Allrighty all you Rx badd-asses... I've done a ton of searching and reading on backfiring. I am trying to get to the bottom of this with my car. Everything was perfectly fine and then I ported my Zenki wastegate to 30mm and put my girl back together and is backfires like mad during deceleration. Especially above 3500.
A lot of guys say its "normal" and that they like it. I think I read somewhere that HAILERS said, that to him it just seemed like a backfiring car may be out of tune.
Sounds good to me. I personally love the rotary hum the most when I am declerating in gear; and now it studders and bucks slightly. Sigh...
So in my searches, these are the things that I've read/found to cause this problem.

1. Rich Exhaust Mixture
2. Crank Angle Sensor out of alignment
3. Bad Plugs/Wires
4. Mal-Adjusted TPS
5. Exhaust Leak/Vacuum Leak
6. BAC valve?
7. Leaking/Bad Injectors

This is assuming your car has no more Cats and ACV/emissions equipment. Sone the ACV has an Anti-Afterburn system in it.

I would really like to tackle this issue with some of you wiser guys/gals. A lot people are just "dealing" with this it seems.
So... We'll start with my case! :P

1. Rich Exhaust Mixture.
If anything, I've only leaned out my exhaust/intake process with my current mods, which are at the bottom of this post. Plus, my car NEVER backfired before I ported the WG.

2. Crank Angle Sensor out of alignment
I just checked my timing today and it all was right on.

3. Bad Plugs/Wires
I do have new plugs. The wires do need to be replaced, but if they are the problem, that means they went bad between turing my car off to port the WG and the 2 days later I turned it back on. I suppose it could happen!?

4. Mal-Adjusted TPS
I am broke at the moment but soon, I'll purchase a multimeter to adjust the TPS. I had adjusted it before with the LED method and things were fine. Again,if it's this, it went bad in the two days my car was down.

5. Exhaust Leak/Vacuum Leak
I have replaced all my exhaust gaskets and intake gaskets. Gone over the engine bay with carb cleaner and the "Hose in the ear" trick and, was unable to locate any vacuum leaks. To be sure though, I removed my whole intake and redid everything twice! Alas, to no avail...

6. BAC valve?
Now, the BAC valve is often blamed for bad idle things, I'm not sure if it's at fault for my problem, but I blocked it off and unplugged it just to be safe. No effect. And, my car idles great!

7. Leaking/Bad Injectors
I just had my injectors serviced by Marren, 3000 miles ago. So, I don't think that thats it.


My next things on my upgrade list are an AFR and boost gauge.
I've put these essential things off because I've been powermod friendly with my
car thus far; with only doing the RB downpipe/Pre-Silencer and 50mm catback.

So, in a couple months I'll be able to tell what my mixtures are, and whether or not that was my problem. Which I doubt for the reasons I explained earlier.

So in a nutshell... Can my ported WG make my car backfire!? That is sure what is seems like!

Here is a few thanx in advance!

My car...
10th AE
Racingbeat Downpipe w/ Presilencer, 50 mm catback
Vac spider/AirPump/ACV/EGR removed, retained twinscroll, BAC and Hotstart assist
Injectors serviced by Marren, 3000 miles and 1 year ago
MOP removed and pre-mixing (OF COURSE!)
30mm Port on my Zenki!

 

The coils could be bad but probably not. If you can adjust the tps with the multimeter it would be more accurate. When you check the tps make sure that the ohms flow from idle(1000) up to full throttle(5000, give or take 1000) evenly. It could also be the water thermo sensor or the O2 sensor.

 

damn... sry, New O2 also... Hmm water thermo sensor... I'll have to check up on that...
Keep 'em comin guys!

 

Your best bet is the water thermo sensor since it tells the computer what the air/fuel mixture should be. So if its running rich then there could be too much fuel which would "blow out" the spark from the plug which would cause the car to backfire.

 

I garauntee this problem is TPS-related. The injectors are supposed to be turned off any time the throttle is closed. No fuel means no stuttering or bucking under decel. Guess which sensor tells the ECU when the throttle is closed?

BTW it could not be the thermosensor, O2 sensor or coils.

 

The O2 is only used during closed loop and light cruis. I say your TPS went bad. Try unpluging it. The ECU will default if it is missing. You run a little more rich without it but it will give you some idea as if it is your TPS or not. You realy should buy a 25$ multi meter it will help.

 

tps

 

TPS = Throttle position sensor BTW

 

You have fresh air getting into your exhaust this causes large backfires. I blew a few mufflers apart like that. I also fixed someone else's car that the dealership couldn't fix. It took me 30 seconds to sort out where the problem was. The owner was quoted $500 to fix it cost him $25 and some exhaust cement. All I did was ask the owner when it all started...thats right I put on a new rear muffler.. Did you use a new gasket with the Muffler....Nope what for?? That is your air leak causing the backfire .....Your shitting me. No just take the muffler off get a new gasket and some cement and put it back together.

Next Week

Hey Smithy my cars stop backfiring........No **** I told you so!!!!!! Much cheaper than $500 too!

Michael Smith
P.S. the dealership mechanic works with rotarys maybe once a year. I do it every day and love the smell of freshly cooked rubber first thing in the morning.

 

you should try to reset your timing...that was happining to me then i reset my timing and it never backfired after that, it was all good!!!