All of a sudden I'm getting 2-5 degrees of retard at idle, it seems to go away as the rpms pick up, but sometimes it sticks around all the way up to around 2000rpms. And all the time with no knock counts going up.
Was running fine after heads/cam swap for a few days. Then driving to work all of a sudden feels like its pulling a boat behind me because of the spark retard.

As the MAP KPa gets higher at idle, the spark retard climbs right with it...so the less vac at idle, the more retard...the graph lines in DataMaster are almost right in sync with each other for MAP and Retard.

BLMs are perfect at 128 at idle and no more than 132 at part throttle and cruise.
Rpms at idle are 700-800rpms
Timing at idle according to Datamaster is 34-35*
MAP KPa is a bit high at 71-75KPa (it pulls about 12inHg of vac at idle)
MAF reading is 11-12afgs, it does not surge up and down but is constant.
IAT is anywhere from 96-136 degrees.
*
Cam specs are 236/242 at .050, .597/.583 on 114 LSA.

I've already changed PCMs and tried 2 different LT4 KMs, no change. Tried a completely stock tune, no change.
Change the knock sensor, no change...

Any other ideas are welcome

 

34-35* advance at 700-800rpm seems excessive. Stock tuing is 18-22* at that rpm. And, if you are getting 2-5* of knock retard at idle, that would indicate a programmed value for advance of 36-40* at idle, which is way too much.

A MAP of 71-75kPa at idle does not correspond to 12"Hg vacuum. That would be about 8"-9"Hg. Unless you are well below sea level or barometric pressure is 32.6"Hg, which is not likely. A MAP that high at idle should be setting a code for high MAP.

What does total advance do when the retard and MAP are increasing? Sounds like they may have the idle advance table screwed up, increasing adv with MAP.

 

Total advance drops to about 30-31 degrees as the MAP and retard go up.
It starts at 950rpms, 34*, 2* retard, and MAP of 60.2.
The MAP slowly creeps up to 76KPa as the rpms drop and settle at 650-700rpms and retard is 4.6* and total spark is 30*.

This is over a period of about 10-12seconds after releasing throttle in park.

The Closed TPS vs RPM table has the spark set at 35* for 400-1200rpms.
I was told about 30-34* is about right for this cam at idle. My truck has 25-27* at idle.
I did not find a idle timing table that is vs. MAP pressure, only rpm?
But it appears from what I'm observing, it is correlating to what I see in the tables I did find for idle/Closed TPS.


I'm not certain what the rpms were doing when I hooked the vac gauge up, they very well could have been in the 800 range when it pulls better vac, but no codes are being set. I did not have the scanner hooker up then so that may explain the descrepancy there.

Let me try to reduce the ClosedTPS timing down to around 30* and see what happens. Something does not makes sense though since it did the same exact thing with the stock factory tune which has 20* in the idle timing table.

Would that explain retard without knock counts though?

 

It's entirely possible to get knock retard with no change in knock counts, and its possible to get increases in knock counts without knock retard.

 

In that case is it true knock? I always thought for it to be true knock detected by the knock sensor than it would affect the counts.

If it is true knock, then backing that idle timing off may cure it. I'll try that.

 

The knock counts appear to be driven by internal PCM calculations based n various sensor inputs and operating parameters. I really don't know how they are arrived at. But reviewing literally hundred of scans for people, the knock count is generally not something to worry about. Just look at the knock retard.

The KS "hears" noises, whether they are from "real" knock or "false" knock. That noise signal goes to the PCM, and if it gets past the filter in the knock module, the PCM retards timing. There is no way for the PCM to know if its real or false, and there is no way that is could magically increment the knock counts only for true knock and not increment it for false knock. It has no way of knowing the source of the noise.

 

Thanks Fred, I'm going to get the car back this week and try a few things based on this info.
I did not mean to say if the computer determined whether its false knock or not. Just was not sure that the PCM could retard timing by other means rather than just the signal from the knock sensor.

On my vacuum, that 12inhg was in Park is why it was higher than the 71KPa in the log as that was in Drive, so that explains why its less..had a brain fart I guess when I posted that, but it appears that when the throttle is released the idle goes to 800-900 then drops down to 650-700 which then pulls less vac.
Thanks

 

Ok, set timing at idle down to 27-30* from 35 in order to maintain what little bit of vac I have at idle, no change, still pulls 3* at idle.
Removed the accessory belt as the AC was making a little bit of noise...no change still 3* retard at idle.
Switched Knock modules with another LT4, a f-body LT1, an Impala LT1, and some unknown KM and still 3* with all of them.
Switched PCM's, still 3* retard at idle....
WTF!!!
Keep in mind it idled fine for several days after the heads/cam install just fine with no knock retard...then just started doing this out of the blue and won't stop.
any other ideas anyone?

 

And you don't have a code for a faulty knock sensor?

 

Nope, all codes are clear, and I forgot to mention, the knock sensor was swapped out also.
Try to determine if the wire is frayed somewhere but that would not be consistant with the knock going away once off idle...

 

The knock has went mad now, getting the max in the tables no matter how hard or soft I mash the pedal....only time it doesn't have spark retard is when its coasting 0% TPS....
I'm sick of looking and don't hear anything. This is the same tune basically as it was before it started doing this...soo..
I've now zeroed out all of the max retard tables and now no knock on the scan tool I could give a ratz azz now if its real or not...had with this car. It ain't worth jack with 100k on the clock so I'm going to drive till it falls aprt now then part it out.