Intermittent engine 'rattle' when accelerating
 

Im experiencing an intermittent rattle/knock from the engine bay (on the drivers side) when accelerating between 3k to 4.5k rpm. I've been unable to replicate the noise when in neutral and free raving the engine. It tends to occur when the engine is warm, never when cold. Sometimes I'll go a day without any issues and other days I'll hear it almost everytime I accelerate regardless of which gear. I have a 2014 MT fr-s with 70k on the OD. Mods include a drop in filter, catted ft-86 header, and OFT tune. I purchased the vehicle used with 62k mile and the noise was present when the vehicle was stock so it doesn't appear to be related to any of the mods. No other issues when it's making the noise, power loss or the like. It doesn't appear to be rod knock (not metallic sounding). Others have posted identical description of the issue but have not commented on a cause and or fix. I want to chalk it up to a noise these engines make but it appears to be happening more frequently which concerns me. Doesn't have the load pop associated with DI seal issues and only happens under load. If it's the valve timing, as some have speculated, why is it intermittent and present with or without the tune? It's loud enough passengers have asked what it is which tells me again it's not normal boxer sound.

I've spent hours trolling other posts and again it doesn't appear I'm the only one experiencing this problem. However I've yet to hear from anyone who has diagnosed/resolved it. I'm getting increasingly frustrated with it and would appreciate if anyone has experience with a similar issue and what came of it.

One last observation, when it's making the noise the engine sounds slightly rough when cruising at engine speads below 3k RPM. Hard to describe the rough sound but kind of like a faint rattle. On days I'm not experiencing the acceleration knock this rough sound isn't there.

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Hello mjfulk and welcome to our forum...........:clap:

Does your aftermarket header have (or retained) any heat shields .. ?? If so, that would be the first thing I would check (to see if they are lose or hitting the frame).

The next thing I would check, is to see if any of the under panels are lose.

The next thing to check is to see if any of the exhaust pieces oven come close to something else, especially when the engine is torqueing over.


humfrz

Use oft to log engine parameters

Log iam it should be 1
Log flkc fine knock cintrol, see if it goes negitive when you experience the knock

If itx an auto check the the air pump at rear of engine

Does it sound like this?

https://youtu.be/9cAH2hyn4zs?t=13s

Is your overpipe stock? What about your front pipe?

Any one of those could cause rattle and the noise can be transmitted across the chassis.

If the rattle/noise is RPM specific then usually something is loose and not an internal problem.

Wow, thanks so much for the quick responses. From what I can tell its rpm specific but since it's only present in a relatively small range I can't say that with any level of certainty. From what I can tell the video sounds similar to my noise. Do you know what the cause was? Since it was present when stock I've been assuming it wasn't related to either the tune of headers. The headers do not have a heat shield but the under panel was reinstalled. All other exhaust pieces are stock. I'm located in Cheyenne at an altitude of roughly 6,200 ft. Stupid question but does high altitude reduce the risk of knock. Thanks again for all the responses, I really appreciate it.

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Only way to rule out heat shields on OP or front pipe is to take them all out and test drive. In my video the issue was the header heat shield, it was all bolted together well but some portion of it was rattling, I didn't care to take it off to check.

The underbody may be loose, check the hardware to see if anything is loose or missing bolts.

-alex

My vote is pretty much 100% heat shield.

Catted FT86SF header doesn't have a heat shield, but mine rattled like crazy against the skid plate, until I gave the skid plate a little bit of a bend where it was touching. If you pull off the skid plate, you should see some obvious wearing on the metal where it's touching. Just bend that bit out of the way with a hammer or your heel.

The overpipe has a heat shield on it.

It's my understanding that, on newer engines at least, the tendency to knock is less at higher altitudes.


humfrz

I'm going to get under the car here in the coming days and check the exhaust and underbody for anything that is loose or has evidence of rubbing. I don't want to get my hopes up but something simple like that would be the ideal outcome here. I'll let you know what I find out one way or the other. Thanks again.

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Here is a video of the noise. Not the best quality but the sound does come through on it. Update but for the first time I was able to replicate the noise when reving the engine in neutral this morning. Not sure if that eliminates some causes.

https://youtu.be/lt7w4y4m7iI

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The ECU is causing the intake to gag, because your leg is ugly ...... :barf:

(sorry, I can't hear the sound that you're referring to ....:(..)


humfrz

Once again, sounds like VVT overlap from the OFT tune.

Happens at 4s-5s, 7s-8s, 12s, a little at 24s, 38s-42s etc. right?

If you want to get rid of it you'll need to change your current tune to a custom map (you could pay Shiv at OFT for remote tuning work, he should know what to change to get rid of it which will likely result in some power loss in that 3.5k-4.5k range) or go back to stock. Don't believe me? Drain the tank, put 93 octane in it and flash back to the stock map on your OFT, noise gone. You can even flash to OFT's stage 1 map and hear it come right back. I believe most tuners say it is harmless, whether you trust that is up to you.

Once again in case you didn't bother to read it the first time I linked it for you.
http://www.ft86club.com/forums/showthread.php?t=59475

I've read the threads on VVT noise from various tunes but I'm not convinced it's what I'm experiencing. First the intermittent nature of the noise. Why would it come and go from day to day drive to drive and be happening more frequently over the last several months. Second, and more importantly, the noise was occurring before I installed the tune and headers when it was completely stock. The last couple times I've flashed back to the stock tune it occurs with the same frequency as with the tune.

I'm so desperate to get this addressed I decided to upload the video, complete with my gross leg and all.

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Well it sounds precisely like my car on OFT tune, you have to nail the load and throttle position, repeatable but sometimes it can be tricky to coax out.

If it's not that then I'd go with what others have said, some heat shield/undertray is loose and needs to be tightened.

Good luck.

I swung by the shop this afternoon and the head tech went for a ride with me. After hearing the noise a handful of times he's almost certain it's valve noise. With that being the case the question remains why its occurring more frequently and with the stock tune and we'll as the OFT tunes. If it continues to get worse is it a problem that needs to be addressed and if so how. Feels good to get closer to the answer but still some unknowns remain.

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Did he expound on that .... ??

If it does have something to do with the valves, yes, it should be taken care of.

What should be done .. ?? That would depend on what's wrong.

Most likely the head on that side would have to be taken off and the valve train inspected.

If I were you, I'd still check for something rattling, before I tore into the engine.


humfrz

He mentioned the VVT system as the likely source. I'll apologize here for my ignorance concerning VVT in general but he mentioned several things in the system that could be the cause. I asked if he thought it could be a panel on the bottom or something in the exhaust system. His response was that the rate of the rattle and tone made him pretty sure it wasn't either of those but rather a valve issue. I still plan on getting under the car this weekend to see if there is anything obvious.

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histortically rattle at 3K, sounds like its from engine bay and its manufactured by the six star oil eater, its prob a heat shield.

I was able to get under the car and took the two bottom panels off. The metal one under the engine and fiberglass one under the transmission. After driving around for a day and a half the noise remained unchanged. I looked at the exhaust and didn't see anything obvious that would be causing the issue. I also had the chance to change the tune between the four tunes with the oft.. Stg 1 EL, UEL, e85 EL, and e85 UEL (after filling up with e85 and following the recommended ecu learning procedures). The noise is present and random with each tune. Perhaps it occurs more often with stg1 EL but that could have just been the day. On that note any thoughts on the tune to use with a catted header? Finally I also data logged for the first time this morning with the oft tablet. What should I be looking for concerning knock?
Thanks

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Did you take off the heat shields on the overpipe/front pipe? The heat shields have several overlapping components that may cause rattling.

Also, it is rare but there is the remote possibility that the front pipe catalytic converter is bad. Mine was replaced under warranty because the honeycomb assembly came apart, was not making noise but was loose when you take off the front pipe.

-alex

Thanks Alex, I'll take a look at the heatshields this weekend. In the meantime I've been doing some research on the data logging I did today. My values for FLKC and Adv Multiplier (I assume that is IAM) are constant at 0 and 1 respectively. My only concern is that they are exactly 1 and 0 without any change. Is that correct or an indication those parameters aren't reading?

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Holy shit, that word pounded me in the face, I wasn't ready for that fancy word wtf

Ya, I got that word out of mrs humfrs's big book of words ...... :D


humfrz

not sure what kind of info it can show you, but your looking for knock related or kknock sensor related if your concerned with knock ... but knock is pretty distinct, look up an video of a subaru knocking and youll be able to tell immediately

Hello, I have the same problem in my BRZ. Could you solve it?