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Car Making Loud Backfires

rad100

By rad100,
in Engines & Forced Induction

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rad100 Grand Master

rad100

Posted
Posted

hey all,

just picked up my car from getting tuned and stuff.

now what happens is when i accelerate and then either clutch in or let it rev down i get 1 or 2 massive back fires.. almost like if i was to do a keybanger!

it happens in every gear, and around the 1500-3000rpm..

the car has no boost leaks before the exhaust as we pressured the intake to hear for leaks but there all secure..

would having an exhaust leak cause this? as in the exhaust is sucking in air and mixing with the unburnt fuel and creating an (explosion)?

also,

my hiflow 7400cc stock injectors dont seem to be firing even at idle? is this due to them being too hiflowed?

mods:

rb25det unopened

stock exhaust manifold

z32 afm

nisstune rb20 ecu

eboost

fmic

3inch turbo back no mid mufflers or cat.

740cc hiflow stock injectors

gt3076r .82

turbosmart ultragate 38mm external wastegate

cheers Adrian!

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Adriano Grand Master

Adriano

Posted
Posted

What do you mean by the injectors arent firing at idle? The fuel has to be coming from somewhere? I would say the ttp min setting needs to be adjusted as the larger injectors need less ms on overrun. You are running a recirculating BOV aren't you?

rad100 Grand Master

rad100

Posted
  • Author
Posted

im running all standard lines to bov etc..

um it was tuned in adelaide buy the speedlab..

he worked on getting them to work better on idle..

its really anything under 1500rpm..

once u put some pedal into it, the car runs mint..

rad100 Grand Master

rad100

Posted
  • Author
Posted

he thinks the 740cc injectors are too hiflowed for the stock ones.. so there not firing even under idle. like the car bounces from slightly lean to slightly rich..

he also thinks there may be an exhaust leak which is sucking air in under de-acceleration which is mixing with the unburnt fuel and making the (explosion).

MBS206 Grand Master

MBS206

Posted
Posted
he thinks the 740cc injectors are too hiflowed for the stock ones.. so there not firing even under idle. like the car bounces from slightly lean to slightly rich..

he also thinks there may be an exhaust leak which is sucking air in under de-acceleration which is mixing with the unburnt fuel and making the (explosion).

If that's the case, your whole tune should be richer then what the actual AFR was reading...

But more it sounds like the injectors should be replaced... 700cc should idle perfectly. And if you check all the exhaust and find no leaks I'd be looking at the tune and injectors.

rad100 Grand Master

rad100

Posted
  • Author
Posted (edited)

nah bluey white smoke..

just about to pull plugs out. wait for the tool..

i would have thought missfire = black smoke due to unburnt fuel?

but this is white.. turbo is new, oil is new, plugs were new, injectors new... hmmm

oh ans splitfire coilpacs

Edited by rad32
MrStabby Grand Master

MrStabby

Posted
Posted
he thinks the 740cc injectors are too hiflowed for the stock ones.. so there not firing even under idle. like the car bounces from slightly lean to slightly rich..

he also thinks there may be an exhaust leak which is sucking air in under de-acceleration which is mixing with the unburnt fuel and making the (explosion).

Do you KNOW they're not firing at idle or just SUSPECT it? If the car is extra rich at idle/low load but ok otherwise, then the injector latency setting may be too big. However if the latency is too low you'll get extra lean at idle/low load when its ok at load...

If the system is working in closed loop control (ie the o2 sensor is being used) then its supposed to bounce from lean to rich and back again constantly - thats how it works.

BTW black smoke = rich, white/blue smoke is oil burning.... nasty.

rad100 Grand Master

rad100

Posted
  • Author
Posted

well i just pulled the plugs out and 1,4,5 were very wet.

then we cleaned them put them back, started it and same,

then we unpluged the coilpacks and 2,3,6 made change and ,1,4,5 mad no change.

does that mean 1,4,5 are getting too much fuel?

as they would be making the car miss?

i dont know why white smoke would be coming out?

yesterday the car was running fine (black smoke) so richish.

paulR32gtr Mentor

paulR32gtr

Posted
Posted

Bluey/white smoke means oil and possibly water is getting in to the combustion chamber / exhaust - never good unfortunately...

Off the top of my head could be piston rings, a cracked head or blown turbo seals... could also be valve stem seals but doesn't sound like it

A few things you can check:

- Take the pipes off the turbo compressor and check for excessive oil - stuffed turbo, could also be coming from the exhaust side - a bit tricker to get the dump pipe off but a potential source. This can also cause problems with fuelling as air can move between the intake and exhaust

- Get a compression test done on the engine

- Check the water in the radiator, if it looks milky/oily you are most likely looking at a cracked head

paulR32gtr Mentor

paulR32gtr

Posted
Posted

Bluey/white smoke means oil and possibly water is getting in to the combustion chamber / exhaust - never good unfortunately...

Off the top of my head could be piston rings, a cracked head or blown turbo seals...

A few things you can check:

- Take the pipes off the turbo compressor and check for excessive oil - stuffed turbo, could also be coming from the exhaust side - a bit tricker to get the dump pipe off but a potential source. This can also cause problems with fuelling as air can move between the intake and exhaust

- Get a compression test done on the engine

- Check the water in the radiator, if it looks milky/oily you are most likely looking at a cracked head

rad100 Grand Master

rad100

Posted
  • Author
Posted

oils fine, water is green, turbo is brand new and is all good..

what would be the reasong behind cyl 1,4,5 not making a difference when i unplug the coilpacks?

coz this would be the issue with the car running on less cyl yeh?

also does the gt30 need a more restrictive oil feed?

i dont believe i have any of the issues above as it only did 20 dyno runs and has been fine before that. and was also fine when i drove it off the car trailer..

its like something happened overnight..

paulR32gtr Mentor

paulR32gtr

Posted
Posted

When you say the plugs were wet - were they fouled with fuel, or were they wet with water?

Run through the basics air, fuel, spark, compression.

Air = your problems dont sound like a problem with air but check all intake piping is connected properly, there are no forgotten rags blocking intercoolers etc

Fuel = while the car is running you should be able to feel the injector pulsing, you could also check fuel pressure if you have the gear - would recommend a mechanic for this

Spark = you really need a spark tester for this these days - there are old methods but can potentially cause damage to the ignition module - mechanic would have one

Compression = compression test - again you need the gear

Once you have narrowed it down to one of the basics above, or none of the above, you can proceed to the next steps of diagnosis.

Not sure about restrictors for GT30 - I know first hand the GT2860 series have built in restrictors in the oil inlet - if you have a photo upload it, but worth checking with the experts - give GCG or similar a call.

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