engine misfires on rough road - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

PabloN · 02-12-2017, 03:07 PM

Pardonez moi if this topic was brought up before--it didn't show up on a quick search. Many years ago (2013) my wife and I took my year-old FR-S on a road trip to Colorado. Somewhere in South Dakota there was a section of highway with pavement stripped down to a corrugated surface. I kept up with the traffic and the engine started running real rough. I took the next offramp and then the engine ran smooth again. I opened the hood and all the visible wire connections looked ok. I began worrying it was a gremlin Toyota and Subaru had overlooked. But when we got going again I kept the speed a bit lower, and I never had that problem again.

Just last week I read how some cars have a "rough road" sensor (not ours, I think). Apparently without this sensor, vibrations from a rough road can fool the knock sensor into causing engine misfires. If the problem doesn't persist, the misfire record gets erased from the onboard diagnostics. I don't know for sure this is what happened, but at least it sounds reasonable...

Kodename47 · 02-12-2017, 05:21 PM

Quote:

Originally Posted by PabloN

Apparently without this sensor, vibrations from a rough road can fool the knock sensor into causing engine misfires.

I highly doubt this is true, to get the correct frequency of detonation into the engine block from the road surface (via tyres, suspension, bushes and engine mounts) has got to take the perfect set of conditions, if it's even possible at all. Even then, it shouldn't cause misfired.

PabloN · 02-12-2017, 06:24 PM

Quote:

Originally Posted by Kodename47

I highly doubt this is true, .. if it's even possible at all. Even then, it shouldn't cause misfired.

OK then I guess what a rough-road sensor must do is prevent OBD indications of misfires that aren't actually there (and not actually cause misfires). In my case, I guess the easiest explanation is bad gas that by coincidence made the engine run rough I was on the corrugated road.

GsxrMe · 02-13-2017, 08:04 AM

Overpipe is slapping the engine and giving the knock sensor a run for its money? If you have ECUTEK, hook up your cable and look for knock correction when going off road again.

humfrz · 02-13-2017, 12:23 PM

Quote:

Originally Posted by PabloN

Pardonez moi if this topic was brought up before--it didn't show up on a quick search. Many years ago (2013) my wife and I took my year-old FR-S on a road trip to Colorado. Somewhere in South Dakota there was a section of highway with pavement stripped down to a corrugated surface. I kept up with the traffic and the engine started running real rough. I took the next offramp and then the engine ran smooth again. I opened the hood and all the visible wire connections looked ok. I began worrying it was a gremlin Toyota and Subaru had overlooked. But when we got going again I kept the speed a bit lower, and I never had that problem again.

Just last week I read how some cars have a "rough road" sensor (not ours, I think). Apparently without this sensor, vibrations from a rough road can fool the knock sensor into causing engine misfires. If the problem doesn't persist, the misfire record gets erased from the onboard diagnostics. I don't know for sure this is what happened, but at least it sounds reasonable...

I'd just chalk it up to ...... an aberration ......

humfrz

guybo · 02-13-2017, 12:56 PM

What makes you think that the engine was misfiring? Did you get a CEL for a misfire code? If so, which cylinder?

What did the car actually do whenyou drove down that road?

strat61caster · 02-13-2017, 03:19 PM

Were you on cruise control or did you have your foot on the gas?

I hit a bump and got a coilpack CEL once, I think what happened is my body bounced over the bump causing me to lift off and get back on the throttle really quick, got some tip-in funkiness on the early '13 tune and CEL. Cleared it and it hasn't been back since even though I know the coilpack is bad, it only shows up under track conditions.

PabloN · 02-13-2017, 03:45 PM

Quote:

Originally Posted by guybo

What makes you think that the engine was misfiring? Did you get a CEL for a misfire code? If so, which cylinder?

What did the car actually do whenyou drove down that road?

We were on a road trip and I didn't try get the problem diagnosed. It went away when I was on the off/on ramps, and when I was on smooth roads. I don't recall if the CEL came on or not (this was many years ago), but if it did then it didn't stay on for long.

I was probably jumping to a conclusion about misfires, but the engine was running very rough, meaning I needed more accelerator than normal to maintain speed. Because the road surface was a bunch of periodic bumps, the vibration was periodic and felt like the mechanical equivalent of a buzzing sound--very disturbing, I've never felt anything like it. The the vibration might have had a component related to the cylinder firing rate (= RPM/120, or around 20 Hz at 60 mph) or a harmonic. In these conditions is it possible the knock sensor was getting a signal that fooled the ECU into doing something to the engine timing?

Ultramaroon · 02-13-2017, 06:57 PM

Quote:

Originally Posted by PabloN

I was probably jumping to a conclusion about misfires, but the engine was running very rough, meaning I needed more accelerator than normal to maintain speed. Because the road surface was a bunch of periodic bumps, the vibration was periodic and felt like the mechanical equivalent of a buzzing sound--very disturbing, I've never felt anything like it. The the vibration might have had a component related to the cylinder firing rate (= RPM/120, or around 20 Hz at 60 mph) or a harmonic. In these conditions is it possible the knock sensor was getting a signal that fooled the ECU into doing something to the engine timing?

I'll guess the nannies were kicking in pulling the throttle and the buzzing souind was the nannies applying brakes to individual wheels. It's a distinct buzz that rattles the whole chassis.

guybo · 02-13-2017, 07:00 PM

Yeah that sounds more likely. I don't think it was an engine misfire. Did you notice the brake pedal feeling any different?

Those sorts of bumps sound like they may cause wheel spin, I think Ultramaroon nailed it.

PabloN · 02-14-2017, 08:52 AM

Quote:

Originally Posted by guybo

Yeah that sounds more likely. I don't think it was an engine misfire. Did you notice the brake pedal feeling any different?

Those sorts of bumps sound like they may cause wheel spin, I think Ultramaroon nailed it.

I don't recall using the brakes until I was on an offramp, but that's definitely possible. Thanks.

Ultramaroon · 02-14-2017, 01:43 PM

Quote:

Originally Posted by PabloN

I don't recall using the brakes until I was on an offramp, but that's definitely possible. Thanks.

No driver input involved. When VSC kicks in and starts grabbing the rear brakes it sounds/feels like a giant fart.

PabloN · 02-14-2017, 04:36 PM

Quote:

Originally Posted by Ultramaroon

No driver input involved. When VSC kicks in and starts grabbing the rear brakes it sounds/feels like a giant fart.

Understood. I just meant I didn't notice any difference in brake feel. Thanks.

Ultramaroon · 02-14-2017, 07:17 PM

Quote:

Originally Posted by PabloN

Understood. I just meant I didn't notice any difference in brake feel. Thanks.

Here's a crazy coincidence. I was trying to think of a clip where I've heard the VSC kicking in. Then out of the blue @HotLeopardMama pointed me right to it.

Must've had your ESP cranked up to 10.

Anyhoo, check out @soulreapersteve's first clip. It's kicking in like crazy. Does that sound familiar?

http://www.ft86club.com/forums/showp...postcount=9277

02-12-2017, 03:07 PM	#1
PabloN Senior Member Join Date: Jul 2012 Drives: 2013 Scion FR-S, M/T argento Location: Northern Illinois Posts: 133 Thanks: 109 Thanked 71 Times in 45 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	engine misfires on rough road Pardonez moi if this topic was brought up before--it didn't show up on a quick search. Many years ago (2013) my wife and I took my year-old FR-S on a road trip to Colorado. Somewhere in South Dakota there was a section of highway with pavement stripped down to a corrugated surface. I kept up with the traffic and the engine started running real rough. I took the next offramp and then the engine ran smooth again. I opened the hood and all the visible wire connections looked ok. I began worrying it was a gremlin Toyota and Subaru had overlooked. But when we got going again I kept the speed a bit lower, and I never had that problem again. Just last week I read how some cars have a "rough road" sensor (not ours, I think). Apparently without this sensor, vibrations from a rough road can fool the knock sensor into causing engine misfires. If the problem doesn't persist, the misfire record gets erased from the onboard diagnostics. I don't know for sure this is what happened, but at least it sounds reasonable... Last edited by PabloN; 02-12-2017 at 03:51 PM.

02-13-2017, 08:04 AM	#4
GsxrMe Senior Member Join Date: Jul 2015 Drives: Late 2014 Subaru BRZ Location: Cape Coral, FL Posts: 557 Thanks: 20 Thanked 183 Times in 139 Posts Mentioned: 5 Post(s) Tagged: 2 Thread(s)	Overpipe is slapping the engine and giving the knock sensor a run for its money? If you have ECUTEK, hook up your cable and look for knock correction when going off road again. __________________ 2014 Subaru BRZ FBM Turbokit: GTX3076R - ECUTEK HRI FlexFuel tune - FBM 3" Turboback Exhaust - 550cc Injectors - Walbro 485 Fuel Pump - 4bar Map Sensor - FBM Oil Pan - ACT SB7-XTSS - AMSOIL all fluids - Forester XT Oil Cooler - Cusco engine, trans mounts - Whiteline rear differential bushings - Perrin shifter bushing - Firehawk 235/45/17 - AEM Failsafe

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
MY15 Idle Dip and Misfires	Tectoniic	Software Tuning	18	10-08-2019 01:26 AM
Engine Running Rich, P0102 P0108 P0113, and Misfires	Votlon	Engine, Exhaust, Transmission	12	01-21-2017 03:38 AM
Misfires	Turdinator	Engine, Exhaust, Transmission	10	01-08-2015 10:19 PM
Sputter/Rough engine at start?	iLaw	Engine, Exhaust, Transmission	3	10-22-2014 08:21 PM
Push Start Rough Engine Start Up	joergasm	Engine, Exhaust, Transmission	3	12-12-2012 03:44 AM

02-13-2017, 12:56 PM	#6
guybo Huge E85 fan! Join Date: May 2016 Drives: 2016 Scion FRS Location: Tampa, FL, USA Posts: 1,850 Thanks: 539 Thanked 1,010 Times in 605 Posts Mentioned: 32 Post(s) Tagged: 0 Thread(s)	What makes you think that the engine was misfiring? Did you get a CEL for a misfire code? If so, which cylinder? What did the car actually do whenyou drove down that road?

02-13-2017, 07:00 PM	#10
guybo Huge E85 fan! Join Date: May 2016 Drives: 2016 Scion FRS Location: Tampa, FL, USA Posts: 1,850 Thanks: 539 Thanked 1,010 Times in 605 Posts Mentioned: 32 Post(s) Tagged: 0 Thread(s)	Yeah that sounds more likely. I don't think it was an engine misfire. Did you notice the brake pedal feeling any different? Those sorts of bumps sound like they may cause wheel spin, I think Ultramaroon nailed it.

User Name		Remember Me?
Password