npbassman

On a 93 LT1, ZF6 I seem to have some pinging under medium load mostly while cruising/giving it a little gas in 5th or 6th. Honestly, I'm unsure if the pinging is new or not because I just changed out a very loud exhaust for a Corsa system. Now that I can finally hear other things inside the cabin, I notice a ping that may or may not have been there all along. I have yet to see if the car is throwing any codes.

Assuming that the ping is new, I have made only two changes this season. First is the addition of a 2.5" Corsa cat back system which replaced a 3" flowmaster system. I know that the Corsas are considered one of the top flowing exhausts for these cars but surprisingly I did notice a little bit of power decrease after I installed them. Any chance that I need a retune due to a little more back pressure? I'm unsure if the PO ever got a custom tune or if I'm stock.

The second change is, I added some Chevron to the tank this spring because my fuel gauge is stuck. It's slowly working the gauge loose but it is an additive to the fuel so I'm wondering if that can contribute to a ping.

Finally, this is not a change but one thing to keep in mind is most of the 93 octane gas in there right now is from last year mixed in with some stabil and now Chevron.

So what do we think here? Should I be patient and just see what a fresh tank of gas does? Should I add octane boost to the current tank of gas? Do I need a tune?

Thanks for the help!

racebum

bad gas
excessive oil burning
too much timing
bad plugs / wires


those are a few of the more common causes

GREGGPENN

yes

no, just don't "force" it to ping. you can refill it once it gets below 1/2 tank to dilute the older gas. (Repeatedly)

Tune up? Maybe....but do the fresh tank first. Drive it more and don't assume it needs a computer tune unless you've changed something from the OEM config.

383vett

Check timing, check egr.

samsonb

Just curious how bad wires would cause knock on acceleration?

Could a clogged/clogging cat cause knock?

leesvet

weakens the spark. sometimes spark is 'late' do to higher resistance, less voltage because of energy leaks, cross firing from other wires.

if anything, a clogged cat would smooth it out with the excess backpressure maintaining tension on the piston. There would be no power, but no knock either.

samsonb

I had read of a clogged cat making the engine run hot, which could cause it to detonate.

I had put in a new negative backpressure EGR valve in mine due to getting knocks and noticing the valve was bad. The EGR valve holds vacuum when I test it with my mightyvac. But with the engine running, I can't pull a vacuum on it, and I can't get the engine to stumble. I was thinking maybe too much backpressure was keeping it from opening as it opens just fine with the engine not running. You should be able to open the EGR with the engine running under vacuum to get it to stumble. I may just get the cat pulled and a pipe welded in its place just to rule that out.

npbassman

Just a follow up here. I think I may have found out what my problem was with the pinging. After I created this thread, I drove it until I had about about 1/4 tank to go. I then filled it up with "fresh" 94 octane at a Mobile station and it still ran like junk. As a matter of fact, it ran worse! Basically pinging all over the RPM range, noticeably less power, etc.

Read this.

I have only driven the vette 3 to 5 times since that last fill up (mid/late May) so I still have 2/3 tank left from that time frame. I took her out last night to run an errand and the entire time I'm thinking - WTF is wrong with this thing?? I then read the article. So, this morning I decided to throw some octane boost in there and wouldn't you know, it wakes the car right up. Pinging gone. Power back. Son of a.....

I don't think it is mentioned in this article but I read somewhere that fuel in some gas stations were being cut with 15 to 20 percent water.

Now the question is, should I siphon that stuff out or just let it run down with the octane boost?

mcsports965

WTF water in fuel at gas stations???
Ive heard of water seeping into underground fuel tanks at gas stations due to wear and or faulty set ups but never intentionally added....
Wouldnt that cause a lot more damage to your vette then just pinging and knocking?

basselope

Some amount of water in under ground fuel storage tanks is pretty much a given, so these systems are designed with that in mind. The fuel pickup in the storage tank does not quite reach to the bottom, leaving a space for water and sediment to rest since gasoline is lighter than water and will separate and rise to the top. The tanks are "supposed" to be monitored (either by a sensor or the old fashioned "stick and putty" method) and the bad stuff pumped out when the water level rises to a certain height.

That said, it is still possible for some of the gunk in the bottom of the storage tank to be stirred up during fuel deliveries to the station. Additionally some (and I stress "some") fuel pumps are equipped with an in-line check ball that is glued in place with an adhesive which instantly releases in the presence of water, shutting off the pump and keeping you from contaminating your vehicle. You would have to ask at the individual station to find out whether or not their pumps are equipped with this type of check ball.


I'll also toss in a little personal experience with ping in my 94 LT1.
At 110k miles I pulled out some nasty looking Delco spark plugs and replaced them with a set of NGK TR55GP plugs. I immediately noticed better starting, idle and power. I also started to experience light pinging under medium load. On my next fill up I moved up to the next higher octane fuel and everything has been great ever since - about 2000 miles.

Just my 2 cents, but I wouldn't be too anxious to "fix" anything until you run out all of that old gas. If you still have pinging, pull a spark plug to make sure the ones you have aren't eroded away. Always start with the simple things. Even though you are driving a vette, it's still a car & follows the same rules as other cars. Beyond that, this forum is a great resource with lots of friendly folks willing to help out a fellow driver... always my first stop when I have a project.

Happy Motoring!

pcolt94

I think you maybe mean ethanol (alcohol). That would have some sensibility to what you are saying.

You could pull the pump unit out and check at the sock for derbies and look in the tank to see if you can see any water at bottom.

On a stretch of a suggestion,
I might also want to check the fuel pressure under load to make sure it stays at the proper psi levels. It might ping if it got to lean.

Roustabout

(1994 lt1 vette stock)
really hopefuli posting write area
Replaced opti a year ago. All issues but ping gone.. it seems to be most on warm day. I just pushing 74000 miles. Issue It comes a goes. No codes.. it just at point busting into pinging. never really getting onto pings but its starting.. power is not there At this point .. kick it down it comes alive. Wires new and plugs. New opti new water pump. All hoses new. The engine temp not seem play into it. outside temperature seems to.
sometimes it will do it cold out sometimes not do it. Maybe like more chance when it's hot out. I sure likely to do it on a warm day there are times cool warm same . The car is pretty much stock.
i think mpg is down a gal or 2 unless i remembering wrong. Town 16 to 17.. free way 21 to 23.
combination 17 to 20 freeway and cities

Whaleman

Did a job at an airport. The fuel tanks in ground had a hand pump from the bottom of the tank. Every week they would pump with this hand pump until what the got was pure gas. Dan