False Knock Testing - Lean WOT + High INJ Duty %

[Ben E]

My truck is a 1999 GMC Sierra 1500 with a 5.3l engine from an 02 Silverado. It also has a BTR Stage 2 Truck cam (212/218, .553, 113+2). Now I have been tuning the truck myself, with basic knowledge and I have the MAF and VE tables dialed in OK for what I know. I am not tuning with a wideband o2 and I'm just using the narrowband o2's as I don't have the money for it right now.

I believe I'm dealing with false knock, but not 100% sure. I've tried removing some spark and added fuel in certain situations but don't believe it helped. I originally wanted to get the 2002 tune for the added benefits and updates but haven't figured out how to exactly do it whilst keeping my VIN.

I have a log of a short drive with 87 octane fuel and I tried capturing a lot of situations. It was a warm and humid day. I also had my AC running which was an interesting thing, it kept removing spark via torque management every time it kicked in, I think. I also have two short logs on a different day it was a bit cooler and drier also without AC on. However, when I was trying some WOT stuff to see if knock was present or not I was running into I think a VERY lean condition. Another thing that happened is my injector duty cycle % was off the charts, above 100%. My truck has not acted like this ever, so something strange is happening.

So my first question is how to deal with false knock, if it exists and how to not run into real knock when attempting to fix false knock. I want to try some 100 octane fuel but haven't been able to get it since my station just ran out or shut it down for the time being. I know without a doubt I probably should desensitize the sensors just a bit since the valve train is quite loud. Since there is more knock download RPM than high RPM situations for some reason.

My next question since it popped up whilst testing for the knock issues. During WOT roughly around 3.5k+ RPM and higher or so, my o2 sensors start reading very lean, the o2 sensor voltage basically bottoms out. Another thing that happened is the injector duty cycle % went well beyond 100% usage. Neither of these things have ever happened before. My INJ Duty got close to 100% but never above, plus my o2 sensor voltage has always been 850+ MV during WOT. There is also a lack of power once I was reaching about 4.5k RPM, that's why in the logs I let out lower than my 6k shift.

Would anyone know why all of a sudden I'd be out of fuel when my truck has never acted this way before? Is it possible an injector or something is failing so then computer is asking for more fuel when there isn't any? Another thing I saw is one time my B1 o2 sensor read very low, while the B2 o2 read almost fine. However, I don't have a catalytic converter on B1 (Driver side) the passenger side still has one. The last thing I can think of is my gas tank had less than 6 gallons of fuel in the tank, probably close to 1-3 gallons, so is it possible that I was sucking air? There was NO surging of any kind during these tests except MAYBE the last 3-4 minutes of the PT 2 log but I think that was just knock retard.

I did just put an order in for some 8.1l injectors just to cover my butt with fuel and they're not large enough that I should have issues with idling or anything like that. We'll have to see how that works later on.

Tune) Build 12.2 - A safe tune with few changes to current Build 12.7. NO MAF or VE changes or Spark changes.
Tune) Build 12.7 - The current file I used to test for knock, and the one that has odd fueling issues.

Log) Build 12.2 - The safe tune with a few WOT pulls that shows the old status of how the truck acted.
Log) Build 12.7 - The log with testing 87 octane fuel.
Log) Build 12.7 c) PT 1 - Log testing some kind of 87/93 octane mix hopefully mostly 93 was in the tank with fueling issue.
Log) Build 12.7 c) PT 2 - Log still testing 93 octane, with fueling issue.

[5FDP]

Part of the problem is not having the VE and MAF tuned with the wideband, just looking at the trims it's not dialed in good enough yet. Incorrect airflow tables can cause you all sorts of problems with drive-ability and with timing/knock.

Part of the knock problem is burst knock is some spots of the log, saw it pulling timing at random and lots sometimes. I max out the burst knock table as it's a predicted knock table that just gets in the way sometimes. 87 octane on a cammed motor is asking for knock as well, 89 or higher is the only thing I'd ever run.

[Ben E]

I get that without a wide band o2 sensor that I won't get the whole picture but the narrow band o2 sensors should give me a pretty close picture when dealing with normal driving. So I did a fair bit of driving in different conditions, probably nearly 12 hours with for the VE table and MAF calibration. After getting the VE table within +/- 2 percent of 0 for long terms, and MAF was dead center my truck ran quite well. So with the long term fuel trims in check I was pretty happy. Eventually I'll go back over them, especially once I get the new fuel injectors and I'll try those and see what those do.

However what I don't understand is why all of a sudden fuel delivery would be so wack after no changes for almost a month.

I'll still have to figure out the knock. I feel like it's false since the times it pops up is strange. Plus a 6 point octane jump doesn't remove all knock even on the low octane timing table seems odd.

[reubone]

Just for fueling it looks as if your filter is clogged or your pump is giving up. You start to run lean under medium load which shoots your long term trim way into the positive which in turn add to your pe fueling request. Before it did not do this as it appeared that your fuel system, while high in duty cycle, could handle the load. The fuel trim were slightly to the negative which is about ideal. The ecm can add but not take away from pe on its own. As far as your knock issue goes, disable burst knock and test again.

[jimmyblue]

Misfiring will also produce indicated-lean results on
NBO2 and LSU4 WBO2 sensors. You can even get to
so rich that misfiring gives you a lean reading (been
there) - along with false trimming even richer, which
makes even more misfiring.

Things like an over-wide plug gap or weak plug wire
insulation can give you a spark fail-to-fire misfire that
appears only at higher cylinder pressures. This may be
visible in the individual "cylinder mode misfire" PIDs. A
too-narrow (like fouled) plug gap can make a too-weak
kernel that maybe is OK at light load low RPM but
fails to complete the burn at higher RPM. Fouling can
also cause preignition that gets picked up as spark
knock when the timing happens to be right (i.e. a
knock event that falls within the "filter window" of
the knock detect function, which looks for a ping
that follows spark and tries to reject non-spark-
induced knock events, since it's got no control over
preignition).

Any misfire stands a chance of pushing a bunch of
unused air out to the exhaust, which will be (mis-)
interpreted by the O2 sensors as lean incoming
mixture regardless of actual mixture.

Point being, you sometimes have to dig deeper to
see if you truly have an AFR -delivery- problem or
a AFR -instrument- problem (often, that the sensor
fundamental assumptions such as complete burn and
nothing but spent products in the pipe, are violated
by some mysterious reality).

[Ben E]

Apologize for my absence. Jimmy, that is a lot of information that seems to make sense but I don't understand it but that's OK! Thank you though. Haha.

Back to the false knock and fuel issue. The fuel issue has been fixed, once I had more than 6 gallons of fuel it is back to normal. I think the fuel pump was sucking air or something, who knows?...

So I went out and bought some 100 octane fuel so the mixture in the tank has to be 97+ as I was running on fumes of 93 and I bought 10 gallons of race fuel. I even removed all burst knock as 5FDP suggested. I believe it helped but I am going to go back to factory values or half of it just for protection as my truck is a daily driver.

Now even with this race fuel I'm still getting knock. There is no way this can be real, correct? The knock on the logs seem to act the same or similar in some ways. I will say there was a definite improvement with random knock signatures when going from 87 to 93, but not really different from 93 to 100.

Now another thing I tested whilst I had some race fuel left in the tank I tried leaning out my PE by 0.020 to see if more knock occurred, or if I got more power out of it. I don't think there was more knock, but I feel like there was less power by the numbers in the log.

Lastly I guess, does anyone have tips on how to desensitize the knock sensors the correct way to get rid of the false knock? As in my tune there are 3 different settings. Tip in TPS, vs. RPM vs. Cyl, and then global gain vs. MAP vs. Cyl. I will say the values in the newer operating system in the 2001-2002 file has more parameters and also almost twice as dull knock sensitivity. However, I don't want to use those values without the extra parameters that GM added.

Log - Build 12.8 - Regular drive with 100 octane fuel, plus 0 burst knock like 5FDP suggested.
Log - Build 12.9 - Short drive with 100 octane fuel, leaner PE (By the value of 0.020 across the board).

[steelmesh]

You need a wideband O2 sensor to tune WOT. WOT causes the fueling system to go into Open Loop. LTFT/STFT are Closed Loop values; you must tune closed loop areas with LTFT, a WBO2 won't help with closed loop tuning.

If you're tuning WOT without a WBO2, then you're doing it wrong. Even if you don't have it connected to the scanner, sounds silly but video recording the WB gauge next to your tachometer will be invaluable information to correct WOT fueling.

WBO2 sensors are affordable now, there is no excuse to not invest in a $150 WBO2 kit (controller, sensors, gauge kit) when you are modifying your vehicle (risking damage $$$) and you already came up with money to buy the tuner. I don't mean to come off rude, I am trying to be real.

[Ben E]

Thank you. I'd like to invest into a wide band sensor but it's not in the budget currently. Plus I gotta do some research first to figure out how to get it to be recorded in a standard MPVI unit. However I've gotten my truck running pretty well even with nearly zero knowledge of the stuff which makes me happy.

I'm sure there are a lot of fine details that I'm not aware of and not how they effect things which I will eventually get to. But for the time being I'm happy, just trying to get the knock stuff tidied up as it pulls so much power even though there really shouldn't be knock on 93 and definitely not 100 race fuel.

I guess I'm gonna go try buying an 01-02 computer and use some credits on that sucker so I don't fry my computer and try to get the better parameters.

[steelmesh]

I wonder if this is still valid for logging WB02 without the inputs: https://www.corvetteforum.com/forums...hp-tuners.html

[5FDP]

Yes, using the EGR circuit still works for logging the wideband.