View Full Version : Random Misfire P0300 started today in the RAIN


AgentLS1Z
11-04-2010, 08:31 PM
Is it the 02 sensors??? I've mostly been getting P0300. I got a Misfire on Cylinder #1 code, and a P0113 IAT sensor code. P0300 keeps coming up and its running like its only working on 3 or 4 cylinders. Its pretty bad. It's been raining constantly today and the misfire randomly started today. What do you guys think?

Car is 02 Z28

AgentLS1Z
11-04-2010, 09:39 PM
any 1?

tording99Z28
11-04-2010, 09:46 PM
If you have a misfire on Cylinder 1 then I am sure its cylinder 1. You probably have a fouled plug or a bad wire on cylinder 1. Check the wire first and make sure its on securely on the plug and on the coil pack.

AgentLS1Z
11-04-2010, 09:50 PM
yeah the cylinder 1 code came on only once. Random Misfire comes on now. I'll check it again right now. Thanks for the advice.

tording99Z28
11-04-2010, 09:51 PM
I would still check #1 first then if you don't find anything check the others.

AgentLS1Z
11-04-2010, 10:15 PM
I just went out to check it/test drive it again. Was running fine for 1 minute then started missing again. I checked the code it random misfire came up again. Just P0300. When I had a 98 Z28 this same problem happened and it turned out to be the 02 sensors. I'll check cylinder 1 tomorrow. Should I try swapping the plug and plug wire to cylinder 2 and see if that code comes up? Fuel injectors are fine.

tording99Z28
11-04-2010, 10:17 PM
its possible its an O2 sensor but but I would check the cylinder it called out first then if that doesn't fix it then check them all. Yes you could try swapping the plug wire to a different cylinder and see if it the code changes to a different cylinder. How old are the plugs and wires? If they are original then might be as good time as any to just replace them.

AgentLS1Z
11-04-2010, 10:24 PM
I just got the car in May. The wires are gray and I believe they are original. Car has 76000 miles. Also, after driving it smells like burnt toast in the engine bay. It almost smells like a burnt clutch. Any ideas?

Kevin01Z28
11-04-2010, 10:55 PM
I agree, check the number 1 cylinder first. How bad is the miss? Does it feel like one cylinder, or is it just running like total shit (like a whole bank is missing)?

If you had a way of logging the car, or even a handheld tuner where you could see the O2's mv readings you could easily rule those out. You could however wait till the car cools completely, crank it up and drive it before it warms up and falls into closed loop and see if it misses. If it doesn't miss at first and immediately does after its warm, then there you go. I just got a P0300 code today, because of a bad o2 senser...

AgentLS1Z
11-04-2010, 11:03 PM
yeah it runs fine when its cold then goes into miss mode. Feels like a whole bank! Runs like total shit. 02?

Kevin01Z28
11-04-2010, 11:14 PM
yeah it runs fine when its cold then goes into miss mode. Feels like a whole bank! Runs like total shit. 02?

Sounds like it to me.. You know anyone that has something you can check them with?

AgentLS1Z
11-04-2010, 11:30 PM
I could bring it to a mechanic. Is there anyway I can check them? Can I switch the front ones to the back?

Kevin01Z28
11-04-2010, 11:41 PM
I could bring it to a mechanic. Is there anyway I can check them? Can I switch the front ones to the back?

Front and rears are not interchangable. For what is costs a mechanic to diagnose it you could buy one. I would rather do that, I don't trust anyone with my car. You already have the misfire code. It may take some time to throw a code for the oxygen sensor, mine hasn't yet

AgentLS1Z
11-05-2010, 09:53 AM
Oh okay...how bad is it to drive the car with misfires?

Kevin01Z28
11-05-2010, 11:24 AM
Depends on how bad it is. Lockup with be disabled, and depending on your stall size will depend on how much extra heat is built in your tranny. Could foul plugs if its running rich on that bank...and being pig rich isn't the best thing for cats. You could remove the o2 sensors and see if they have any build up on them and clean them, worth a shot.

AgentLS1Z
11-05-2010, 12:59 PM
Is it possible that the fuel filter is clogged? I ran my car on empty for a while a couple days ago. The fuel needle was way below E. I put a bottle of Techron Fuel System Cleaner in the tank hoping that would be my problem. Just now the car was running fine up and down the highway and all the power came back. When I went to start it again later the misfire came back and is constantly there. I think I may go with new 02s. Should I get 4 new ones?

Kevin01Z28
11-05-2010, 03:21 PM
Is it possible that the fuel filter is clogged? I ran my car on empty for a while a couple days ago. The fuel needle was way below E. I put a bottle of Techron Fuel System Cleaner in the tank hoping that would be my problem. Just now the car was running fine up and down the highway and all the power came back. When I went to start it again later the misfire came back and is constantly there. I think I may go with new 02s. Should I get 4 new ones?

If you cant remember the last time you changed the filter I would change it. I would leave the rears alone until you get a code for them...I assume you have cats. You could buy one sensor and see if you get lucky the first try, then swap sides if the miss doesn't go away. I doubt both of them are bad.

MR_M
11-05-2010, 03:42 PM
Is it the 02 sensors??? I've mostly been getting P0300. I got a Misfire on Cylinder #1 code, and a P0113 IAT sensor code. P0300 keeps coming up and its running like its only working on 3 or 4 cylinders. Its pretty bad. It's been raining constantly today and the misfire randomly started today. What do you guys think?

Car is 02 Z28

Does the car have headers? Water could be getting on the o2 sensor wires causing the misfire. When it rained, my last car would misfire occasionally. Turns out, my o2 sensor wire extensions connections were getting wet. If you don't have extensions it'd be worth checking the condition of the wires to make sure they're not getting water into the connections/wire itself.

AgentLS1Z
11-07-2010, 04:30 PM
Does the car have headers? Water could be getting on the o2 sensor wires causing the misfire. When it rained, my last car would misfire occasionally. Turns out, my o2 sensor wire extensions connections were getting wet. If you don't have extensions it'd be worth checking the condition of the wires to make sure they're not getting water into the connections/wire itself.


No the car doesn't have headers.

I changed the fuel filter and the car was running good. But now the misfire is back. I'm not sure what the problem is but i'm leaning towards it being an 02 Sensor. I'll scan the codes again asap

themack56
11-07-2010, 04:51 PM
No the car doesn't have headers.

I changed the fuel filter and the car was running good. But now the misfire is back. I'm not sure what the problem is but i'm leaning towards it being an 02 Sensor. I'll scan the codes again asap

i have the same issue random missifres.

i changed the front o2s on both sides and still. changed fuel rails and fuel injectors and still also changed spark plugs and wires and still.

im beggining to think it may be ground related?

AgentLS1Z
11-07-2010, 05:58 PM
i have the same issue random missifres.

i changed the front o2s on both sides and still. changed fuel rails and fuel injectors and still also changed spark plugs and wires and still.

im beggining to think it may be ground related?

hmm, so it could be anything electrical?

themack56
11-07-2010, 06:08 PM
hmm, so it could be anything electrical?

i dont see why not.


ive tried everything. oh and i even took out my fast intake and resealed completely and still. ive checked for vacuum leaks and nothing.

horsepower_junkie
11-07-2010, 11:29 PM
Does your car have a cold air intake? If so it could be possible that you could've got some water on the maf giving you funny readings... How good is your scanner can you watch livedata on your maf, tp.... I would take a look there since it just did it in the rain

AgentLS1Z
11-08-2010, 08:55 AM
I have an SLP lid...Yesterday I drove it and codes P0301 and P0650 came up. When driving it home P0300 came back on and P0650 is still there. I'll try changing plug/plug wire on CYlinder 1. How do I fix P0650?

AgentLS1Z
11-08-2010, 08:16 PM
Okay the P0300 keeps coming back, its the only code now. Light flashes and the car runs very rough. Is it possible that the MAF is bad? Can I disconnect it and see if it drives better. Can I drive the car around with it disconnected?

AgentLS1Z
11-08-2010, 09:09 PM
Okay I just noticed when at night when the autolights are on there is a "humming/crackling buzz" noise near the light swich/fusebox area...when I turn the healights to the on position the noise mostly goes away with some residual cracklin'. Is that a short, or is something not grounded properly??? I recently installed HIDs...i got 55w HIDs no Relay, and they work good.

frack
11-08-2010, 09:57 PM
I had the same issue with mine a little while back. Went through some water and ended up getting some in the connector. Check it and make sure its dry. I used a hair dryer to dry out the connector leading up to the 02 sensor and ended up having to buy new O2. Fried the fucker. It was only 2 or 3 inches of water, but at 60 mph it will cause havok.

Kevin01Z28
11-08-2010, 10:16 PM
Okay the P0300 keeps coming back, its the only code now. Light flashes and the car runs very rough. Is it possible that the MAF is bad? Can I disconnect it and see if it drives better. Can I drive the car around with it disconnected?

Unplug the MAF and see what happens. Yes you can drive it like that, just will default to SD mode and throw MAF codes.

Okay I just noticed when at night when the autolights are on there is a "humming/crackling buzz" noise near the light swich/fusebox area...when I turn the healights to the on position the noise mostly goes away with some residual cracklin'. Is that a short, or is something not grounded properly??? I recently installed HIDs...i got 55w HIDs no Relay, and they work good.

The headlights and fan relays all have a common ground next to the fuse block/driver's headlight assembly under the hood. Shouldn't have anything to do with you missing/stubling issue. Only so many things it can be...have you changed or altered anything else before this issue began???

I also have an SLP lid and have never seen enough water in my intake to cause a MAF malfunction/stumble, or any amount of water that I can remember.

AgentLS1Z
11-11-2010, 01:59 PM
update: I brought the car to the dealership and they cleaned out the fuel injection system and adjusted the cam and crankshaft timing. The guy said that could be the problem and also the sparkplugs and wires could be the problem. They were gonna charge me $600+ for a sparkplug and wire change so I just told him to do the timing and cleaning. He did that and changed plug wire for #7...They charged me $340 for that. When I drove the car home the car was fine but then started to miss again! When I drove it later in the day the car ran fine. It seems that every other time I start the car it misfires. When I notice the car starts to run rough I shut it off and start it again, and the miss goes away! This is kinda odd. My next step is to change the plugs and wires. What do you guys think?

Kevin01Z28
11-12-2010, 02:55 PM
update: I brought the car to the dealership and they cleaned out the fuel injection system and adjusted the cam and crankshaft timing. The guy said that could be the problem and also the sparkplugs and wires could be the problem. They were gonna charge me $600+ for a sparkplug and wire change so I just told him to do the timing and cleaning. He did that and changed plug wire for #7...They charged me $340 for that. When I drove the car home the car was fine but then started to miss again! When I drove it later in the day the car ran fine. It seems that every other time I start the car it misfires. When I notice the car starts to run rough I shut it off and start it again, and the miss goes away! This is kinda odd. My next step is to change the plugs and wires. What do you guys think?

The pcm is in complete control of all ignition timing. What exactly did he do to "adjust" the cam and crank timing..?? Did he pull the timing cover from the front of the engine and adjust the cam/crank sprockets???? WTF..

Its pretty far fetched to think that plugs and wires will cause a dead miss like you described in earlier posts, but anything is possible depending on there condition. You also said that it does fine when its cold/warming up, or open loop. Now the miss is intermittent, and stops im guessing for a brief time after you stop the engine and restart it.

The dealership had to have scanned your car, did they look at the o2 readings, or any other sensors? Sounds like they just read the code and changed some parts. The oscillations should bounce somewhere between 100 - 900mv's while in closed loop, sometimes a little lower than 100. When my o2 was going bad it was reading as high 1100mv, but not always missing until it would just flatline. Then it would run complete shit, ses light would blink, P0300 code. When i commanded open loop the miss was gone. I changed to o2's (went ahead and did both) runs perfect.

The dealership should easily be able to diagnose this.. My advice since you payed them $340, take it back and make them fix it since they didn't the first time.