Michael Ozorowsky

iTrader: (1)

what causes backfiring? My car when warmed up is fine, but when cold if I go half throttle or more it backfires like crazy. Kind of embarrassing when driving down the road. Is that timing? Or what could that be? Sorry to be dumb.

ps: Using Hp tuners.

Bombguy99z28

I think its actually called freefiring, basically when you come off throttle you have unspent fuel burning in your exhaust, kinda like in nascar when you see the flames shoot out when they come off the throttle.

I'm sure someone else can provide a more enlightening explanation, I've never really tried to tune it out but I guess it could be a combination of dfco and other tables that might come into play when you come off throttle.

Michael Ozorowsky

iTrader: (1)

so is that bad? Will it hurt anything? Can I raise/lower timing? Sorry to be dumb, but need to be pointed in right direction.

Bombguy99z28

Assuming that what i described is what you are experiencing, no it won't hurt anything. Timing certainly might have an affect on it, like I've said, I've never really tried to get rid of it.

ringram

IMO retarded timing will affect this. You can try advancing up timing at the points where you are experiencing it. If you have a non stock cam you might find you cant get rid of it and will need to accept that some "popping" is inevitable.

macsperformance

iTrader: (2)

I assume without seeing the event actually take place or when it takes place it is more than likely due to two things. In a warm-up condition the engine uses additional fuel injector pulse width. This additional fuel if not tapered or set properly can cause an over rich mixture. With you saying it is ok when warm shows me that after the cold start enrichment tapers off the A/F mixture for your car is more suitable for the amount of ignition timing you have within those cells.

One: the A/F may be to rich in those portions of the map while in after/cold start enrichment.

Two: more than likely this is due to to little ignition advance. The spark initiation is starting too late after peak cylinder pressure has already occurred ATDC and the air and fuel mixture is still burning while the exhaust valve opens. This popping you here is the actual combustion process continuing out into the exhaust.

On some of the cars I get they have this situation primarily on the overrun portion of the map (heavy throttle application at high rpm and then a sudden closing of the throttle). This is easily remedied, I lean the A/F's out as lean as I can go to support normal combustion and add ignition timing.

It may be helpful to post up the timing map and/or show or tell us log data about when this occurs relating to coolant temps, A/F's and timing values.


Good luck friend
Chris Macellaro

white2001s10

iTrader: (4)

Need more information. Backfiring through exhaust or intake?
and have you changed heads or camshaft?

Michael Ozorowsky

iTrader: (1)

yes aftermarket heads/cam cam is Comp Cams 230/234 591/598 on a 114lsa

It is backfiring through exhaust. God I hope it's not through intake but I don't hear anything through intake

I'll get you a copy of my timing values. If you PM me and provide me with email I'll send you a copy of the actual bin file.

Also could someone pm me so I can email you a scan? I just don't feel my tune is right and would like pro to take a look at it.

white2001s10

iTrader: (4)

Well that changes a lot. Anything valvetrain related can allow backfiring in the exhaust. An exhaust valve not seating correctly due to bad seal, bent valve, broken spring, valve-stem binding, rocker arm binding, or even a bad lifter to name a few. That may take some time to troublshoot, though you can normally check out the springs fairly easily.

As for the tune, if it backfires on decel, that's different from backfiring during acceleration. Decel is mostly in the low-load section of the VE table. DFCO cuts fuel on decel and normally prevents backfire when decelerating. A mechanical cause for decel popping would be an exhaust leak fairly near the head.

Backfiring or popping under acceleration caused by the tune, is usually from not enough spark advance, but to get this symptom your advance would have to be rediculously low.
Mechanical possibilities for popping during acceleration include but aren't limited to the ones I listed above in the first paragraph.

Too lean under load can also cause popping but with it you normally get severe surging and a huge power loss at the same time. Have someone experienced ride with you to see how it feels when this happens.

okls1

My car also backfires probably above 2500 rpm when i push in the clutch get slight backfire pop. If around 4000rpm its worse. Is this hurting anything? I think the car is running a little rich but has been tuned with hptuners before. Should I get the car tuned again? Thanks

white2001s10

iTrader: (4)

That sounds purely like a small exhaust leak. No it shouldn't hurt anything at all unless it's ahead of your front O2's.

okls1

Ok thanks. I think I might have heard a leak but its probably from the clamps on the headers to the h pipe. I guess I will have to get under there an check it out. I have the wider clamps but maybe just cant help little leaking? Thanks for the help.

okls1

Ok thanks. I think I might have heard a leak but its probably from the clamps on the headers to the h pipe. I guess I will have to get under there an check it out. I have the wider clamps but maybe just cant help little leaking? Thanks for the help.