iansw

iTrader: (7)

When Downshifting especially from 3rd to 2nd or 2nd to 1st, I get a pretty nasty backfire sometimes.

Right now I'm running the following setup:
V2
2.87" Pulley
370cc Injectors
JWT SC programmed ECU for 370cc injectors
Warpspeed Y-Pipe
Warpspeed Straight Pipe
Warpspeed straight through (no resonator) B-Pipe
Stillen Exhaust

I'm thinking it's not really a problem and is just caused by the openness of my exhaust, but i want to make sure.

EGT's are steady and low when this happens and it seems to happen more when the car is slightly cold. Whether I'm boosting or not doesn't seem to matter as it seems to happen at about 2500-3000RPM usually with my foot off the gas.

If I rev the engine a little as i shift and grab higher into the lower gear, it doesn't happen.

Just want to verify what I'm seeing/hearing.

Thanks!
IanS

bosco500

Probably just running a little rich. Have you tuned w/ a wideband yet?

Confused

iTrader: (4)

z or max maf?

iansw

iTrader: (7)

Max MAF - what the JWT is currently programmed for.

I am running a little rich - and haven't tuned yet.

Pretty much what I suspected - just wondering if it could feasibly damage anything.

IanS

maximase86

iTrader: (24)

I think it would have to be related to how rich the car is running. When you let off the gas the a/f ratio gets incredibly rich that your having some unburnt fuel, and it's igniting in the exhaust system because of the heat. The good part is you don't currently have a cat on. If you were backfiring with a cat, you would definately screw up the cat. I've heard it could hurt the muffler/exhaust piping, but I can't confirm it, so take it with a grain of salt. That'd be my 2 cents.

S

DA-MAX

iTrader: (10)

probably the straight pipe and running slightly rich...maybe fuel is puddling in the pipe and igniting, nothing big. my n/a Integra with a striaght pipe would backfire a lot on the 3-2, sometimes blow a flame...got rid of that though, no more straight pipe till I put the turbo on, than time to blow big flames

stephenlc

iTrader: (1)

The SRT-4's backfire all the time. They don't have any mufflers just resonators and they run pretty rich and backfire all the time. The open exhaust and running rich makes you backfire.

iansw

iTrader: (7)

OK - thanks for verifying what I thought.

Looks like it's nothing major to worry aobut until I get on a Dyno.

Stephen Max

iTrader: (59)

Ian,

You might have a damaged injector o-ring, causing fuel to leak past the injector into the manifold. This happened to me once and it gave me the same symptoms you're describing. I pulled an injector and didn't smear oil on the o-rings when I reinstalled it, and right away my engine started popping and backfiring when letting off of the throttle, and it idled very rich. Evidently the o-rings are damaged pretty easily.

iansw

iTrader: (7)

Interesting - when you say the O-Rings, do you mean the Insulators at the bottom of the Injector, or the rings around the injector in the rail?

These Injectors were never removed from the rail, so the only thing I added was the Insulators at the bottom.

I was told that my richness is due to running 40PSI with the Aux pump and the Walbro plugged in. Although when I unplug the Aux pump - I still run 40PSI.

Thanks!
IanS

Stephen Max

iTrader: (59)

I'm talking about the small o-rings at the pintle end of the injectors. They seal the space between the small end of the injector and fuel rail to prevent fuel leakage into the intake. You can check for leakage by removing your intake manifold and lifting the fuel rail up out of the lower intake manifold. Leave all the fuel lines connected, then turn on your ignition to get the fuel pump to build up fuel pressure. Any leakage large enough to cause backfiring should be pretty evident.

The Walbro fuel pump by itself will produce 40 psi at idle, and that can be a source of richness. I'm using an adjustable fpr to reduce back to 34 psi.

iansw

iTrader: (7)

Ok - When I had my CPS problem last week and didn't yet know that the CPS was the problem, I checked for exactly that. No leaks anywhere I could detect.

I'm pretty sure it is the Walbro - so I'm going to get a FPR (good to have one anyway I suppose) and go from there.

Also - didn't your car idle poorly when you had that problem? My car idles 100% perfectly.

IanS

Stephen Max

iTrader: (59)

Yes, it did idle poorly.

IceY2K1

iTrader: (3)

Also, if your BOV is after your MAF, whenever you shift, the BOV opens releasing metered air, which means the ECU dumps excess fuel. Once that excess fuel heats up enough, *BOOM*. Not necessarily 'bad', however on cars with catalytic convertors, I'd be worried the shock/heat could damage it.

iansw

iTrader: (7)

In this case, BOV is not after the MAF, and I have no Cat.

But soon I will have a Cat again - and I'd like to fix this.

Sounds like the FPR is the way to go.

IanS

IceY2K1

iTrader: (3)

Might still happen in that case...not sure what the MAF sees when the air travels backwards through the MAF. Air was already metered and the fuel dumped after you slam the throttle plate closed, so that should still cause a rich condition.

Just thinking out loud here.

iansw

iTrader: (7)

Maybe - but others have that setup with no issues and I had this setup with stock ECU and Injectors for over a year without it.

I'm still pretty confident it's just the Walbro. It doesn't happen enough, and the idle is perfect enoug, that I don't think it's super rich.....just fairly rich.....probably like 9.5:1 right now....Just need to tune it out once I get to a Dyno.

IanS

Jeff92se

iTrader: (82)

I thought you told me your FPR had a base fuel pressure adjustment?

iansw

iTrader: (7)

My FMU does - but only under boost. Doesn't work at idle.

As soon as boost starts it drops the FP to whatever baseline I tell it to.

SSR Engineering

If your running stock cats then it could damage a cat or an o2 sensor, considering the fact that you say the flames are coming from the muffler it's more then likely not going to hurt anything, a little carbon never killed anyone

iansw

iTrader: (7)

I don't have any flames coming from my muffler - I think someone else was saying that.

Anyway - thanks for the verification.

iansw

iTrader: (7)

Interesting - I finally got dry roads in Seattle (rare in the winter) and got to make a good 3rd gear run.

EGT's went up to 1450. So that tells me most likely I'm only running rich down low.

Dynoing tomorrow, so we'll find out for sure.

IanS

luckee2bhere

iTrader: (1)

I get backfire sometimes...but I am NA...thats not bad is it?

iansw

iTrader: (7)

AFR looked pretty good on the dyno (except at the end, where it seems I'm maxing out my MAF)

Tlaking to some people, it seems my exhaust simply is very open, causing backfire - I'm not running rich at all (for a boosted car)

Stephen Max

iTrader: (59)

Very likely. From what I've seen using my wideband O2 sensor, JWT did a good job keeping afr stoichiometric at low throttle settings and at idle, which are the conditions you're at when you shift.

ejj

iTrader: (5)

You should rig up a spark plug so you do! When life gives you lemons...

Prodeje79

Did you get to the bottom of the backfiring problem?

I am very close to obtaining a very similar setup.
So I am concerned with your status.

My JWT ECU got to JWT today.

My setup would be:
V2
2.87" Pulley
370cc Injectors
JWT SC programmed ECU for 370cc injectors , z32 maf, (walboro 255 if possible)
Cattman SS Y-Pipe
Straight Pipe
Greddy catback Exhaust
MEVI
SARD FPR
I would not be running a FMU or aux fuel pump or SAFC.

I realize you have a 3 inch exhaust now, but that made it even more open?