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Back firing is the result of.......

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Old 08-12-18, 12:07 AM
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Back firing is the result of.......

So an occasional back fire at 7k or above when shifting is caused by?? Speaking like... 7k shift from 2nd into 3rd and a single POW!!!! .. The search never gave too much. So let me rephrase the question.
can back fire be a result of
Too lean?? ( my most important reason)
Too rich?? I dont care that much
Fouled Plugs or other ignition problems.
Or low fuel pressure?
Excessive fuel pressure ( or like stuck open injector)

I am mainly concerned of lean conditions. Happened today 3x in a row and I have had an occasional pop from time to time, but nothing consecutive. . Put on dual oil coolers and nothing to do with fuel or ignition was touched... that I know of.

DP, highflow cat, and rb dual tip. 11-11.5ish on the boost.

Last edited by Testrun; 08-12-18 at 05:29 AM.
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Old 08-12-18, 02:53 PM
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An AFR gauge would give you an answer to if the engine goes rich or lean during your shifts. I assume you have the stock ECU? Or Apexi?
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Old 08-12-18, 03:00 PM
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Apexi the afr seems to be around 11.3-11.8 ish. How much do I trust the afr?? No idea really. It is an AEM eugo
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Old 08-12-18, 03:01 PM
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It is rather difficult for me as I have not developed the "eye" for it yet. The afr changes so rapidly lol
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Old 08-13-18, 12:07 PM
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To your original question the backfires can be caused by any of those things. Need to dig into the scenario where it happens a bit more.

When I'm at the race track my car will pop and shoot fire at the top end of the RPM range when making a full throttle upshift. The pop/flame/backfire comes between shifts when I let off. Assuming your backfire is a single one and comes after lifting off, then it's likely the rich gasses being ignited in the exhaust. If the backfire is before you lift and while still on the throttle then I'd look elsewhere for the cause.

If you were having lean backfires at full throttle and full boost at 7krpm your pop would likely be followed by a non-running engine.
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Old 08-13-18, 12:36 PM
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Your car is running rich and it's super regular for FD's to backfire.
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Old 08-13-18, 12:43 PM
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^ What they said.
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Old 08-13-18, 01:14 PM
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Thanks!! I like rich. This is what I was thinking, but wanted to confirm. So if I switched to a resonated mid pipe would I be shooting flames??!!?? Lol. I may have to try that.
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Old 08-13-18, 02:16 PM
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are you still running on the base map from PFC?
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Old 08-13-18, 05:42 PM
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No. Ari from rx7.com put a map in
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Old 08-15-18, 03:10 AM
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never heard anyone complain about shooting flames

Cars that shoot flames from the exhaust are always better than ones that dont.
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Old 08-15-18, 10:13 AM
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Originally Posted by Ricebox View Post
never heard anyone complain about shooting flames

Cars that shoot flames from the exhaust are always better than ones that dont.
agreed
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Old 08-15-18, 10:31 AM
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I think he was concerned about the popping noise he heard being from detonation versus from a rich AFR condition. Glad it seems to be all fine for you, Testrun.
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Old 08-15-18, 10:33 AM
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Yes I was. When I get back into town I will take her for a run and try my best to see what the afr is doing upon shifting.
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Old 08-15-18, 10:35 AM
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Sounds like a plan. FYI - I was so rich the my car shot 6 ft. flames out of the back and burnt my bumper above the exhaust. Not that made me complain.
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Old 08-15-18, 11:37 AM
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In my experiences,

Audible backfiring, like a loud pop is usually a lean condition, rather than a rich condition. Which on normal setups, the deceleration fuel cut causes a lean condition at throttle-lift, accompanied with the super hot exhaust causes auto-ignition in the exhaust itself, heard as the loud pop at throttle lift-off. Rich condition throttle lift, with deceleration fuel cut DISABLED is usually just a big flame, not much noise in my experiences.

If its popping under load, you've got retarded timing issues or definitely its running lean. Should not be popping with the throttle down
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Old 08-15-18, 11:58 AM
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Great!! Just when I thought I may be in the clear lol. So upon lift off throttle and shift at high rpm what AFR do I not want to be over?? Like 11-11.5ish AFR around 7-7.5k? Around 11-11.5 psi boost?
I didnt have a pop before soooo... maybe it is something else. I will be changing plugs asap and after I know it isn't ignition related I will be adding the twin power.
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Old 08-15-18, 12:12 PM
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Before my highflow cat install I had a couple runs on video. 9.3 psi was the max I saw and I was in the high 11 AFR. 11.7, 11.8
I will try to get some vid and see when I get back. Of course my damn tach and speedo are acting up again. Speedhut is in the future.... near future j guess damnit.
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Old 08-15-18, 01:13 PM
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In most cases, it doesn't really matter what your AFR is when you let off the throttle. If the engine is in decel/no load and throttle plate is closed it really makes no difference whether its rich or lean, besides fuel economy. The only time this might matter is on a high overlap motor with lots of port timing, and/or and engine that has no oil metering pump, thats doing some heavy decel on a racetrack, whereby the engine may be reliant upon the 2-cycle oil during decel to keep the housings lubricated and/or the high overlap causes exhaust gas reversion back into the intake upon decel which may bring up the heat housings/intake charge before reapplying throttle and diluting that vaccuum pullup
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Old 08-15-18, 01:15 PM
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Originally Posted by Monsterbox View Post
In most cases, it doesn't really matter what your AFR is when you let off the throttle. If the engine is in decel/no load and throttle plate is closed it really makes no difference whether its rich or lean, besides fuel economy. The only time this might matter is on a high overlap motor with lots of port timing, and/or and engine that has no oil metering pump, thats doing some heavy decel on a racetrack, whereby the engine may be reliant upon the 2-cycle oil during decel to keep the housings lubricated and/or the high overlap causes exhaust gas reversion back into the intake upon decel which may bring up the heat housings/intake charge before reapplying throttle and diluting that vaccuum pullup

lol I had to read that about 4x, but I think I get it.😁
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Old 08-16-18, 01:59 AM
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Mid 11's are fine for AFR. Don't run bad gas. I mix high grade and 100, but I don't drive as much as I'd like. A little peace of mind...

Make sure your fuel cap is good and don't leave the tank half empty. That'll help prevent condensation and water in the tank, which could cause knocking.
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Old 08-16-18, 02:07 AM
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And, putting some money in a good tune would be a smart investment. You mentioned you had a map loaded, but that's no replacement for a real tune.
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Old 08-16-18, 06:31 AM
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Thx Narfle. I am trying to figure out where in South FL to go for a tune. Also I have a VP race fuel station about 15 min from me. I never knew that! I planned on topping her off with either 96 or 100. I am probably little over half tank 93 and premix. I've always ran 93 and premix.
Anyway, if you know of someone by me who has a clue please let me know.
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Old 08-17-18, 02:27 AM
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Originally Posted by Testrun View Post
Thx Narfle. I am trying to figure out where in South FL to go for a tune. Also I have a VP race fuel station about 15 min from me. I never knew that! I planned on topping her off with either 96 or 100. I am probably little over half tank 93 and premix. I've always ran 93 and premix.
Anyway, if you know of someone by me who has a clue please let me know.
I'd recommend Roger @PRO's tuning in West Palm. he helped me fix a bunch of issues on my car and tune. there are a bunch of members on here who can vouch for him. unfortunately he only tunes as a side job now. send me a PM and i can get you in touch with him.
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Old 08-17-18, 03:15 PM
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Thx
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