can any one help have a flat spot on my 52reg wrx at between 5k and  6k have tried changing airflow,o2 sensor and boost sensor nothing shows on ecu as a fault

and garage are running out of ideas and are telling me I may have to change ecu serviced/cambelt change done but flat spot still haunts me any ideas guys???

Book some dyno time get some real time diagnostics on it to check the ECU / map also have you got any mods on the car

As said before do you have any mods like an Induction kit or dump valve. without it being mapped to be there. Not always the case for something so small but always advise to have a map done after.

Thanks for reply no mods to car can i reset ecu by diconnecting battery as i wanted to see if flat spot clears and were could i get it dyno tested

Your welcome. And some people will say it will reset after taking the battery off. But I doubt it works with the new age so would need to be done through the OBD. And as for the Dyno test I'm not sure around your area sorry :)

just to update you guys I did disconnect battery (and press brake to clear memory) and for the last 5 days no problems but on way home tonight flat spot has returned so am I looking at getting a secondhand ecu

hopefully that will resolve the issue

ok this is a update on flat spot- a new ecu was found and fitted for a very good price as I was warned it could be ALOT of money,

but surprise surprise falt is back what else can I try as my patience and bank account cannot last forever

Only other thing's I can think is clean the boost solenoid, and check the sparkplugs. There is the coilpacks too but would have thought you would get a code from them with a misfire. But I could be wrong. Not sure if anyone else could have a better answer or not.

And sorry to hear about the ECU not working :(

boost solenoid was changed for another one (but not new) and a boost dial fitted for a day to see if and drop off of boost and plugs were changed on service (fault was there before service)

What is strange is when new airflow switch fitted fault went for about 6 weeks !!!!

some one has mentioned about injectors but doesn't make any sense why fault goes when battery disconnected and then like clockwork returns in same revs

silly question but what does coil pack do?

In short a coil pack is the part that supplies spark to the spark plugs. you have a new age same as me so there a single unit that goes onto the 4 plugs, but I'm sure if it was there would be a misfire code, if I'm not mistaken. 

have you had a compression test done ? just trying to think of things it could be you seem to have done everything that makes sense to change :(

I dont believe it is a misfire as that would manifest itself throughout more of the rev range not just clear itself after a rev point

 

As the flat spot isnt there constantly I would say you have an issue with fuelling. You reset the ECU and that cleared the problem for a short time but then it came back. Changing the ECU worked then it came back, changing the air flow switch worked and then it came back.

 

I believe something somewhere is telling the ECU at that part of the rev range the mixture is running rich and the fuel is being cut as a consequence.

 

As there are no fault codes the car thinks everything is fine and running correctly.

 

So my personal suggestion comes back to the rolling road to understand what is the actual air fuel mixture at those revs and what info is being sent to the ECU and from where.

 

If there was an issue with the injectors themselves it would show throughout the range but the fact that it does work some of the time points towards the physical stuff being ok but the signals being corrupted somewhere

 

There are some nifty ODB attachments which will send info to your smart phone as you drive along - this may be useful prior to spending on a rolling road session if you want to continue to investigate yourself

ok update on flat spot- boost is only 0.5 and have been told should be 0.9 rolling road showed no other faults so what are you thoughts???

I have been told it is one of 2 things or possibly both, so lets see what you guys suggest!!!!

ps.boost solenoid has been changed

at what point on the dyno trace is the boost coming in, is the boost constant throughout the run, what was the air fuel ratio at the flat spot, how did that compare to the rest of the trace?

ok will try and answer-air fuel mix normal and doesn't drop off or do anything silly-boost starts at 1800rpm then increases 0.48 at 5100rpm then drops to 0.35 until 6000rpm and then stays straight until 7000rpm

sorry also understand from people that boost should be 0.9

Hi I have a flat spot from 1st when leaving a roundabout it just does not move quick. Also revs keep going up and down until press acceleration. Mine 07 Subaru Impreza estate 1.5 r