multiple piston missfires

[DWosik13]

i own a 1996 v6 GT
according to my computer in my car i have multiple pistons missfireing ive tried fuel injector cleaner didnt work to well and i was wondering what other things i should try...

[sudden_impulse]

Check your plugs and wires to make sure they're connected properly and aren't grounding out or ruined. Check your injectors and fuel rail for problems.

[DWosik13]

well my plugs and wires are all new but how would i go about actually testing the injectors and or the fuel rail?

[doobiess]

check your coils and or module at autozone if i remember right.. a single coil will cause 2 cyl not to fire right...

[mattcow]

check your air filter and all connection on your intake.

[4kQuad]

You have the 3.4 and the back plugs are a real pain to get to. I would guess they are old and the problem. Thats my "guess"
More than one person has found the front ones have been changed at some point, while the back ones look like they have not been.

[rixGAphx]

'96 3.1 V6; 11-yrs old, prolly 120k miles total.
FI cleaner thru the tank didn't solve the problem.
You JUST replaced all the plugs and wires.
Did you use ACDelco platinum, either 'RapidFire' or 'Professional Dual Platinum'?

Based on expensive similar problems 2 yrs ago with my '96, I'll bet that your engine is running verrrrry rich, with injector(s) that are stuck partially-open by a microscopic grain of sand stuck in the orifice.
FI cleaner only disolves built-up varnish, and it can't dislodge this obstruction.

First step would be to replace the main (front) O2 sensor if it hasn't been changed.
It's only intended to last 80k miles, and it starts loosing accuracy after ~50k miles.
It's located on the top of the rear intake manifold, and requires the special $10 'universal' O2 sensor socket for R&R.
A new O2 sensor will give more-accurate results to the PCM, and it may be able to 'trim' the injection to compensate for the injector maladies.
* * *
Second would then be to have the fuel pressure tested.
There's a test port on the passenger side end of the rear fuel rail, kinda behind/below the PS pump.
It's a Schraeder valve that looks kinda like a tire valve, and works the same.
A shop will have a gage to attach and measure pressure.
Your fuel pressure is regulated by the Fuel Pressure Regulator (duh :D ), a round metal device the size of a Hostess cupcake, located at the driverside end of the front fuel rail.
If the FPR isn't bleeding-off enough pressure, the injectors will squirt too much fuel each time.
A DIY test of the fuel rail is to turn-off the engine and remove the key, then CAREFULLY depress the 'pin' in the Schraeder valve. Raw gasoline should spew out, about 1 tablespoonsful for about 6" :eek: Have a heavy shop rag there to catch it; no sparks or smoking!!!
Now repeat the same test, but wait 20 minutes fter sutting-off the engine before depressing the vavle pin. My *guess* is that NO fuel will come out except a couple dribbling drops. This is because all the pressurized fuel oozed thru that leaking injector during the 20 minutes.

Your best bet, IMO, is to find a reputable shop that does pressurized injector cleaning, mebbe $120?
They will use the same chemical as the bottled FI cleaner you used, but they will force it thru the injectors at pressure high enough to dislodge the obstruction that is preventing your injector's needle from seating and closing the orifice.

Either that, or remove the UIM (Upper Intake Manifold) and fuel rail, and replace the injectors with re-builts (about $75 each) or new ($100-140 each).

There is no effective DIY method to clean or rebuild the injectors.
* * *

I don't think this is ignition-related, for 2 reasons:
* Your symptoms are identical to mine, and the problem was FI, not coils or ICM (Ignition Control Module).
* If it were a SINGLE coil, then you would be getting misfire codes for that pair of plugs, say P0302 and P0305, rather than P0300. When more than 2 cylinders are misfiring, the PCM just reports 'multiple/random' misfires.
* * *

Don't let this problem go, hoping it will get better.
It won't!!
And, you will soon kill the catalytic converter as it tries to clean the very dirty exhaust, and its O2 sensor will also die.
Your gas milage is terrible, and the savings in gas alone in the next 6 months will prolly pay for this service.

Hope this helps,
-Rick

PS:
Change your fuel filter.
Changing it won't fix the current problems, but it prolly hasn't been changed for more than the recommended 30k miles, and it may have CAUSED the present condition by allowing crud to pass.
You don't want to immediately crud-up the injectors that you're going to pay to have cleaned.

[95CombatGA]

trust this guy, he knows a lot. btw i just had the same problem with a 99 sunfire 2.2 same ses code but since i did the plugs and wires 3 weeks ago for a cyc 2 misfire, i went right for the coils, and sure enough, 1 coil was toast. luckily for me, my coil packs are the same for the sunfire, so i tossed in 2 of mine old but working ones ( found 3 packs and module online brand new for 30 bucks) and car runs smoother than ever....

just dont over look what
rixGAphx says even if u fix the problem, u should still tune up ur car regardless