07 Sierra knocking

[ScarTissue48]

Have an 07 Sierra that was just rebuilt that I'm trying to get dialed it. Heads have been ported, stage 2 truck cam, cold air and long tubes. Considerable milling done on the head and block during rebuild, running 7.285 pushrods.

So since i've had it back together, I've been battling a random knock issue that i can't seem to figure out. It seems completely random and it usually doesn't seem like it's actually knocking, but this morning it was definitely rough. The last week or so I've been shifting over to E85 to see if the higher octane would help cut the knock down. I got the maf looking pretty good and then switched over to VE, got that looking fairly good and then last night re enabled the maf and set the dynamic airflow stuff back to stock, so the truck would run off both tables as it does stock.

I had desensitized the knock sensors at one time trying to eliminate false knock, and went ahead and set those values back to stock also. Knock is way worse this morning than it has been, even though my fueling should look pretty decent. It's definitely running rich this morning, but I kind of expected it to be off some as it's cold this morning for the first time all year and Ive been tuning in warmer weather. The knocks seem to be at part throttle or tip in, but it doesn't seem consistent. The knock is usually less than 1* of retard at random times. I really am at a loss as to what my fix for this is, any advice would be great.

These logs are me VE tuning and then the 2 from this morning are 1 while it was still warming up, and the 2nd one my laptop died on the way to work. So not great data but you can get the gist of what it's doing and how it's running. Felt like it was running great yesterday after I had the VE table looking good, this morning felt sluggish and just all around not great with the maf reenabled.

My main concern is getting the knock issue figured out, another thing I really dont know how to fix is the super rich idle, especially on the low rpm/kpa sections on the VE table. Plus it always seems to idle rich....would I need to add more airflow to the idle base airflow table? Also stumped on that.

Yesterday while logging VE, even though I wasn't lean, the truck did make a couple hard misses....i would've expected it to be bad knock but it didn't register anything on the scanner. Other than that, the truck ran better on VE only than it has since I've got it put back together. The misses were at part throttle....maybe tip in or a little after.

Any advice or tips is greatly appreciated! Thanks,

10-18.hpl
10-18 2.hpl
10-18 3.hpl
10-18 4.hpl
10-19.hpl
10-19 2.hpl
Updated knock sensors.hpt --most recent, reenabled MAF and set knock sensors to stock
VE TUNING.hpt-- previous tune, set for VE logging

[5FDP]

I think you are being worried over nothing with the knock, it's not doing any harm to have less than 1-2 degree of knock at part throttle. The computer is pulling that minimal amount of timing away faster than you can blink an eye and is totally fine.

I do notice you are running pretty darn low timing at partial throttle though, some of the spots where it's showing knock the high octane timing curve only has 4-10 degrees of timing in it.

I don't see a wideband in the logs so I'm not sure how you are tuning the MAF/VVE tables, the fuel trims aren't exactly the best way to do it with a camshaft and open loop EQ ratio table isn't setup to command 1.00 for all the cells at operating temp and intake valve temp. You still have values of .96 and 1.05 and those throw off your data.

Plus you don't want to be mixing in E85 without a sensor to read the alcohol content and adjust the stoich ratio for you. Fueling is always going to be off if you don't know what the stoich needs to be.

[ScarTissue48]

I think you are being worried over nothing with the knock, it's not doing any harm to have less than 1-2 degree of knock at part throttle. The computer is pulling that minimal amount of timing away faster than you can blink an eye and is totally fine.

I was actually thinking I might have been more worried about it than I should, appreciate the info!

I do notice you are running pretty darn low timing at partial throttle though, some of the spots where it's showing knock the high octane timing curve only has 4-10 degrees of timing in it.

Yea that's actually the stock timing table. I had toyed with the timing a bit, increasing to see how the drivability and throttle response felt and also to see if I could get rid of the knock....I ended up bumping it up some and then backing it all the way back down fighting the knock and eventually just set it back to the stock table. What would you guess a safe amount would be to bump that table up?

I don't see a wideband in the logs so I'm not sure how you are tuning the MAF/VVE tables, the fuel trims aren't exactly the best way to do it with a camshaft and open loop EQ ratio table isn't setup to command 1.00 for all the cells at operating temp and intake valve temp. You still have values of .96 and 1.05 and those throw off your data.

Plus you don't want to be mixing in E85 without a sensor to read the alcohol content and adjust the stoich ratio for you. Fueling is always going to be off if you don't know what the stoich needs to be.

Yes I've been committing the cardinal sin of using the narrowbands. Honestly it looks like I need to do some more reading on EQ ratio and stoich and all that. I've been reading some on it and it looks like I definitely shouldn't have went the e85 route...I was thinking I may have had higher compression that was causing that knock and was raising the octane to see if got any better.

I had the truck maf only and logged the fueling and tweaked it on the way home from the pump, added a little more ethanol each day for a while and logged and tweaked on the way home. The truck actually feels like it runs better even though it sounds like I'm out in left field with the EQ ratio not being adjusted and low timing. And dialing in the VE table really made a noticeable improvement, but it's still not what it should be and I appreciate you pointing me in that direction!

Sounds like I need to ease it back to pump gas and get the EQ and PE EQ ratios figured out and that timing table touched up and go from there. And buy a wideband.

[ScarTissue48]

I worked to get the MAF dialed in after going back to 91 octane and switched over to VE this evening trying to fix that table.....below are my logs. The first one is logging MAF and then i switched over to VE and i had a couple questions if someone doesn't mind chiming in.

1. The knock i'm seeing....is only when actively stepping on the throttle....holding it at certain points doesn't really show knock but even slight bumps in the throttle show knock immediately. I would assume this is tip in knock and I need to desensitize the sensors to get rid of it....does that sound accurate? Any insight on the knock?

2. What needs to do be done about the extreme numbers at the low rpm / high map areas of the logs? Still showing super rich in those areas and can't get those to respond to anything.

Also, when maf is diabled, ones every 3 or 4 times i driver the truck I will have a hard miss....scares the hell out of me every time but doesn't register as knock or anything....don't know what in my VE table would be causing it but it did happen one time on log 3 or 4.

Any help is appreciated!
10-30.hpl
10-30 2.hpl
10-30 3.hpl
10-30 4.hpl
Back to VE.hpt

[ScarTissue48]

Bump

[kevin87turbot]

I worked to get the MAF dialed in after going back to 91 octane and switched over to VE this evening trying to fix that table.....below are my logs. The first one is logging MAF and then i switched over to VE and i had a couple questions if someone doesn't mind chiming in.

1. The knock i'm seeing....is only when actively stepping on the throttle....holding it at certain points doesn't really show knock but even slight bumps in the throttle show knock immediately. I would assume this is tip in knock and I need to desensitize the sensors to get rid of it....does that sound accurate? Any insight on the knock? Zero the burst knock table and see if the retard is eliminated.

2. What needs to do be done about the extreme numbers at the low rpm / high map areas of the logs? Still showing super rich in those areas and can't get those to respond to anything. Change the Dynamic RPM Disable number to a high value...such as 8000 rpm when you're in SD mode.

Also, when maf is diabled, ones every 3 or 4 times i driver the truck I will have a hard miss....scares the hell out of me every time but doesn't register as knock or anything....don't know what in my VE table would be causing it but it did happen one time on log 3 or 4.

Any help is appreciated!
10-30.hpl
10-30 2.hpl
10-30 3.hpl
10-30 4.hpl
Back to VE.hpt

[Dutch]

I worked to get the MAF dialed in after going back to 91 octane and switched over to VE this evening trying to fix that table.....below are my logs. The first one is logging MAF and then i switched over to VE and i had a couple questions if someone doesn't mind chiming in.

1. The knock i'm seeing....is only when actively stepping on the throttle....holding it at certain points doesn't really show knock but even slight bumps in the throttle show knock immediately. I would assume this is tip in knock and I need to desensitize the sensors to get rid of it....does that sound accurate? Any insight on the knock?

2. What needs to do be done about the extreme numbers at the low rpm / high map areas of the logs? Still showing super rich in those areas and can't get those to respond to anything.

Also, when maf is diabled, ones every 3 or 4 times i driver the truck I will have a hard miss....scares the hell out of me every time but doesn't register as knock or anything....don't know what in my VE table would be causing it but it did happen one time on log 3 or 4.

Any help is appreciated!
10-30.hpl
10-30 2.hpl
10-30 3.hpl
10-30 4.hpl
Back to VE.hpt

For starters, what injectors are you using? Have you recalculated the compression ratio after milling the head and block?

If the compression ratio has increased, you might find you'll need *less* spark than factory under lower loads. For emissions reasons GM (and most manufacturers) adds considerable spark under coasting/very light loads.

If you are using aftermarket injectors, can you return to the stock injectors for the initial idle/low load VE adjustments? It is next to impossible to tune with bad injector data.

The Hard miss you're reporting sounds like a fueling issue, and I wouldn't touch anything relating to KR and mid/high load spark until you have that figured out.

But first, verify the engine is healthy, free of carbon, spark plugs look good and are the appropriate heat range, etc.
If you can, visually confirm the pistons are free of carbon by peeking down the spark plug holes.

Bad spark knock sounds like this:
https://drive.google.com/file/d/19n_...DDcTODLxbHEHwM
https://drive.google.com/file/d/19ZC...ew?usp=sharing
Always be listening for it.

Make sure to also log Knock Learn Factor: that tells you how much the ECM is favoring the Low Octane spark table. This tells you how often the ECM thinks the engine is knocking.
ECM 12796 (Knock Learn Up) is how much the ECM adds to the learn factor when KR exceeds a certain amount.
ECM 2707 (Knock Learn Down) is how quickly the Learn Factor returns to 0 after knock is suppressed.

1. To disable tip-in spark retard, zero out ECM 12765 (Burst Knock Retard vs Cylair Delta). However the KR amount does not align to tip-in knock. If your Knock Learn Factor is not 0.00 then what youre seeing is not tip-in knock: the ECM believes knock is occurring.

2. The factory knock sensor thresholds for your truck are quite sensitive. I believe what you're seeing in the logs is noise. Long tube headers in particular tend to confuse the knock sensors.
You might find you have to add quite a bit to these thresholds, particularly at lower RPMs, to suppress the false knock.
If you do, I would increase the Knock Learn Up coefficients so the ECM takes more aggressive action to suppress it.

But again get your fueling under control before modifying knock thresholds.