backfiring!!
20 February 2011, 02:56 PM
#32
There seems to be a difference of opinion on whether its safe to decat a classic or not.Surely mappers arnt inventing potental problems.In the post mods enginetuner states the exhaust is safe as long as the catt is left in,although a decat is prob not the reason for backfireing surely over boost can be with a unmapped car,i guess its each to there own 
20 February 2011, 04:44 PM
#33
There seems to be a difference of opinion on whether its safe to decat a classic or not.Surely mappers arnt inventing potental problems.In the post mods enginetuner states the exhaust is safe as long as the catt is left in,although a decat is prob not the reason for backfireing surely over boost can be with a unmapped car,i guess its each to there own
Decatting a classic will not make it blow up. The only thing it may cause is a slight boost increase on account of a little less back pressure. This is fine as the ECU will cope with up to 1.2 bar after which there is a fuel cut to avoid damage.
20 February 2011, 05:47 PM
#34
Well you might well be right,as i dont own a classic and you do,however if i was looking for advice as shanegs was theres no point asking Enginetuner when he meets him as he will be told to put the catt back on and it looks like he has decided he doesnt need to.And to be fair to mappers they dont tell you to decat so they can map all they say is dont do one without the other
Last edited by bugeyejohn; 20 February 2011 at 05:57 PM.
20 February 2011, 07:35 PM
#35
Scooby Regular
iTrader: (6)
Join Date: Oct 2002
Location: North West
Posts: 1,134
Likes: 0
Received 0 Likes
on
0 Posts
I ran an MY99 uk turbo on a full decat with k&n panel filter and sti intercooler from around 15k miles to 65k miles over a 6 year period, never missed a beat, had it on the rollers at Prosport and Pete said it was spot on. He did also say that some cars are ok, others aren't, considering they do mapping there he could have easily talked me into a remap but he didnt, so I would get it checked just to make sure it's right
20 February 2011, 08:04 PM
#36
Scooby Regular
Join Date: Nov 2006
Location: Near Sheffield
Posts: 380
Likes: 0
Received 0 Likes
on
0 Posts
Nobody is going to bite the hand that feeds them. Decatting a classic will not make it blow up. The only thing it may cause is a slight boost increase on account of a little less back pressure. This is fine as the ECU will cope with up to 1.2 bar after which there is a fuel cut to avoid damage.
Decatting a classic will not make it blow up. The only thing it may cause is a slight boost increase on account of a little less back pressure. This is fine as the ECU will cope with up to 1.2 bar after which there is a fuel cut to avoid damage.What this does, is it increases the engine load to levels far beyond what the current OE map is created for. The maximun load in the OE map may be 2.5 grams per revolution and now the engine is seeing loads of up to 3.2 g/rev.
What this means is that the timing that is set at loads of 2.5 will now be used at the higher loads and thus the engine will det.
It's a little bit more complicated than that but thats it in a nutshell. There are other negative aspects as well.
20 February 2011, 08:31 PM
#37
I ran an MY99 uk turbo on a full decat with k&n panel filter and sti intercooler from around 15k miles to 65k miles over a 6 year period, never missed a beat, had it on the rollers at Prosport and Pete said it was spot on. He did also say that some cars are ok, others aren't, considering they do mapping there he could have easily talked me into a remap but he didnt, so I would get it checked just to make sure it's right
My guess is there also other factors, driving style, dump valves,induction kits,i think rather than take the risk i wouldnt be taking it a bit easy until i knew for sure,rather than gunning up the road and finding out mine wasnt one of the ok ones 
20 February 2011, 09:47 PM
#38
Scooby Regular
iTrader: (2)
Join Date: Feb 2010
Location: Colchester,Essex
Posts: 1,037
Likes: 0
Received 0 Likes
on
0 Posts
It sounds just more like popping due to the mods rather than proper 'back firing'
Id also been told that its mainly the newage set up which is more necessary for a remap when decatting.
Id also been told that its mainly the newage set up which is more necessary for a remap when decatting.
20 February 2011, 10:50 PM
#39
Scooby Regular
Thread Starter
Join Date: Feb 2011
Location: somerset
Posts: 47
Likes: 0
Received 0 Likes
on
0 Posts
some times its just little pops an some time loud bangs from exhaust id def say a backfire
21 February 2011, 08:00 AM
#40
Scooby Regular
Join Date: Nov 2010
Posts: 97
Likes: 0
Received 0 Likes
on
0 Posts
This is a little misleading. Yes its true that the ecu will add more fuel where the engine is over boosting. The problem is, when the cat has been removed it increases the engines Volumetric efficiencey (VE). I.E it consumes more air per revolution of the engine. This is due to the exhuast having a hugh restriction taken out of it.
What this does, is it increases the engine load to levels far beyond what the current OE map is created for. The maximun load in the OE map may be 2.5 grams per revolution and now the engine is seeing loads of up to 3.2 g/rev.
What this means is that the timing that is set at loads of 2.5 will now be used at the higher loads and thus the engine will det.
It's a little bit more complicated than that but thats it in a nutshell. There are other negative aspects as well.
What this does, is it increases the engine load to levels far beyond what the current OE map is created for. The maximun load in the OE map may be 2.5 grams per revolution and now the engine is seeing loads of up to 3.2 g/rev.
What this means is that the timing that is set at loads of 2.5 will now be used at the higher loads and thus the engine will det.
It's a little bit more complicated than that but thats it in a nutshell. There are other negative aspects as well.
This is even more misleading. Most (all?) OEM maps go far beyond what the engine is designed for. The maps are actually quite decent, biggest problem with them are generally very rich AF readings all the way to fuel cut. Its once you go beyond the factory fuel cut point youre going to be a pioneer on OEM maps, but that requires its own, not always clever modification.
21 February 2011, 08:27 AM
#41
Dont listen to much on hypoconders decatting their car and dont dare hitting the throttle until some tuner can ripp them off on a remap.
You have a little thing called a air flow sensor in your intake (by the air filter). When decatting, you get more exhaust out of the cylinders, so therefore you can get more air in. More air requires more fuel. Without the air flow meter this would be bad. very bad. But that little sensor reads that you get more air in, and therefore increase the amount of fuel injected.
The "problem" with this little sensor though, is that even small leaks, from intake pipes, intercoolers, BOV`s etc also reads as air into the engine. Some FI systems wont allow fuel cut with a certain amount of air flow through the MAF. They then inject fuel as if the air flow enters the engine. This cause backfireing, even flames when enough ignities on the hot turbo.
So have fun. Pedal to the metal. Invest in a wideband AF meter if youre worried about running into problems with fueling.
Oh, just for the fun of the examples, a Nissan 200SX, with virtually the same fuel injection as your scoob, can handle a boost increase of over 100%, 3" exhaust, FMIC, and even mild camshaft replacements without a remap. So dont tell me removing a cat will blow up a scooby engine.
You have a little thing called a air flow sensor in your intake (by the air filter). When decatting, you get more exhaust out of the cylinders, so therefore you can get more air in. More air requires more fuel. Without the air flow meter this would be bad. very bad. But that little sensor reads that you get more air in, and therefore increase the amount of fuel injected.
The "problem" with this little sensor though, is that even small leaks, from intake pipes, intercoolers, BOV`s etc also reads as air into the engine. Some FI systems wont allow fuel cut with a certain amount of air flow through the MAF. They then inject fuel as if the air flow enters the engine. This cause backfireing, even flames when enough ignities on the hot turbo.
So have fun. Pedal to the metal. Invest in a wideband AF meter if youre worried about running into problems with fueling.
Oh, just for the fun of the examples, a Nissan 200SX, with virtually the same fuel injection as your scoob, can handle a boost increase of over 100%, 3" exhaust, FMIC, and even mild camshaft replacements without a remap. So dont tell me removing a cat will blow up a scooby engine.
and as for compareing a nissan 200sx to shanegs car are you for real,a 100% boost increase with no remap take your tool box,at the end of the day we dont want shaneg to have problems if he takes notice of this god help him.
21 February 2011, 08:41 AM
#42
Scooby Regular
Join Date: Oct 2008
Posts: 378
Likes: 0
Received 0 Likes
on
0 Posts
i ran my classic turbo 2000 without a remap on a decat for over 4 years doing nearly 70000 miles!! I got the backpops too!!! other than that the car still runs strong with its current owner who did get it remapped for a whole 10bhp increase???? at a cost of £400!!
21 February 2011, 08:43 AM
#43
Scooby Regular
Join Date: Nov 2010
Posts: 97
Likes: 0
Received 0 Likes
on
0 Posts
Id say this is slighty missleading a statement of pedal to the metal to someone with a obvious running issues and as for compareing a nissan 200sx to shanegs car are you for real,a 100% boost increase with no remap take your tool box,at the end of the day we dont want shaneg to have problems if he takes notice of this god help him.
and as for compareing a nissan 200sx to shanegs car are you for real,a 100% boost increase with no remap take your tool box,at the end of the day we dont want shaneg to have problems if he takes notice of this god help him.He has no running problems. He has backfiring when hes off throttle. So does 99% of all other "free" exhaust turbo cars.
Edit: Comparing to the 200sx is just to display what stock EFI`s really can do in most cases. Ive used stock EFI`s many times, changing to bigger turbo`s, increasing boost, and Ive even replaced the camshafts once on stock EFI. Thats the great thing with the MAF sensor. unlike the MAP or alpha-n (TPS as load sensor), the MAF system`s can measure the actual amount of air entering the engine, and computes its load based on that. Then a long mathematical calculation, using its fuel and ignition tables, temp sensors, rpm sensor ++ calculates the injector opening times and ignition timing. Therefore, as long as you are withing the OEM tuned limits (Mostly set by a fuel cut in the upper scale of the fuel table(not part of the fuel table)), you can realatively safe do most mods to your engine, even increase displacement. Shure, in extreme cases you definately SHOULD get a proper tune, or at the very least monitor AF values and knock, but minor mods like a exhaust upgrade is IMHO nothing to worry about, and most mods WILL WORK WITH NO PROBLEMS.
Best regards from someone who has actually done this several times before.
Last edited by The king; 21 February 2011 at 09:12 AM.
21 February 2011, 01:54 PM
#44
He has no running problems. He has backfiring when hes off throttle. So does 99% of all other "free" exhaust turbo cars.
Edit: Comparing to the 200sx is just to display what stock EFI`s really can do in most cases. Ive used stock EFI`s many times, changing to bigger turbo`s, increasing boost, and Ive even replaced the camshafts once on stock EFI. Thats the great thing with the MAF sensor. unlike the MAP or alpha-n (TPS as load sensor), the MAF system`s can measure the actual amount of air entering the engine, and computes its load based on that. Then a long mathematical calculation, using its fuel and ignition tables, temp sensors, rpm sensor ++ calculates the injector opening times and ignition timing. Therefore, as long as you are withing the OEM tuned limits (Mostly set by a fuel cut in the upper scale of the fuel table(not part of the fuel table)), you can realatively safe do most mods to your engine, even increase displacement. Shure, in extreme cases you definately SHOULD get a proper tune, or at the very least monitor AF values and knock, but minor mods like a exhaust upgrade is IMHO nothing to worry about, and most mods WILL WORK WITH NO PROBLEMS.
Best regards from someone who has actually done this several times before.
Edit: Comparing to the 200sx is just to display what stock EFI`s really can do in most cases. Ive used stock EFI`s many times, changing to bigger turbo`s, increasing boost, and Ive even replaced the camshafts once on stock EFI. Thats the great thing with the MAF sensor. unlike the MAP or alpha-n (TPS as load sensor), the MAF system`s can measure the actual amount of air entering the engine, and computes its load based on that. Then a long mathematical calculation, using its fuel and ignition tables, temp sensors, rpm sensor ++ calculates the injector opening times and ignition timing. Therefore, as long as you are withing the OEM tuned limits (Mostly set by a fuel cut in the upper scale of the fuel table(not part of the fuel table)), you can realatively safe do most mods to your engine, even increase displacement. Shure, in extreme cases you definately SHOULD get a proper tune, or at the very least monitor AF values and knock, but minor mods like a exhaust upgrade is IMHO nothing to worry about, and most mods WILL WORK WITH NO PROBLEMS.
Best regards from someone who has actually done this several times before.
Engine tunners pack up your tools there not needed.
21 February 2011, 06:21 PM
#45
He has no running problems. He has backfiring when hes off throttle. So does 99% of all other "free" exhaust turbo cars.
Edit: Comparing to the 200sx is just to display what stock EFI`s really can do in most cases. Ive used stock EFI`s many times, changing to bigger turbo`s, increasing boost, and Ive even replaced the camshafts once on stock EFI. Thats the great thing with the MAF sensor. unlike the MAP or alpha-n (TPS as load sensor), the MAF system`s can measure the actual amount of air entering the engine, and computes its load based on that. Then a long mathematical calculation, using its fuel and ignition tables, temp sensors, rpm sensor ++ calculates the injector opening times and ignition timing. Therefore, as long as you are withing the OEM tuned limits (Mostly set by a fuel cut in the upper scale of the fuel table(not part of the fuel table)), you can realatively safe do most mods to your engine, even increase displacement. Shure, in extreme cases you definately SHOULD get a proper tune, or at the very least monitor AF values and knock, but minor mods like a exhaust upgrade is IMHO nothing to worry about, and most mods WILL WORK WITH NO PROBLEMS.
Best regards from someone who has actually done this several times before.
Edit: Comparing to the 200sx is just to display what stock EFI`s really can do in most cases. Ive used stock EFI`s many times, changing to bigger turbo`s, increasing boost, and Ive even replaced the camshafts once on stock EFI. Thats the great thing with the MAF sensor. unlike the MAP or alpha-n (TPS as load sensor), the MAF system`s can measure the actual amount of air entering the engine, and computes its load based on that. Then a long mathematical calculation, using its fuel and ignition tables, temp sensors, rpm sensor ++ calculates the injector opening times and ignition timing. Therefore, as long as you are withing the OEM tuned limits (Mostly set by a fuel cut in the upper scale of the fuel table(not part of the fuel table)), you can realatively safe do most mods to your engine, even increase displacement. Shure, in extreme cases you definately SHOULD get a proper tune, or at the very least monitor AF values and knock, but minor mods like a exhaust upgrade is IMHO nothing to worry about, and most mods WILL WORK WITH NO PROBLEMS.
Best regards from someone who has actually done this several times before.
21 February 2011, 06:32 PM
#47
Scooby Regular
Join Date: Nov 2010
Posts: 97
Likes: 0
Received 0 Likes
on
0 Posts
Buy a AF gauge and listen for knock next time you mod your car.. (Or does the tuner mod it for you too mommys boy?
) Maybe youre in for surprise.... If you find something wrong, go to your precious tuner. Mostly though, they`re not needed until you start maxing your injectors, or if you want that extra 10hp or whatever someone further up the post claimed to gain.
21 February 2011, 06:41 PM
#48
Scooby Regular
Join Date: Dec 2010
Location: staithes near whitby,n,yorks
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
its not that dear to chip up the early ones,ive seen the chips mapped to your supplied spec for £60 ish,then £25 to get old chip removed+a socket fitted then you can fit either chip to match having or not having your cat on.
ive chipped vag petrols+diesels for years and always fit a socket after old chip removed[via non destructive method],my european supplier of my VAG maps has told me he can supply me with impreza turbo maps no problem to match any mods i do or undo.
and before anyone asks"no i dont want to do scoobys as well...lol"
ive chipped vag petrols+diesels for years and always fit a socket after old chip removed[via non destructive method],my european supplier of my VAG maps has told me he can supply me with impreza turbo maps no problem to match any mods i do or undo.
and before anyone asks"no i dont want to do scoobys as well...lol"
21 February 2011, 06:56 PM
#52
Scooby Regular
Join Date: Oct 2008
Location: around the vallys in my red scoob
Posts: 430
Likes: 0
Received 0 Likes
on
0 Posts
my99 turbo had a 3inch miltek with sports cat when i put a dumb valve on it popped . when i took the sports cat out and replaced it with a decat it popped with flames
21 February 2011, 08:46 PM
#54
Scooby Regular
Join Date: Dec 2010
Location: bridgend
Posts: 183
Likes: 0
Received 0 Likes
on
0 Posts
I fitted an indigo gt turbo back (with screamer pipe) exhaust to my RA, and it did over boost when going for it, changed
It back to the de-catted centre section and back box and it was fine again, sometimes a map is needed, my mate was running a turbo back exhaust on his classic with out a problem, map's ain't always needed and this site is a mappers dream
It back to the de-catted centre section and back box and it was fine again, sometimes a map is needed, my mate was running a turbo back exhaust on his classic with out a problem, map's ain't always needed and this site is a mappers dream
Well shaneg i think we can safely say youve heard both sides now,what was the question again 
21 February 2011, 10:11 PM
#56
Scooby Regular
iTrader: (8)
Join Date: Jan 2008
Location: Burnley, Lancs
Posts: 513
Likes: 0
Received 0 Likes
on
0 Posts
I've just spent 3k building my engine and upgrading my turbo, and to be honest, I'm not leaving my 3k and hard work in the hands of a 150 quid Maff sensor. Yeh sure decatting and throwing a dv is one thing and the maff will cope to some extent, but the car won't be at its best. ThT bothers some owners and not others. changing turbos and injectors and relying on the oem limits of the MAff to sort is suicide! How many people know what these oem limits are and what mods will keep within these tolerances? I'm guessing a handful of people on this site, and I'll bet 95% of them are mappers. To the average scooby owner I think it's worth the fee for a mapper to check, and most of the mappers on here won't con you into a map if you don't need one. I think 100% peace mind knowing your car is running right, is better than wondering when and if it will go pop!!!
21 February 2011, 10:33 PM
#57
Oh is mapping worth it,id say yes but i could be wrong,but in case im not carry one of these http://cgi.ebay.co.uk/Good-Emergency...item20b37f7466 If shanegs car is backfireing for about £70 its checked,hes got a good mapper near him that wont rip him of and if it doesnt need a map which it looks like he might not great,better that than take advice from someone who hasnt seen the car heard it or even know it and who i suspect were go very quiet if it all goes wrong.
Last edited by bugeyejohn; 22 February 2011 at 10:38 AM.
Thread
Thread Starter
Forum
Replies
Last Post
