Misfire on cylinders 1, 3 and 5

Posts specific to the 3.0 litre NA H6 engine

Misfire on cylinders 1, 3 and 5

Postby gui67 » Sat May 21, 2022 5:15 am

Hi,
i just bought a 2006 3.0 Automatic Subaru Legacy EDM.
The CEL light is flashing and I get P0301, P0303 and P0305 codes: Misfire for all cylinders of bank 1...
and P0172 system too rich bank1

It runs fine when cold, but when the temperature increases, after 10 minutes drives, the CEL flashed and the car starts to drive rough, the idle is unstable, it shakes.

We replaced all 6 spark plugs, the coil from Cylinder 5 (the one that had the most misfire errors), switch the front AVCS valves, replaced the rear AVCS valve with the one from a 2nd car, exchanged the front O2 sensors.
when working on the car, I noticed that the previous owner emptied the catalysators....

I wanted to connect ECU flash and get the ROM, so I looked for the green connectors but they were already connected: we were driving with the connectors connected.
(On my 05 spec B, when they are connected the fuel pump is cycling and CEL is blinking)
So I disconnected them and tried to drive again, then the P0420 appeared. and it disapeared when the connectors were again connected...
I suspect the ECU was modified to avoid the P0420 CEL when connecting the connector. I am tryiing to get back to the original ROM, we will see if it is possible.

I am also thinking about an injector problem, I will get them cleaned.

Would you have an idea what else could cause a misfire on all 3 cylinders from bank 1?


the spark plugs where also very strange when we replaced them:
cylinder 5 and 4 were like new the ceramic completely white and clean
Cylinder 3 and 2 were completely black
The 2 other where "normal": clear ceramic and metal but with signs of combustion

Thank in advance
Guillaume
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Sun May 22, 2022 1:40 am

Further investigations this morning showed that the injector n° 1 has been replaced in the past. the part number is not the same.
We will check if it is interchangeable.

And also someone put a jumper wire between the injector 1 and 3... (on the ECU wire)
So I suspect that both injectors were opened whenever the ECU drived the 1 or the 3. So cylinder 1 and 3 were getting twice as much fuel as the other, explaining the black spark plugs and the leaning of bank 1 and thus misfire on the 5...

Would you have a wiring diagram of the injectors in order to test the continuity between the ECU and the injectors? I have the wiring diagram for the 2005, but the wires are not the same color and it seems that they do not go to the same ECU pins: we tried this morning but I got no continuity from none injector.

Best regards
Guillaume
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Sat May 28, 2022 2:16 am

The car has been built in february 2006.
Can I assume it is using the rom D0XJ001R and simply flash this one?
Is there a possibility to check and avoid bricking the ECU?
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Sat May 28, 2022 4:41 am

So for the misfire problem, after checking the wiring harness, the injectors,... as there was no signal on the oscilloscope at the injector, we backed the ECU in the oven at 190°C for 8 minutes.
Problem solved. No more misfire, the engine runs smooth.

only problem left is to get access to the rom in order to set it for E85. If any of you have an idea what is possible without bricking the ECU?

thanks in advance
Guillaume
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Re: Misfire on cylinders 1, 3 and 5

Postby Stifull » Sat May 28, 2022 2:48 pm

Did you have fries with that and what did you baste it with.. Great that you got it solved. Our sti, after having a very dodgee windscreen replacement done leaked like a sieve and saturated the ecu and the whole car refused to do anything. It was sitting on the side of the road between Jundy and Thredbo for 10 days in 60cm of snow until the towie could retrieve it. It dried out and all worked well again. Had the windscreen redone properly by Jindi Subi shop.
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Re: Misfire on cylinders 1, 3 and 5

Postby bigBADbenny » Mon May 30, 2022 3:54 pm

Interesting fix! Where did you get the idea to reflow the entire ecu?

To tune the ecu, you’ll need a Tactrix openport2, Romraider and ecuflash.

Swapping ecu’s without a dealership security recode is apparently possible by swapping over the security eeprom chip between ecu’s.
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Thu Jun 02, 2022 6:08 am

HI, I have the openport cable, Tactrix and ECUflash.
It is working great on my 05 M6 Spec B which I modified . But not on this one (06 3.0 AT): I can datalog while driving but not read the ECU.
and the green connector was already connected while I purchased the car, it seems that connecting the connector disables the P0420 error code as it does not appear even without the catalitic converters. and if I open the green connectors, the code shows up.
Connecting the green connector does not cycle the fuel pump like on the other car.

I got the information to put the ECU in the oven from an Outback forum: https://www.subaruoutback.org/threads/2008-3-0-fix-for-ecu-not-sending-injector-pulses.527609/

I don't know if the dealership has the possibility to reflash the ECU to the stock configuration overiding the "tuner's protection".
otherwise, just as you proposed there will be only the possibility to swap the ECU and keep the original security Eeprom.
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Re: Misfire on cylinders 1, 3 and 5

Postby bigBADbenny » Thu Jun 02, 2022 4:41 pm

Lookup the diagnostic mode plugs in the FSM, there’s another set behind the glovebox iirc.
I forget the rest of the info eg whether one or more sets need to be plugged.

For the tactrix, you might need to use an ecu alias, eg from an adjacent ecu in the ecuid list on Romraider.

No wait, if the car was tuned and the tune was locked, you’ll need to get the ecu unlocked prior to retuning.
Or if you can connect, reflash with the stock rom (ThrottleHappy)

Or if it runs well, leave it, eg if it’s auto and tuned by ThrottleHappy aka Matt McLeod, then the auto also would have been tuned for better response & drivability. Sean Regan aka Sick Chips on FB or MadmanSean here can unlock ecu’s either remotely or send in.

Share a datalog with h6 tuning parameters and I’ll peep it in MLVHD. :good:

Deets here:
viewtopic.php?f=6&t=36932&p=452065&fbclid=IwAR05VdOgUo6rgQ8JkYSk3OnZKw2V9YE-uCLRlA7Jl7TphPlrksOuWlhpea4#p452065
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Fri Jun 03, 2022 3:33 am

Thank you very much for your answer, it allowed me to see that there is a second connector inline with the one I used on mine.
Now that both were connected I managed to get into the test mode and download the ROM.
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Fri Jun 03, 2022 4:16 am

Hello, Here is the Rom I finally managed to download.
Unfortunately it does not match the definitions I have in ECUflash.
Let me know if you manage to read it.
My goal is first to tweak the injector size to drive with E85 and in a second step try to adapt the Merpmod for flexfuel using a 0-5V input like I did on my 05 SpecB.
Attachments
3.0 stock 20220602.zip
Rom for 2006 AT 3.0 Legacy
(336.54 KiB) Downloaded 94 times
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Re: Misfire on cylinders 1, 3 and 5

Postby bigBADbenny » Fri Jun 03, 2022 2:31 pm

I’ll take a peek, also check your PM’s for more info.

Which sensor delete would you use on an H6? Maf volts or rear o2?
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Thu Oct 06, 2022 2:44 am

gui67 wrote:So for the misfire problem, after checking the wiring harness, the injectors,... as there was no signal on the oscilloscope at the injector, we backed the ECU in the oven at 190°C for 8 minutes.
Problem solved. No more misfire, the engine runs smooth.

only problem left is to get access to the rom in order to set it for E85. If any of you have an idea what is possible without bricking the ECU?

thanks in advance
Guillaume


OK, after some time the problem came back: misfire cylinder 1, and engine running very rough
I soldered a wire between the output of the chip managing the injector and the pin 8 of the ECU. it was running fine for a few days but came back...
So I will try to solder directly the wire on the pin of the chip instead of soldering it on the trace a few mm away.
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Re: Misfire on cylinders 1, 3 and 5

Postby Stifull » Thu Oct 06, 2022 11:40 am

That's odd.... :D
Current Subarus
07 Liberty GT (mine) 180kwt on 16lb
98 WRX Club Spes 2 with 2.5ltr upgrade(mine) sub 14 sec
99 Ver 6 Sti also with 2.5ltr upgrade (son) sub 14 sec
02 WRX Bugeye Hatch lots of goodies(wife)
09 Non Turbo Impreza(daughter#4)
Previous
98 GC8 WRX Hatch(daughter#1)
02 Bugeye WRX (daughter#2)
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Re: Misfire on cylinders 1, 3 and 5

Postby bigBADbenny » Fri Oct 14, 2022 11:05 am

Sean Regan, aka Madman Sean aka Sick Chips might be able to diagnose, repair and reflash your ecu?

He's here and on FB too.
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Re: Misfire on cylinders 1, 3 and 5

Postby gui67 » Sun Mar 05, 2023 5:36 am

Just as an update, I resoldered the pins of the injector driver chip, the one s for cilinder 1 which was seeing bad signal by applying the soldering iron tip on the small pins.
it is now running great since 4 month.
So I think the problem is solved.
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