Random misfire all cylinders

[zactek]

Here is the log

BtSsm_20180306_213629_knock-2.csv

[relative4]

Yeah, I would start with a smoke test.

[heiche]

It's odd that in the log nothing significant happens, then bam, misfires in all cyls, iam drops, etc. It's like the ecu has a stroke, then recovers. What error codes do you get after this happens?

[zactek]

It's odd that in the log nothing significant happens, then bam, misfires in all cyls, iam drops, etc. It's like the ecu has a stroke, then recovers. What error codes do you get after this happens?

 

That's exactly what happens,out of nowhere exactly 10 minutes after I start the car; little backfire and a little bucking/ shake for a minute. Then,like nothing happened for the rest of the ride. NONE of this happens if I let the car warm up,then drive.

The codes are P0301,302,303,304

 

Zack K

[Perscitus]

How is the battery connection, battery V while this happens? log that too next time and see if you can notice an abrupt drop in Battery V (too bad we can't log or see ECU supplied V too at the same time).

 

Maybe it is the ECU harness/plug, ground acting up?

But yeah, doesn't explain why it seems to happen like clockwork.

[xt2005bonbon]

Yeah, I wonder if there is either a loose wire or a cracked vacuum hose hiding somewhere.

[zactek]

I finally got a chance to check battery cables and vac. lines. Battery cables and terminals are clean and tight,all 5 grounding points are good as well ( the 2 head-to-frame rail ones are a year old)

All vacuum hoses are tight (all are silicone less than 2 years old,ziptied)

I ran another log with battery voltage logged ( when it bucked again) but I don't believe voltage fluctuated much (I also have a voltage gauge mounted inside)

When the car bucked,the CEL flashed but didn't stay on,the misfire counts on my BtSsm monitoring screen all went to 0,then the car acted normal again while driving.

How hard is it to get to the ECU ground?

Log is attached

 

Thanks,Zack K.

BtSsm_20180312_060058_knock-1.csv

[xt2005bonbon]

Have you ever logged the fuel pump duty cycle? I am just thinking if the pump is beginning to fail or something.

 

IAM went from 1 directly to 0.25 and then to 0. That's pretty drastic. And then while the IAM is at 0, you even have FLKC as low as -11.75 already learned. That's interesting.

[xt2005bonbon]

also, your idle fuel trims indicate a lean condition: your long term fuel trim was set around 14% and yet the ecu was still adding another 4-6% of fuel.

So, even though all vac lines appear to look good, you may still have a vacuum leak somewhere. Or MAF issue.

[relative4]

Visually inspecting vacuum lines is a waste of time. The reliable way to find a vacuum leak (as strongly suggested by your idle trim) is a smoke test.

[zactek]

Visually inspecting vacuum lines is a waste of time. The reliable way to find a vacuum leak (as strongly suggested by your idle trim) is a smoke test.

 

Ok,I guess I gotta find a competent shop that can actually do a smoke test in my area...

Any precautions? I never had this done...

 

Thanks, Zack K.

[relative4]

Paint can smoke tester is $80 on eBay, or DIY for less.

[zactek]

Went to a bunch of shops today,found 3 that had smoke machines. After listening to my problem,all 3 told me I'm wasting my time and money,and to look elsewhere,like injectors,fuel pump or MAF.

I CAN get one of those smoke testers from eBay,but no garage or a place to hook my compressor to an outlet. Meanwhile,I'm gonna try to log my fuel pump duty cycle during my bucking,and look for more shops. I AM sceptical about a vacuum leak because HOW would it be intermittent??

 

Zack K.

[xt2005bonbon]

Cracked line could lead to intermittent issues. bad maf connections could do that too.

[zactek]

Cracked line could lead to intermittent issues. bad maf connections could do that too.

 

I totally agree,but ALL of my vacuum hoses are new silicone,not cracked,and ziptied. I could barely pull them off if I wanted to. New Turkey Lord metal T under the IC. Most of my hoses are silicone,save for a few heater hoses. Any way to check if MAF is bad other than swapping?

 

Zack K.

[xt2005bonbon]

I can't remember if I posted on your thread the interesting behavior that occured on both of my cars: btssm app running on my phone, car idling, placed phone in engine bay, wiggled the MAF wire while starring at the btssm app. Lo and behold, the fuel correct started to jump around. You could also hear the engine rpm changing. ymmv, but it does not hurt to try this. Essentially, I had a poor connection between the maf and wiring harness. Sprayed some electronic whatever it's called cleaner and it's been better.

 

Try that if you have not already. If still no change, try cleaning the maf.

 

Also, do you still use the stock IC? Are you on a stock tune? IC could be leaking a bit (e.g. bottom left corner closest to turbo).

[zactek]

I can't remember if I posted on your thread the interesting behavior that occured on both of my cars: btssm app running on my phone, car idling, placed phone in engine bay, wiggled the MAF wire while starring at the btssm app. Lo and behold, the fuel correct started to jump around. You could also hear the engine rpm changing. ymmv, but it does not hurt to try this. Essentially, I had a poor connection between the maf and wiring harness. Sprayed some electronic whatever it's called cleaner and it's been better.

 

Try that if you have not already. If still no change, try cleaning the maf.

 

Also, do you still use the stock IC? Are you on a stock tune? IC could be leaking a bit (e.g. bottom left corner closest to turbo).

 

You haven't mentioned it,but I will try that,thanks!

Stock IC,but it has the Barbeanman reinforcement kit,no visible leaks (oil)

MAF has been cleaned

Tune is Cobb stage 2 for last 3 years ,no problems.

 

Zack K.

[zactek]

I made another run while logging fuel pump duty cycle. Not really sure what it's supposed to be doing,maybe someone can look at it and tell me if something's up? A friend is gonna lend me a good working MAS to rule that out.

 

Thanks, Zack K.

BtSsm_20180314_213206_knock.csv

[Perscitus]

Not sure how useful it is to log LPFP DC (Low Pressure Fuel Pump Duty Cycle) on Subarus. Sort of like Fuel Temp.. its there but can't help diagnose anything or reverse out any symptoms or issues based on ECU behavior controlling it.

 

What you can look for to confirm 'normal' behavior is: 100% DC on cold start, and potentially under WOT. Depending on the ECU table values that 100% might be 80, 85, 99, etc.

 

Then as the engine warms up and reaches operating temp Fuel Pump DC should drop in steps... to sth like 60 or 75 then on to 25 or 33 or similar at warm idle. Its unlikely to ever read 0% even when engine breaking or coasting in neutral, clutch-in, etc.

 

The Fuel Pump DC table has 3 steps usually: low, med, high and all the ECU does and this param should show is stepping between these (simple PWM control) to save on pump life (instead of running them 100% like old cars)

 

These steps vary based on Injector PW/DC, RPM, Coolant Temp, not much else.

 

The reason the param is useless is regardless of injector leaks or clogs, pump or fuel filter, pre-filter clog, the ECU will NOT command a higher Pump DC to try to compensate... just do its usual thing regardless of fuel pressure.

[zactek]

Not sure how useful it is to log LPFP DC (Low Pressure Fuel Pump Duty Cycle) on Subarus. Sort of like Fuel Temp.. its there but can't help diagnose anything or reverse out any symptoms or issues based on ECU behavior controlling it.

 

What you can look for to confirm 'normal' behavior is: 100% DC on cold start, and potentially under WOT. Depending on the ECU table values that 100% might be 80, 85, 99, etc.

 

Then as the engine warms up and reaches operating temp Fuel Pump DC should drop in steps... to sth like 60 or 75 then on to 25 or 33 or similar at warm idle. Its unlikely to ever read 0% even when engine breaking or coasting in neutral, clutch-in, etc.

 

The Fuel Pump DC table has 3 steps usually: low, med, high and all the ECU does and this param should show is stepping between these (simple PWM control) to save on pump life (instead of running them 100% like old cars)

 

These steps vary based on Injector PW/DC, RPM, Coolant Temp, not much else.

 

The reason the param is useless is regardless of injector leaks or clogs, pump or fuel filter, pre-filter clog, the ECU will NOT command a higher Pump DC to try to compensate... just do its usual thing regardless of fuel pressure.

 

Ok,so it sounds like my pump is doing its' thing; 100 on cold start,then 33 during cruise/warm idle and 67 during moderate boost/ higher RPM's. After I try this different mas, I just might be down to fuel pressure reg. or bad injectors, everything else seems to be checking out.

 

Zack K.

[zactek]

Well,the new MAS didn't solve the problem, although the car is smoother overall with crisper throttle response,lol. I'm gonna send out my spare set of injectors to get professionally cleaned and try wiggling the mas harness while looking at the BtSsm to see if anything is out of the ordinary.

 

Zack K.

[lilredwagon]

Before you throw more money at it, try this voltage regulator mod:

 

https://forums.nasioc.com/forums/showthread.php?t=1602651

 

Read through the thread for other ways to implement the diode, I cut up a blade fuse and wired it up as a fuse so it can be reversable if it didn't work. I did this years ago on my WRX, and it helped everything about the car.

 

When I picked up my 2008 Outback XT, it had a stumble/stutter under 2K and it occasionally threw a misfire CEL. So the other night, I pulled my modded, diode-fuse out of my WRX and put it in the Outback, and the car's been running MUCH smoother since. I've been monitoring my voltage as I drive and it's not overcharging anything, so it's fine as far as I can see. And going on 5 days now, the car seems to be perfectly happy. I have a new set of coils waiting to go in, but after doing this, I might return them. Hope it helps your situation!

[zactek]

Before you throw more money at it, try this voltage regulator mod:

 

https://forums.nasioc.com/forums/showthread.php?t=1602651

 

Read through the thread for other ways to implement the diode, I cut up a blade fuse and wired it up as a fuse so it can be reversable if it didn't work. I did this years ago on my WRX, and it helped everything about the car.

 

When I picked up my 2008 Outback XT, it had a stumble/stutter under 2K and it occasionally threw a misfire CEL. So the other night, I pulled my modded, diode-fuse out of my WRX and put it in the Outback, and the car's been running MUCH smoother since. I've been monitoring my voltage as I drive and it's not overcharging anything, so it's fine as far as I can see. And going on 5 days now, the car seems to be perfectly happy. I have a new set of coils waiting to go in, but after doing this, I might return them. Hope it helps your situation!

 

Thanks for trying to help,but I don't think that voltage is my problem. Optima battery and Maniac Motors hi- output alternator both less than 2 years old. Clean and tight battery terminals and all grounds,voltage meter in cabin for monitoring voltage,never less than 14.2V at idle,and doesn't drop/ fluctuate when my bucking occurs.

I can drive for days on the street below 50 mph without any problems,idle is perfect. BUT once going on the highway at higher load,will do it exactly 10 min after starting.

 

Zack K.

[xt2005bonbon]

Sound system in car?

[zactek]

Sound system in car?

 

Bone stock stereo