Knock... maybe?
06-20-2010, 01:42 PM
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Knock... maybe? Help guys! My trans am started sending lean codes and making weird noises above 4k rpm about a month ago. I have a Predator (u7198), so it ran it through live data mode to view and then compensate for my high (23,25%) LTFT's. I got the FT's where they should be and noticed that when it started making the weird noise it would show up in the knock sensor monitor, but it didn't send any code. I'm not really sure if it's detonation or not, it doesn't sound like it to me. The best way i can describe it that it sounds AND feels akin to driving over a rumble strip at 75mph. I used to have a smog headed 355 nova that would knock in the summer if i got too overzealous with the timing and it doesn't sound like that thing did. According to my predator the timing is showing 40 at idle and it decreases with engine speed (now I'm really baffled). I took 2deg out from 2k to 4k and i took out 4deg out from 4k to 6k. Guess what, the knock/noise got worse and happened at like 3500rpm! WTF! I figured I'd better quit and ask the experts. My only mods are slp lid, egr cut off, coolant bypass, ported tb, and a dump after the y pipe. Oh, I also added PE (2k to 4k=2%, 4k to 6k=4%) until my o2's were showing .8 to .85 at WOT. If anyone has any advice it would be greatly appreciated.
06-20-2010, 02:51 PM
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You need to figure out why it is so lean... hate to say it, but you should have done that a month ago when it first threw the code - not continue to drive it and especially not go WOT on it. Hard to tell what the noise is over the internet - you need to get some help (local help) with it if you don't know what it is...
06-20-2010, 03:31 PM
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I got the lean condition resolved right away, I just meant that they both happened at the same time at the track. It never knocked like that before. I changed the injector slope and got the FT's where they belong but it still detonates. I'd been just sitting in the garage all month until yesterday when i tried to take out some timing to see if that would help. I just took it out 5min ago and the timing numbers made more sense (not sure why). It is at 31deg at idle, 37deg at 2krpm. I ran it harder and harder (with no knock) until i felt comfortable with a WOT run. It ran strong up to about 5500 and then showed it pulling 3deg of knock retard just before i let off. I already have 4deg of retard being pulled out of it, should I take out more? I've seen other guys posts where they are adding like 6deg, what gives?! I run 92 octane.
06-20-2010, 03:40 PM
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When you make changes like that do you have to give the computer time to put them into effect or does it happen right away? When I changed the timing I just drove the car around for 20-25min, cut it off, did my thing, started it up and let her have it.
06-20-2010, 09:38 PM
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The timing is (according to the predator) bouncing between 35 and 37 degrees at WOT and yeah, I am definitely going to get a good wideband soon. I was hoping for now that I could just use the o2 voltage as a guide until I got one. As far as fuel pressure goes, I'll pick up a gauge as soon as i can get to the parts store. I'm assuming (?) the fueling is ok now because the o2's are reading right at .8 to .85 until i let off. I'm just finding it hard to believe that it needs this much timing pulled out of the diablo tune to run right. I still don't think it sounds like detonation but I don't know what else it could be
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06-21-2010, 08:03 PM
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+1, too much timing.
+1, can't use narrowbands for tuning, but 800-850mV loosely indicates not quite rich enough (but you can't tell without a wideband).
Also, check other mechanical conditions:
- rail pressure (as said by Old Geezer above),
- oil pulled in thru PCV,
- air leaks.,
- carbon deposits,
- overheating,
- MAF reading low (dirty).
+1, can't use narrowbands for tuning, but 800-850mV loosely indicates not quite rich enough (but you can't tell without a wideband).
Also, check other mechanical conditions:
- rail pressure (as said by Old Geezer above),
- oil pulled in thru PCV,
- air leaks.,
- carbon deposits,
- overheating,
- MAF reading low (dirty).
06-26-2010, 11:07 AM
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Yeah, I was just trying to get by until I could buy a good wideband. I have retarded the timing as far as my tuner will go and it is still showing 21deg at idle and 38deg at cruise (2k rpm). There is a local shop that I've heard good things about so I think I'll drop it off there. Thanks for the help guys.
