2012 GT500 Issues with Knock/Fixing False Knock

[MelloStang2010]

I've had my gt500 for about a 1.5 years now and have been plagued with knock issues the entire time trough out the different mods on the car. Knock sensors are kicking back between 1-3 degrees on wot but it never holds steady but jumps around.

Current mods on the car are
PMAS Intake
Ford Racing Mono Blade
VMP high flow elbow
Dynatech 1 7/8" headers with off-road x pipe
Corsa Sport Quads
VMP 2.5" pulley
Whiteline Rear Sway bar
BMR lowering springs with Viking rear Shocks
NGK TR6 spark plugs gapped to .032
Tuned by VMP

Ruled out bad gas, used multiple gas stations, used octane booster, and even blended 110 octane fuel into the tank which had no effect. I've gone over the exhaust at least 5 times now but there is still a rattle coming from somewhere even after adjusting everything and checking all the clamps. Even grabbed the over axle pipe and shook it back and forth and I couldn't get it to touch anything under the car or come close. Rattle is audible between 2500-3000 rpms and can be heard outside the car when backing up slowly.

I've become beyond frustrated with this issue as the car isn't performing even remotely close to where it should be. I dyno'd it today and it made a disappointing 530 to the wheels. I put it on the same dyno with just a pulley, intake, cat delete, and tune and it made 586rwhp. So I'm wondering if anyone on here has dealt with false knock (I cannot hear any audible detonation noises or pinging) or anything like this and if they were able to find a resolution to this issue. So anyone got any ideas? I can attach datalogs if it would be helpful.

 

[moncho]

Go ahead and include your datalog. Do you have a current tuner your dealing with?

 

[Black Cobra '99]

A friend of mine had a similar rattle, it turned out some baffles inside the muffler were broken. Just a thought.

 

[jazz05]

I would check mufflers with a scope if possible,

 

[MelloStang2010]

I'm still working with VMP on the issue. At this point I think they just nerfed the tune to cover themselves because they aren't here and cant physically see what the car is doing so they just want to be safe while the knock sensors are still active which I understand. So fixing the knock sensor issue is my main focus, if I can find the source that's causing it and fix it VMP will be able to actually tune the car. I attached two datalogs below one from being on the street and the other on the dyno from yesterday. I cant hear any noises that are indicating that the engine itself is detonating but the exhaust is pretty loud and hard to hear over.

In the next few weeks the car is getting a new clutch, driveshaft, mgw shifter, and motor mounts (for the whipple that will be going on the car after the clutch is broken in) so the exhaust will come apart for that and we will try and be as diligent as possible reassembling everything. I was hoping for more ideas of what can cause false knock other than an exhaust rattle. Only other think I can think of is the sway bar due to how it attaches to the axle housing that its transmitting vibrations but it would have to be an insane amount to go through the diff, driveshaft, and transmission to disrupt anything.

 

[MastaAce03]

I had a recent rattle with my exhaust. The screw that goes through the rubber grommet that holds the muffler hanger worked its way out a few threads. Tightened the screw back down, problem solved. Something to check out.

Frustrating as hell, I know.


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[MelloStang2010]

Man I didn't even think about the hangers themselves. I'm definitely going to check them out tonight since they are easy to get to. Unlikely they are the source but like you said something else to look at.

 

[moncho]

Did VMP provide the config file for the PIDS? Take a look at the PIDS I'm using, they were provided by my tuner. I would consider using the PIDS I'm using see attached datalog. You're AFR looks good, seems you have an O2 sensor in each bank (AFR1/AFR2). Run LiveLink for the catalog file. You won't be running PIDS with a "Z" as that's for a Zeitronics controller. The file I attached is a second gear pull to 5k RPM. I've got an '07 so all PIDS may not match. Since your going with a bigger blower you probably going to want to log boost as well. I don't have knock sensors so I can't really help in that regard.

 

[Black Cobra '99]

One idea is to pick up a knock monitor, you can check various parts with it and see what exactly is causing the knock.

 

[RedVenom48]

Is the off road x pipe from Dynatech, or did you have their flange stubs welded to an X pipe?

 

[Snoopy49]

Did VMP provide the config file for the PIDS? Take a look at the PIDS I'm using, they were provided by my tuner. I would consider using the PIDS I'm using see attached datalog. You're AFR looks good, seems you have an O2 sensor in each bank (AFR1/AFR2). Run LiveLink for the catalog file. You won't be running PIDS with a "Z" as that's for a Zeitronics controller. The file I attached is a second gear pull to 5k RPM. I've got an '07 so all PIDS may not match. Since your going with a bigger blower you probably going to want to log boost as well. I don't have knock sensors so I can't really help in that regard.

Just in case someone doesn't have a program that will read a csv file.
log0019.pdf

 

[MelloStang2010]

Is the off road x pipe from Dynatech, or did you have their flange stubs welded to an X pipe?

It's dynatechs x pipe so no welds just bolted together. the fitment isnt the best on it. that clamp that is circled only tightens so much. If you pull the xpipe off you can actually spin the legs that go to the collect with minimal force even though I have tightened them as much as physically possible. Im thinking about possibly having those two parts welded together in case that clamp is vibrating a bunch, but I was having this problem before I installed the longtubes.

Got a response from VMP, they are asking me to do a wot pull and then immediately pull the spark plugs to look for speckling or anything else that is abnormal and send them pics so I will probably do that today. Ill also post them here. Gunna be beyond furious if I picked up a car with barely 5k miles on it and the engine was hurt.

 

[Casper cobra]

better to have this test on dyno to shut off engine direct after the run and do not keep it at idle. this will give clear pic for tuner.

 

[RedVenom48]

@MelloStang2010 Id have those pieces welded. From how you've described it, those arms are loose.

 

[MelloStang2010]

So I pulled all of the spark plugs to check them. Some of the gaps weren't right so I brought them down to .028 but for some reason I couldn't get cylinder 3 to come out. The spark plug socket wouldn't seat on the plug so I shot some compressed air down into the cylinder head and this plastic grommet came flying out. I'm guessing it fell off of the original spark plug socket when I changed them over a year ago and it's been sitting there since. Grabbed some more datalogs but it didn't make a difference on the knock. I'm going to have the x pipe welded and see if that makes a difference.

 

[MastaAce03]

So I pulled all of the spark plugs to check them. Some of the gaps weren't right so I brought them down to .028 but for some reason I couldn't get cylinder 3 to come out. The spark plug socket wouldn't seat on the plug so I shot some compressed air down into the cylinder head and this plastic grommet came flying out. I'm guessing it fell off of the original spark plug socket when I changed them over a year ago and it's been sitting there since. Grabbed some more datalogs but it didn't make a difference on the knock. I'm going to have the x pipe welded and see if that makes a difference.

Any signs of detonation on the plugs?


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[MelloStang2010]

Any signs of detonation on the plugs?

Didn't see any metallic specks. I took pics though, looks like just carbon build up. I did a wot hit then drove maybe a half mile into my garage and pulled the plugs. Should I change the plugs to something different?

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[MastaAce03]

How much boost? Stock blower?

I don’t see any issues with how your plugs look, so that’s great.


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[merkyworks]

Maybe its the camera angle / lighting but the plug in the 4th pic doesn't looks right. The electrode tip looks like its burned while all the other tips look nice and shiny.

 

[MelloStang2010]

How much boost? Stock blower?

I don’t see any issues with how your plugs look, so that’s great.


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Yeah stock blower, the gauge on the dash shows like 12-13lbs right now. Was like 15lbs before longtubes.

Maybe its the camera angle / lighting but the plug in the 4th pic doesn't looks right. The electrode tip looks like its burned while all the other tips look nice and shiny.

I think it's the side of the plug. It's just carbon build up so it looks darker on that one side. I also took these in my garage. If I was getting spark blow out or the plugs were jacked I should be getting misfires and codes.