cylinder missfire

[gtpq43]

hi i have a 98 gtp with about 64,000 miles on it and im not sure if this problem happened because of when new spark plugs were installed or not but for a while now ive been getting major missfires from the #4 cylinder when i take off too fast or when im at higher speeds it will just start to missfire unless i press gas down...ive had it in since original plugs were changed and had new plugs and wiring put in they have also changed the fuel regulator and new injector was put in but i still have this problem i hope someone can please help....?

[gtpq43]

oh yeah and also my car hasnt been starting up right away like it should ....it takes like 5 sec or so rather then starting right up when you turn the key

[kilroypr]

If you go to http://www.zzperformance.com and check under the bad mod list they tell you that changing the fuel regulator is not really adding you anything but hurts you a lot. That could be the 5 secs start up problem.
The other thing. Related to the misfire on 4, it could be on any spark, but, as Ripn12s made me think a little this afternoon looks like the car is running too lean on the high rpm band(Not enough gas could cause a cyl to miss). Be carefull, my car was pulling really strong and because it was somewhat lean I think it cracked piston 5. Before that I got the car in the shop with a broken engine it could misfire on 4, 1, 3, 5 or 6. Be carefull that your car is not running too lean. When the car runs to lean the pistons are running too dry on the cylinder causing the friction temp to raise more than required and thus causing the cylinder wall to crack or the piston to break.
In your case if always that you race the engine you get the miss definetly check the O2 reading to check if you have a 2 lean mixture. If that is the case you have to make the mixture a little more richer to prevent overheat at the cyl wall or piston rings/head. That is really bad for the car and could really break something from the piston head to cyl walls.

[Mdonahue]

I have had problems with plug before. I install new champion plat plugs and experiance missing problem. I went back the boush 4 prong plugs to solve this problem.

I have 1999 GTP with 130000.


My current problem is 171 lean fuel SES code.

I've replaced the fuel pump, the vaccum harness. I have a fuel pressure regulator on order. But I am wonder if I should install an adjustable reg, performance part instead of the OEM.

My fuel pressue is about 40 psi, should be about 55.

Do I need to install a small pulley if I get an adjustable regulator?

[AKWE-gt]

gtpq43 you could have a broken or soft valve spring.

[MoshimoGTP]

Check the Fuel Injectors, mine was the problem. I has the same problem with cylinder 3, i has a BAD fuel injector...

Check it!

Hope this helps

[97grandprix]

I had a miss fire in cylinder 6, and it turned out to be a bad coil, due to a bad wire arcing. i would take a look at your coils

[nate2424]

Originally Posted by 97grandprix

I had a miss fire in cylinder 6, and it turned out to be a bad coil, due to a bad wire arcing. i would take a look at your coils

I have the same problem right now. I replaced the coil wires, plugs, and still have it. I guess what I would like to know is should I go to the injectors next? do a compression test?

[GTP Dad]

Two things that may help all of you. If the coils are original then change the coil on the plug where you have a misfire. If you are getting a lean condition the problem may be a dirty MAF sensor. Clean it using electronics cleaner, allow to completely dry before reinstalling. If you find that you need to replace injectors, ZZperformance has a good deal on injectors for the L67 engine. Somewhere around $150 for a complete set. Can't beat that price.

[kustomkid54]

Originally Posted by GTP Dad

Two things that may help all of you. If the coils are original then change the coil on the plug where you have a misfire. If you are getting a lean condition the problem may be a dirty MAF sensor. Clean it using electronics cleaner, allow to completely dry before reinstalling. If you find that you need to replace injectors, ZZperformance has a good deal on injectors for the L67 engine. Somewhere around $150 for a complete set. Can't beat that price.

Over a year old, and got the right answer after all.

[GTP Dad]

I didn't even pay attention to the date this was originally posted when I responded. Guess old age is finally starting to take its' toll.