2001 impreza 20N Misfire/Low on power

[Dylan20N]

Hi

I have recently bought a 2001 Impreza 20N for a good price, though it needs some things sorted.

When trying to accelerate, particularly when cold the engine seems to misfire or loose power one way or another at various engine speeds, and it seems to be less of an issue once you get to the 3000rpm area. This is making the car very hesitant to accelerate.

I have given the air flow meter a good clean with a mass air flow sensor cleaner, this did not have any effect.

I was thinking it could be one of the coil packs or something else ignition related.

I was wondering if anyone has experienced this or if this is a common problem any info would be welcome.

[Rosssub]

AFM 7/10, Coil 2/10, Something else 1/10.

Try another AFM out first, then try swapping Coil/Coil Packs. Might pay to give the Plugs a check while your in there too, Condition and Gap.

Have you had any CEL\'s or tried Diagnostics?

[Dylan20N]

You mention trying another AFM out but not quite sure how as they are pretty expensive, and will take at least a little while to get a second hand one.

The previous owner tells me he had the spark plugs changed a few months ago so that is potentially where the problem began. Do you know what the gap should be on this engine? Also is it necessary to lift the engine slightly to get the clearance for the coils/plugs to come out?

I dont have any engine error lights on though, and i have tried connecting both the black and green diagnostic plugs and don\'t seem to get anything like an error code from that.

All that happens when i connect the black plugs is the engine check light flashes continuously (could not find any info on what that means) as i believe the code for no engine error is 4 long flashes. Also tried an OBD2 diagnostic tool which although being the wrong standard tells me there are no error codes stored.

[Kiwi_Fozze]

Throw the obd2 diagnostic tool out, they can\'t read jap subies pre canbus (2006 ish)

I\'d be looking plugs coils or afm. Plugs should be gapped to .7mm or there abouts.

[Rosssub]

Is the 01 20N Impreza an EJ204? With Dual AVCS?

[Dylan20N]

 kwi_fozze said:

Throw the obd2 diagnostic tool out, they can\'t read jap subies pre canbus (2006 ish)

I\'d be looking plugs coils or afm. Plugs should be gapped to .7mm or there abouts.

So i pulled the coils and spark plugs out and discovered the plugs had between .9 and 1.1mm gap so i made them all 0.7mm.

The car is still misfiring but it does seem more responsive, noticeably picks up revs quicker which helps but it is still struggling when actually driving.

The question is which to replace first the coils or the AFM?

[Rosssub]

I thought Naturally Aspirated Spark Gaps are around 1.0mm, 0.7mm is for Turbo Engines that will blow out Spark on a 1.0mm Gap. :-\

If not the Extra Gap is hard on Ignition items like Coil Packs etc.

If it\'s actually dropping Cylinder/Missfiring go Coil Packs.

If it\'s just stuggling, or low on power go AFM.

[Nachoooo]

 Rosssub said:

Is the 01 20N Impreza an EJ204? With Dual AVCS?

I believe these early EJ204\'s were only single AVCS, just on the intake?

The oil pressure sensors can get clogged up in their gauze filters, and in some cases the gauze filters can fall apart, causing the sensor to misread. This only applies if you have the EJ204 engine haha

[Rosssub]

 Nachoooo']

[quote name='Rosssub said:

Is the 01 20N Impreza an EJ204? With Dual AVCS?

/quote]

I believe these early EJ204\'s were only single AVCS, just on the intake?

The oil pressure sensors can get clogged up in their gauze filters, and in some cases the gauze filters can fall apart, causing the sensor to misread. This only applies if you have the EJ204 engine haha

I\'m pretty sure it is an EJ204/Single AVCS.

That would/could explain Dylan20N\'s problem. Intake Cam Timing off on one Bank. I\'ve read a good write up/thread on that exact fault and the issues it causes but have no idea where I read it. :

Was the solution to just remove the Gauze completely?

Edit: Dylan what is your Engine Code on your Passenger Strut Tower Chassis Plate/Tag.

[Dylan20N]

How do i know which version engine i have? the engine code shown is EJ20-b35... if that helps

I am not sure how to tell if it is actually misfiring or just low on power but maybe if i better describe the issue.

The loss of power only seems to happen at specific engine speeds so you will be accelerating then when it hits one of the problem engine speeds acceleration goes to zero basically then when engine speed increases slightly it has more power or torque and away you go, then at next problem engine speed the problem repeats, this does seem to occur even at slightly higher engine speeds but seems to be much less of an issue once you get over the stated max torque area of 3200 rpm, or its potentially just the fact that its spinning faster and more power and more torque.

If is was just reduced power i would have though it would be more constant throughout the rev range?

[Rosssub]

 Dylan20N said:

How do i know which version engine i have? the engine code shown is EJ20-b35... if that helps

Not AVCS then. AVCS Engine code would be EJ204??? Being 2001 it\'s a V7

Is it actually loosing a Cylinder and Running on 3 when it happens?

The fact that it is worse when cold, also comes right above 3000rpm. With no CEL\'s and is Idling smooth - suggests AFM.

Which could also be effected or get slightly better with you closing the Plug Gaps.

[Dylan20N]

I am not sure how to tell if it is actually misfiring or just low on power but maybe if i better describe the issue.

The loss of power only seems to happen at specific engine speeds so you will be accelerating then when it hits one of the problem engine speeds acceleration goes to zero basically then when engine speed increases slightly it has more power or torque and away you go, then at next problem engine speed the problem repeats, this does seem to occur even at slightly higher engine speeds but seems to be much less of an issue once you get over the stated max torque area of 3200 rpm, or its potentially just the fact that its spinning faster and more power and more torque.

If is was just reduced power i would have though it would be more constant throughout the rev range?

[Skatieguy]

 Dylan20N said:

I am not sure how to tell if it is actually misfiring or just low on power but maybe if i better describe the issue.

The loss of power only seems to happen at specific engine speeds so you will be accelerating then when it hits one of the problem engine speeds acceleration goes to zero basically then when engine speed increases slightly it has more power or torque and away you go, then at next problem engine speed the problem repeats, this does seem to occur even at slightly higher engine speeds but seems to be much less of an issue once you get over the stated max torque area of 3200 rpm, or its potentially just the fact that its spinning faster and more power and more torque.

If is was just reduced power i would have though it would be more constant throughout the rev range?

I had something similar to this happening in my v7 STi, turned out it was a faulty coil pack, sounds exactly like you\'re describing. Also depended on hard you were pressing the throttle as well on my one, seemed to stop completely after about 5500 rpm, and started around 3200 rpm.

[Dylan20N]

its hard to tell if it is misfiring partly because i have not owned the car long and it being so quiet is not very audibly obvious that its misfiring, but i think it runs more rough when the power loss occurs so during the loss of power despite being steady on the accelerator it is a bit jerky.

Except my problem is occurring most noticeably below 3200rpm and a bit over that and to be honest i haven\'t had it over 5500 yet. It seems to me like its engine load related because the problem seems to worst at low rpm/low torque/low power.

[Dylan20N]

 Rosssub']

[quote name='Dylan20N said:

How do i know which version engine i have? the engine code shown is EJ20-b35... if that helps

/quote]

Not AVCS then. AVCS Engine code would be EJ204??? Being 2001 it\'s a V7

Is it actually loosing a Cylinder and Running on 3 when it happens?

The fact that it is worse when cold, also comes right above 3000rpm. With no CEL\'s and is Idling smooth - suggests AFM.

Which could also be effected or get slightly better with you closing the Plug Gaps.

Im not sure how to tell if it is running on 3 cylinders when it happens, but is is much worse when cold and less of an issue over 3000rpm, it also runs perfectly smooth when idling. so im thinking maybe i should just go for the $140 AFM available at sub euro parts and see how it goes. (dunno if they will take accept a return if it doesn\'t help).

I know it is likely unrelated but does the fact that is seems slow to start up mean anything or is it just a flat four thing? Im used to my primera which starts within about 1 second.

[Dylan20N]

Ok so i found this in another subaru forum thread.

"Rough idle and disconnect the AFM. If it still runs then its AFM because the ecu has compensated for dodge idle AFM readings. If it does stall when you disconnect AFM then chances it isnt AFM."

So then i tried it on my car, started it up let it idle then disconnected the AFM and after a second it stalled. So do i take that to mean the AFM is fine? i.e. is this a legitimate test method and do i go for coil packs?

[Rosssub]

 Dylan20N said:

Ok so i found this in another subaru forum thread.

"Rough idle and disconnect the AFM. If it still runs then its AFM because the ecu has compensated for dodge idle AFM readings. If it does stall when you disconnect AFM then chances it isnt AFM."

So then i tried it on my car, started it up let it idle then disconnected the AFM and after a second it stalled. So do i take that to mean the AFM is fine? i.e. is this a legitimate test method and do i go for coil packs?

No, that one works if your Idle is rough afaik. Your Idles ok.

Being a Boxer/Flat 4, you would know if it was running on 3.

Because you have single Coil Packs, a faulty one would cause a definite Misfire. All four would have to be faulty together to cause what your describing. So unlikely? Also a Coil/Coil Pack has to be near Dead before its effected by Engine Temps.

I still reckon go for a new AFM. Maybe a Member near you has one you can try out.

For the slow/hard starting. Check the Cranking Voltage of your Battery, check the condition of your air cleaner.

Also a failing/worn Fuel Pump can cause slow/hard starting too afaik. Could also maybe cause your Engine trouble, but would think it would have failed completely by now???

[Dylan20N]

is there any sure way to tell if it is misfiring or running on 3 cylinders all the time or during the loss of power?

[Rosssub]

 Dylan20N said:

is there any sure way to tell if it is misfiring or running on 3 cylinders all the time or during the loss of power?

Engine note/Exhaust noise should change.

Engine will seem much Lumpier.

Put a Dud Spark Plug in and go for a drive. Gauranteed 3 Cylinders

Edit: Or just unplug a Coil Pack, but I think that will cause a CEL?

[Dylan20N]

yeah that is the trouble for me. this is my first Subaru and it had this issue when i got it so i don\'t have much to compare it to.

[Rosssub]

Sweet, you\'ll know it like the back of your hand soon enough.

Being that you now know how to read fault Codes and Reset your ECU Connecting Green and Black Diagnostic Plugs.

You could start it up. Then unplug one Coil Pack, this will cause that Cylinder to loose all Spark and you can see what only 3 Cylinders is like. Even go for a short drive.

Then Read your CEL fault Code for the Ignition Fault. Then Reset ECU.

Edit: Although when you plug the Coil Pack back in the CEL will go out anyway, because the Fault disappears.

[Rosssub]

Sorry, got confused and my brain was referring to this thread. Regarding Diagnotic Plugs and ECU Reset.

http://www.clubsub.org.nz/forum/index.php/topic,41812.0.html

[Dylan20N]

 Rosssub']

[quote name='Dylan20N said:

Ok so i found this in another subaru forum thread.

"Rough idle and disconnect the AFM. If it still runs then its AFM because the ecu has compensated for dodge idle AFM readings. If it does stall when you disconnect AFM then chances it isnt AFM."

So then i tried it on my car, started it up let it idle then disconnected the AFM and after a second it stalled. So do i take that to mean the AFM is fine? i.e. is this a legitimate test method and do i go for coil packs?

/quote]

No, that one works if your Idle is rough afaik. Your Idles ok.

Being a Boxer/Flat 4, you would know if it was running on 3.

Because you have single Coil Packs, a faulty one would cause a definite Misfire. All four would have to be faulty together to cause what your describing. So unlikely? Also a Coil/Coil Pack has to be near Dead before its effected by Engine Temps.

I still reckon go for a new AFM. Maybe a Member near you has one you can try out.

For the slow/hard starting. Check the Cranking Voltage of your Battery, check the condition of your air cleaner.

Also a failing/worn Fuel Pump can cause slow/hard starting too afaik. Could also maybe cause your Engine trouble, but would think it would have failed completely by now???

Ok so today i did a few things to try and sort it out, to rule them out for good i took the coils to the auto electrician and they all seemed perfectly happy.

Then when i got home i had a closer look at spark plugs for any cracks etc and all was fine there, then swapped all coils and plugs into different cylinders hoping for some kind of change in engine behaviour no real luck there.

Also while under the bonnet i noticed that the actual plate under the bonnet says the engine code is EJ204 not EJ20-b35... as mentioned before (so this oil pressure sensor issue is a possible culprit)

Another thing i noticed while checking the ground cables the one from the battery to the engine had another grounding aftermarket cable going to the body of the car, despite there being a a nice thick ground from the battery to the body already.

I also cleaned out a fair bit of black dirt from the throttle body butterfly valve, and once the car was all back in one piece it stalled just after starting the first time then went back to the same old slow starting loosing power behaviour as before. Only now i notice there is white smoke coming out of the exhaust doesn\'t seem like its just steam.

[Rosssub]

Yes you have AVCS, that could be causing your issues. Cams not advancing on one Bank, or Cams stuck at Full Advance.

Check out this thread regarding oil in Loom from blocked AVCS Oil Feed:

http://www.clubsub.org.nz/forum/index.php/topic,20261.0.html

And this AVCS Thread on Sensor Fault from Oil Filter slipping into Sensor:

http://www.clubsub.org.nz/forum/index.php/topic,23227.0.html

[Marky]

Its a subaru

Chances are its the afm

you\'re going in circles trying to find the fault, my money says just take it somewhere who can chuck a scanner on it and look. If its a misfire it\'ll show as a rich idle, if its a dud afm it\'ll show as fluctuating voltage at idle (more than what should be normal)

Just cleaning it wont sort it, and neither is unplugging it a proper test. They can go a bit crook and just read a bit off (like... out of calibration) so the thing runs rich or lean across the board, it would explain a sad idle and poor performance when driving

Most things are very easy to diagnose via what the ECU knows already, you don\'t necessarily have to do trial by replacement like an older model