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help. sputtering popping and backfireing under boost.

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help. sputtering popping and backfireing under boost.

Old 06-28-2012, 04:17 PM
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Default help. sputtering popping and backfireing under boost.

this is a small t25 turbo running a 1.6 16v suzuki engine. it has a wide band 02 sensor that is staying around 14-1 inder boost but will start to pop and kinda sound like it backfireing when the rpm get up around 4000rpm during wide open throttle.

the internal wastegate is set at 8psi and i havent seen it open so im shure its still pretty low boost.

im just running it off factory efi for now and have the initial timeing backed off from 8 degress to 5 right now.

i have a friend who is running this same setup but havent been able to get ahold of him for any info and im conmpletely new to turbos. any help would be great.
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Old 06-29-2012, 08:26 AM
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14's under boost is a bit lean.

Any chance it's spark blowout? What are you using for ignition?
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Old 06-29-2012, 09:18 PM
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the plugs are gapped at 30 right now. theres 300 miles on the complete rebuild and new plugs,cap and rotor. this engine ran flawlessly last weekend and as soon as i added the turbo it started doing weird stuff.

stock efi is now backed down to 0 degress at idle but seems to jump up to like 40 before tdc when the rpms come up.

it seems like the afr is jumping all around when idleing it strtes getting lean like 17-1 ans when i rev it it goes to 12-1 when its just running down the road it stays near 14-5 but as soon as the boost kicks in itll start popping and losses power.

also while messing with it today it seems like the engine runs without the 02 sensor i tried swapping in a differant one and no change so i unplugged it and its still acted the same plug in or not.

the cel light has been reading aok the hole time.
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Old 07-02-2012, 09:46 AM
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If this is a totally stock distributor type ignition, try adding an MSD 6BTM or similar CDI / timing retard device.
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Old 07-03-2012, 06:49 PM
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stock dist. but like i said earlier my buddys is running bone stock and kicking ***.

today i swaped out ecu and maf and was hopeing to do a 02 but the one i pulled from my buddys didnt fit.

after all this swapping i finally unplugged the 02 sensor and started the rig and with no 02 at all it ran just the same as it did this hole time. my guess is that the engine is running in a ''limphome'' mode and isnt being controlled by the 02.

looking further into the limphome feature of this engine it says that even tho the engine is running in open loop it still will NOT throw a engine light at all. the check engine light has never came on and i guess if the 02 is the problem it never will. huh?

i pulled all the turbo stuff and put it back to stock and its back to running like it always has even with the 02 unplugged.

anyhow ill be installing a brand new 02 and putting all my turbo stuff back on and ill report back when i get the results.


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Last edited by nickrocks; 07-03-2012 at 07:11 PM.
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Old 07-04-2012, 09:22 AM
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Could be ignition (spark blow out) But if your running low amounts of boost and your gaped to .030 then its really doubtful in my opinion if your ignition is in ok shape.

If your running 14+ AFR under boost then it could just be that your way too lean, fuel cut basically. I would get the AFR to be a constant 12.5:1 or less first and see if that helps before chasing the ignition down.

I tune for 12:1 for up to 6psi 11.5:1 for up to 9psi then 11.0:1 for levels up to 15psi. I have alky injection also so thats why its a tad lower AFR then peak Tq range. So without my alky running the afrs are roughly 1pt higher. I would say that 12.5:1 is the safest lean AFR to go. 14's AFR will burn up some rings and such in time if your on it for a while.
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Old 07-04-2012, 11:32 AM
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i know the factory efi will try to keep the a/f ratio at 14.7 it should aways stay near that number on a stock motor with no turbo.

im looking into ways to add another injector without being over complicated.
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Old 07-04-2012, 08:05 PM
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Had same problem. Gap plugs at .02-.022, your Proly boosting higher then u think. Do u have a gauge?
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Old 07-05-2012, 04:12 AM
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Originally Posted by nickrocks View Post
i know the factory efi will try to keep the a/f ratio at 14.7 it should aways stay near that number on a stock motor with no turbo.

im looking into ways to add another injector without being over complicated.
I wouldn't be so worried about the spark gap till you get the afr down pat. .028-.030 is plently tight enough IMO> The tighter the gap the less powerful of a boom=less fuel needed and lower afrs. So tightening the gap may help but its just a bandaid for the real issue you may have.

Are you not able to tune the ecm?

Am I the only one that sees hes runnign 14+ AFRs with boost and how big of a issue that is?? This really jumps out as a major issue that will inevitably kill any motor.
14.7 afr with boost is just asking for a catastrophy.

Last edited by fasteddi; 07-05-2012 at 04:16 AM.
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Old 07-05-2012, 08:16 AM
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Very true ,,,,that bandaid might be why my motor left? Wasn't getting enough fuel?
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