PE mode not engaging when it should

[RRRocketMan]

When I say "should" I realize there's a bunch of stuff that determines when PE turns on that depends on more than just 1 variable but I don't know how complex the calculation actually is. Suffice it to say, I did a scan recently and noticed knock that shouldn't be happening. The O2 readings didn't rail like they should have under some fairly heavy throttle. Have a look in the attached log to see what I mean. I did a bunch of excel analysis and I believe this is fuel related but I can't figure out why it's happening. Anyone have any insight?

2013 Camaro SS Manual 9000 miles, Stock

[5FDP]

Post the tune.

[RRRocketMan]

Posted

[madmann26]

Posted

Start with changing 'enrichment ramp in' to 2.0.

This tells the PCM to go to PE mode much faster.

[RRRocketMan]

Start with changing 'enrichment ramp in' to 2.0.

This tells the PCM to go to PE mode much faster.

You know what's funny? I JUST lowered that value. Reason is this. My old car, which was a grand am gt used to have burst KR problems and after dozens of tunes I realized the fuel was coming on too quick and increasing the charge density and flame speed causing knock that would only get worse from there.

After seeing the default PE AFR on my camaro I was like YIKES that's low!! 11.something seems really rich for an NA car so I upped it and then wanted to slow the onset to prevent knock. I guess this engine's a whole different animal though.

[RRRocketMan]

Actually, from the description in HPT, isn't enrichment ramp in meant to change the rate at which your target PE AFR is reached ONCE PE has been enabled? I suspect this wouldn't affect the knock that occurs prior to PE enable, is that correct?

I don't have an "acceleration enrichment" table or else I'd work with that. I think AE would really help here.

[madmann26]

Actually, from the description in HPT, isn't enrichment ramp in meant to change the rate at which your target PE AFR is reached ONCE PE has been enabled? I suspect this wouldn't affect the knock that occurs prior to PE enable, is that correct?

I don't have an "acceleration enrichment" table or else I'd work with that. I think AE would really help here.

Well,

PE is a flat, commanded value once either throttle area or KPA or both are reached.

As for the AFR itself, you make max torque with 11.9 and max HP with a 12.5. It's up to you really. I prefer to run a little rich in my GEN3 truck.

You definitely don't want to lower it, lowering the value (ie, moving closer to zero) will delay PE engagement even longer. Change it to 2.0.

Edit:

As for the knock, start my pulling some spark back in the tune. If the values in the log do not change at all, then it's false knock.

[mowton]

There is knock even when PE isn't commanded so I don't think it is entirely a result of PE, though I would like to see it come in a bit earlier than 55% pedal. Lately I have not been seeing the ability to set the Normal PE Throttle values on the newer tune files, only the hot? Maybe a gas saving precaution!

As this is a stock file/car, I would think GM Engineering had figured out how to preclude knock under normal driving (which the log supports) and wouldn't think an owner would have to tweak a tune after 9000 miles. Sounds like something else may causing this situation, or GM deems this to be acceptable :-)

JMHO,

Ed M

[RRRocketMan]

Great...

Being able to tune PE Enable TPS is kind of a big deal. Thanks for commenting though guys.

As for the knock when not in PE, I suspect PE should be kicking in earlier and for the low manifold pressure knock... perhaps air temperature is making it worse? I don't know what else to think at the moment. The engine is clean, I'm using 91 octane, the spark is stock (and therefore a bit conservative). I just don't get it.

[5FDP]

It kinda just is what it is. The "knock" at low throttle input and while just bumming around is just kinda how they are. It's not like it can do any harm to the car in anyway.

My friends 2011 silverado is the same way, just random knock while driving around and it's so fast it just there and it's gone.

[RRRocketMan]

It kinda just is what it is. The "knock" at low throttle input and while just bumming around is just kinda how they are. It's not like it can do any harm to the car in anyway.

My friends 2011 silverado is the same way, just random knock while driving around and it's so fast it just there and it's gone.

Yeah I'm inclined to agree.

I had a bit of inspiration over the last couple of hours and looked deeper into the log. I think the (low pressure) knock might be my fault. There seems to be a high density of knock events at between 1300 and 2000 RPM and on my histogram there's usually a steep trace through the cells up to high pressure but without changing engine speed much. I think I was bogging the engine in high gear. Probably saw a gap in traffic and wanted to pass but forgot to downshift or something. Noobie mistake but I could see the sudden excess cylinder pressure causing a bit of knock because there's so much resistance on the pistons due to the unfavorable gear ratio. Since those cells in the histogram are of no importance to someone racing, I should be fine to drop the timing a bit in case I make that mistake again so she doesn't knock. In a proper drag race those cells wouldn't get referenced anyway.

[SICK WS 6]

After seeing the default PE AFR on my camaro I was like YIKES that's low!! 11.something seems really rich for an NA car so I upped it and then wanted to slow the onset to prevent knock. I guess this engine's a whole different animal though.

Using a wideband I hope? Didn't see any mention of it or see it in the log.

There is knock even when PE isn't commanded so I don't think it is entirely a result of PE, though I would like to see it come in a bit earlier than 55% pedal.

Agreed. Not sure why the the values in the tune posted are higher than the stock 2013 M6 file I have, but they seem awfully high to me.

Also want to throw this out there.
http://www.hptuners.com/forum/showth...t=camaro+knock

[RRRocketMan]

I don't have my wideband yet. I was referring to the commanded AFR. I realize there's no accuracy in that but the fact it was set in the 11s for N/A when my old car was set in the 13s confounded me.

My spark table is higher than yours for the same engine? This is news... wonder if I loaded the wrong file initially or something.