Slight backfires (?)

[CJFusco]

A few days ago, I did a tune up on my car, replacing spark plugs, the wires, air filter, oil change... at (roughly) the same time I replaced the stock FPR with a 3.0 unit so I can safely run the LBE (=slightly more boost).

Since then, I've noticed that if I let off the gas abruptly in 1st or 2nd, I'll get a little bit of a backfire. In 2nd it's more of a muffled "burble", but in 1st its more of a "pop".

I know that high-performance cars sometimes have "burbling" from exhaust off-throttle. Is this what I am experiencing? Or is it something I need to address (such as running lean)?

[Blondie]

Could just be excess fuel in the exhaust being burned. How much pressure is goin through those injectors?

[CJFusco]

Injectors are stock.

[fast924S]

SOunds like your running rich, whats your fuel pressure at??? How much boost are you now running??? I noticed you have a chip and a 3-bar fpr, Where the chips made to run with the FPR, The new chip set may have new fuel tables that run the injector durration longer, SO the longer durration plus the added fuel pressure from your 3.0bar FPR might be making it run a little rich.
FUSCO, Your starting to put alot of go fast stuff on your 951, I think its time to invest into a WIDEBAND A/F sensor so you can tell whats going on.

[CJFusco]

Yeah, I ordered the 951Max chips before I got the FPR. I wonder if Russell can rework the chips to include the FPR... in any case, running rich is far better than running lean.

I know that AF mixtures on modern cars are dynamic and change based on RPM, gear, air condition, etc., but if I am running a little rich at low RPM in low gears, this would mean I am generally not running lean at high RPM, at boost, in higher gears? To me it sounds like a (comparatively) good thing, even though I know that in a perfect world I would want to be running neither rich nor lean at all RPMs.

[pozican]

CJFusco - Where are you shifting it?

If you are shifting pretty high, they will pop.

Try shifting earlier and see what happens.


My AFR was perfect, and mine does this also.

[CJFusco]

It sounds like a pretty common problem. It only really happens when the car is warmed up, in low gears, and when I let off the gas abruptly (esp. if the turbo has begun to spool). I probably won't be driving the car too hard today (rain), but I will see if I can narrow down the circumstances a little.

[pozican]

Originally posted by CJFusco
It sounds like a pretty common problem. It only really happens when the car is warmed up, in low gears, and when I let off the gas abruptly (esp. if the turbo has begun to spool). I probably won't be driving the car too hard today (rain), but I will see if I can narrow down the circumstances a little.

Sounds good.

Try just going 25% throttle up to the high range, and let off to shift, see if it backfires.

Then try WOT (when it's dry )

Then try WOT to 4k

But like I said, mine does it too -- GREAT AFR, I'll get the stats when I get home today (need to take some more pics of my car for sale too)

[rberry951]

This is normal, some cars do it with my chips and some do not. I'm not quite sure what the difference is in the cars, by guess is whether they have any vacuum leaks or not. But the first thing people notice is the burbling and/or popping when they lift or shift. This has more to do with timing than fuel. The timing curve in my chips is kind of funky, there's a couple of steep slopes in specific areas of the part throttle and WOT maps that will help low end torque and the very bottom end of the spool-up area. When you lift or shift you're going backward through the part throttle map and when you go through this timing area is when it happens. You'll also notice when you lift abruptly the car decellerates hard, throwing you forward instead of kind of 'coasting' down, this is the proper behavior. People have gotten so used to the sluggishness of the stock and other aftermarket chips they think something's wrong when the experience real performance.

Regards,
Russell

[pozican]

YAY for real performance!

[CJFusco]

Originally posted by rberry951
People have gotten so used to the sluggishness of the stock and other aftermarket chips they think something's wrong when the experience real performance.

Regards,
Russell

Hah, yeah this is true. My car is noticeably quicker in all gears and at all RPM with very minor mods (Russell's chips, 3.0 FPR, LBE running "near" stock boost setting). As a matter of fact - now, I don't want to sound like I'm advocating any kind of speeding or racing on the street... but... well, suffice to say that when I drive this car I definitely feel like it's the fastest thing on the road at that given time.

Drive safe, ya'll.