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Engine Knock Thread

15K views 161 replies 15 participants last post by  jayochs 
#1 ·
Ok, I needed to make a new thread, since my old one was mainly about my tune, which I thought was making my engine knock but it only exacerbated the problem.

Pretty much, I got an MPT Performance 87 tune as I wanted to keep the car running 87 because well, the 3.7 was made to run regular, and now in NJ with this ridiculous 12% gas tax, i'm in no mood to be paying almost $3 a gallon for 93.

So I got my MPT tune and I noticed the engine would always knock in low rpms when giving it gas. it's a quick little CLONK sound. i have no idea if it's pre-ignition, or spark. I ran data logs and everything, sent to MPT, and I had 4 revisions done, and they all knocked exactly the same. I'm over my month period since getting the tune, so I doubt they'll help anymore, but pretty much if these 4 didn't fix it, they can't fix it because it obviously has to be a problem with my car.

i thought it was the tune, but when i went back to stock, i realized i could SLIGHTLY hear it when shifting. not always, not 100% of the time, but it was still there. the tune exacerbated it because, i believe, the increased throttle response would allow for more throttle at lower rpm's when i shift, thereby pushing the engine and making it knock more than it did stock..that's my theory anyway.

MPT's response was stop using 87, try higher grades, and if that fixes it, that's your problem. that was a lot of people's responses, too. they also said to try quality gas stations..problem is, the only stations by me are Wawa (which apparently is crap, who knew, i always used it..), Lukoil, and Sunoco.

so i tried 93 from Sunoco. it knocked slightly (3rd gear is always the culprit, when I shift into 3rd in my neighborhood around 20-25mph and give it gas as i come out of the shift, it would knock) and SOMETIMES it did it with 93, but even when i slammed gears hard at low speeds, 93 didn't seem to really knock.

which brings me to this: the 3.7 was made for 87; hell, so is the 5.0. why in gods name does MY 3.7 require 93 in order to like 98% stop knocking? i mean hell, it didn't even 100% fix the issue.

i'm not getting a CEL saying my knock sensor is bad or anything, i don't think there's any issue, but i have no idea. again, idk if it's preignition or spark. I've got a video if anyone wants to listen and see what their opinion is; i've already spoken to both Volt and VIG about this, and Volt's even looked at my datalogs and we haven't come to any conclusion. the sound i hear to me sounds identical to when you don't give the car enough gas from a standstill when you're letting off the clutch and the engine starts to knock.
https://www.youtube.com/watch?v=IAk7iTiGqgs
In this video, at exactly 9 seconds, you can hear the first knock when I shift into third..it's after the sound of the shifter going into gear. then skip to 53 seconds, and right after i go over the speedbump and shift, you can hear a loud knock. it's like a clanky CLONK sound. it's weird.

https://www.youtube.com/watch?v=DylFSDrjxgk
in this video, goto 39 seconds. i'm purposely doing crappy shifts because that's when i can always reproduce it. you'll hear it shift into 3rd, then clonk.


Problem is, if I put it back to stock and bring it to ford, i guarantee when they goto drive it, they won't hear it..because even I barely hear it on stock, but it's slightly there. i can't bring it there with the tune, which they would 100% hear, so is my only recourse to bring it to a shop i trust with my tune on and ask their opinion? i don't want to ruin my engine, and i don't want $450 to have gone wasted with this tune.

is this something that could potentially be alleviated by colder/warmer spark plugs, or something? i'm not a gearheard so unfortunately i'm not well versed in any of this.
 
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#70 ·
I suppose your cats could be melted inside. That'll sure mess things up. Our company truck had bad cats, 02 1500 Dodge. Had loss of power but I don't remember it pinging. Wouldn't pull a hill worth a darn. We use it for motorcycle pick up for customer break-downs. Get a big ol fat H_D bagger with all the customer gear and the two fat riders in the cab and you have a load. Muffler shop put all new exhaust on her and she ran like a new truck. Had 150,000 miles when we did that. Still running great.
 
#71 ·
I'm starting to think, you have a broken or weak springs in your pressure plate making the sound :)
 
#72 ·
that wouldn't be good lol. but the quality of gas affects it though. when I run 93 it hardly knocks.
 
#74 ·
I don't think i did a log on 93, though. only 87.
 
#75 ·
Well, that's the next step. I am still convinced that if you could audibly hear engine knock that loud it would be shooting a rod through your oil pan. I am also not convinced the situation, namely a shift where things are inclined to rock and shift, is correct for engine knock.
 
#79 ·
I've checked intake. I've opened it up and put it back together many times, never noticed anything. is there another way to check? as for the maf, I don't have any electronics cleaner on me so I'd have to research how to clean it.

but in terms of running lean, isn't that the measurement of air/fuel mixture that's in the center screen? mines normal from everything I've read online about it for these mustangs. idles at like 13.9 to 14, flooring it can go as low as 12, and when coasting shoots up to 20.
 
#81 ·
just curious, I got a 91 performance tune too and never tried it. should I fill 93 and flash the 91 tune to try it out? or still try the 87 tune? I do wanna try that 91 one day haha
 
#82 ·
Well, for the sake of discussion, if we think the 87 tune is "knocking," 91 probably isnt going to be any better.

I would say to datalog the 87 tune with 93 in the tank. If the issue is still apparent in the datalogs, we can try the 91 tune to simply rule that entire 87 tune file out.
 
#83 ·
when i ran 93, i didn't really notice any knock sounds. so i'll have to just datalog while driving around and look at the knock sensor values to see if it's actually knocking inaudibly. but as far as audible, i didn't notice it. i'm full tank now so it'll take me a while to run it down to near empty.
 
#84 ·
btw volt, check out that guys thread about clutch/transmission sounds...sounds like he's got the exact same knocking sound i have. and someone else in there has it too.
 
#89 · (Edited)
lol i know it's not audible. this is the V4 tune where i DON'T hear it at all.

on V1, it goes up to 4 and above, remember? that's when i DO hear it.

guys, please answer me this, because this is what happens and everyone seems to be ignoring this:
i posted a video of what the engine sounds like when it lugs and is about to stall when you start off really bad on a manual. lots of cars do this. my old 01 frontier did this. as you start to give it gas, and you have a bad start, the engine knocks like all hell. i posted a video showing this. in this video, you'll hear the exact same knocking sound as i hear on my V1 tune frequently.

if a bad start causes the engine to lug and knock, why would anyone think the noise i'm getting when on the V1 tune is NOT related to the engine when it's the same exact sound?
 
#90 ·
Because you are still confusing "a knocking sound" with actual engine knock. When you lug the engine that bad and have a bad start, the engine is PHYSICALLY knocking around because of the soft stock motor mounts, soft K-member mounts, the soft stock trans mount, the soft diff mounts, etc... there is nothing stable holding the engine, so when it is fighting to stay running it is flopping around .

Again, the knock sensor is a microphone, if there is loose exhaust, loose motor mounts, loose anything clunking and banging around, the knock sensor will pick it up. The situation you are describing, from a physical, tuning, engine dynamics standpoint, does not, cannot, and will not produce pre-detonation. Not unless your engine is already dead from some other occurrence. You are hearing drivetrain noise.

The best thing to do at this point is stop watching youtube videos and try to find other mustang owners in your area and drive / ride in each other's cars and go from there.
 
#91 ·
hold your horses...I was under the impression the knocking sound from bad starts was misfiring and pre detonation. I think I read it on like a Subaru forum where a guy asked about the noise as well and that was everyone's response. so you're saying knocking from a bad start ISNT pre detonation?
 
#99 ·
No, i'll reiterate a few points i've made before, but obviously things get lost over this much time and this many posts.

1. If we were basing this decision purely off an audible inspection, and i heard what you have posted in your videos, if that were actual pre detonation it would be shooting a rod through your oil pan. Knock isnt even noticeable from a power delivery interrupting standpoint until around 4-6*, let alone being able to actually hear it.

2. There is a lot of slack in the drivetrain. I can get under my wife's car and rotate the driveshaft by hand maybe 5-10* back and forth. Every time you get on the gas, there is essentially slack in the drivetrain that has to be taken up. I can tap the gas in her car at low rpm 4th gear and get a slight clikc / clunk as that slack is taken up. It does not do it every time we drive, BUT it is a situation i can replicate almost on demand.

3. The situation present in a bad start: low rpm, low to mid throttle, low load... these are just not the situations where pre-detonation exists *on a healthy motor*. Like i said, this 3.7 engine at 1000 rpms isnt even making over 100 ft/lbs. With such low airflow, no VVT advance, even the most aggressive spark timing (which lets be honest, the stock Ford tune is not using) should not cause enough cylinder pressure to ignite the mix before the spark plug fires.

4. The fact that your datalog does show slight knock ****** during daily driving conditions is likely an unrelated issue. Again, have we be able to compare daily driving on the 93 tune? Have we compared to other people's daily driving logs? I dont think the tiny little hiccups in your log i remember seeing are enough to be noticeable, and certainly not enough to be audible.

5. You also have to consider where you are getting your information. A subaru, most likely is turbocharged depending on which forum you were looking at. High throttle and low RPM on an NA engine does nothing, it just doesnt make power. High throttle at low RPM on a small turbo car can create an insane amount of boost. On the mazdaspeed3s i predominately tune, i can have over 30 psi at 2500 rpms if i wanted. THAT would wreak havoc on a motor and would almost certainly lead to knock. I believe that is why you were getting the responses you were off of that particular forum.
 
#92 ·
I agree with Volt...I'm not convinced it is engine knock either. But we are not hearing it in person. I'm not in the mood to read through this thread again but if you shift into 2nd and 3rd at over 3k rpm do you hear it, and does it make more than1 knock?
 
#93 ·
sometimes. and it'll be like one clicky knock sound. sometimes it does it over 2500, others it doesn't. it's not that consistent but when I drove the other day, it was consistent where everytime I gave it gas, period, it knocked. then I flashed v4 tune and it didn't knock anymore.
 
#94 ·
You said your gas stations suck, i had an '00 eclipse and everytime i bought gas from the natives the engine knocked lol (huffing it and replacing with water maybe? Lol) im almost positive my gas tank had water in it. Ran it bone dry and fueled up at big name stations and never had the problem again.


Sent from my iPhone using Mustang Evolution
 
#96 ·
so i gotta drive 20 miles just to fill up? lol nah
 
#98 ·
I wonder if there are multiple issues....

there is a tune that is bad (or gas)

the rest may be just the normal clunks in the drivetrain/shifting low rpm.

on the gas issue and I am doubtful this is your issue..way back when I learned not to get gas from the one place that was always way less than all the others. idk if this is still true but I do avoid the cheapo stations.
 
#101 ·
so I took my 12 V6 MT 3.31 with suspension mods out of hibernation yesterday. I have a single thunk (muffled metallic) when I accelerate around 2-3K after coasting (easily heard). I'm fairly confident it's the drive train/drive shaft. I then tried accelerating when going up a moderate hill at the same rpm...you could hear some lugging. I ain't worried about the sounds mine made...I'd call them normal.

Jay,

I offered b4 if you ever come up to CT you and I can compare sounds.

Mud
 
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