grrrr.... engine knock

[Formulaboy95]

Well, I now know why I am losing power on the top end. Car always feels like it stops pulling hard after the 8th mile. I just bought the PCM logger after I noticed the knock count go up at the track this last sunday.

What would cause 6.9 degrees of knock at 86mph, that it would not at the same rpm at a slower speed?

I put it in a nice zipped excel spreadsheet.

[Injuneer]

Couldn't get the file to open.

Is the retard possibly happening at the shift point? How long does the knock retard (not knock) last?

[Formulaboy95]

I used the latest winzip for that. Here is a pdf version.

[Joe 1320]

While not the tuning guru that Fred is, I see a few things. 02 counts from 900 and up are definately on the rich side and imbalanced from bank one to bank two, also showing imbalance in the fuel correction from bank one to bank two. On average you are seeing a 60+ milivolt difference between bank one and bank two 02 sensors.

Have you checked for any exhaust leaks upstream of the 02 sensors? If you do, the computer recognizes the the additional air as being lean when in reality it is not and compensates by adding fuel, creating a rich condition. Excessively lean or excessively rich will cause knock. The other thing I would check is the coil module. I have seen poor contact in the connector due to pin misalignment that caused the same symptoms that I see here.

Why would it do this at WOT and not do it a slower speeds? simple.... Load. The more resistance against the powertrain ie; the more throttle applied and/or the higher the speed (wind resistance like at high road speeds) the more fuel and air crammed into the engine. Cylinder pressure goes up and any problems with ignition or fuel are multiplied. WOT in first gear may not cause any knock. Second gear, because of increasing wind resistance and load may start to show knock. You can be into third it will get worse, 4th may not even be drivable at WOT. It all depends on the severity of the condition.

I'm sure Fred will dig into it a little deeper.

[Formulaboy95]

I recently added headers, and am getting a tit-tit-tit noise(sounds like at y-pipe flange). Gaskets look properly aligned, and bolts have been re-tightened. I reset the computer 2 days ago. It seems like the problem has been there for some time, as this was the reason for getting headers. Top end was falling flat after the 8th, and I am standing on the pedal.

On my way to Island to log a few runs... Changed the oil, added 1qt of a lucas oil additive to 4qts 5-30 Mobil1 synthetic. Going to add 1-1.5 gallons of 100 octane to see if that helps. Seems to lower my times usually, but it is worth a shot.

[Injuneer]

Do you feel a stumble when the knock retard shows up? Beyond the loss of power you would feel when the engine loses timing? If you look at the point where the knock starts in 3rd gear, the trans has shifted and the RPM has dropped down where it should based on the gear ratio change, then there is a sudden burst knock. That triggers the knock retard and it takes a second or so to decay, then there is another burst of knock. When this happens, the RPM starts to jump all over the place, increasing by as much as 250rpm from one scanner frame to the next, and losing almost as much rpm in the next frame. Instead of gradually increasing at WOT, the rpm is jumping up and down. At the same time, the MAF GPS starts to rise and fall in the same pattern. And, MAP is starting to bounce around too.

Almost seems like something is starting to happen that is causing all these things.... and one thing would be misfiring, possibly as a result of cross-firing in the wires, or a faulty Opti high res pulse pattern throwing the timing off. If you had a misfire, say too far in advance of TDC on one cylinder, you are going to get a burst of knock. This would also explain the loss of MAF flow, as the cylinders are not combusting properly, and a cylinder firing while an intake valve was open would cause erratic MAP readings.

How good are the wires? How old is the Opti? Can you feel the stumble, or is it just a sense that the engine isn't pulling as hard as it was?

One other thing I was thinking of, but I don't know a whole lot about the programming provided for the A4.... could the convertor have locked up at the point the knock burst occured? I don't know if the convertor will only lock up in 3rd or 4th, or if it will lock up at that low an RPM in 3rd. Just a thought, but I know nothing about the A4 shift and lockup programming.

As far as the rest of the scan, Joe hit the nail on the head.... the left side is probably experiencing a "false" lean, and pushing the LTFT up to 144 on that side. That in turn is causing the left bank injector pulse widths to be almost 10% higher than the right bank, and you have the left O2 readings showing the 50-60mV richer readings.

Have you put a 4.7Kohm resistor in the IAT sensor socket? Appears the IAT is locked at 58degF. A remote possibility this is contributing a little to the problem, if you are actually experiencing a temperature increase in the inlet air at any time, or if it is a lot warmer than indicated. There is an elusive 3deg of spark advance that some people attribute to an unfound table relating spark advance to IAT. If you are masking the true intake air temp, it could be giving you a bit too much advance. Or maybe you are actually seeing 58degF on a constant basis. It just seems that in most logs that I look at, there will be a degree or two of drop on the IAT over the course of a full WOT run.

[Formulaboy95]

Thanks Fred/Joe. Well I went back out to the track yesterday, and logged all the runs. First run was 93-94 octane mixed, half a tank. Slight knock up top. So, I decided to try and add some higher octane gas to see if that would have any affect on knock. They were all out of 100 & 104, so I bought 2 gallons of the 110. (If the 02's go, I will replace them)

2nd run - 8th mile burnout let off the gas before the wall, still pulled 6 degrees.

Next 2 runs - no knock/very minimal .3

So now I am really confused... False knock or real knock?
Plugs are NGK TR-6 gapped at .035, 2 months old & I cleaned them when I did headers, wires are pretty new - showed no signs of heat damage, looked like I just took them out of the box. Opti - about 5 months old.
I was thinking of pulling the IAT resistor, this Sunday I am going back for the last track day, so I will try that then.

[Injuneer]

What were your ET and MPH for both the 1/8th and 1/4 on the two good runs?

[Formulaboy95]

Well, it was only 1 good run. I could not seem to get the right tire pressure, and shock combo to hook up. The higher octane gas may also have had some factor too, or it was just the track conditions getting worse. The 3 runs where I had to back off of the gas were still 100.xx. The first run was 13.466@103.85 w/a 2.079 60', no burnout, dr's @38psi. Hooked almost perfect, barely spun at all. The knock was 6.3 degrees at 93mph, and slowly faded away at 104.

Is the 103.85 on par with the ET, or should the ET be lower?

[Injuneer]

103-104MPH looks pretty decent.

What I was looking for was the 1/8th and 1/4 ET and MPH for a few of your runs. If you had the complete time slip, including 60-ft, it would also help. What I wanted to look at was how the 1st 1/8-mile compared to the last 1/2 of the pass, to see if you really were falling flat on the top end.

Is Sunday 11/21 the last open race day at Island? I'm tempted to pull the car together for one more attempt to spray the 300-shot before the year is over.

[Joe 1320]

Just a thought..... open up the hood at night and throw a few revs. Look for any blue glow around any plugs/wires and especially the coil.