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False Knock with ATP Downpipe

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#1
Had a pro-tune done by Randy with stock DP and CBE (resonator & muffler delete) a little while ago and was seeing 24.5 psi pulls with zero negative correction, car was running great and I was extremely happy. Went ahead and installed ATP DP and now am seeing -3 correction. I contacted Randy immediately and he stated that some of the aftermarket DPs can cause excess NVH causing false knock symptoms. He has been gracious enough to revist my tune and we have been exchanging logs to fix the problem.

Anyone else had experience with false knock after a DP install?

Is not having the OEM bracket creating this problem?

Do the pros outweight the cons regarding DPs? Or vice versa?
 


Perfblue15

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#2
I'm running the atp pipe on my car with a e30 tune running a lot of advance. I rarely see negative corrections on hard pulls. I think it's just your down pipe/car. Or maybe some bad gas ?
 


pwnall1337

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#3
I'm pretty sure a DP requires a tune. To add to that, going from a catted DP to a cat less DP definitely requires a tune.
 


dyn085

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#4
Were the negative corrections consistent between cylinders/rpms/logs/etc or were they completely random?

DP absolutely requires retuning due to the changes in the catalytic converter and overall size/flow.
 


OP
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Thread Starter #5
Were the negative corrections consistent between cylinders/rpms/logs/etc or were they completely random?

DP absolutely requires retuning due to the changes in the catalytic converter and overall size/flow.
It was fairly consistent which led me to believe it was something else causing it. I have no doubt the DP causes some NVH but I couldn't comprehend the amount I was seeing. Anyways, I am pretty sure I have narrowed it down to my CFM breather cap being completely plugged. Going to do some logs now that I have fixed the problem and will report back.
 


dyn085

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#6
It was fairly consistent which led me to believe it was something else causing it. I have no doubt the DP causes some NVH but I couldn't comprehend the amount I was seeing. Anyways, I am pretty sure I have narrowed it down to my CFM breather cap being completely plugged. Going to do some logs now that I have fixed the problem and will report back.
Fairly consistent corrections do not indicate false knock as false knock is erroneous and inconsistent. Unfortunately, I had to work through that issue on my FoST when I replaced the RMM (and ultimately had to revert back to OEM). I've seen lots of claims, but I don't think I've seen logs of a single aftermarket part on the FiST that actually caused false-knock.

Nonetheless, it wouldn't hurt to verify that none of your clamps are touching anything and that all of your mount bolts are tight. Definitely curious to see your outcome/solution.
 


OP
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Thread Starter #7
Epic fail, was not the CFM breather. I would love if someone could look at my log and tell me what they think is going on. PM me if you want to help.

It seems consistent to some degree and then just jumps a couple of points negative correction.
 


westcoaST

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#8
Take a look at where your downpipe is sitting with respect to the frame. Is it or your exhaust hitting anywhere on the frame? You may want to get and attach a camera to your frame in this area to see if you are getting any metal-to-metal contact or verify movement while you get negative corrections. If movement is in fact causing the negative corrections, I would adjust your downpipe from the flange that attaches to the exhaust by losening all clamps bolts and working from the downpipe flange towards the muffler. Might help to take a flashlight and look for wear or polish marks on your downpipe or frame. I purchased a very small camera from ebay specifically for this type of testing.

http://www.ebay.com/itm/White-Mini-SJ1000-HD-1080P-12M-Sports-Helmet-Action-Waterproof-Dash-Camera-Cam-/261254638577?ssPageName=ADME:L:OC:US:3160

That being said, did you notice, or test for these negative corrections with the OEM downpipe? I'm thinking it may be more of a knock sensor issue. You may need to replace your OEM downpipe, go back to the dealer and get this sorted out. I have a 2J Racing downpipe. It also has no bracket, but I've had Randy tune my engine recently, and have only gotten positive corrections. My DP is wrapped, and installed according to the method shown in my build thread. I'll take a look in my mechanics manual for the knock sensor locations. I believe that they should be in the head somewhere.
 


OP
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Thread Starter #9
Take a look at where your downpipe is sitting with respect to the frame. Is it or your exhaust hitting anywhere on the frame? You may want to get and attach a camera to your frame in this area to see if you are getting any metal-to-metal contact or verify movement while you get negative corrections. If movement is in fact causing the negative corrections, I would adjust your downpipe from the flange that attaches to the exhaust by losening all clamps bolts and working from the downpipe flange towards the muffler. Might help to take a flashlight and look for wear or polish marks on your downpipe or frame. I purchased a very small camera from ebay specifically for this type of testing.

http://www.ebay.com/itm/White-Mini-SJ1000-HD-1080P-12M-Sports-Helmet-Action-Waterproof-Dash-Camera-Cam-/261254638577?ssPageName=ADME:L:OC:US:3160

That being said, did you notice, or test for these negative corrections with the OEM downpipe? I'm thinking it may be more of a knock sensor issue. You may need to replace your OEM downpipe, go back to the dealer and get this sorted out. I have a 2J Racing downpipe. It also has no bracket, but I've had Randy tune my engine recently, and have only gotten positive corrections. My DP is wrapped, and installed according to the method shown in my build thread. I'll take a look in my mechanics manual for the knock sensor locations. I believe that they should be in the head somewhere.
I am going to go over my install today after work. Yes my tune was completed with the OEM DP and was running perfect. I then added the ATP and saw the negative corrections. I will check for contact today otherwise I am going to reinstall the OE pipe.
 


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#10
Have you tried running Cobb's OTS maps? Not sure what other mods you have but maybe Stage 2 or 3 and see if you get negative correction.
 


BoostBumps

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#11
Have you tried running Cobb's OTS maps? Not sure what other mods you have but maybe Stage 2 or 3 and see if you get negative correction.
This...

Load up Cobb stg 3 and run some logs...If your not seeing any negative corrections or high knock counts then this would suggest that the current tune your running may simply be too aggressive...
 


dyn085

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#12
I'm thinking it may be more of a knock sensor issue.
Strictly my opinion, but from having gone through the tuning process for both my FiST and FoST I would not see that as likely. Granted, all cars are different and some can have quirks or bad parts, but my FiST logs were rock-solid, especially when compared to the FoST. The FiST community doesn't share much in terms of datalogs (compared to the FoST community), but I haven't actually seen logs in the FiST community with false knock yet-at least not created by an actual part as opposed to the maintenance surrounding it.

I'll probably create another thread later (to avoid mucking-up this one) to give a visual comparison between a car that needs tuning versus one with false knock.
 


OP
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Thread Starter #13
I reinstalled the OEM DP tonight and logged same negative corrections???? I installed the Stage 0 map and logged consistent positive corrections up to a full +6. I beginning to think I need to start over from the beginning and retune for the DP from scratch. I honestly can't understand why it went from one extreme to another running the same tune before and after DP. I have been told the DP doesn't require that much tuning after install and should run fine even with out.
 


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#14
Wasn't your custom tune working fine with the OEM DP before? Something does not seem right. Did you try logging with the OTS Cobb Stage 1 or 2 programming? Did you fill up your gas tank recently, maybe bad gas? When running Stage 3 I never saw negative correction until I filled up at a Sunoco station one time and I was seeing negative correction every time I moved past half throttle (seems like a got 87 and paid for 93). Negative correction issue went away after refilling my tank. Something to consider.
 


rodmoe

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#15
I reinstalled the OEM DP tonight and logged same negative corrections???? I installed the Stage 0 map and logged consistent positive corrections up to a full +6. I beginning to think I need to start over from the beginning and retune for the DP from scratch. I honestly can't understand why it went from one extreme to another running the same tune before and after DP. I have been told the DP doesn't require that much tuning after install and should run fine even with out.
Anything else change like gasoline ? forgive me if you touched on this before just spitballing here ..
 


OP
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Thread Starter #17
Wasn't your custom tune working fine with the OEM DP before? Something does not seem right. Did you try logging with the OTS Cobb Stage 1 or 2 programming? Did you fill up your gas tank recently, maybe bad gas? When running Stage 3 I never saw negative correction until I filled up at a Sunoco station one time and I was seeing negative correction every time I moved past half throttle (seems like a got 87 and paid for 93). Negative correction issue went away after refilling my tank. Something to consider.
I stricly use Chevron 94 no ethanol because I believe it to be the best we can get here in BC, Canada. My next fill up I am going to try Chevron 91 w/ethanol. I am in the process of putting some stage 0 datazap together to see if there is any obvious variable.

Yes it was running excellent on the tune before the DP.
 


iso100

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#18
Randy said the way to eliminate false knock as a possible cause of negative corrections is to run his map slot 4 which is -1 global spark and do some logs. If there's no negative corrections then it's not false knock as false knock is usually so severe it is present all the time, regardless of global spark settings. If you are just getting it (-1.6, -2.3) sometimes then most likely you're now at the limits of what your current fuel (in the tank that fill-up) and humidity/temp can handle. Load a prior revision that's less aggressive and see what happens.

I've saved every revision throughout the process and labeled them accordingly... even the revision that was overly aggressive.
 


OP
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Thread Starter #19
I am still working through this issue. I am back to OEM DP again and RRM. What I can tell you so far is removing the aftermarket RRM has made the single largest improvement in smoothing out the corrections. I can't say for sure it was the problem because I haven't done enough logs yet.
 




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