The car is very new and just broken in. I now have 1500 on the OD and have done 1 oil change, so I decided to open it up a little bit (also have blackwing and Crosa installed and wanted to hear it roar). The first few times, everything sounded great. The car lost almost all traction in first, but pulled very nicely through third. Then the other day I took a friend for a ride and he urged me to show him what it would do. I nailed it and got traction this time (it was very impressive) and he was saying WOW! as he was glued to the seat (this guy has a ws6 TA and he said it felt much quicker than his). I went for it one more time from a roll, but this time I heard some clatter (that sounded like the valvetrain) at the top of 1st and 2nd (around the 5k mark).

I wanted to do some more experimentation, but there were cops everywhere. Since then, the roads have been wet and I have not had a chance to see if it is a reproducible sound. I’ve only had it up in the 5k rmp range 4-5 times now.

Any ideas on what this might be? Could this be the dreaded piston slap? I’m jumping the gun a little here and should wait till I have more details (have an autotap on order), but I figured why not. The forum has worked very well for me thus far.



[Modified by QuickSilver2002, 6:33 AM 4/8/2002]

 

What octane fuel are you using :confused: and are you sure it was your valves

 

Probrably detonation. Once the computer learns your proper driving habits it should adjust the timing as needed. If not have it checked.

Bob

 

Not sure exactly where the sound was coming from, but it sounded clattery (could have been anything, but sounded like something I had in an 80,000 mi pontiac 400).

As far as the fule goes, think I was running 93, but i was actually spacing out the other day in a hurry at the pump and could not remember if I hit the right button.

So, what does detonation sound like? Can you hear it on an ls1, or does the pcm adjust the timing before you can hear it.

 

Can certainly hear the detonation (pinging). When I changed my computer program the first two runs at WOT I thought something in the the engine had broken off and was going through the top of the motor. After the car noticed the program, and my driving habits all was well. Hope this is the case for you also.

Bob

 

It's probably just detonation. You're not going to get valve float unless you're wacking the redline (even then, with the rev-limiter, you shouldn't get any there either) and I think piston slap is turning into a Corvette Forum urban legend.

Let the computer get used to your driving habits and make sure you put in premium gas. It should clear up, if not, see the dealer.

Mike :flag

 

Ok, sounds like it is detonation.

So help me out here, I’m very new to these fly by wire systems. Detonation is caused by a lean condition right! But I read that the fuel tables and PCM fuel delivery algorithm are completely different at WOT compared to non-WOT situations (think it is called power enrichment mode). My understanding is that in this mode it shoots for a 13:1ish (max power) mix, does not adjust short term trims, and only uses the MAF instead of both the MAF and 02 sensors.

So to get adjustments made to the long term fuel table for WOT mode, do I need to run the car at WOT. Will normal driving modes have impact on those fuel tables?

Also, how reliable is the knock sensor? How do they work internally? Understand it retards timing to compensate for the condition, but how does it detect the condition. Can you tap on the intake manifold with a hammer and trigger it (seems like someone suggested this as a test method for the sensor)

Well, I guess I will understand much more once I get that Autotap. A scanner seems like an absolute necessity these days, can’t wait to get my hands on it.

 

It might be possible that what you are hearing is the popping of your injectors. the stock injectors are very noisy.