Intermittent Pulsing Power Delivery
 

Hi guys and gals. I have just purchased this very clean and completely stock 2005 WRX Wagon. 65,000 miles. It has a few niggles however, despite coming from a dealer.....

https://farm8.staticflickr.com/7326/...d1556435_c.jpg

One of them is it accelerates rapidly in 1st, 2nd and 3rd gear seemingly fine; however in a different situation, cruising at 50mph or so in 4th, if you open the throttle, it initially boosts and accelerates for a second, then it backs off a bit for a second, then boosts again, then backs off and so on. It doesn't make any change in sound (no audible detonation, knocking, pinking etc). It's not a clean cut in power, just a fade in and out, in and out. The same happens in 5th gear at higher speeds. I won't jump to suggestions just yet as I'd like some ideas please. It's on Texaco high octane fuel. I am a mechanic with 23 years experience but know very little about Subarus!

Your help is very much appreciated thank you.

Ferg

I would get it of the Texaco for starters. Go for Shell V Power or Tesco 99 and see how you get on:thumb:

OK thanks. I did wonder. It's like it's crappy fuel and it's protecting itself, backing off ignition advance.

Its the most logical thing to do first, and it wont cost anything to do. See how you get on.

If its a uk car it should run fine on 95 ron fuel let alone texaco high octane.

This page mentions the symptom under section Wastegate Creep: http://www.scoobypedia.co.uk/index.php/Knowledge/BoostRelatedIssues so I'll also investigate which set-up my car has. UK car.

If was like cutting power and then pushing power kinda like rapid fire then I would say it's hitting boost cut off, as those are the gears which you will notice it

Which then you would need to make sure the waste gate pipe is connected and no dodgy boost controllers etc

Depending where you are I would Google one of the Subaru specialists in your area and ask them to give your boost lines the one over and check everything is connected up correctly

Another sign would be high fuel usage

maybe not boost cut but if you have a leak in the boost control solenoid vacume hoses you'll get small surging of the turbo when your pushing it.

It goes mostly unnoticed in 1st/2nd gear as it's over that quickly the BCS doesn't have time to do much. Under load in higher gears the car isn't hitting target boost so oscillates between over and underboosting ever so slightly.


Have an eyeball over the BCS pipes:
https://static.cobbtuning.com/cobbtu...stSystem_1.jpg

And also check around generally for leaks in the intake pipes/intercooler pipes as it doesn't take much to monkey things up.

Sometimes the BCS lines will get brittle with the heat so may even be handier to replace them. If they look like they've been replaced recently then you may have the wrong boost restriction pill in place. See the yellow dot in the pipe coming out of the compressor housing? In there is a brass pill with a hole in it, this slows the air heading for the wastegate and helps the car reach higher boost targets (as well as the BCS bleeding air off to the intake pipe).

if the pill is the wrong size and nobody told the ECU about it then it just waves around trying to hit the target boost.


You could try cleaning the BCS as well, if they get mucked up they can become sticky and slow to respond. Just take it off the car, attach some wires to it from the battery (doesn't matter which way round you have the postive and negative) you'll hear it click. Fill it up with carb cleaner (or MAF cleaner if your cleaning your MAF as well) and click it a few times - rinse and repeat :)


*edit* also if you have a vagcom lead/diagnostic lead/bluetooth OBD reader you can log boost pressure. Should be around 14psi / 0.9 bar or 18psi/1.2 bar if it's had the PPP kit fitted.

I have to say it amuses me when everyone jumps on the "it must be dodgey fuel, only the best 99 ron for my standard uk model wrx" Vacuum issues would always be the first thing to look along with logging.

but didnt you know, only STI's can handle the true power of 95 ron. WRX engines will only run on 2000 ron plus octane booster and jiblet booster and dry fuel and meth injection. Anything less and your an animal..... "should've bought an STI?"

Giblet booster is the boy, it gets right into the fellangy and adds torques to the shaft inputs.:p

One person has mentioned the fuel and as an easy enough thing to discount it's worth trying a different higher octane petrol. It's highly unlikely to be the fuel but I suppose people are only trying to help. The last post by bludgod is just stupid and invites trouble. Not doing yourself any favours, albeit your penultimate post was informative and helpful.

Lighten up, the OP has been given enough info to get on with, while we await him coming back, a few light hearted comments are not the end of the world.

Jesus, I only mentioned trying different fuel as I have owned a 05 wrx for 3 years and mine used to do similar things and different fuels varied it greatly i.e the better ones virtually eliminated it to the point where it wasn't an issue anymore. But what do I know :Whatever_

To many confrontational tools on here of late, who are so eager to jump on someone who might of got something slightly wrong and or they don't agree with! Boring!

Isn't this just normal hesistation? My Subaru suffered from this in the mid range until it was remapped. I thought this problem was quite common. Just my thoughts.

hey sorry if you thought I was jumping on you, I was more having a pop at the usual wagon of people posting "should've bought an sti" as an answer to damn near everything.

yes maybe it is fuel or maybe it's something else. There's plenty of info there for him to digest - tho I don't recommend eating the jiblet booster as the aftertaste isn't too good.

There shouldn't be too much hesitation on a standard car - but there definitely shouldn't be any pulsing of the power delivery unless something isn't working as it should.

Generally if its w**k fuel the ECU will back off the timing and it will stay there for some time so you would feel a small drawback in power until the fuel quality is improved. He's described power coming and going and I've only seen that when over/underboosting due to a duff boost control loop (either vac leak/BCS failure/boost leak/exhaust leak/other leakages).

We will all wait with excitement to see what findings our poster comes back with!

Thank you for your replies and help, especially bludgod for your lengthy post. I checked the layout and removed the boost control circuit yesterday and visually checked the hoses and fitting. I checked the pill was in the right place and cleaned everything with brake cleaner until it ran clear and carefully blew out with air line. I haven't yet checked operation of the valve on the bench. I refitted everything checking for tight clips and neat routing. Despite running Shell V Power, it still surges, like cycling between full and half throttle once a second. I will check operation soon and go for a drive checking boost via OBD (Car doesn't have a boost gauge). This seems to be a common problem with no clear answer however when I find my car's problem I'll post the answer!
Thanks all for your help.

are you using a USB plug in cable OBD plus laptop for data logging or one of those bluetooth code readers? Don't be surprised if you can't see anything with the bluetooth code readers and logging apps for your fone/tablet, they rarely catch anything due to very slow update speeds (when compared to the laptop and USB cable).

If you can log:
wastegate duty
manifold relative pressure(boost)
MAF (either in g/s or volts)

It should put you on the right track, if your using a bluetooth jobby you may need to do separate runs for each item to try and improve the graph quality.

Could anything from spark plugs at the wrong gap, coil packs on the way off, maf giving up or maybe even your O2 sensor failing I would check the spark gap and coil packs first as that's easy to do and not expensive

At lunchtime at work I took the valve off and tested it on the bench. It seems to be operating well. Fast and quiet. I cleaned it during operation anyway and refitted.
I have a Mac Tools ET97 fault reader at my disposal but in the live stream list it doesn't show anything related to the turbo system. I also have access to an all singing all dancing Snap-On unit but haven't tried that yet. I'll road test again tonight and also just try the turbo outlet connected to the actuator which should give steady lower boost. Cheers all.

There is a multi pipe vacuum/solenoid device that suffers from hardened rubber ends, when any of them come loose from the solenoid, you will get a crappy ride when coming on and off boost.check them all.

In behind this regulator thing..
https://i870.photobucket.com/albums/...k/IMG_1396.jpg

OK, thank you, will do.
Following the bench test and cleaning, the boost oscillation is still present. Next trial was to take the power supply off the control solenoid so it cannot open. Needless to say it cannot bleed control pressure away from the actuator so the actuator sees all the boost pressure and operates nice and early resulting in low boost. Low but steady boost - no oscillation on road test. One might therefore assume the oscillation is as a result of the solenoid opening and closing at the rate I'm experiencing oscillation.

Should it stay open all the time on high boost? Or should it rapidly and variably pulse to regulate the control pressure? What signal is it likely to see? What sort of frequency?

Cheers

why dont you do a bit of logging to see what is actually going on ?

You need to get logging and see what's what, it could well be that an issue is still present but you can't perceive it because the change in boost is so small.

The valve oscillates when in operation and the ecu uses a modulated pulse width to achieve the smooth boost curve we normally get. Usually if the system can't maintain its targets then it's the result of a change in the system. Maybe a more free flowing exhaust, maybe a less restrictive air intake, cat removal can all play their part. Most likely cause though is going to be a boost or vacuum leak somewhere. When the amount of air floating around in the system isn't what mr subaru engineers designed it for then the settings in the ecu aren't right any more so you get rapid over and under shooting of the boost target.

Cracked or broken lines are possible, broken turbo intake pipe maybe (underneath of course where you can't see it) Or even a disconnected line on the manifold could all do this for you.


Check each and every line for cracks and breaks, have a spray around with carb cleaner or ez start and listen for changes in engine note, if possible find someone with an open port or vag com lead to do a bit of diagnostic work for you.

Thanks all. Will do. I haven't yet because I don't get much time to work on it because I work all day on other people's cars! It's also best to do one thing at a time so it's clear what fixes a problem. I'm working through this methodically. I'll post when I know something more. Cheers for your help.

if you can only do 1 thing at a time then I say make logging the next step, once you can see what's actually happening and check the fuel corrections stored in the ECU it could well point you to the right location.

When were the plugs last done?

Hi! Did you fix it?

Thanks

My money is on the MAF :)

Hi guys. Still not fixed despite new plugs, MAF, MAP and a thorough check-over. Heading to a rolling road soon.