Hey everyone,
Here's the situation:

2001 coupe. 40 K miles. When I test drove the car about a year and 5 K miles ago the engine was pinging a little but I happened to know that the dealer had put regular gas in it. They ran it out and filled it up with premium and there was no problem, even in 5th or 6th gear with the throttle floored. Just came back from a 4 K cross country and during it I started to notice some knocking under hard acceleration. Thought it might have been some bad gas but it has continued after several tanks of premium. I'm currently working with my Chevy dealer doing a oil consumption test to collect data points so I can take the amount of oil I'm burning (approx 1 quart every 1000 miles in city driving, and I do drive the car quite hard) to fight GM to get the redesigned 2002 pistons installed. Don't know if the oil consumption/piston slap (moderate when the engine is cold) problems may contribute to this new engine knock. Any suggestions? Would rather take it to a Corvette specialty shop since it is out of warrenty, but maybe it's better to address this with the dealer as part of a connection to the oil consumption/piston slap problem.

Thanks,
Mark

 

Original plugs?, if so go with iridium..........

 

Plugs causing pre-detonation?? How? I was originally thinking something might be up with the timing but that should all be controled by the ECU. Unless the ECU might be going bad.?

 

Check the knock sensors. There is a service bulletin about the knock sensors going bad so maybe you won't have to pay for it. I had the exact same problem in my 2001 and that was the cause. Also, even with a bad tank of gas, the knock sensor should retard the timing so that it wont ping thus I think its probably one of the knock sensors.

 

That's what I'm talkin' about! Thanks. Knock sensors would make sense.

 

You're welcome! Let me know how it works out. Here is the technical service bulletin. Print it and bring it with you to the dealer. Good luck!
alain

http://www.corvetteactioncenter.com/....php?qstId=261

 

With 40K miles and just doing 4K across country with different types of smog fuel the O2s at this point could be too lazy and or too dirty.
Maybe 1 or more injectors are too dirty and partly clogged.
Somewhere between aircleaner and throttlebody loosened up and is sucking more air in.

 

Also at 40K it would be worth it to de-carbonize the engine.

 

mpmussel,
My stock plugs were so bad I couldn't believe the car was still running. Yes, bad plugs can cause pinging. Read this. Its about airplane engines but the basics still apply. Its easily one of the best articles I have every read on the subject in its presentation and real-world perspective.

http://www.avweb.com/news/columns/182132-1.html

Detonation is the uncontrolled "explosion" of the fuel charge in the cylinder as opposed to the controlled flame front that generates from the top of the cylinder via ignition by the spark plug.

If the spark plug is bad, then a small ignition event is started, but it isn't hot enough or fast to complete the burn so it creates a very localized flame front that starts the problem. Due to the small ignition event the unburned portion of the fuel/air mixture pressure rises VERY quickly and explodes, causing the ping.

Usually, when your ignition system is healthy, the flame front is ignited by the plug at the proper time (i.e. timing advance etc) and generates a nice, relatively controlled burn as opposed to letting Mother Nature and Sir Isaac Newton go hog-wild inside your cylinder.

A bad plug cannot generate the spark necessary to ignite the fuel charge in this controlled manner. Worse yet, is a combined event where the weak spark contributes to the rapidly increasing pressure of the unburned fuel/air mixture and a hot carbon spot on your piston that does the same thing on the piston end of the cylinder. The result is two detonation "events" that meet in the middle of the cylinder (one travelling down, and the other travelling up) GREATLY increasing pressure within the cylinder.

Instead of chasing down the knock sensor issue, FIRST do a decarb, THEN change your plugs and use a good copper NGK like a NR-55 (if memory serves)...do them in that order as the de-carb process may foul your new plugs.

I think your pinging problems will go away. I do agree that your excessive oil consumption may (as well as your crank-case vent...probably time for a catch-can) contribute to the problem by creating more carbon build-up in your combustion chamber. Slow RPM driving will also lead to excessive carbon build-up...the famous 1600-rpm-80-MPH-in-6th-gear-on-a-long-road-trip kind of slow.

Of course, thats just from my VERY basic knowledge of the phenomena, and it has served me well in the air at least. I don't want to be accused of putting out bad info as the gospel...not an expert and don't claim to be one either. FWIW

R/
Dustin

 

Even if you put 87 octane in the car, it shouldnt ping!!! You have some sort of a problem! Yes, excessive oil comsumption can cause ping. It can also cause excessive carbon in the combustion chambers (raises compression and cause hot spots) which would need to be removed using a decarb procedure. If the knock sensors are NOT doing their job, you will also hear knock! With premimum fuel and a properly operating engine, you should see ZERO knock!!!

BC

 

If your burning that much oil you've probably got enough crap built up in your combustion chambers and the tops of your pistons to cause some detonation, try doing the decarboniztion procedure.

 

Thanks Dustin,

What is the catch-can and crank-case vent? I've heard this before but never really understoond.

Mark

 

What do I do for the decarbonizing procedure (i.e. dealer job?). I was going to get some Techron fuel injector cleaner for the first step of troubleshooting, along with taking a look at the sparkplugs.

Mark

 

Use Sea foam

 

Crank-case vents allow pressure inside the crank-case to be relieved (sometimes to the atmosphere). On the Corvette, it is plumbed back into the the throttle body (positive crank-case vent).

Oil vapor is present in the pressurized "gas" that is being vented out of the crank-case and since it goes back into your combustion chamber, you are burning a combination of oil vapor, air and fuel...the burnt oil is deposited on the piston tops and combustion chamber as "carbon".

From what I have read, oil vapor can also effectively reduce the octane rating of gasoline although I don't know anything about the subject...just relaying info, good, bad or otherwise. It does seem to make sense though, as octane is simply the gasoline's resistance to detonation.

A catch-can is a device that is plumbed into the vent line before it goes into the throttle body. The open chamber within the can allows for the heavier oil vapor to "distill" (for lack or a better term) out and collect as liquid oil in the bottom of the can. The lines going into, and out of the can are mounted on the top. Relatively cleaner air is then vented back into the TB reducing the carbonization of the combustion chamber and pistons.

Do a search...there was a great thread illustrating the plumbing of the catch-can.

Again not claiming to be an expert, just stuff I have picked up in the past. The catch-cans DO work...you'll be surprised to see how much oil you'll drain out in a short time. Some cars vent more oil vapor than others, though so YMMV.

R/
Dustin

 

1 quart / 1000 miles is a bit of oil! That may be directly related to your pinging. Try a PCV catch can to see if the pinging is reduced!

 

Hi Mark,

As an additional aide, here is a helpful link to the Decarbonization Procedure for the C5:

https://www.corvetteforum.com/techti...=212&TopicID=1

Best Wishes to you.

 

The only problem is if he's using this much oil then it's coming in thru the oil control rings and a catch can will not solve this.

 

yep....you are correct!

 

Seafoam will get rid of the most stubborn carbon deposits, especially gets rid of the PCV oil getting sucked in. Just get the Seafoam and a LONG length of 3/8 inch vacuum line. Enough line to go from the PCV vacuum source all the way inside the car from the passenger side window (this way YOU can control the flow of seafoam into the intake and control the RPMS by yourself). It's cool and fun to do. Do this to a fully warm engine. Race the engine to about 1000 to 1500 rpm, keep it steady. Stick the end of the hose into the can and suck up a little seafoam. Your RPMS will drop, so make sure you keep it running. The last inch of seafoam in the can.....suck it up and STALL OUT. Let it sit at least an hour, eben overnight if you want to.

The next day, it will be real hard to start, but it will eventually and get ready to smoke out your neighbors. Clear it out best you can and drive away (your neighbors will appreciate you leaving town !). Then blow the hell out of it untill there's no more smoke.

Done. Still pings a little, trry it once more. Then change the oil since it will be filthy.

Good luck. And if you change plugs BEFORE you do the decarb....go for the Delco iridiums. They are the best. And don't gap them, you will ruin them if you do.