Cylinder 3/4 roughness only in gear at idle?

subydude · 11-30-2019, 10:01 PM

I'm chasing a cylinder roughness issue in cylinder 3 and 4 on a fresh build.

It only counts up at idle (1k rpm) when in gear or coasting. So coming off the freeway if I clutch in and go to neutral it will count up in 4 and some in 3 until I stop, then it goes back to zero. Car doesn't feel like it's misfiring at all.

While stopped if I put it in gear it immediately starts counting up in 4, doesn't matter what gear. And when I go back to neutral it goes back to zero. I can listen to the exhaust and tell there's no misfire going on.

As stated, fresh build, fresh valves, known good coil packs, have swapped injectors around, running speed density, fresh fuel pump and filter, new spark plugs.

Is it possible it's from mounts or something else? The car has Cusco engine mounts, a kartboy dog bone, window weld trans mounts, and home brew very stiff cross member bushings. I also have a light weight flywheel in there, but OEM crank pulley.

Any advice or thoughts?

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gaby · 11-30-2019, 10:23 PM

Lighter flywheel and Forge pistons will increase idle roughness. What is the count?

subydude · 11-30-2019, 10:27 PM

4 counts up to 50-60 or more and then resets. As soon as I pull it out of gear at idle it goes to and stays at 0. It's only when the car is in gear below about 1,500 rpm, and pretty much at idle 99% of the time.

Car does have CP pistons at 3-3.5 thou PTW. Forged rods and OEM crank with stock heads/cams/valves. Nothing special, and it runs fine in boost or otherwise. It's only at idle in gear that it seems to really advance the count.

gaby · 11-30-2019, 10:31 PM

Cp pistons are very hard, they are loud. I personally have CP pistons. I lowered the timing to not more than 40 before 90gsload. That helped a bit. As long as your compression is good and the ECU is not pulling timing, you should be ok.

subydude · 11-30-2019, 10:37 PM

It's running roughly 17 degrees timing during, not pulling any for it that I can see in the logs. Engine has maybe 50 miles on it so things are still good.

gaby · 11-30-2019, 10:39 PM

how is the IAM and the learning values?

subydude · 11-30-2019, 10:44 PM

Fine so far.

kopele · 12-01-2019, 01:58 PM

Have you tried adding timing in those areas?

2slofouru · 12-01-2019, 02:37 PM

Maybe one of those two cylinders is just a tad more lean because of injector variance and exhibiting it only at idle because of idle afr?

subydude · 12-01-2019, 02:43 PM

Quote:

Originally Posted by 2slofouru

Maybe one of those two cylinders is just a tad more lean because of injector variance and exhibiting it only at idle because of idle afr?

Unfortunately no. I forced idle in OL as a test and even with it idling at 11.5-12:1 it would count up. I have also switched injectors around and it does not follow them.

It's only when the car is in gear or in neutral rolling to a stop around 1k-1.4k rpm.

I did try adding a little timing at idle just for fun and will test today.

subydude · 12-01-2019, 08:10 PM

So I think I have it narrowed down to the neutral switch. I've swapped everything else and finally unplugged harness stuff until I narrowed it down to the neutral switch. With the switch unplugged it counted right up, with it plugged in it stopped.

Since the switch should be 12v in gear and grounded when in neutral is there any way to test besides swapping sensors?

gaby · 12-01-2019, 09:21 PM

Quote:

Originally Posted by subydude

So I think I have it narrowed down to the neutral switch. I've swapped everything else and finally unplugged harness stuff until I narrowed it down to the neutral switch. With the switch unplugged it counted right up, with it plugged in it stopped.

Since the switch should be 12v in gear and grounded when in neutral is there any way to test besides swapping sensors?

Romraider logger will tell you if is on or off.

subydude · 12-01-2019, 09:38 PM

The Cobb I have shows it turning on and off.

gaby · 12-01-2019, 11:03 PM

Make sure it doesn't stay on or off between gears. mine is inverted polarity do jdm transmission switch.

subydude · 12-02-2019, 10:40 AM

I have a spare from another case that I'm going to plug in and test tonight to see if the issue is the same. If so then maybe a wiring issue. If it solves it then I'll have to swap the switch.

subydude · 12-05-2019, 12:57 PM

Following up on this, I tested with another neutral switch and the issue remains. Only counts up misfires in gear at a stop, or when in neutral coasting to a stop, so basically below 1,500 or so rpm at 0 mph in gear or below that rpm coasting in neutral.

Still only on cylinder 4 and 3 really, even after swapping injectors, coils, etc.

I have the factory grounds in place, but did put phenolic spacers in so I was thinking of running a few extra just to test. I also was wondering if an alternator could cause the issue at idle, or the fuel damper at the feed/return. It all seems to be low airflow/fuel flow (sub 1,500 rpm) and seems related to the neutral switch.

Again, still not actually misfiring, so it seems to be a false reading.

11-30-2019, 10:01 PM	#1
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	Cylinder 3/4 roughness only in gear at idle? I'm chasing a cylinder roughness issue in cylinder 3 and 4 on a fresh build. It only counts up at idle (1k rpm) when in gear or coasting. So coming off the freeway if I clutch in and go to neutral it will count up in 4 and some in 3 until I stop, then it goes back to zero. Car doesn't feel like it's misfiring at all. While stopped if I put it in gear it immediately starts counting up in 4, doesn't matter what gear. And when I go back to neutral it goes back to zero. I can listen to the exhaust and tell there's no misfire going on. As stated, fresh build, fresh valves, known good coil packs, have swapped injectors around, running speed density, fresh fuel pump and filter, new spark plugs. Is it possible it's from mounts or something else? The car has Cusco engine mounts, a kartboy dog bone, window weld trans mounts, and home brew very stiff cross member bushings. I also have a light weight flywheel in there, but OEM crank pulley. Any advice or thoughts? * Registered users of the site do not see these ads.

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11-30-2019, 10:23 PM	#2
gaby Scooby Specialist Member#: 94097 Join Date: Aug 2005 Location: Tucson, AZ Vehicle: 2004 WRX Hybrid GT35 [email protected]	Lighter flywheel and Forge pistons will increase idle roughness. What is the count?

11-30-2019, 10:27 PM	#3
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	4 counts up to 50-60 or more and then resets. As soon as I pull it out of gear at idle it goes to and stays at 0. It's only when the car is in gear below about 1,500 rpm, and pretty much at idle 99% of the time. Car does have CP pistons at 3-3.5 thou PTW. Forged rods and OEM crank with stock heads/cams/valves. Nothing special, and it runs fine in boost or otherwise. It's only at idle in gear that it seems to really advance the count.

11-30-2019, 10:31 PM	#4
gaby Scooby Specialist Member#: 94097 Join Date: Aug 2005 Location: Tucson, AZ Vehicle: 2004 WRX Hybrid GT35 [email protected]	Cp pistons are very hard, they are loud. I personally have CP pistons. I lowered the timing to not more than 40 before 90gsload. That helped a bit. As long as your compression is good and the ECU is not pulling timing, you should be ok.

11-30-2019, 10:37 PM	#5
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	It's running roughly 17 degrees timing during, not pulling any for it that I can see in the logs. Engine has maybe 50 miles on it so things are still good.

11-30-2019, 10:39 PM	#6
gaby Scooby Specialist Member#: 94097 Join Date: Aug 2005 Location: Tucson, AZ Vehicle: 2004 WRX Hybrid GT35 [email protected]	how is the IAM and the learning values?

11-30-2019, 10:44 PM	#7
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	Fine so far.

12-01-2019, 01:58 PM	#8
kopele Scooby Newbie Member#: 363007 Join Date: Jul 2013 Chapter/Region: MWSOC Location: MO Vehicle: 2008 STI Black	Have you tried adding timing in those areas?

12-01-2019, 02:37 PM	#9
2slofouru NASIOC Supporter Member#: 90539 Join Date: Jul 2005 Chapter/Region: South East Location: Lake Charles Vehicle: My BOV goes COVFEFE!	Maybe one of those two cylinders is just a tad more lean because of injector variance and exhibiting it only at idle because of idle afr?

12-01-2019, 08:10 PM	#11
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	So I think I have it narrowed down to the neutral switch. I've swapped everything else and finally unplugged harness stuff until I narrowed it down to the neutral switch. With the switch unplugged it counted right up, with it plugged in it stopped. Since the switch should be 12v in gear and grounded when in neutral is there any way to test besides swapping sensors?

12-01-2019, 09:38 PM	#13
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	The Cobb I have shows it turning on and off.

12-01-2019, 11:03 PM	#14
gaby Scooby Specialist Member#: 94097 Join Date: Aug 2005 Location: Tucson, AZ Vehicle: 2004 WRX Hybrid GT35 [email protected]	Make sure it doesn't stay on or off between gears. mine is inverted polarity do jdm transmission switch.

12-02-2019, 10:40 AM	#15
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	I have a spare from another case that I'm going to plug in and test tonight to see if the issue is the same. If so then maybe a wiring issue. If it solves it then I'll have to swap the switch.

12-05-2019, 12:57 PM	#16
subydude Scooby Guru Member#: 80649 Join Date: Jan 2005 Chapter/Region: South East Location: Columbia, SC Vehicle: 2000 2.5 Auto-X RSTi Dusty	Following up on this, I tested with another neutral switch and the issue remains. Only counts up misfires in gear at a stop, or when in neutral coasting to a stop, so basically below 1,500 or so rpm at 0 mph in gear or below that rpm coasting in neutral. Still only on cylinder 4 and 3 really, even after swapping injectors, coils, etc. I have the factory grounds in place, but did put phenolic spacers in so I was thinking of running a few extra just to test. I also was wondering if an alternator could cause the issue at idle, or the fuel damper at the feed/return. It all seems to be low airflow/fuel flow (sub 1,500 rpm) and seems related to the neutral switch. Again, still not actually misfiring, so it seems to be a false reading.