Knock acceptable while "cruising", how much?

[ahl395]

I've changed plugs too but haven't checked compression. I suspect it's fine as the car had less than 10k miles and no behavior I'd attribute to serious damage.

Do you see knock under the same conditions as I am? Accelerating through the gears?

Edit I see you have an auto. When are you seeing knock?

I know one member had alot of "false" knock that was similar to our condition and ended up finding low compression and air puffing out of the oil cap when off/running. Seems rare that is the cause but still worth mentioning.

My false knock is very similar. I can be just cruising at a steady speed and see +1-3 suddenly, slowly fades away. Also under light accel I can see between +1 and +4 sometimes. It's all semi-repeatable but also random. Torco doesnt seem to do much if anything to help it.

Unrelated, I also get some real knock sometimes. +1-3, the reason I call it real versus false, is it happens when under load. Usually at or near WOT. Due to shitty gas in my area, which is why I'm adding methanol injection soon.

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[Oakley_5OH]

Sounds pretty much identical to mine, but yours may be even more significant. 75% of the time I see less than 1*. Sometimes I see more but it's almost always less than 2*. About 1* of the time I'll see 3-4*

Something I haven't mentioned is that Occasionally I'll see knock when revving the car too. Like rev matching for a downshift or just blipping the throttle.

Do you monitor lambs also? Do you see the car go rich on tip-in throttle?

99% of the time it is as low as you. Usually +1/+2. 4.89 was just the highest I’ve seen and it was only for a second, if that. Mine sounds exactly the same as yours. I started noticing it after downshifting and making a turn at 2nd or third doing like 20-30 mph and ever since then I can’t stop looking at it. I’ve been trying to find it for the past three months and still nothing.
I am sure I missed it, but what mods do you have? And no, I do not. I honestly have no idea wtf I’m looking at hahaha

I’ve worked with my tuner and after showing him some of the times that it has happened in logs and then showing him WOT pulls, he’s at the same crossing point as me. But is 100% certain it is false based off of the randomness of it. The car runs nearly perfect at WOT, but intermittently normal driving right after a shift it shows.

 

[markmurfie]

Just so every one is aware, You can have your tuner turn down their sensitivity in select areas. Its not exactly like its a global setting like turning down a microphone. If the partial throttle area between 2500 and 3500 is giving you what you are certain is positive knock, that area can be desensitized and it does not effect WOT between 3000- 7800. So you are not losing any knock safety in the more dangerous areas.

In fact looking at the tables in HPT ford has most cylinders pretty desensitized below 3000RPMs, except the front two one and five.

 

[ahl395]

Just so every one is aware, You can have your tuner turn down their sensitivity in select areas. Its not exactly like its a global setting like turning down a microphone. If the partial throttle area between 2500 and 3500 is giving you what you are certain is positive knock, that area can be desensitized and it does not effect WOT between 3000- 7800. So you are not losing any knock safety in the more dangerous areas.

In fact looking at the tables in HPT ford has most cylinders pretty desensitized below 3000RPMs, except the front two one and five.

Thanks for the info.

How is it capable of monitoring knock in each cylinder when there are only two knock sensors?

 

[markmurfie]

Mainly the crankshaft position sensor.

The disadvantage our cars have compared to the FRPP tunes, eco boost, or 2018 mustang gt is when knock is heard it pulls from all cylinders and when it is not it adds to all cylinders. This limits its effectiveness to the weakest cylinder. We still have all the window filters and sensitivity stuff per cylinder, other wise it wouldn't be very effective at reducing false knock.

 

[ManBearPig]

The only mods I have right now is an MBRP catback and steeda springs. I had a set of cat deletes but removed them because I was convinced they were the source of the problem. I only started noticing this after I deleted the card, but I think that's just coincidence. Back on the factory headers and cats I saw no change.

I took the catback completely off and drove around for about 3 miles to see if maybe the exhaust was causing a problem and I just couldn't find it. Didn't help.

I don't like the idea of desensitizing the knock sensors but I wasn't aware you could do so at only certain rpm/load/conditions. My tuner has told me time and time again that this is normal and I shouldn't worry about it, so I'm not even sure they'd be willing to turn them down anyway. If they do, will that effect how the car adds timing at part throttle? It seems it may allow the car to add too much timing and then it may start knocking for real

As to the guy that had this happen then found low compression, if I recall he was seeing +10 under part throttle and was boosted. I suppose it wouldn't hurt to do a compression check but I can't see that being a real issue for me. The car has less than 10k miles and is pretty much stock, and does not seem down on power

 

[mustang1]

is this knock acceptable ? stock, 93 octane

 

[ManBearPig]

Am I reading that graph correctly? You appear to have knock all over the place. I must be reading it wrong

I did get confirmation from lund that they command .85 lambda at tip-in so it's normal that I'm seeing this. They are hesitant to desensitize the knock sensors but they say if I really want them to, they will. I appreciate their hesitation because I still don't think I should need to do this.

At what point do I deem it as false? Just because I get sporadic knock on known good fuel and the stock tune? Maybe my engine was built on a Monday and some tolerance somewhere is too loose and it's making noise that I can't hear?

Are these knock sensors designed to look for frequencies specific to spark knock or will anything else internal set them off? Rod knock, excessive valvetrin noise, etc?

 

[mustang1]

I don't know. That was a one hour data log, and then I graphed the Knock column. I haven't looked at the XLS any further but from a couple of previous data logs, I don't think it is pulling timing under load.

 

[ahl395]

Am I reading that graph correctly? You appear to have knock all over the place. I must be reading it wrong

I did get confirmation from lund that they command .85 lambda at tip-in so it's normal that I'm seeing this. They are hesitant to desensitize the knock sensors but they say if I really want them to, they will. I appreciate their hesitation because I still don't think I should need to do this.

At what point do I deem it as false? Just because I get sporadic knock on known good fuel and the stock tune? Maybe my engine was built on a Monday and some tolerance somewhere is too loose and it's making noise that I can't hear?

Are these knock sensors designed to look for frequencies specific to spark knock or will anything else internal set them off? Rod knock, excessive valvetrin noise, etc?

Would commanding a richer lambda resolve the tip-in problem?

Most of the time you can determine it is false knock if
-Torco and fuel from a different station doesn't fix it
-It is happening under light or no load.

They are designed to look for the specific frequencies of knock, and at the times when knock is likely. They are more advanced than just a microphone. Unfortunately, it is obviously still not perfect and can be fooled. Most often the cause is something hitting the header/exhaust, since it is bolted directly to the engine the sound resonates well to the knock sensors. There has also been talk about a very stiff suspension and differential being able to cause false knock, since it transmits NVH through the car and possibly to the knock sensors. As well as loose objects hitting other parts of the body.

is this knock acceptable ? stock, 93 octane

I don't know. That was a one hour data log, and then I graphed the Knock column. I haven't looked at the XLS any further but from a couple of previous data logs, I don't think it is pulling timing under load.

+5 is high, but with that long of a log it is hard to tell anything. I would try to keep the log short and do some cruising and some pulls and you will be able to more easily match up load with the knock.

 

[mustang1]

looking at the XLS a little closer
all of the 3.5+ is < 1/4 throttle
WOT is < 1, with a few ~ 1.25

 

[ahl395]

looking at the XLS a little closer
all of the 3.5+ is < 1/4 throttle
WOT is < 1, with a few ~ 1.25

I would try with a can of Torco in the tank and see what your log look like. Not alarming numbers but could be better if it's real knock. The 1-1.25 could be from bad fuel and/or too much timing commanded in the tune.

 

[stevnoof1]

is this knock acceptable ? stock, 93 octane

I would not consider that acceptable man you should try to run some race gas.

 

[stevnoof1]

I went to a different gas station this week and my part throttle knock is not nearly as bad as last week. I Was headed to the track tonight to do some 1/4 mile logs but they shut it down. I'm gonna keep trying different gas stations. I have tried race fuel before and I run e85 sometimes it still has knock but I think it gets worse with bad fuel. I may try a different tuner at some point.

 

[Oakley_5OH]

The only mods I have right now is an MBRP catback and steeda springs. I had a set of cat deletes but removed them because I was convinced they were the source of the problem. I only started noticing this after I deleted the card, but I think that's just coincidence. Back on the factory headers and cats I saw no change.

I took the catback completely off and drove around for about 3 miles to see if maybe the exhaust was causing a problem and I just couldn't find it. Didn't help.

I don't like the idea of desensitizing the knock sensors but I wasn't aware you could do so at only certain rpm/load/conditions. My tuner has told me time and time again that this is normal and I shouldn't worry about it, so I'm not even sure they'd be willing to turn them down anyway. If they do, will that effect how the car adds timing at part throttle? It seems it may allow the car to add too much timing and then it may start knocking for real

As to the guy that had this happen then found low compression, if I recall he was seeing +10 under part throttle and was boosted. I suppose it wouldn't hurt to do a compression check but I can't see that being a real issue for me. The car has less than 10k miles and is pretty much stock, and does not seem down on power

Yeah - I am completely against desensitizing the knock sensors as well. I've been told to just let it go because it is so intermittent and that it should definitely be false, but at this point I am obsessed with trying to find out what is wrong.

So with my issue, I used to have MBRP and had it and changed out to a Corsa Sport and still have knock. So I do not think it is Cat Back related. I was thinking about putting on the stock headers just to prove a point to the company I purchased the headers from since they are stating that I am the only one with this issue. I originally thought the pipes were vibrating off of each other, but the more and more I mess with it, I start to think it is not that.

The only thing I can think of is if the the connectors between the cat back and the headers (whether stock or not), the header bolts/studs themselves, or motor mounts. So that brings me to a couple of questions.

- When you did the cat deletes, did you have to take the headers off of the car or did you leave them on the car?
- Did you mess with the motor mounts at all?
- In relation to when you started seeing/noticing the knock, when did you put the lowering springs on? The reason I ask is because I have heard that random suspension parts have been known to vibrate on the body and somehow cause false knock and at this point I am up to try anything to try and find the reason lol.
- No other parts have been added to the car at all besides cat delete/exhaust and springs?

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