KNOCK KNOCK (Knock Retard Issue)

[Steeda]

Gents:

This is a recent problem, it happened after I replaced my thermostat, Water pump, and Fuel filter-not that it's related.

I live in new England, and run 87 octane - the winter blend here sucks. temperatures have been cool and the IAT has been between 40 and 58 Degrees.

My 03 is stock, just an open-element intake, and 20" rims. 169,000 miles

I am very religious with the maintenance on the vehicle--- so for purpose of this post lets say its super well maintained.

Every Thing in this post is measured with the scan gauge over 2 tankfuls. No Codes.

Tank 1: 87 octane- TPS 99% KRT 84 temp 195
TPS 28% KRT 19-24 Temp 195
At tip in it had zero KRT and would only show these numbers at steady state. Naturally I was alarmed so second tank i put in 91 octane

Tank 2: 91 octane- TPS 99% KRT 58 Temp 195
TPS 28% KRT 0
TPS 60% KRT 44
Once again this is not at throttle tip in =but after

In both cases i didn't make a note of rpm, but mental note was 2900-4500 I got off the throttle pretty quick when i saw how lean it was.

Thoughts? Basically its bothering the heck out of me. I NEVER had any noticeable KRT on the scan-gauge before this.

I'm wondering if the Fuel filter is to blame.... or a bad knock sensor with no code???

Thanks guys.

[The Roadie]

Have you ever Seafoamed it? Change plugs to Delco 41-103 at 100K miles?

[Steeda]

The delco's were changed at 120K. I did run that plug if i recall correctly.

As for seafoam, -not since winter 2012... but the truck has only had about 5-6000 miles on it since then- I had a company car for a while.

It's due for a seafoam.... for sure.

[Trail X]

I'm sorry, I'm not familliar with the KRT values you're reporting. What do they signify, what sensor is the gauge reporting? What are your symptoms? Also, are these stored values from the SG with a code? Or are these just values you wrote down when you noticed a knock?

[Steeda]

James-

Actually- I can never hear spark knock (detonation) what i felt was a surging under throttle. Or- it seems to "lay down" - have reduced power- at certian times.

I hooked up the Scangauge II and am tracking the:

KRT (knock retard timing) It measures how many degrees of timing the computer is pulling to eliminate detonation- it is basically reading the signal from the knock sensors and then making adjustments.

TPS: Throttle Position Sensor

I can cycle through other gauges also- Timing, Open or closed loop, load, etc....

When I feel the Surging or the loss of power- is when i see the Timing retarded in the 50-'s through 80's

I know that under WOT our trucks have about 25-30 degrees of total timing advance..... which means when i see a 50 for example, it has pulled the timing down to a estimated -20 degrees.


That answered what i was "feeling" but now im trying to figure out why.

[Trail X]

Ok, makes more sense now. I hadn't seen the KRT gauge... did you plug that in as an Xgauge?

To be clear, no codes reported?

No knocks felt or heard, which makes me suspect the knock sensor itself of being bad, or possibly a bearing of some sort going bad that's giving the knock sensor a bad reading, which the computer sees as a reason to pull timing.

[Steeda]

Ok, makes more sense now. I hadn't seen the KRT gauge... did you plug that in as an Xgauge?

To be clear, no codes reported?

No knocks felt or heard, which makes me suspect the knock sensor itself of being bad, or possibly a bearing of some sort going bad that's giving the knock sensor a bad reading, which the computer sees as a reason to pull timing.

Sorry for the long response time- Been doing more driving and "logging"

No codes Still-- and yes the KRT is an Xgauge.

Now- IF I recall correctly,our trucks vary cam timing at 3000 rpm.

Since running 91 octane- all the part throttle knock retard is gone.... until it hits over 3000 rpm. It creeps up.

AT WOT- still 28-38 degrees knock retard.

Are our trucks advancing cam timing over 3000?

[Trail X]

I'll have to defer that question, as I do not know. Lots of engine knowledge over on GMTNation too, might be worth posting your issue there too.