finding false knock

[4to8]

I'm having trouble taking down false knock on my car. Are there any known trouble areas that people have found. I know on the 11-14's it was the over the axle pipes that would hit. Mods are mbrp street, jlt and lund tune. Thanks for any help.

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[Grimace427]

How do you know you have false knock? Have you tried fuel from multiple stations and logged them?

 

[4to8]

Two stations so far and added octane booster. Tuner said it could be either of those options. I'm going to try more stations to make sure. It could just be the gas but I figured I would check if there were any common issues like the previous model.

 

[rainier446]

Two stations so far and added octane booster. Tuner said it could be either of those options. I'm going to try more stations to make sure. It could just be the gas but I figured I would check if there were any common issues like the previous model.

A quick and easy test would also be putting a gallon of e85 in the tank. No matter how crappy the gas is, it will alleviate any skepticism as to whether it's the fuel or false knock.

 

[Reds197]

Don't use E85 if you are not tuned for it.
Get some 100 octane unleaded race gas instead of booster. This will tell you if its false. Make sure all the exhaust clamps are tight.

 

[Grimace427]

How much knock are you seeing? Positive knock I'm assuming? How much timing is being pulled and is it during tip-in, low rpm WOT, or WOT all the way through the RPM range?

 

[rainier446]

Don't use E85 if you are not tuned for it.
Get some 100 octane unleaded race gas instead of booster. This will tell you if its false. Make sure all the exhaust clamps are tight.

E85 is easier to find, and you absolutely can put a gallon in with 14-15 gallons of 93 to test for knock. That bring's the ethanol level to about e15-e20, hell most gas is 10% ethanol anyway. Ethanol is much better at knock reduction than regular gas, it also burns much cooler which is why so many people tune for it and get another 30-40whp with just running e85.

Should you put a whole tank in without a tune? Hell no. But you can put in a gallon for testing purposes, also a good method if you're traveling and get a tank of bad gas while tuned.

 

[4to8]

the knock is switching from negative(-.9433) to positive(.55) around 5500 rpms saftot (23.5). then continues to increase as the rpms rise rpm 7100 knock 3.695 saftot (25). This log was with octane booster and going through retightening all the exhaust connections.

I'm pretty sure it is bad gas cause I looked at an earlier log where and I was seeing rpm 5300 saftot 18.5 knock 3.953. This log was with out octane booster.

I need to get the tank low and put some different gas in and get some more logs.

I couldn't figure out how to upload in excel but the log is in txt doc. the columns are off from their headers but are in order

 

[Grimace427]

Watching your timing it seems to continue increasing as RPM's rise, up to 26 degrees which isn't bad at all. I agree try different gas but without octane booster first just to be absolutely sure. Negative knock means the PCM is adding timing which is a good thing. Some knock at tip-in seems normal.

 

[dubster99]

E85 is easier to find, and you absolutely can put a gallon in with 14-15 gallons of 93 to test for knock. That bring's the ethanol level to about e15-e20, hell most gas is 10% ethanol anyway. Ethanol is much better at knock reduction than regular gas, it also burns much cooler which is why so many people tune for it and get another 30-40whp with just running e85.

Should you put a whole tank in without a tune? Hell no. But you can put in a gallon for testing purposes, also a good method if you're traveling and get a tank of bad gas while tuned.

But you need 30% more E85 in order to be correct, which he won't be dumping in. He would be better of with 0% ethanol pump gas if he can find it.

 

[Obsol3te]

Sorry new to this crap but trying to figure out this knock b/s because I'm having the same issues. Negative knock is a good thing? And from his log, 'saftot' would be total timing? What are these cars shooting for as far as total timing on 93(tuned)?

 

[Reds197]

Sorry new to this crap but trying to figure out this knock b/s because I'm having the same issues. Negative knock is a good thing? And from his log, 'saftot' would be total timing? What are these cars shooting for as far as total timing on 93(tuned)?

Yes negative knock means the computer is adding timing to make maximum power. If you are tuned right you will usually see a -1 or -2 number max. If you see much higher the tuner didn't add very much timing to begin with. Tunes can also limit how much the computer will add.

A positive number means the computer is reducing timing to make safe power.

 

[4to8]

Anyone have any other ideas on where this knock is coming from? I'm still getting 3+ degrees with 93 octane plus lucas octane booster. I went through the catback and made sure everything was tight and there was good clearance. Not sure if it could be the jlt oil separator or something with the cai rattling.

 

[V8EATR]

Yes negative knock means the computer is adding timing to make maximum power. If you are tuned right you will usually see a -1 or -2 number max. If you see much higher the tuner didn't add very much timing to begin with. Tunes can also limit how much the computer will add.

A positive number means the computer is reducing timing to make safe power.

What he said. I was confused by this as well at first with my hptuners software. Some systems will show positive KR as adding timing. The knock system in these cars can add up to 10* of timing when no KR is detected.

 

[rainier446]

But you need 30% more E85 in order to be correct, which he won't be dumping in. He would be better of with 0% ethanol pump gas if he can find it.

Not trying to discredit anyone, but I just want to make sure nobody is confused from our discussion.

Regular pump gas 'normally' contains up to 10% ethanol, so your car is already used to detecting it. 0% ethanol gas is not better than the ethanol versions.

Leaded fuel is what I believe you're talking about. Ethanol doesn't burn as clean as gasoline but it is far better at knock reduction and raising the octane level. Leaded fuel is also great at knock reduction, but of course was discontinued in the 80's.

Pure gasoline is better in terms of efficiency and clean burn but ethanol is superior for knock reduction and power. Lot's of people switch to e85 or e30 because of the power they get from it, the power comes from being able to add more timing without fear of popping a piston or snapping a rod.

My old car and my friends car were basically the same, except he ran e30. I made 270whp and he made 300. Difference? About 6 degrees of timing.

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