Paul94Z28

Hello-

I have been chasing a knock problem on my 94 Camaro and am looking for some assistance. I have the LT4 KM and headers and hotcam kit as "noisier" mods.

I took the car to the track and ran a datamaster file on it. I am getting 7 degrees of knock retard above 4400 RPM all the way to the redline at 6200.

I looked in the service manual for diagnosis: The L Term fuel trim counts are good at about 128 throughout the range. The EGR is working per specifications.

I am thinking I may have a header collector leak that presents a problem at that RPM. Any ideas? I have the Edelbrock TES shorties. I bought new collector gaskets and was going to try replacing those.

I talked to Ion at MadZ28 and he thought I might have an additional problem with fuel delivery. My FP tests showed normal readings at idle and WOT (vacuum tube off). My time was about .5 seconds slower than normal, so it is big impact on 1/4 mile performance. I have not changed the fuel filter in about 5 years, but I have not driven the car more than 10K miles in that time frame.

Any thoughts or similiar experiences?

Thanks,

shoebox

Around 4500 RPM is where knock likes to show up in my engine, as well. Not saying I have a cure, just letting you know that it is not uncommon. I have seen other posts of people saying the same thing.

Injuneer

You can't necessarily look at the LT fuel corrections at WOT (Power Enrichment mode) for meaningful info. They will default to 128 if your PCM is "cutting" fuel in the high load fuel cells. You need to look at the LT's at part load/part throttle.

What do the O2 sensor mV's look like at WOT when it starts to experience knock retard? While the sensors aren't very accurate at the A/F ratios required for max power/torque, they will show you gross indications of leaning out if the mV's drop significantly.

Why did you take the vacuum line off for your WOT fuel pressure test - not the way to do it. In effect, you created a vacuum leak. The mere fact that you are at WOT means there is no significant vacuum level in the manifold. What were the readings for the fuel pressure?

EGR isn't really a factor at WOT, since the EGR system doesn't operate at WOT or above 3,500rpm.

Have you tried putting in some 100-octane unleaded fuel to see if the knock goes away? That helps determine if its real knock, or false knock.

Is there any possibility that you have:

-a header component close to a chassis part or to the steering shaft?
-a loose motor mount on the passenger side (KS is right enxt to it)?
-a high voltage plug wire running in parallel or extremely close to the KS wire?

Paul94Z28

Thanks for the replies. I will provide the additional info:

Fuel Pressure: 39 after pressurizing, 40 at idle, 40-47 with throttle application.

After looking at the file, the knock first appears at 1275 RPM(4.6 degrees)(O2 - 62, 71), then remains but goes to down to 1.7 degrees at 4225 PM (o2 - 928, 910). At 4350 RPM it is at 7 degrees (o2-924,932) until I shift at 6200.

What other info can I post?

Thanks Guys!

Injuneer

Those O2 levels at higher RPM would tend to indicate its not running out of fuel.

The low level O2 readings at 1,275RPM may just be a "transition".... you opened the throttle rapidly, and it took a fraction of a second for the fuel to catch up.

Paul94Z28

I will look for the items you mentioned and replace those gaskets. I will let you know when I go to the track next and take another datamaster capture.

Thanks for the assistance!