Well, I've been having fun in the car since I got it back from remap with Andy F. Nothing extreme, just pottering around and listening to the funky sounds. But its about time I get to a problem I think.

I have one now, which unfortunatey could mean a number of possible things which you guys might know more about than me.

I noticed it yesterday first off when I took my mate out. I turned off a roundabout onto a 60mph zone and put my foot down in 2nd gear. Within a few moments it felt like the car had hit the limiter and kicked me back, but I knew I was no where near the rev limit. Nevertheless, I changed up a gear and foot down, all was fine. 4th gear, spot on, 5th, same. Amazing speed

Today, with the car fully warmed up again, I pulled away from a junction and put my foot down and it did the same again, seemed to boost then hit the invisible limiter! Changed up a gear and it was ok. Slightly sluggish for a second but then fine.

Went for some food earlier with the missus, and although I wasnt giving it some welly, it felt like there was too much air trying to get through the exhaust and it was hesitating, and when I did put my foot down it was like I was forcing the air through so I could get some speed up. The exhaust pops when it does it too.

It was like how it is on some mornings in her Evo when its cold. Foot to the floor and its slowly building up revs before spinning into life.

Its random and doesnt happen all the time, but like most things, its annoying.

Now, I've read a lot of posts and come up with a few things :

MAF failing - dunno if its the right symptoms.
Clutch slipping - surely not with an AP Racing clutch
Overboosting - again, could be? I think Andy set it to 1.3bar and its peaking at just over 1.5 at the moment due to the weather.
Spark plugs - also changed them recently
Something else?

Any tech bods have any handy tips or advice? Might be nothing, but I wouldnt want to rish anything

Cheers guys!

Its an Impreza P1 by the way. Front Mount intercooler, decat exhaust system and Apexi mapped, AP clutch, Walbro fuel pump, K&N 57i etc.

 

Oh and could be coil pack but my main theory is MAF or overboosting

 

shouldnt b overboost as the car should have the 2.5bar map sensor as standard which should be easily adequate to cope with the boost u r running.

 

The boost cut will come in as and when the mapper set it for..... Andy mapped mine previously to 1.3 bar and anything over 1.5 would cause the boost cut.....

However saying this I don't believe it is overboost, any overboost is normally achieved in the higher gears (3,4,5) with the higher load. 1st and 2nd don't meet the peak boost without a boost controller.

Do a sensor check via your PFC Commander and you can see how your sensors are behaving, you can then see if it is the MAF or any other sensor.

It wont be the clutch as this wouldn't cause a cut but the revs would just increase as if the car is in neutral.

The Spark plugs should be PFR7B'S and not 6B's as some people use.... Coils and spark leads would normally be in higher gears and prevelant in more than one gear...

But the best advise anyone could give you is to call Andy up and get him to have a look at it again. As he mapped it he will have the best knowledge of the car.. I'm sure he will be able to sort it straight away.

 

Thanks dude. Top stuff.

I have concluded that it could be fuel starvation. The petrol light had come on and I really should have kept on top of it. Its been filled up again now and seems to be running fine and boosting well.

Could running less than 1/4 tank cause hesitation with the Apexi ECU/Fuel tank position etc or will I still have problems?
Its boosting at 1.5 bar in all gears and holding boost at 1.4bar ish.

 

Running under a 1/4 hasn't affected mine in the past, but I wouldn't recommend doing it too often...

Have you got an aftermarket boost controller? The boost seems quite high for the lower gears especially on standard turbo....

 

No aftermarket boost controller, no. Its a 2000 Impreza P1 and I must admit when I got the car back on Wednesday with over half a tank left I had absolutely no problems whatsoever regarding this issue.
It only started to do it when I took my mate out in it yesterday afternoon. Just less than 1/4 tank and I pulled off a roundabout and put my foot to the floor in 2nd gear when it boosted to just over 1.5bar then kicked me back. Changed to 3rd gear and accelerated, and it was spot on, same with 4th and 5th. Pick up and acceleration was amazing. At first, I did think I'd somehow hit the limiter, but now its happened again I know for a fact I was way off and the only thing I could think of over the past couple of hours was it was a fuel cut off or similar.

Since filling up an hour or so ago, it boosted in 2nd gear to just over 1.5bar and I got the warning light on the defi's. 3rd and 4th gear boosted to 1.5bar and held boost with no warning light. 2nd gear then boosted to 1.5bar again and held with no warning light this time. Everything seems spot on. I never really experimented with it as I just wanted to get home to be honest, but I'm hoping it wont happen again if I keep a healthy tank of petrol at all times. Hopefully...
Just confusing as to why it happened in the first place

 

Must be the colder air up there allowing it to boost so high..

There is no reason that Fuel cut would occur due to a low tank of fuel, or none that I can think of.... It may have been that when it cut previously, it hit the boost cut threshold and it hasn't boosted that high since.... If it is only once or twice and a rare occurence than I wouldn't worry too much, however if it becomes a daily occurence i would get it checked again.

Also 1.5 on a standard VF may not last long..... One of Andy's TDO5 Specials would be

 

Cheers mate

I'd ideally just like to pinpoint the cause of the hesitation to be honest. Its happened 3 times, which isnt a lot as you can relate, but in my opinion its 3 times more than I'd like!
It does feel like you're hitting the rev limiter, thats the only comparison I can make as to what its like. I'm obviously not hitting it, though, thankfully.
Yeah the air is pretty dense in Cumbria at the moment, thus causing the boost levels I presume.
Cannot knock Andy's work at all, he's an absolute wizard and certainly knows his stuff, no wonder so many people recommend him. Its just something I'm doing wrong I guess and thats why I'd like to isolate it. I think he's is in St. Lucia at the moment for a couple of weeks, too.

Thanks for the comments dude, very much appreciated
Hopefully you know where I'm coming from with the problem, no matter how trivial it may sound

Andy did say the car was on its limits now regarding the turbo and injectors. Any further performance trek would involve uprating both.

 

Glad to be of help mate..

Andy is definitely a Magician when it comes to mapping cars...

I know exactly how you feel, I get paranoid if there is a slight hint of anything being wrong, even if its a little rattle I haven't heard before...

When it is hitting a boost cut it will feel as if the car "hits a brick wall". It could also be Spark leads, they caused a similar problem on my car when on boost, after a change to some Nology Hotwires it was fine. The car also felt a bit sluggish before the leads were changed, which could be similar to the sluggish acceleration you described earlier. Do you know which plugs have been used, are they uprated ones?

 

They are the NGK PFR7B's mate, and only fitted a couple of weeks ago prior to the FMIC and remap etc.
Paranoia isnt the word! I've kept every single part I've replaced and the car is still under warranty until July/August, but I still panic if I hear any noise out of place.
Its running FMIC (hybrid), Afterburner decat, Magnex centre and Afterburner Vortex, AP Racing clutch, Walbro fuel pump, K&N 57i which is fitted to the MAF, this is bracketed to the engine, which Andy told me it shouldnt be as it will cause vibrations and damage the maf, so thats why my first thought was it could be the maf had failed. I'm sure I'd get other symptoms though, and as it is the car at this moment seems to be running fine (once again though, I am unaware as to whether the hestition has cleared up). Its not really like hitting a brick wall as such, its more like putting it in 2nd from 3rd when it should be put into 4th. That sort of stop/shudder in performance for that split second until you change up again. Annoying to say the least. I've just got lack of fuel being fed through causing the problem running through my head now, even though I know thats probably far from the problem

 

MAF causes lumpy idle in cases also, so I don't think its that. I don't think it could be down to the fuel being low but I know what you mean, that when you get something in your head you just believe that is the problem....

This just sounds like Leads to me. I had very similar symptoms and the missfire would cause the exhaust to pop also...

with mine it would Jerk violently when on boost but when you change gear would be fine afterwards, until you are at standstill for a bit again and it would repeat on boost.

Or finally the fact that it is extra cold is causing the car to run very rich and putting the mixture out of line how it was mapped. This could also cause similar problems. If the leads haven't been changed to uprated ones then I would anyway just for better performance. If this isn't the cause then Andy will have to look at it with his trusty laptop and find the problem from there.

 

It would also be good to check your commander to see if all your sensors are working ok.

On the menu go to ETC, and the go to the SW/Sensor check. Any sensor which are not behaving correctly will flash intermittantly, could rule out some options if all of these show up ok....

 

I don't know about the 'pops' but if you're boost sensor pack becomes contaminated with oil (they can over time, or after a good thrashing), it will overread and cause wastegate to open and you loose all power, feels like you're hitting a brick wall.
New boost pack or just clean it out and pipes with carb cleaner.

The fact you have mentioned other symptoms suggest it might be something else tho.

 

Cheers again guys. Some great advice there. It hasnt done it again since I filled her up with petrol, and a lot of people have suggested fuel starvation could be the root. I'll check the controller and see if the sensors are fine, too

 

Tried to see if the just under 1/4 tank hesitation would still be in effect and unfortunately it is. Am I right in thinking that fuel starvation could well be the route of the problem after all?

I'll check tomorrow to see if over half a tank gives the same results

 

Also, I must add that I did not suffer this problem before it was mapped, and it has an uprated Walbro 255 fuel pump. Surely I'd get the fuel starvation prior to any modifications if its so common? Or does it only occur on uprated pumps and/or remaps?

 

That is strange.... I was running about 350 bhp at 1.4 bar in my RA before, it was also Andy F mapped, with near exact same mods as yours, however I used to run it under a 1/4 tank regularly and it didn't ever have any sort of detrimental effect....

Have you got a FPR? Could it be when the fuel is low the standard FPR is not working well enough with the Walbro pump?......

 

Dont actually know if its got a regulator. I would presume so. Been advised that The sock filter that comes with Walbro pumps is smaller than the standard one and as such won't sit in the fuel as much as the standard one, and with the car being mapped more aggressively than standard when it is driven hard the fuel will move around a lot more.
Saying that, I didnt fit the pump so I dont know if they used the original filter or not. lol.

Hmm...

 

Quite a few people on here have experienced issues when running a quarter of a tank or less especially going around bends (consistent with the rounabout), the chances are if Andy says you are at the limit for your injectors/turbo, then it could be that you are hitting 100% injector duty, and with the low fuel in the tank this is causing a possible starvation, it doesnt explain though why it only does it in 2nd gear, unless you are at higher revs than when in 3rd 4th and 5th. Also like you previously mentioned, if it has the Walbro sock fitted to the pump instead of the oem sock then that could also add to it.

Personally I would ask whoever fitted the walbro to see if they used the new sock (maybe even check yourself as its only a 20 min job)

 

I'm going to fill up at lunch time today then take her for a quick blast. If it still does it then I'll know its not fuel starvation, at least.

Its just an annoyance really.

 

Here is an example pic of the boost settings. This is not my pic, I have found it on another thread.



Now, my settings are 0.8, 1.0, 1.2 and 1.3bar boost maps.
I then have 30, 36, 44 and 49, then my fuelling (I think) is 255, 255, 255 and 200. Does anyone know why the last one for 1.3bar boost would be 200 and not 255. Would this cause my problems?

Again, the above pic is just as an example. My figures are above.

 

I asked Andy about this once and was told that it was measuring the Sensitivity of the ECU and as you drive around on the max setting of 1.3 bar the sensitivity of the ECU will decrease- it is normal.....

 

Yeah, thanks mate. Found that out now, too. You also cant set the fuelling figure.

Hmm. I've been advised to reduce the duty by 2% on the 1.3bar setting to see if that helps. I'll do so if the fuel topping up scenario doesnt work.

 

This problem is common and is fuel starvation. The main issue is that the Impreza fuel tank isn't a single big tank at the rear - it has a sort of saddle design with two sections at either side of the propshaft. The fuel pump takes fuel from just the right hand side.

When it's quite full, then there isn't a problem, as the fuel flows freely between each side and there's still enough left around the fuel pump to supply the demands of the engine.

However, when the gets low (about 1/3 to 1/4 of a tank), if you go quickly arounda right hand corner, most of the remaining fuel flows into the left hand side. If you then accelerate hard in 2nd gear (and now with your remap the car will be much quicker in this area), and fuel in the right hand side will be pushed to the back of the tank. This means there isn't enough fuel to satisfy the engine's requirements, and the result is just like hitting a brick wall for a brief moment.

When this happens, it allows the remaining fuel to return to around the fuel pump, and also allows more time to fuel from the other side of the tank to be pumped across. When in 3rd and 4th gear, the acceleration isn't quite so severe, and the fuel won't be forced at the back of the tank as much.

This is very common, even with standard cars at Knockhill. There's a long straight, followed by a tight hairpin and then an uphill straight which you start off in 2nd gear. Exactly the right conditions to shift most of the fuel to the other side of the tank, and what's left gets thrown to the back, meaning the fuel pump is starved for a short period of time.

What can be done about it:

1) Never let the fuel get too low.
2) If the fuel is low, and you have gone around a fast right hander, either short shift into 3rd, or ease off slightly in 2nd gear around the peak torque/power area (3,50 - 6,000 rpm) which gives the fuel tank enough time to recover.
3) Sti sell an expensive custom fuel pump housing that keeps enough fuel around the pump even when there's little fuel left.
4) Fit a swirl pot which keeps a store of fuel in a special container fitted inside the engine bay. Means you can run virtually empty and still feed the engine with all the fuel it needs.
5) Make up your own baffle design or housing for the fuel tank with rubber bellows etc.

John

 

Just a thought could it be when they put in the fuel pump the filter at the bottom of the pump is in the wrong position as the don't fit in the same way as the original ones I had this with mine and I took pump out and repositioned then filter and it was fine the filter should sit in a dip in the tank witch covers the lower quarter of the tank cheers

 

John, many thanks for that explanation. Thank you, superb detail. I'm hoping this is what it is. However, sometimes it happens on straights, and the corner I'd just taken was a simple juntion maybe 100 yards prior to the pedal being slammed. Would this still cause the problem, bearing in mind the petrol situation and it being forced to the back and less than 1/4 tank?

Good stuff. However, unfortunately I'm not that technically gifted as to know the ins and outs of positions and the like
I'm all for trying things and having a bit of DIY but could you be more detailed with the correct position for the pump? I'm confident the garage should have known how to put it on, but can understand if its different to the original then it could indeed have been placed wrongly. Thanks mate.

 

JohnS, thanks for that detailed reply. I never even knew any of that tbh. I consider myself informed now though. I have been known *cough* to drive with the said low fuel light on, on many occasions. lol. And still floor it in second.

 

on a walbro pump the filter bag is smaller so if you look in your tank you will see where it goes down so you reposition the filter to fit. this was a last resort with mine and it worked//

 

Just an update, I've just found out that when the uprated Walbro fuel pump was fitted, they used the sock filter that came with it, not the original filter.

Any chance of this causing problems?