Knock retard and negative fuel trims

[onspeed]

Hooked up my HPTuners to my Camaro today and did some scans. Camaro has an L26 engine block+heads w/stock l36 intake, high flow cat, and magnaflow catback. Otherwise stock and stock tune. However my LTFTs are all ~ -8% and I'm also seeing some knock retard at part throttle, around 1-3 degrees. What gives? Maintenance wise it's in a good condition, fuel filter, air filter, plugs, wires, and coils all good.

Going to try putting higher octane gas and see if that does anything.

[WarShrike]

Re: Knock retard and negative fuel trims

reset fuel trims after you add the high octane, drive it around for awhile and then scan after it finishes learning.

Do you have a wideband?

[onspeed]

Re: Knock retard and negative fuel trims

Not in this car, no. With an essentially stock car and stock tune, I should be seeing fuel trims around 0 and no KR right? I expected a positive fuel trim if anything considering the marginally larger valves from the l26 head and the e10 gasoline nowadays.

Negative fuel trims on both banks means something like a bad spark on both side or a leaky injector on both banks? Coils aren't brand new, but are within the last 15,000 miles I'd say, probably less. Same with wires and plugs. O2 sensors are good too.

[WarShrike]

Re: Knock retard and negative fuel trims

Make sure you don't have a broken motor mount. Any mechanical clinking rings those sensors like a bell.

[onspeed]

Re: Knock retard and negative fuel trims

I think it's probably a heatshield or exhaust piece or something that's banging around. Maybe the motor mount, although at idle I don't see anything too bad in terms of shakiness. My Z06 shakes much more, although the sensor location is different. Normal street driving I don't see any retard. WOT pulls I see a degree or two at most, but if I lug the engine, like WOT at in 5th at 45 MPH, I see 11 deg, which is the maximum amount of retard the tune allows. I think I'll just let it be.

[Gutless]

Re: Knock retard and negative fuel trims

Ive been fighting a mid throttle knock also. I can make 8PSI on 89 WOT and not have nay KR but at 5" or so in second gear acceleration it pulls 3-4 but somtimes 10 degrees out. The cylinder density isnt there to knock so its obviously false. Its the same as yours, only when the motor is lugging. at a 55+ cruise it wont KR.

Ive searched some for where its picking the noise up and cant find anything. I just attributed it to the fact that the headers and cam make a bit more 'clack' and 3800 knock sensors are almost too sensitive and are picking up noise as knock.

There is a table for knock sensor enable RPM. Set it to like 3000 and it shouldnt ever matter.

[Hib Halverson]

Re: Knock retard and negative fuel trims

Hooked up my HPTuners to my Camaro today and did some scans. Camaro has an L26 engine block+heads w/stock l36 intake, high flow cat, and magnaflow catback. Otherwise stock and stock tune. However my LTFTs are all ~ -8% and I'm also seeing some knock retard at part throttle, around 1-3 degrees. What gives? Maintenance wise it's in a good condition, fuel filter, air filter, plugs, wires, and coils all good.

Going to try putting higher octane gas and see if that does anything.

If you're seeing -8 fuel trim consistently, that means your system is somewhat rich.

Part throttle KR can be indicative of cheap gas or false knock. You need to determine which.

First thing to do is run some good fuel though the engine, then take some scans with HPT and see of the KR issue goes away or is, at least, mitigated.

[onspeed]

Re: Knock retard and negative fuel trims

I ran some better gas, and also increased the KR decay rates and decreased the base KR attack, and most part throttle KR is gone. High loads seems to trigger the knock sensors much more, like WOT in 5th. But I did a 0-80 MPH run, 1st through 3rd WOT, and the KR was more like a degree or two scattered. I'm pretty sure it's not actual knock, so I'm not going to worry about it. Probably have a heatshield banging around somewhere, or maybe a lost socket or wrench on the Kmember.

As for fuel trims, I've no idea why I'm seeing the -7% across the board on a stock MAF and VE maps with e10 gas. Maintenance wise, just about everything has been replaced at some point in the last couple years. Only thing I can think of is maybe a few bad injectors? Regardless, 7% isn't too bad. If it gets worse I'll look into it.

[ssms5411]

Re: Knock retard and negative fuel trims

-7 isn't bad when your positive then its pretty bad.

[TBO98]

Re: Knock retard and negative fuel trims

If you have changed the air intake or taken out the screen from the TB it can skew the trims. Make sure your FP regulator is not leaking, the most common thing that will cause rich trims. 7% is not that bad though.

[thebeewantsboost]

Re: Knock retard and negative fuel trims

get a wideband, and clean your maf, and reset fuel trims. KR on a stock tune isn't surprising. i had it on mine. negative fuel trims do seem a little weird.. anything done to your intake. would introduce more air and show you positive trims. could be o2 sensors. could just be the stock tune. its gonna make you even more rich at wot which is robbing power which is good news for ya. KR under low rpms/high load will show a ton of knock. some people have desensitized their sensors with resistors. i didn't have to. i had trouble with KR but it turns out it was mostly legit. try higher octane or pull some timing. remember that pulling timing in your tune is better than letting the computer pull timing when it senses knock.

[ssms5411]

Re: Knock retard and negative fuel trims

L26 is same compression as L36, L32 is supercharged and lower compression.

[thebeewantsboost]

Re: Knock retard and negative fuel trims

i thought i deleted that, cuz it didn't make sense anyway... my bad