Misfire issue p0303
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Misfire issue p0303 Hello my LT1 brethren,
So I've been going through a rough time with my car this month, the MSD opti died and I went out to buy a AC Delco opti instead. After having some free time, I finally got a chance to install it. I had a couple issues lining the opti up, but eventually I got it on right. Before hand, I made sure to check all the connections and made sure the wheel balancer was on good. While I was installing everything, I replaced the ICM and added the cooling mod. I also replaced the crankshaft sensor as well as the ignition coil: which is a AC DELCO brand.
I finally fired up the car and bled the coolant system, but then I noticed a SES light flashing: my reader said it was a p0303 code cylinder misfire #3. Now my spark plugs are NGK Iridiums specifically "TR55IX IX Iridium " with about a year of use, as well my plug cables which are MSD. I double checked the wiring and it looks fine, but I didn't get a chance to make sure the boot on plug # 3 was good.
Any recommendations on what steps I should take to attack the problem.
If this helps, the 02 sensors are new, my maf has been on there since i bought the car 2 years ago and I did spray maf cleaner on it before I fired up the car.
Otherwise that's all I can think of at the moment.
Any help would be appreciated!
So I've been going through a rough time with my car this month, the MSD opti died and I went out to buy a AC Delco opti instead. After having some free time, I finally got a chance to install it. I had a couple issues lining the opti up, but eventually I got it on right. Before hand, I made sure to check all the connections and made sure the wheel balancer was on good. While I was installing everything, I replaced the ICM and added the cooling mod. I also replaced the crankshaft sensor as well as the ignition coil: which is a AC DELCO brand.
I finally fired up the car and bled the coolant system, but then I noticed a SES light flashing: my reader said it was a p0303 code cylinder misfire #3. Now my spark plugs are NGK Iridiums specifically "TR55IX IX Iridium " with about a year of use, as well my plug cables which are MSD. I double checked the wiring and it looks fine, but I didn't get a chance to make sure the boot on plug # 3 was good.
Any recommendations on what steps I should take to attack the problem.
If this helps, the 02 sensors are new, my maf has been on there since i bought the car 2 years ago and I did spray maf cleaner on it before I fired up the car.
Otherwise that's all I can think of at the moment.
Any help would be appreciated!
Last edited by TransAmFan88; Feb 24, 2012 at 09:19 PM.
Those " NGK TR55IX IX Iridium" were my plug of choice prior to going FI, now I use the 6IX's.
Anyway, check the resistance on your wire (10k Ohms per foot or less)
Cylinder #3 is easy to get to; so pull the plug and visually inspect it. If it looks ok, clean it, then (after clearing the codes) swap it with another cylinder's plug to see if the code follows the plug (if it does, that's your problem.)
Good luck!
Anyway, check the resistance on your wire (10k Ohms per foot or less)
Cylinder #3 is easy to get to; so pull the plug and visually inspect it. If it looks ok, clean it, then (after clearing the codes) swap it with another cylinder's plug to see if the code follows the plug (if it does, that's your problem.)
Good luck!
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Those " NGK TR55IX IX Iridium" were my plug of choice prior to going FI, now I use the 6IX's.
Anyway, check the resistance on your wire (10k Ohms per foot or less)
Cylinder #3 is easy to get to; so pull the plug and visually inspect it. If it looks ok, clean it, then (after clearing the codes) swap it with another cylinder's plug to see if the code follows the plug (if it does, that's your problem.)
Good luck!
Anyway, check the resistance on your wire (10k Ohms per foot or less)
Cylinder #3 is easy to get to; so pull the plug and visually inspect it. If it looks ok, clean it, then (after clearing the codes) swap it with another cylinder's plug to see if the code follows the plug (if it does, that's your problem.)
Good luck!
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So here's what came out of cylinder 3
and here's my screw up on the new one!
I'm going to the store to go pick up another replacement
The wires came out to about 60k on the OHM so those seemed good, so I guess its going to be the spark plug that is the cause of the misfire eh?
and here's my screw up on the new one!
I'm going to the store to go pick up another replacement
The wires came out to about 60k on the OHM so those seemed good, so I guess its going to be the spark plug that is the cause of the misfire eh?
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So a little update, I gapped the new spark plug and installed it. Fired up and it still popped the 303 code. I swapped cables, and the one I swapped with fired up fine but cylinder 3 was misfiring still. I just got a new pcm that came in the mail with a tune from pcm for less, and I'm going to see if my old pcm might be screwed up or something. Do you guys have any other suggestions I should try?
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If all it is setting is a cylinder 3 misfire, it is a pretty simple process of elimination. You need suck squeeze bang and blow on #3.
First guess is you didn't get the #3 plug wire all the way back in the terminal on the new opti. Put a spark tester inline between #3 wire and the plug. See what is says.
First guess is you didn't get the #3 plug wire all the way back in the terminal on the new opti. Put a spark tester inline between #3 wire and the plug. See what is says.
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If all it is setting is a cylinder 3 misfire, it is a pretty simple process of elimination. You need suck squeeze bang and blow on #3.
First guess is you didn't get the #3 plug wire all the way back in the terminal on the new opti. Put a spark tester inline between #3 wire and the plug. See what is says.
First guess is you didn't get the #3 plug wire all the way back in the terminal on the new opti. Put a spark tester inline between #3 wire and the plug. See what is says.
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Just a little update, I checked out the fuel injectors and those seem to be firing fine. I replaced the MAP sensor just for kicks and that didn't really fix the problem. I did check the fuel pressure regulator and the hose going from there to the intake manifold did have a gas smell: I'm not sure if that's bad or not. I took the car for a spin to see the wot feel, and there's definitely a loss of power and some back firing. The RPM's would go up but the speedometer wasn't very responsive. I guess I'll start looking at plugs and wires, just kinda puzzled since they're fairly new. Maybe something was crossed when I plugged everything back in from the new opti install.
I had another note, a friend of mine told me i had some white smoke coming out on the back fire. I doubt its a head gasket causing the misfire. But my guess everyone is going to say: opti, plugs, wires..
I had another note, a friend of mine told me i had some white smoke coming out on the back fire. I doubt its a head gasket causing the misfire. But my guess everyone is going to say: opti, plugs, wires..
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Just a little update, I checked out the fuel injectors and those seem to be firing fine. I replaced the MAP sensor just for kicks and that didn't really fix the problem. I did check the fuel pressure regulator and the hose going from there to the intake manifold did have a gas smell: I'm not sure if that's bad or not. I took the car for a spin to see the wot feel, and there's definitely a loss of power and some back firing. The RPM's would go up but the speedometer wasn't very responsive. I guess I'll start looking at plugs and wires, just kinda puzzled since they're fairly new. Maybe something was crossed when I plugged everything back in from the new opti install.
I had another note, a friend of mine told me i had some white smoke coming out on the back fire. I doubt its a head gasket causing the misfire. But my guess everyone is going to say: opti, plugs, wires..
I had another note, a friend of mine told me i had some white smoke coming out on the back fire. I doubt its a head gasket causing the misfire. But my guess everyone is going to say: opti, plugs, wires..
gas smell from the regulator is bad, if the diaphragm is cracked, or broken, its pumping fuel in the intake from the regulator, with the car running, pull off the regulator hose and see if fuel is pumping out of it
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Ok, I fired it up and took a look at the plug to see there was no fuel coming out. At least I know that wasn't damaging my engine.
Last edited by TransAmFan88; Feb 29, 2012 at 08:52 PM.
my guess would be an opti issue again.. if the plug was good.. then the wire was good.. next in line is the opti. maybe some sort of debris is in it that could be blocking signal. i had a similar issue with my car but my coil was at fault along with a bad coil wire. mine had a high rpm missfire but it wasnt narrowed to one cylinder.
is it possible you could have a bent valve or pushrod? i once had a cylinder 5 missfire in my ls1 that was due to a bent pushrod
is it possible you could have a bent valve or pushrod? i once had a cylinder 5 missfire in my ls1 that was due to a bent pushrod
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my guess would be an opti issue again.. if the plug was good.. then the wire was good.. next in line is the opti. maybe some sort of debris is in it that could be blocking signal. i had a similar issue with my car but my coil was at fault along with a bad coil wire. mine had a high rpm missfire but it wasnt narrowed to one cylinder.
is it possible you could have a bent valve or pushrod? i once had a cylinder 5 missfire in my ls1 that was due to a bent pushrod
is it possible you could have a bent valve or pushrod? i once had a cylinder 5 missfire in my ls1 that was due to a bent pushrod
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So the FPR was changed out, it does run better but there is still exhaust backfire. The SES light still flashes, but there's no code coming up: I believe its because of the tune from PCM for less. I tested spark on plug 1 and 3 and both have electricity going to each one, and I even swapped plugs and wires with 1 and 3 just to test out any other issues. The result was still a flashing SES. Now a week ago roughly, we used that laser gun to test to see the temperature on manifolds to see if the pistons were firing right and I was told the temps looked good: i believe that's how your suppose to see it. What would be the next step in looking for misfiring problems? does this sound like a plug issue still?
I'm leaning towards a DOA Opti
I'm leaning towards a DOA Opti
Last edited by TransAmFan88; Mar 9, 2012 at 08:14 PM.
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I went back and checked plugs and gapping, the wires still look good and there's nothing crossed I'm sure of it. Can an opti run but be defective? In the sense cause a misfire but still have the car be able to fire up and run? Im stumped.
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Ok, I went out and started pulling fuel injectors: one at a time. All of them changed idle except two of them. 8 and 6 did not change the Idle on the engine, and I got a code for p0174. I tested ohms on both, and they read 12.5 to 12.7. I'm going to try a compression test on those two engine bays next, but from what I understand it could be a blown head gasket? any ideas fellas?
Last edited by TransAmFan88; Mar 10, 2012 at 04:29 PM.
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Just to put an ending on this thread. Long story short spark plug wire 8 and 6 were crossed, and I put them in to their right places: now the car runs like a monster again. In closing, I am an idiot and should of double checked wires on the passenger side. Lesson Learned!
Thanks for all the input everyone.
Thanks for all the input everyone.
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Cylinder 3 missfire My 97 Firebird Formula now has a cylinder 3 misfire after I changed out the head gaskets using FelPro. Do you mean to tell me (if I read this correctly) that if I swapped cylinder 6 and 8's spark plug wires when reconnecting everything I could get a code telling me cylinder 3 is misfiring!?
One of those two cylinder's spark plug wire ends has a metal shield on it the other doesn't. Isn't it 8 that has the shield?
One of those two cylinder's spark plug wire ends has a metal shield on it the other doesn't. Isn't it 8 that has the shield?
My 97 Firebird Formula now has a cylinder 3 misfire after I changed out the head gaskets using FelPro. Do you mean to tell me (if I read this correctly) that if I swapped cylinder 6 and 8's spark plug wires when reconnecting everything I could get a code telling me cylinder 3 is misfiring!?
One of those two cylinder's spark plug wire ends has a metal shield on it the other doesn't. Isn't it 8 that has the shield?
One of those two cylinder's spark plug wire ends has a metal shield on it the other doesn't. Isn't it 8 that has the shield?
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My 97 Firebird Formula now has a cylinder 3 misfire after I changed out the head gaskets using FelPro. Do you mean to tell me (if I read this correctly) that if I swapped cylinder 6 and 8's spark plug wires when reconnecting everything I could get a code telling me cylinder 3 is misfiring!?
One of those two cylinder's spark plug wire ends has a metal shield on it the other doesn't. Isn't it 8 that has the shield?
One of those two cylinder's spark plug wire ends has a metal shield on it the other doesn't. Isn't it 8 that has the shield?
your issue is specific to cyl 3...check "carefully" that plug. Also The injector plug for that cyl. You may have crossed a plug wire so # 3 is no longer firing when it is supposed to, if at all, so yes you could also have a crossed plug wire. double check your plug wire routing. Always a good idea to use dialectic grease inside the plug boots
Those factory heat shields can be problematic in that a plug wire boot can arc between it and the heat shield...making it about impossible to see the arc. I don't use them anymore FWIW
