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Old 09-11-2010, 03:39 AM   #1
Scooby Newbie
Member#: 57534
Join Date: Mar 2004
Location: africa
1995 subaru impreza

Default Subaru Legacy B4 RSK detonating

Hello members.
I am from a small country called zimbabwe in africa.
this is the second subaru legacy that i have owned.
These are some of the best cars i have come across, sadly the first legacy i owned was a 2000 model and a b4 also twin turbo.
keeping in mind the first legacy was in worse condition and less powerfull then this 2002 model i have purchased.
The problem i am having is massive detonation.
Im not sure how adaptive the ecu is to poor fuel and i would like to ask what would happen if i was to run a poor grade fuel like 92 octane fuel would it cause the type of detonation im experiencing.
The car drives well and has 124 000kms on it.
I have tried the following.
Replaced fuel filter.
Changed plug gap from 1mm to 0.65mm on all plugs
Serviced and replaced oil with castrol edge 10w-60 cause temps here are quite high average 28 degrees celcius.
Now i have tried adding toluene as a octane booster at a 30% concentration to up the octane an average of 4 points to 95 octane +-
this hasnt helped.
The car is otherwise stock and has heat range 7 plugs factory spec.
exhaust is standard with catalytic convertors still in place.

Ive changed fuel pump as well and tested still have the detonation.
it comes when accelerating at about 3000rpm and can be heard as marbles in a can type noise.

Funny thing is when i drive at a constant 120km/hr and then pull into a suburb and drive around the detonation goes away until heat soak takes place again and bang the det is bang again crackling away.
Eating away at a perfect engine isnt what i want and i would like some advice.

Should i up the fuel pressure to try and curb it ?? of course this would mean running slightly rich ?

Should i get a aftermarket ecu and re map?

Should i get a Afr controller and just map fuel or should i worry about retarding timing as well?

Is there anything else i should be looking at changing or cleaning ?

I have also cleaned out the maf sensor as well with some carb cleaner safe for air flow meters ?

Should i place a bigger hood scoop to try lower intake temps ?

Should i fit a racing air filter as my last car had this and performed ok with out problems of det?

keeping in mind that i dont have access to a dyno here and mapping would have to be on a trial error basis by myself if i was to fit a greddy emanage ?

The fuel we get here sadly inst great and i have the car and dont want to sell it .

I have also owned two wrxs as well and they havent ever had det?

Should i replace the knock sensor ?
or replace the Oxygen sensor as well ?

should this car be adapative to bad fuel ?

What other mechanical methods should i be chasing to try and lower detonation im really stuck ?
driving her like miss daisy to try and not break the engine ?

On a side note the exhaust valve at the rear silencer was stuck and the cable snapped that opens and closes the arm for the rear flap so ive bolted it open in the hope that back pressure was causing the egt's to rise ?

Do these cars have a egt recirc valve that i need to check and if so where is it located?

Hope to hear from you all soon desperate to try and solve this ?

Ps another question.

Is there a difference in compression ratios between the legacy b4 rsk that came out in 1999, 2000 , and 2002?
From what i can see subaru increased the compression ratio from 8:1 to 9:1 ?
is this true and if so would this mean that detonation is more likely on a newer model ?

Africa Zimbabwe
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Old 09-12-2010, 10:13 PM   #2
Scooby Guru
Member#: 4021
Join Date: Feb 2001
Chapter/Region: NESIC
Location: Natick, MA USA
1999 Legacy GT Ltd
Quick Silver Metallic



Is Zimbabwe the country formerly known as Rhodesia ? I believe it was a former British colony that obtained its independence back in the mid 1970ies ?

With regards to your Subaru, the sounds it is making are likely some form of pre-ignition "knock".

Does your car have a "Check Engine" light located in the instrument cluster ? If so, is this light on ? This could mean that a malfunction code has been registered, and through use of a "code reader" one could read the fault code and use this code to diagnose the problem with your car.

I am not sure what sort of automotive supplies are available to you. Do you have retail stores that sell band name aftermarket automotive products ?

I can't help suspecting that this detonation maybe a result of carbon build-up within your combustion chambers. If this suspicion is actually true, the repeated use of a fuel additive designed to clean carbon deposits should help remedy the situation. Here in the United States the brand name "Gum Out" fuel system cleaner is highly recommended another product you might wish to try would be "Chevron" Tectron fuel system cleaner.

Another possibility might be that the fuels available on your country are of a too low an octane rating. You might want to try using a fuel additive designed to increase or "boost" your fuels octane rating.

A third possibility might be that your Subarus knock sensor has somehow failed and needs to be replaced.

Assuming you can obtain a "fuel system cleaner" or an "octane booster" I would try one of these, and if that fails to resolve the issue I would try the other product. As the octane booster would only achieve temporary results for one tank full of gasoline, I would encourage you to try a fuel system cleaner first.

If you can obtain some high quality NGK spark plugs designed for use in your Subaru, you might wish to try them in place of whatever spark plugs you are currently using.

This detonation / knock condition is potentially rather serious and might possibly cause mechanical damage to your Subaru.

Good luck !
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Old 11-14-2010, 04:05 AM   #3
Scooby Newbie
Member#: 57534
Join Date: Mar 2004
Location: africa
1995 subaru impreza

Default Thankyou for the response

Hello and thankyou for the most informative response.
I am currently trying some fuel system cleaners and have been doing so for a while now.
But the detonation seems to only get worse when the temps are up meaning like around 30 Degrees C on average but most of the time aroung 28 Degrees C, thats ambient temps as well.
Keeping in mind that Zimbabwe (Rodesia ) is at a higher altitude then by at least a few thousand meters.
The Fuel we get here i would and can only assume is roughly Ron 93 ??
Not a great fuel.
So i was thinking of taking the car to a subaru dealer to try and get them to diagnose the problem ...
Failing which i will be forced to use aftermarket methods of octane boosting like water injection and ecu reprogramming ?
How ever i have been told by a fellow member of a forum not sure which one that all subarus that are 2002 and over subaru can actually retard timing etc if the car is to be run on a high grade fuel.
I have tried so much from changing plugs to even shortening plug gap to .65mm.
Nothing has helped, although the use of toluene has curbed detonation some what.
I will be travelling to Republic of South Africa soon and will try and source a really good fuel possibly 99 Ron which i am not sure what octane that would relate to but i hope that it works and if it does then im seriously screwed.
I would like to hear your thoughts
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Old 11-14-2010, 04:14 AM   #4
Scooby Newbie
Member#: 57534
Join Date: Mar 2004
Location: africa
1995 subaru impreza


Just found this but how would i know if my car is a Rev D car ?

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Old 11-14-2010, 07:59 AM   #5
Scooby Newbie
Member#: 73609
Join Date: Nov 2004
Chapter/Region: International
Location: Johannesburg South Africa
2002 wrx


Hi Adam

the cars you have are jap spec and expect proper fuel - inside the petrol flap or on a sticker under the bonnet it wants 98 octane

your 93 octane is same as usa 87 octane

you need an octane booster or a remap of oem ecu or replacement ecu to prevent that knock wrecking your engine

I own a subaru shop in south africa and deal with these issues almost every day from either zim / moz / bots / swazi etc etc
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