Hi all,

Having just finished my night shift, I thought I'd go for a little spirited run in the cool air and the clear roads. However, I encountered something very strange...

At around 5500rpm, mainly after coming off a corner, the car suddenly felt as if the fuel cut off or the engine cut out...! It was quite a jolt, then suddenly all went back to normal. No CEL showing or any other problem. Is this overboosting or fuel cut..?

If so, why might this be..?

Car always run on super unleaded with the last tank being V-power. Gauge showing a quarter of a tank.
Mods: Front decat, centre straight through pipe, H&S backbox, Green cotton panel filter. Other than that, standard MY07 2.5 STi spec.D

It's never done this before, but saying that, I recently did a Prodrive drive day and now corner far quicker than I previously did. At first I thought the fuel in the tank may have sloshed around and left the area where the pick up is, hence a bit of fuel starvation, but surely not..?

Any thoughts..??

Cheers,
Nige.

 

Not sure on an 07, but my classic had fuel pick up problems below 1/4 of a tank. First noticed it at an airfield day with Andy Walsh, panicked thinking there was a problem, but Andy just asked how much fuel, said about 1/4 and he said just go fill up, they all do that!

Simple check, fill up and see if the problem is solved.

 

That'll be a job for tonights shift, then testing on empty roads afterwards.

Suppose nightshifts have their plus points after all..lol!!

Nice one..!!

 

It'll be fuel surge, we've had it on our track with much more fuel in the tank.

Keep an eye on your oil level as well.........

Mike

BTW, there weren't any 07MY Spec Ds, they are all 06MY

 

Thanks for the info Mike,

Is there any way to stop or cure it..? Now I've learned to drive it properly, I don't fancy facing the jolt it produces too often, my passengers will think I've got driving issues..!

I didn't come across the surge last Friday up at your place in the STi's, I can't have been trying hard enough..lol!! (ps: If you don't mind me asking, what front brakes were the cars on the short circuit using? I didn't recognise what they were, yet they were quite effective!)

Hmm... oil level. That'll be something to be checked tomorrow night too, as my drive is at a slight angle and the car park at work is nice and level. Admittedly, I haven't kept a very close eye on that...

I wonder if the ppp would help in curing it..?!

And I stand corrected, it's an MY06 spec.D on a 2007 plate...

Thanks again for the info Mike. Much appreciated.

Nige.

 

Had the same on my 04 WRX PPP, got told it was fuel starvation only way to fix was to upgrade fuel pump which I have yet to do
Only happened when low on fuel so I just watch roundabouts when a little lite on fuel

 

It's common on classics, have you checked to make sure your boost solenoid and plumbing's not full of oil? That results in exactly what you've experienced.

 

Uprated pumps not going to make a difference either. I get it on my 02 with third of a tank or less. I think what needs to happen is to fit another fuel pick up on the n/s so that the pump is picking up from both sides of the tank.

 

I had this problem on My07 WRX.
It did not happen untill I put a full decat exhaust on.
It happened on fast roads or motorway when I hit around 5500 revs, however after a couple of times the engine warning light came on but always reset itself.
I took the car to AET AUTOS and they were brill, put on something called a fuel cut defender which was cheap and has stopped the problem altogether.

 

Had it on my 07 WRX coming off a 2nd gear roundabout over a hefty bump with about 1/4 tank left. Happens lots on Imprezas apparently. I am inclined to believe my dealer when he says it's the fuel sloshing away from the pickup in the tank. If it happened just the once I wouldn't worry...if it happens regularly with the tank half full or more, I'd take it in and let someone have a look at it.

 

This is a common issue when upgrading to a full catless exhaust on the 2.5 motors. Causes boost spike which will then hit the factory fuel cut-off. In cases, this will trigger the CEL.

 

i've also heard it happens on rare occassions with the 2.5 and a PPP kit/zorst.
As mentioned, if it happens once forget about it...if it keeps happening, get it looked at...there's a few solutions for boost spike.

 

Yea, get the same in my 07MY06 Spec-D... Its down to the fuel level.

Can I ask, where did you get your front de-cat from?? I assume that you are talking about the wee link pipe between the downpipe and centre section... how long did it take to fit and did you notice a difference in performance/noise??


Cheers,
Grant

 

Hi Grant,

It was a front decat I had removed from my 03 WRX. It was originally supplied and fitted by H&S to my old car who kindly modified it and fitted it to the 2.5 at the same time as I had my old middle section fitted when I bought a new backbox off them. Top people up there I tell ya.

The car sounds like an animal at high revs through tunnels now, feels slightly freer revving and sounds like a Subaru should do. however, I had the small cat pipe, the centre and the backbox all changed at H&S at the same time, so tricky to tell if the small cat pipe made much difference on it's own.

Nige.

 

We had same prob with our 2.5 STI Spec D @ croft. Fitted a Hyperflow Fuel surge tank that keeps an amount of fuel round the pick up and solved the problem on high G corners.

If it occured on straights you would have same prob as Simonb1328 which occurs when fitting full D cat as std turbo overspeeds and boost spikes bringing in the fuel cut, but thats simply solved with the FCD.

cheers, ellie

 

We've been looking at an in tank solution for helping with fuel surge and some of the cars we use on the track have it fitted although probably not the ones used last week. The easiest solution is run more fuel in the tank!

The brakes are something that we are testing, at the moment they don't have the necessary approval to be sold for road use in the UK. We use them on some of the cars on track as they last much longer than the std parts under the extreme use they get here.

Fitting a different exhaust to any current car will need a remap to sort out, all an FCD does is take away the safety control the ECU has over the overboost. What happens when a pipe comes off? The engine will blow up and without a warranty you've got an expensive problem..........

Mike

 

Nige, thanks for the info mate. I ordered the link pipe from H&S and it arrived today and its an up-pipe that I've got. D'oh, will give them a bell to try and get it switched as I dont need an up-pipe at the moment but I do quite fancy getting rid of that CAT below the downpipe!!

Mike, I've got a couple of questions for you mate, hope you dont mind.. Does the 2006- STi come with a Sports CAT in the downpipe as standard?? Also, I had my car on a Rolling Road and the AFR the mixture measured flatlined at 9.1 as that was the lowest the sensor could read. Every other car performed fine on the rollers with average AFR (so dont think it was a dodgy probe/sensor), but mine was VERY rich.. No sign of problems and no ECU fault codes have been stored when I plugged it into a Select Monitor, but it is rather juicy on the fuel even driving sensibly I struggle to get 200 miles out of a tank. If its normal (I was only MY06-onwards on the rollers) then thats fine, if it isn't then I'm a wee bit concerned, surely at that ratio the borewash problem becomes a reality??


Cheers,
Grant

 

Mike, Thank you for the replies.
It's great to have someone on here that really knows what they're talking about.

Not had a chance to fill up a bit more and try it out yet, but it's a good indication that the driving course has worked if I never had surge before..!!

The brakes certainly looked interesting, I won't say any more about what they looked like, but they certainly looked the part, and I think "extreme use" is also a bit of an understatement for how the cars are driven..!!

I'm also interested in whether or not the MY06 spec.D has a sports cat in the d/pipe as standard.

Thanks again for your input and replies Mike.

Grant,
Hope you get your exhaust sorted soon, it makes a lovely noise with the front decat. As for your AFR/fuel consumption, that does sound a bit much. I'm getting 190 as a very minimum out of a tank and have been up in the 270's regularly. And I don't drive like a fairy .

Regards,
Nige.

 

Ref the FCD, mike is correct if the pipe blows off then you have big probs, but may not be aware that the Turbosmart FCD2 we use removes the orig fuel cut but also allows you to program it back in just above the fuel cut to keep the safety control for the ECU.

 

I'd be interested to know about your solution for this?

As i said I have an 02 and suffer particularly badly with fuel starvation when on track. When i was at the ring i was having to fill up every two laps. Just under half a tankish and the fuel cut started. I could get three with out a problem but a forth was a no no. So for safety was refueling every two laps.

 

No UK spec car has what you would class as a Sports cat as std. Our performance package on a 2.0 STi includes a sports cat but we don't fit this on a 2.5 STi as it's not necessary at what we feel is a safe power level of around 320bhp.

We also have concerns about boost control with the std cat removed on 2.5 engines as the wastegate in the exhaust can't reduce boost levels if it needs to for any reason. We tried one test with a downpipe fitted at 'actuator' pressure and found that the boost crept up by 0.3bar at the top end to within 0.1bar of what we were asking for in perfect conditions. It still produced 335bhp but if the ECU decided to reduce boost in response to high temperatures it can't. The resulting det would kill a piston very quickly.

9.1 afr sounds low but bear in mind that the desired isn't much more than that anyway, just over 10 on the low det fuel map and 9.1 ish on the high det map.

I'm on holiday now for two weeks so please don't get too upset when I don't reply.

How am I going to cope without SN............?

Mike

 

my 06 does this off roundabouts with low fuel.

 

Thankyou for the reply Mike, much appreciated.. and enjoy your holiday.


Cheers,
Grant

 

Major problems with boost creep on US Spec 2.5L Subaru models.

Please check this thread:

STI 07 down in compression - Factory 2.5L Turbo Powertrain - NASIOC

There has been a lot of confusion over here on what to do and how to mod with the ecu problems. The US ecu differs from the EU ecu however. Just sharing what we have found over here.

 

Interesting comments there Mike.

The latest UK 2.5ltr models that I've had a hand in have not suffered from creep, this is with the OE system, Prodrive Sports cat downpipe, H&S Sportscat downpipe and full decat systems.
JDM 2.5ltr models however are a different story, swapping the OE downpipe instigates terrible creep that the turbo needs to be modified to regain good boost control.