V4JDMSTi

iTrader: (2)

I've not used my impreza very much - about 3k miles in the last 14 months. I was going to sell it for this reason but have thought sod it, I'll drive it a bit more.

After the last period of non use, which was around 3 or 4 weeks, I filled the car up with Tesco 99 as normal and noticed that it's now popping on most gearchanges and overrun. It used to do it occasionally when really warm but as said it's now much more frequent when up to full operating temp.

The car still has the dp cat but a 3" bore centre and rear box, a greedy vta bov (chavy I know but i quite like it) and a caik. It's a 97 sti and as far as I know is running the standard ecu and therefore has not been mapped. Within the last 1k miles it's had a new coil distrobution block. The HT leads were fine at the time of changing the coil.

I'm presuming it's heavily over fuelling. The exhaust is always covered in black soot. On the last fill up I also noticed that the knock link was illuminating. When I say illuminating this is the first green led above the one that tells you its on, so the "normal" led. It's never before even flashed even set on full sensitivity. However when you tap the block next to the sensor with a spanner it lights up all 5 lights. The sensor is above cylinder No 3.

I first thought I may have had a dodgy batch of fuel. So I used the car conservatively to run the remain 3/4 tank through (all of 126 miles) and then filled up again.

The first led of the knock link still flashes every now and then but not as much and the pops are still there on gear change and over run. I put the vta on the car when I first got it and it didn't pop much back then. Even though the vta momentarily makes the car run a little richer.

So peeps any ideas why all of a sudden it's doing it?

Cheers,

Matt.

KAS35RSTI

iTrader: (73)

Try adding some NF & see if it makes a difference or even better go for a remap.

V4JDMSTi

iTrader: (2)

Why would it only start doing it though? Afaik apart from the name change Tesco 99 is still the same. I'm pretty sure octane booster would only increase the pops due to the increased octane (?). Although I agree it may stop the KL flashing the single light.

No chance of a straight forward remap in a 97. You have to swap the ecu out for an aftermarket item. If it could be mapped I've have had a decat and made a few other tweaks by now.

Big 'D'

Do you still have the std recirc dv, if so I would suggest refitting it just to take the atmospheric dv out of the picture. It would be my first choice in tracing the cause.

Cheers Iain

M4RKG

iTrader: (22)

For some reason mine isnt impressed with Tesco's fuel, knock link on the Apex'I command unit is always higher readings when using Tesco's than using VPower... Plus I get more MPG out of VPower.

In my opinion its Tesco's fuel... but i'm sure other people have opposite stories

I've also heard that Tesco's is quite a poor fuel in comparison... but again, i'm sure other people have opinions of their own

Glowplug

iTrader: (8)

Mine has 3" decat, vta and KnN, it pops on occasions. Started doing it alot more when the lambda was failing/failed . Is the mpg down too?

stef_2010

iTrader: (3)

I'm sure Tesco fuel uses 5% ethanol ? and V-Power doesnt

Dont know if that could make a difference though ?

KAS35RSTI

iTrader: (73)

Ye you would need an aftermarket ecu which can be expensive. To be honest im not to sure about the Tesco fuel i have always used Vpower. The VTA would also cause over fuelling. Apparently the weather change can cause the car to run more rich. Try changing the fuel you use etc & see if it improves. Also the NF will help if your experiencing det & im not sure weather it will make it more rich but i doubt it as i never noticed any pops on my old STi 3 using NF.

V4JDMSTi

iTrader: (2)

Big D - Yes I still have the std recirc so I'll pop (pardon the pun) that back on.

M4rkg - I have a choice of Tesco 99, BP Ultimate (big no no) or Sainsburys SUL (only97 ron). There is a shell garage but it's at least a half hour round trip and in the oposite direction to pretty much wherever I want to go. I may try a tank though to see if it helps as If it was more accessable to me I'd run it on V-power all the time.

As for fuel consumption I see around 16mpg on a mix of plodding around town and motorway driving.

KAS35RSTI

iTrader: (73)

16mpg is pretty bad. When was your lamda sensor last changed?

M4RKG

iTrader: (22)

16mpg?!

What sort of power are you running?

I've recently changed my exhaust manfold from equal length tubular to unequal length ported OE (Harvey's) and have noticed a massive difference in the "pops and bangs", now I barely get any, where as the tubular manifold used to rumble the whole underside of the car in over-run.

I think a remap is on the cards for you my friend, i'm running close to 350bhp and get around about 20mpg just driving around town, goes upto around 25mpg (max) on a run.

V4JDMSTi

iTrader: (2)

b13bat - yup fuel consumption isn't great. As above it's about 16mpg. In past Imprezas I've had abour 24mpg around town with my 95 import wrx, 9 - 14mpg when I had my 93 wrx RA with short box.

I've just put this lower consumption down to it being an STi and the vta coupled with short(ish) journies. I'll see if I can find the thread to check the cel codes and see if it comes up with anything.

Stef 2010 - not sure about the make up of the fuels.

Aladdin - yes I was wondering about the temp change as it's been a bit colder of late. Although on the warm days we have last week it was still doing it. I'm a bit baffled by it. I'll grab a bottle of NF (may even still have a bottle in the shed) and give that a go on the next fill up with 99. Then if that doesnt make any difference I'll try the V-power.

When I refit the std recirc I may take off all the vac and breather pipes and give them a clean out. Worth it?

V4JDMSTi

iTrader: (2)

Aladdin - Lamda hasn't been change since I've had it in the last year and a bit. And I've not seen a receipt for one in the service history.

M4rkG - I love the sound of the equal length headers I had them on my last 2 scoobs. No remap is possible for me. It's a 97 so can't be mapped unless I out the standard ecu and get an apexi etc. Funds just don't allow for that. Power wise my RA was running 280/270 and this one feels far quicker. Also a far bit quicker than my Dad's classic wagon that's running 270/280. I've nto had this one on the rollers yet. I'd like to and was thinking about it but this has put me off for the moment.

350bhp is nice power. Is that in a classic?

KAS35RSTI

iTrader: (73)

You could do but it wont prevent the overfuelling. Best thing to do would be to try the NF, if its still the same then try using Vpower & check the condition of the lamda & get it tested. Personally i would not worry much about running rich but keep a eye on the knocklink. I hate det!!!!

Glowplug

iTrader: (8)

Yeah, 16 is low on a pretty much stock motor.
Easy way to test the lambda is to put a multi-meter to the signal wire, either the ecu end (pin-outs alailable on JGM's site) or find the connector in the engine bay, near the air-box and BCS assemby. It should flick continually from 0.1 to0.9 volts, if it just sits around and does not fluctuate wildly then odds on you need a new one.
It will cause overfuelling as you are doing, as you say, short, around town trips (running in open loop) so the ECU will just be throwing loads of fuel in to compensate.

V4JDMSTi

iTrader: (2)

Aladdin - I'll check the shed for the NF if not I'll grab a bottle. Give that a go if it cures it then that's the way forward. If not I'll sling a tank of v-power in. I might check the breathers / vacs just so I know they're all clear. Plus I can clean them up on the outside and make the bay look a bit cleaner lol. Agree about the det. My biggest fear. If it goes bang I'll be without a scoob for a fair while.

b13bat - I'll get the multi meter out and have a look tonight.

KAS35RSTI

iTrader: (73)

Just make sure you use the proper Nitrous fuel (NF). You can buy it off ebay or even RCM. Hope it gets sorted mate

harvey

iTrader: (48)

If the car wasn't popping and banging in the exhaust prior to a period of inactivity and it is now popping and banging in the exhaust, chances are you have a very small air leak in the exhaust system.
Adding NF will have absolutely no effect whatsoever on popping and banging in the exhaust. NF is an Octane Booster and the popping and banging in the exhaust is unburned fuel igniting. Either there is air there that wasn't there before or there is fuel there because the bottom row of your map is running richer.

V4JDMSTi

iTrader: (2)

Cheers Harvey. I was trying to find the pops and bangs thread you posted on a while back but couldn't find it. I'll give the exhaust a check over. Knowing my luck the standard dp has developed a hole. Which will lead to me wanting a decat which in turn I'll have to by a new ecu for. Funds just don't allow for that at the moment. (the wife still thinks I'm selling it to buy a diesel. )

harvey

iTrader: (48)

Chances are that replacing a gasket, probably the one at the end of the downpipe and the job is solved.

Wagon wheel eater

I have experienced something similar? what would be the consequences of driving hard and ignoring the exhaust leak for a while until funds allow for a new one...? Its just runs rich ? is that all cos I quite like the bangs on over run !

phil84

I would say Harvey is spot on.

I too have been wondering why my93 RA was popping a lot since putting it back on the road.

It hadn't been driven for 12 months ish. I first put it down to not being run for so long and after servicing it, it was still doing it. Tried octane booster as well, that didn't work.

Fuel wouldn't make much difference at all. The only difference between most of them is the additives each company add to it.

Last month I fitted my old HKS blow off valve but still popping on overrun but checked the exhaust system..... downpipe to mid section leaking
since then no probs