it was only 20 bucks so I figured it was worth a try...
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#141936 - 08/15/07 06:35 PM Re: P0300 misfire problem!
Blackarrow98GP Offline
Member
Registered: 06/29/06
Posts: 3618
Loc: CT, U.S.A
A few other things to check, that can cause a PO 300:
If you haven't tried this already, it's worth a shot: Take the car for a ride with the MAF sensor unplugged; if the misfire is gone, replace the MAF Sensor. Clear the code, and take the car for at least three trips, shutting it off for at least two minutes between trips. If the code doesn't come back, good to go!

Vacuum leaks: Check all vacuum lines, and check for leaks around the intake mounting surfaces, MAF sensor, throttle body, EGR valve, EGR adapter and feed pipes, and injector o-rings. Remove the EGR valve, and make sure it isn't partially stuck open. Check the PCV Valve for improper installation, and damaged/missing o-rings.

A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.

Extended idling or short trip driving can leave deposits on the heated oxygen sensors, causing them to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle.

Best of luck in tracking down your problem; I know all too well how frustrating it can be... wink
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#141937 - 08/16/07 12:16 PM Re: P0300 misfire problem!
Emilee Offline
Junior Member
Registered: 08/09/07
Posts: 10
Loc: Ada, Ohio
thanks for the info... I am gonna start narrowing things down one by one... haha. I had a question though. Does anyone know what the proper intake vacuum should be on a GTP? I was gonna check that just to be sure. Also, I read about a lot of people blocking off their EGR. Since that is a hell of a lot cheaper than buying a new EGR and since I don't have emissions testing around here, would that fix the problem if it is my EGR acting up???
I can't tell you how much I appreciate all your responses... I got like 2 on clubgp lol
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#141938 - 08/16/07 01:10 PM Re: P0300 misfire problem!
Blackarrow98GP Offline
Member
Registered: 06/29/06
Posts: 3618
Loc: CT, U.S.A
Vacuum at idle: around -9psi or -18inHg at idle, according to this thread: Questions About Boost
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#141939 - 08/17/07 10:22 AM Re: P0300 misfire problem!
Emilee Offline
Junior Member
Registered: 08/09/07
Posts: 10
Loc: Ada, Ohio
well its not the map and my vacuum is -9.5 psi at idle.... I noticed today when I started it, its misfiring at idle some and it smells like gas around the back header/EGR area. Any suggestions? What about blocking off the EGR? Some ppl have done it so i was wondering if I should?
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#141940 - 08/17/07 10:27 AM Re: P0300 misfire problem!
SlickGTP Offline
Member
Registered: 03/26/07
Posts: 1399
Loc: Houston, TX
Get a light back there and see if the injector o-rings are leaking...

I just had someone around here who was having issues when his injectors weren't sealing correctly all the time. Slightly different situation, but the symptoms are similar.
_________________________

Kinda sorta, yeah, no?

'02 Black GTP - RIP 03/03/08 ||| '06 Black G35 MT6 - Stock ||| '73 Chevy half ton(resurrected)
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#141941 - 08/17/07 10:34 AM Re: P0300 misfire problem!
Blackarrow98GP Offline
Member
Registered: 06/29/06
Posts: 3618
Loc: CT, U.S.A
Pull out the spark plugs, keeping them in order; chances are they're probably gas fouled by now, maybe enough to see which cylinder is misfiring. You may have to put in a fresh set of spark plugs; if it still misfires, try unplugging the Mass Air Flow Sensor first, and see if it runs better.
X2 Slick's comment about the injector o-rings; be sure to check the fuel feed lines as well.
Speaking of EGR, did you remove it and check to see if it is partially stuck open? You might want to try that also.
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#141942 - 08/17/07 11:00 AM Re: P0300 misfire problem!
framos242 Offline
Member
Registered: 07/15/04
Posts: 3141
Loc: Chicago, IL
Quote:
Originally posted by Stauffie'sGTP:
you hafta get "tamper-proof" torx bits...25 size maybe?
T20
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DHP V1.0, Slotted rotors, S/S Brake Lines, Custom CAI, GMPP Handling Kit, KYB's, Jimmy C DP (U-Bend delete w/ Hi-flow cat), Flowmaster Super 40's, drilled 180° T-Stat, Alt. Rewire & Alt. Voltage Booster Combo, 605's, ZZP Motor Mounts

"The only difference between me and a madman is that I am NOT mad!" - Dali
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