Knock Problems from Hell 99 A4 Vette
11-15-2004, 10:20 AM
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Knock Problems from Hell 99 A4 Vette Guys, I need some help with a KR problem with my 99 A4 Coupe.
It has a tune that was derived for a predator tune that I went
12.99 at 107 with.
The problem is I'm seeing KR when I hop on the throttle such
as when I launch or slam into the throttle at 40 mph when
I'm in overdrive.
The logs show the car goes into PE with O2's between 880 and 920,
I know the car is running 12.8 in PE as I have had it dyno'd with
a WB and the KR kicks in.
So I took the car out and ran it nearly empty of gas and
put in 8.5 gallons of 100 octane CAM2 Unleaded Race gas.
The conditions were low humidty, 50 degrees IAT and I was
still seeing the KR.
In playing with the car, I scaled to VE table by 10% and then 20%
to see if it was a SD tune lean spot, no help.
I am thinking I have a false KR issue, but I am very hesitant to
desense the knock sensors.
I know 98's had flaky knock sensors and I'm wondering If I have
them as well in my Vette, as it was built 8/10/98.
Any thoughts, suggestions or wild *** guess's would be helpful.
Thanx, Jeff
It has a tune that was derived for a predator tune that I went
12.99 at 107 with.
The problem is I'm seeing KR when I hop on the throttle such
as when I launch or slam into the throttle at 40 mph when
I'm in overdrive.
The logs show the car goes into PE with O2's between 880 and 920,
I know the car is running 12.8 in PE as I have had it dyno'd with
a WB and the KR kicks in.
So I took the car out and ran it nearly empty of gas and
put in 8.5 gallons of 100 octane CAM2 Unleaded Race gas.
The conditions were low humidty, 50 degrees IAT and I was
still seeing the KR.
In playing with the car, I scaled to VE table by 10% and then 20%
to see if it was a SD tune lean spot, no help.
I am thinking I have a false KR issue, but I am very hesitant to
desense the knock sensors.
I know 98's had flaky knock sensors and I'm wondering If I have
them as well in my Vette, as it was built 8/10/98.
Any thoughts, suggestions or wild *** guess's would be helpful.
Thanx, Jeff
11-15-2004, 12:32 PM
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The front O2s will tell you if it's a lean spot. There are
PE delay RPM threshold and enrichment rates that might
be worth checking out (I set my delay mode RPM to
below my converter stall speed).
With 100 octane I suspect that any WOT knock would
be suppressed if real.
Being as it's a '99, you have EGR and I wonder if (given the
ET) you have gone to an exhaust that eliminates it, but still
have the EGR excess timing in the low RPM, low MAP area
(which you'd "sweep through" on your way to WOT)?
At what RPM does the KR first jump up?
PE delay RPM threshold and enrichment rates that might
be worth checking out (I set my delay mode RPM to
below my converter stall speed).
With 100 octane I suspect that any WOT knock would
be suppressed if real.
Being as it's a '99, you have EGR and I wonder if (given the
ET) you have gone to an exhaust that eliminates it, but still
have the EGR excess timing in the low RPM, low MAP area
(which you'd "sweep through" on your way to WOT)?
At what RPM does the KR first jump up?
11-15-2004, 12:57 PM
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Originally Posted by jimmyblue
The front O2s will tell you if it's a lean spot. There are
PE delay RPM threshold and enrichment rates that might
be worth checking out (I set my delay mode RPM to
below my converter stall speed).
With 100 octane I suspect that any WOT knock would
be suppressed if real.
Being as it's a '99, you have EGR and I wonder if (given the
ET) you have gone to an exhaust that eliminates it, but still
have the EGR excess timing in the low RPM, low MAP area
(which you'd "sweep through" on your way to WOT)?
At what RPM does the KR first jump up?
PE delay RPM threshold and enrichment rates that might
be worth checking out (I set my delay mode RPM to
below my converter stall speed).
With 100 octane I suspect that any WOT knock would
be suppressed if real.
Being as it's a '99, you have EGR and I wonder if (given the
ET) you have gone to an exhaust that eliminates it, but still
have the EGR excess timing in the low RPM, low MAP area
(which you'd "sweep through" on your way to WOT)?
At what RPM does the KR first jump up?
The front O2's sometimes show very low Mv levels as the throttle is coming open on the scan, but as soon as I get over 60% TPS they slam up to at least 880 Mv, which is consistent with the 12.8 which is what the dyno WB showed. The KR appears after the O2's come up, but this maybe a preceding cell issue, not what I'm seeing on the scan. The KR shows up at 1200 to 2400 and sometimes at 3600 to 5800. No C5's ever had EGR. Which tables are you refering to for PE delay?
Jeff
Last edited by Mitzelj; 11-15-2004 at 01:04 PM.
11-15-2004, 01:30 PM
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It's a single field, PE mode delay RPM. If RPM is below this
the PE will be applied slowly at the enrichment rate (don't
know the basis but more is better).
The one or two frames of low-O2 data right before KR
are the probable cause, you can lower the PE MAP/TPS
thresholds to bring it in earlier but it swinging below 0.5
indicates it's not PE's fault, but the speed density tune
isn't even able to keep it right side up. Upping the VE
value at the MAP, RPM that the lean frames indicate
will give you better transient fueling.
the PE will be applied slowly at the enrichment rate (don't
know the basis but more is better).
The one or two frames of low-O2 data right before KR
are the probable cause, you can lower the PE MAP/TPS
thresholds to bring it in earlier but it swinging below 0.5
indicates it's not PE's fault, but the speed density tune
isn't even able to keep it right side up. Upping the VE
value at the MAP, RPM that the lean frames indicate
will give you better transient fueling.
11-15-2004, 02:32 PM
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Originally Posted by jimmyblue
It's a single field, PE mode delay RPM. If RPM is below this
the PE will be applied slowly at the enrichment rate (don't
know the basis but more is better).
The one or two frames of low-O2 data right before KR
are the probable cause, you can lower the PE MAP/TPS
thresholds to bring it in earlier but it swinging below 0.5
indicates it's not PE's fault, but the speed density tune
isn't even able to keep it right side up. Upping the VE
value at the MAP, RPM that the lean frames indicate
will give you better transient fueling.
the PE will be applied slowly at the enrichment rate (don't
know the basis but more is better).
The one or two frames of low-O2 data right before KR
are the probable cause, you can lower the PE MAP/TPS
thresholds to bring it in earlier but it swinging below 0.5
indicates it's not PE's fault, but the speed density tune
isn't even able to keep it right side up. Upping the VE
value at the MAP, RPM that the lean frames indicate
will give you better transient fueling.
Ok, I found the PE mode Delay and it's 0, I scaled the entire VE table by 10% and then 20% and it didn't seem to help the knock. When I was looking at the frames I was watching the O2's swing and it always seems to be at the bottom of the swing when the throttle comes open, I was under the impression that this was normal closed loop operation, but when the TPS jumps the MAF goes out of the equation and it defaults to SD, and then slams into PE, I'm confused is to how this all happens within a frame or two, I wouldn't expect the system to be able to change the fueling that quickly. So if I follow you then I should crank up the VE to prevent a lean condition upon large TPS transients. Thanx, Jeff
11-15-2004, 03:21 PM
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JimmyBlue-
I did a little more analysis of my logs and I am clearly seeing an O2 crash when I have large TPS changes. I'm gonna play with the VE table tonight and see if this helps. I'm seeing the 02 crash primarily a low RPM and hi MAP values. So I scaled the two area where I'm having KR by 3 and then I smoothed the surrounding cells. I'll let you guys know what I find any other thought would be greatly appreciated. Thanx, Jeff
I did a little more analysis of my logs and I am clearly seeing an O2 crash when I have large TPS changes. I'm gonna play with the VE table tonight and see if this helps. I'm seeing the 02 crash primarily a low RPM and hi MAP values. So I scaled the two area where I'm having KR by 3 and then I smoothed the surrounding cells. I'll let you guys know what I find any other thought would be greatly appreciated. Thanx, Jeff
11-16-2004, 09:30 PM
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Guys I think I found the problem, here's the info:
NEW INFO:
I got ambitious and dropped the H-pipe, no broken studs amazing. The CATS are fine but when you tap the passenger exhaust manifold it rattles like crazy. This is clearly the noise I was hearing when I was revving the engine in neutral and I'd like to believe that this was/is causing my KR as I was able to generate a KR event when free reving the engine in neutral.
Is it even possible to have true KR when free reving, I wouldn't think, so since I think the combustion pressures would be much lower than when the system is loaded. So the question is what to do now??
Headers are down the road and I'm not inclined to swap the manifolds with more factory stuff although I would probably try to go to the 2001 style manifolds but they may have pup cats. What year were the pup cats added and was the H-pipe different and the manifolds the same? So I may just desensitize the knock sensors until I get the headers, although I must admit I'm hesitant to do that. Jeff
NEW INFO:
I got ambitious and dropped the H-pipe, no broken studs amazing. The CATS are fine but when you tap the passenger exhaust manifold it rattles like crazy. This is clearly the noise I was hearing when I was revving the engine in neutral and I'd like to believe that this was/is causing my KR as I was able to generate a KR event when free reving the engine in neutral.
Is it even possible to have true KR when free reving, I wouldn't think, so since I think the combustion pressures would be much lower than when the system is loaded. So the question is what to do now??
Headers are down the road and I'm not inclined to swap the manifolds with more factory stuff although I would probably try to go to the 2001 style manifolds but they may have pup cats. What year were the pup cats added and was the H-pipe different and the manifolds the same? So I may just desensitize the knock sensors until I get the headers, although I must admit I'm hesitant to do that. Jeff
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11-16-2004, 09:49 PM
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Originally Posted by jimmyblue
Is the rattle just a loose heat shield? Dog it down
or take it off?
or take it off?
I wish it was that simple, the manifolds on the 97-2000 Vette are double wall stainless with insulation between. They don't have heat shields. So it looks like my only options is to go to headers as I'm not replacing the manifold with another stock style one, in 2001 they went to a cast iron manifold but it won't mate with my h-pipe. So I think I'm gonna put the H-pipe back in and deafen the knock sensors, till I get my header, probably DynaTechs, Kooks or LGs. Also, screwing with the VE table made no diff, still showed knock,I also used the VCM controls to lock the timing to 12 degrees and still showed 9.5 KR, it's gotta be false from the manifold. Jeff
04-11-2005, 08:18 PM
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I defeated the bastage!!! It was indeed a bad manifold, I swapped it out this last weekend and what do you know no more spark knock and no audible rattle in the exhaust. WoooooHooooo. Maybe she'll run couple tenths quicker with no knock retard and fresh rubber. Jeff