P0300 code on 2000 Camaro Z28

**captcorvette** · 03-09-2015, 10:44 AM

My wife's baby is a 2000 Camaro Z28 convertible with the LS1. She doesn't drive it much since we bought it 14 years ago. It has 18,700 miles on it and all with her sedate driving. Interspersed with my spirited driving on the one time a year when I get to play with it----during registration trips.

Six months ago on the way back from registration, which it passed with flying colours, it started running like a washing machine. Missing, no power and alternating between black (fuel) smoke and light grey smoke (coolant?). One the 16 mile trip home the check engine came on all the way to the house.

Did the normal checks, plugs, wires, coolant level, oil level, pulled plugs etc.. Nothing out of normal. Put my scanner on it and it shows "random multiple cylinder missfire). At my whits end trying to figure this one out.

No consumption of coolant or oil. No mixing of fluids. Plugs all look normal. Once the scanner gave me a #7 cylinder missfire so I double checked it. No issues and started the car again and never received the #7 missfire again. Still just the random multiple cylinder missfire code and nothing else.

I put the car to bed for a few months as it was so frustrating. Today cranked it up again and for the first couple of minutes ran perfect. No missing, no smoke. Then after a couple of minutes running I shut it down to re-check fluids and all other components that came to mind. All normal.

Cranked the engine up again and this time after it started it gave me one rather loud noise just once that sounded like to metal planks hitting each other---but just once not more times. Just the once. But the very light grey/white smoke at all RPM's.. Car will go WOT with ease but I don't keep it there but momentarily than back to idle. Smoke all through the cycle until shut off.

Fuel is kept full but a product like gas-renew is added when the fuel is getting stale or when the fuel smell from the tank is suspect.

Coils were all tested with a new coil out of the box replacing each coil in turn with no change in the symptoms or the problems.

Have a Launch scanner, and AutoTech 7000 scanner and a GM Tech I. However it has been my experience that sometimes people (read me) make the same mistake over and over thinking they doing things correctly not realizing their initial mistakes. More minds on the problem should help with the solution. Yes could just take it to the agency but local agencies will not accept cars over 8 years old. Could push the issue but that doesn't usually help with an objective inspection when the inspecting mechanic has already had his nose twisted by having to work on "old cars". None of the scanners have provided me with any accurate information regarding this problem that I can find or understand. I might just be looking for the wrong inforamtion and not understanding what I need to look at and why. Therefore the purpose in my seeking guidance from others with more direct experience on the LS1.

Sounds like a vacuum leak but I am a babe in the woods on the LS1. Vacuum leaks on an LT-5---yep loads of experience as have had my ZR-1 for many years and it is vacuum sensitive. I can ALMOST pull the plenum with my eyes closed.

LS1? Not much experience but it does in fact sound like a vacuum pipe off the sensor but I cannot find such an animal on this engine.

Checked the car a bit more this morning and it runs fine, no missing and no smoke for the first 2 to 3 full minutes. Then starts making the smoke, missing and running rough at about the 3 to 4 minute mark. To me it would appear that the issue is only showing up when a "sensor" is feeding information into the computer. Not experienced enough to know which sensor would give this type of incidation when it has failed or is malfunctioning.

Some new information the wife just passed along to me. She had the engine steam cleaned the day before this all started and I was not aware of that fact. Possible factor? Perhaps the guy with the pressure washer taught a part to swim? Did check the PCM connectors but no sign of water in them. Used some electra clean on them for good measure.

I have now checked the MAF, the connections to all the sensors, opened and checked (cleaned with electric contact cleaner) ECM connectors. Also blew the coil connectors out, made sure they were dry and then gave them a shot of electric clean. No indications of any problems with all the above. Checked the car and cleared the code. Let the car sit for a couple of hours until it was cold. Started and exactly the same events happened in the same order and same timings. I am under the impression that the 3 minute is a common point for many engines to go from open loop to closed loop. Was told that it was a function of temperature but one of the mechanics that works on the F1 course here poo pooed that stating it was a function of time only and gave me references galore. One even from a physics forum discussing Stoic--which OK now I get that bit.

Car runs well until 3 minutes. To me, and again I will always listen to more experienced voices, it seems this has eliminated everything except the ECM and the 02 sensors. But it would mean that BOTH 02 sensors failed at the same time. The only code is still the P0300 multiple random cylinder misfire. I don't appear to be any further along on this problem than I was back in August. Any sage ideas and or advice? Thank you.

**pajeff02** · 03-09-2015, 12:02 PM

Welcome to the site. The fact that it runs ok in open loop, and then acts up when it switches over to closed is somewhat telling. Unplug the MAF sensor and tell me what it does.

**captcorvette** · 03-09-2015, 08:04 PM

Originally Posted by pajeff02

Welcome to the site. The fact that it runs ok in open loop, and then acts up when it switches over to closed is somewhat telling. Unplug the MAF sensor and tell me what it does.

Thank you. I am 9 hours ahead of you so will try it first thing in the morning and let you know. Start the car without the MAF sensor plugged in? Or start the car then unplug the sensor? Think someplace in the process I did exactly that but the smoke was still present. Will try both procedures again and get back on the site.
Capt.

**35th-ANV-SS** · 03-09-2015, 08:53 PM

Start it with it plugged in....once symptoms start, unplug it and see it the stumbling stops.

**captcorvette** · 03-10-2015, 02:18 AM

First thing this morning started the car after looking over all the general items to see if any new visuals were there like fluid levels etc.. All the same. Car ran just fine for a bit over the 3 minute mark. Then the white smoke and slight missing started. Took photos of the smoke. Removed the MAF sensor plug. No change. Still slight miss and white smoke. Let it run about 5 minutes but had to open the double garage doors to have the smoke exit before it activated the smoke/fire alarm system. Symptoms stayed the same. Accelerated the engine up to near 3,000 rpm and held it there, then slowly reduced the RPM's. No missing during high RPM, acceleration or De-celleration. Once returned to idle same slight miss started. Scanned the codes as the check engine light was on from the time the missing/smoke started. Two codes. One P0300 which was the second code and the first code was MAF low voltage. Shut the car down. Restarted and waited for the check engine which came on at the 3 minute point. Only the one code----P0300.

**0rion** · 03-10-2015, 05:46 AM

Either I missed it or you didn't say.....have you checked fuel pressure? I don't really think that's the issue but worth checking off the list.....should be 58psi.....miles on fuel filter? One thing that comes to mind is the coolant temp sensor. Look at the sensor data in your scanner and make sure it makes sense.....same for the air intake sensor. Just make sure those make sense. If it's 40f outside make sure those sensors aren't showing -20f or something crazy like that. Are there no other codes than the misfire? I had also though maybe you had a stuck air pump valve that's dumping fresh air into the exhaust stream creating a false lean condition but that should throw a code if that's the case.
It does sound to me from what you're describing that the car is running fine in open loop but as soon as it goes to closed loop something is skewing the fueling on the car. That kinda narrows it down to the things I've listed. The MAF controls fueling on cold starts so if it were the MAF it *should* do it at first start up. My guess would be one of those things I listed in the order I listed.

**captcorvette** · 03-10-2015, 06:18 AM

Have not put the pressure gauge on the fuel rail but just checking visually via the schrader valve the pressure appears to be good. Fuel filter has the same mileage as the car. 18,500 miles. Have not checked it but will first thing in the morning. Will also check the sensors are showing something logical. There are no other codes other than the P0300. When the car's rpm's are increased the missing goes away but the white smoke is still present.

**JayTA98** · 03-10-2015, 09:02 AM

I will also check the fuel pressure as suggested with a fuel pressure gauge. It could be your O2 sensors. Have you checked all around and underneath for any melted wires?

I used to wash my engine all the time but not with a pressure washing machine and I never has issues. You mentioned vacuum leaks. Do you hear one? If so have you checked the whole PCV plastic tube that goes around the back of the intake from one side to the other?

**captcorvette** · 03-10-2015, 09:29 AM

I do not hear any vacuum leaks my concern is that this engine was acting just like my LT5 with a vacuum leak on with the stumbling etc.. I still cannot find the 02 sensors. Have the diagram that shows where they are on the exhaust but I cannot find them or the wires that do to them and I have looked all around the exhaust shields with a light and remote mirror. Also I don't remember right off the PVC tube you are asking about but it just might not have impressed me as being suspect or out of place. First thing in the morning will give it a thorough look. Car has never had a heating issue and no wires look to have been excessive heat exposed. Will double check that also tomorrow morning. There are two "plugs" one in each exhaust just above the collector but for the life of me I cannot find any 02 sensors or the wires that would go to them. I guess I will get out my little remote TV camera and have a complete look in all the nooks and crannies. Thanks for the reply.

**0rion** · 03-10-2015, 11:12 AM

Originally Posted by captcorvette

I do not hear any vacuum leaks my concern is that this engine was acting just like my LT5 with a vacuum leak on with the stumbling etc.. I still cannot find the 02 sensors. Have the diagram that shows where they are on the exhaust but I cannot find them or the wires that do to them and I have looked all around the exhaust shields with a light and remote mirror. Also I don't remember right off the PVC tube you are asking about but it just might not have impressed me as being suspect or out of place. First thing in the morning will give it a thorough look. Car has never had a heating issue and no wires look to have been excessive heat exposed. Will double check that also tomorrow morning. There are two "plugs" one in each exhaust just above the collector but for the life of me I cannot find any 02 sensors or the wires that would go to them. I guess I will get out my little remote TV camera and have a complete look in all the nooks and crannies. Thanks for the reply.

the plugs you're seeing are the O2 sensors. Should be a harness coming from it down to a connector that drops off the k member. There are 2 more after the cats but only the 2 up by the manifold control fueling. I would be surprised if the sensors are bad at 18k miles but I guess stranger things have happened. As for the vacuum leak the most common spot by far for vacuum leaks on these cars is where the pcv line turns to go into the intake manifold behind the throttle body. That line likes to crack right on the backside of that bend. You wouldn't see it until you pull it off to look at it. Typically with a vacuum leak you'll have a change in the idle of the car due to the extra un-metered air entering. Again.....not something I would suspect from what you're describing but free and easy to check. As you can tell from the posts......there's a laundry list of things it *could* be so it's just a matter of you knocking these things out one by one until you find the culprit.
Can you look at fuel trims with your scanner? If so look at your long term fuel trims and see what they are and post those up. Also...check that fuel pressure with an actual gauge. I've seen a drop by just a couple psi keep a vehicle from even starting. Not something you're going to see by just pushing on the valve.

**pajeff02** · 03-10-2015, 02:58 PM

Is there any odor to the smoke you are experiencing? Does it smell sweet like coolant, rich like raw fuel, or in any way oily?

**captcorvette** · 03-10-2015, 07:53 PM

The smoke has no smell that I can tell. Doesn't look or smell like oil burning smoke. Doesn't look or smell like unburned fuel. Does not have the glycol burning smell. Looks, smells like steam. Yeah I know if it looks like a duck, quacks like a duck----but I cannot find any fluid being consumed. That is what has me scratching my watch and winding my butt.

**0rion** · 03-11-2015, 01:46 AM

what kind of temps are you guys seeing there? I have no idea what kind of weather patterns you guys have. Is it getting cool enough at night that you could be seeing condensation burning off on first start up? The LS1 is notorious for condensation.....at least out here. The 04 GTO I had was probably the worst car I've ever had as far as condensation but the fbody does it too. I could actually hear the water gurgling in the mufflers on the GTO and it would spray it out the back when you rev'd the car up. The fbody will drip out of the cutout. Sounds to me like that's what you're describing.

**pajeff02** · 03-11-2015, 03:12 AM

Certainly sounds like condensation.

**captcorvette** · 03-11-2015, 03:13 AM

This is our "driving season". We have about 9 months of temperatures between 60F at night and low '80's in the day time. Weather will start to change at the end of April. Now we are in the sand storms followed by light mist or fog.

Checked the EGR pipe today and all is good. Put a welding rod up the exhaust with a white cotton cloth on it. Came back out black with some type of petrol based oil. Smelled like WD-40. I double checked the oil, coolant, brake resavoir and could not see any decrease in level. Now I am wondering if the "inspection" place at the DMV might have sprayed WD40 or the like in the intake. I have heard of them doing this to check their "sniffer" machines. Don't ask as they do lots of things that are strange here. If they did wondering if this would have started this problem? If it did happen and it is causing at least part of this problem then how would one correct this massive SNAFU?

Humidity here goes from about 30 ish % to high '90% but that usually only happens in the hot months when the temps are normally low 100's F at night and mid 120's F daytime. Normally condensation is not an issue except when the temperature dew point are close.

Did not see anything that raised a red flag with the scanner hooked up and taking running readings. Still stumped here.

**pajeff02** · 03-11-2015, 03:15 AM

The PCV systems on our cars are notorious for sucking oil. Usually not enough to drop the oil level unless your engine sees sustained high rpms, but enough to coat the intake and run it through the combustion chambers.

**0rion** · 03-11-2015, 03:21 AM

yep....and you'll have some soot in the tailpipes just due to incomplete burning. Completely normal....especially with the misfires. I have a feeling it's condensation. Does it go away once the car is good and hot? What about those coolant temp and air intake temp readings? Still need to check fuel pressure too.

**captcorvette** · 03-11-2015, 03:29 AM

This is our "driving season". We have about 9 months of temperatures between 60F at night and low '80's in the day time. Weather will start to change at the end of April. Now we are in the sand storms followed by light mist or fog.

Checked the EGR pipe today and all is good. Put a welding rod up the exhaust with a white cotton cloth on it. Came back out black with some type of petrol based oil. Smelled like WD-40. I double checked the oil, coolant, brake resavoir and could not see any decrease in level. Now I am wondering if the "inspection" place at the DMV might have sprayed WD40 or the like in the intake. I have heard of them doing this to check their "sniffer" machines. Don't ask as they do lots of things that are strange here. If they did wondering if this would have started this problem? If it did happen and it is causing at least part of this problem then how would one correct this massive SNAFU?

Humidity here goes from about 30 ish % to high '90% but that usually only happens in the hot months when the temps are normally low 100's F at night and mid 120's F daytime. Normally condensation is not an issue except when the temperature dew point are close.

Did not see anything that raised a red flag with the scanner hooked up and taking running readings. Still stumped here.

**0rion** · 03-11-2015, 03:35 AM

woops....missed that the first time through. Next up would be fuel pressure.

**captcorvette** · 03-11-2015, 03:35 AM

This is our "driving season". We have about 9 months of temperatures between 60F at night and low '80's in the day time. Weather will start to change at the end of April. Now we are in the sand storms followed by light mist or fog.

Checked the EGR pipe today and all is good. Put a welding rod up the exhaust with a white cotton cloth on it. Came back out black with some type of petrol based oil. Smelled like WD-40. I double checked the oil, coolant, brake resavoir and could not see any decrease in level. Now I am wondering if the "inspection" place at the DMV might have sprayed WD40 or the like in the intake. I have heard of them doing this to check their "sniffer" machines. Don't ask as they do lots of things that are strange here. If they did wondering if this would have started this problem? If it did happen and it is causing at least part of this problem then how would one correct this massive SNAFU?

Humidity here goes from about 30 ish % to high '90% but that usually only happens in the hot months when the temps are normally low 100's F at night and mid 120's F daytime. Normally condensation is not an issue except when the temperature dew point are close.

Did not see anything that raised a red flag with the scanner hooked up and taking running readings. Still stumped here.