captcorvette

My wife's baby is a 2000 Camaro Z28 convertable 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. Intersperced with my spirited driving on the one time a year when I get to play with it----during registsration 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 recieved 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.

I have run out of RPM, airspeed, altitude, runway and most importantly IDEAS. However I do have one other attribute----I easily listen to others with more experience, ideas and suggestions.

I may not be Ross Periot but I am all ears.

Now to tell the wife the continuing bad news that
she will not drive this in the upcoming parade.

It goes without saying that all help keeping me out of the dog house will be greatly appreciated.

Nickshookie

Cant help you on the smoking or the sound aspect however with the misfire it could be as easy as a bad coil pack. Im sure you could try to swap it with another one of the other cylinders coil packs and if the misfire moves to the other cylinder the coil pack is your issue. That was what was wrong with a v6 bird i had. Gl!

kaharvey88

iTrader: (9)

Have you thought of leaking brake master causing brake fluid to be pulled into the engine through brake booster? May sound stupid, but I've heard of it before. Should be able to check brake fluid level and pull vacuum hose on booster to verify. Hope you get it figured out and good luck!

01M6TA

iTrader: (1)

why would you be in the dog house because her 15 year old car is broke! i dont care about miles...its 15 years old!! sounds like either a massive vacuum leak or possibly bad fuel. how are you treating the fuel with it sitting for so long? Im thinking bad fuel cause vacuum leak shouldnt cause smoke.

captcorvette

Yes I agree the car is 15 years old. However it has been in our possession its entire life. The car is inspected, cleaned, serviced and cared for on a weekly basis even if it is not driven but around the block. 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 not cleaned the injectors and that is on the list if I cannot find any other suggestions that make sense or that I have forgotten to perform.

As a side note. I have a hobby garage that have had for over 25 years and my car collection get regular attention from me now that I have semi-retired. I am not a trained auto mechanic but have been working on cars, motorcycles and aircraft all my life. Have a Launch scanner, 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. Therefore the purpose in my seeking guidance from others with more direct experience on the LS1.

I agree on the 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.

Excuse the verbosity please but this is important to me and I enjoy learning new things. If I have stepped on toes I do apologize. Nothing in this post was meant to be aggressive, argumentative or boastful. Just a serious inquiry and request for assistance and education.

im28702

My c5 had an O2 sensor wrote that was intermittently grounding causing what you speak of, and it didn't throw a code. Could be a falling upstream O2 sensor...

captcorvette

Thanks for the suggestions. Checked brake fluid and was same level as always. Checked O2 sensor seemed OK but replaced it with one out of my C5 roadster. No change and the C5 ran fine with the switched sensors.

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. Any ideas out there?
Thanks,
Capt.

97camaroguy

iTrader: (5)

Well something that would change from the point of start up to the 3-4 minute mark would be your ECM switching from open loop to close loop.

You should dig deeper into the oxygen sensors I think the previous fellow might have had something there.

Replace both upstream ones for starters with brand new ones. Don't be swapping old parts as they can never definitely rule out anything.

Does your scanner interpret oxygen sensor data?

97camaroguy

iTrader: (5)

Check out this link. It is a different motor but sounding like the same issue that you're stating

https://ls1tech.com/forums/lt1-lt4-modifications/1663643-oxygen-sensors-longtube-headers.html#post17564605

captcorvette

Thanks for the info.. Will check this out first thing tomorrow morning when I go back to the shop. Scanner is Techscan 7000 so not sure about the information I am getting on the 02 sensors. Will dig into the manual a bit and see. Thank you very much.

captcorvette

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?

Bowtie316

iTrader: (1)

Definately check o2 sensor voltages. Also look at fuel trims after it goes into closed loop.

What about mass air flow, does the pcm ignore this until closed loop? Might take this connector apart and make sure it's clean and dry.

97camaroguy

iTrader: (5)

Check into the o2s but first disconnect the coil pack main harness on each side and blow out both connectors real good. I've seen this happen to a car right after being hit with the pressure washer

01WS6/tamu

iTrader: (37)

Pull the PCM connectors and look for water intrusion in the connector shells and on the pins in the pcm.

01M6TA

iTrader: (1)

i think the guy is spot on with the open loop-closed loop. check MAF...possibly replace. it may have gotten wet.

captcorvette

OK thanks again for all the suggestions and education. 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.

Am I still all wet on this diagnosis?

Bowtie316

iTrader: (1)

It can certainly still be a single O2 sensor. Buy you an obd2 bluetooth adapter and get torque pro app for android or equivalent Iphone app, It will cost you about $20. This will be the cheapest way to scan all of the engine parameters.

captcorvette

OK some progress but still have the same basic fault/code. Still PO300 multiple cylinder misfire. My scanner while doing a current read on misfire shows only number 4 & 5 cylinders. All other cylinders not indicating a miss. Have changed the 4&5 coils, no improvement, 4&5 plugs no improvement, 4&5 plug wires with no improvement. Car does seem to run without missing until it goes into what I assume is "closed" loop at the 3 to 4 minute mark or when the temperature comes up to normal which over here is very quickly.

On the highway and with higher rpm's there is no indication on the scanner of any of the cylinders missing. Idle sensor the culprit? Something else to look at? MAF? OR? Still really confused about what is happening with this motor.

Majestic9C1

iTrader: (19)

check the EGR valve if it still has it.. also check all the vac hoses for cracks or splits..

blackbyrd

iTrader: (14)

its an odd request but try this

get it in the garage with no-low light. turn the car on and inspect the valve covers and look for electrical arc'ing.

unfortunately as our cars age the wiring becomes more and more brittle and what you could have is a worn spot on the bulk harness for your coil packs were it wraps around the corner on the rear of the head. Inspect that and see if you can either see an arc, or if you can find any areas where the wire core is exposed.

essentially its voltage dropping the ignition signal so a cylinder isnt getting a full spark. If this is your problem of course.

It takes quite a few cycles for the ECM to narrow down a misfire, so if you are getting a random misfire code dont clear it out let it keep going. the system runs a series of checks before it gives a fault code, but it needs to follow its process of counts before determining which cylinders are misfiring. If you clear the code you clear the counts and it has to start all over.

i might also check the grounds on the back of the heads for corrosion