Intermittent engine 'rattle' when accelerating

[mjfulk]

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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[humfrz]

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

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

[steve99]

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

[mav1178]

Does it sound like this?

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.

[mjfulk]

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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[mav1178]

Originally Posted by mjfulk

The headers do not have a heat shield but the under panel was reinstalled. All other exhaust pieces are stock.

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

[Tcoat]

Originally Posted by mav1178

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.

[thriller]

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.

[guybo]

The overpipe has a heat shield on it.

[humfrz]

Originally Posted by mjfulk

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


humfrz

[mjfulk]

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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[mjfulk]

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.

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[humfrz]

Originally Posted by mjfulk

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.

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

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


humfrz

[strat61caster]

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