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View Full Version : Backfire on decelleration (And good tech ?'s)


Ess14
08-05-2005, 04:13 PM
S14
S13 blacktop

My blacktop backfires as a decellerate, most commonly inbetween downshifting. It may happen when in any gear but is most common when slowing down to a stop going from 3rd -> 2nd I get a backfire. Sometimes it will not, sometimes it will be subtle, but ussually it backfires. It is also more common after I'd been spooling and afterwards slow down. Now I found that my BOV diaphragm is busted, I just ordered a type RS and am putting it on ASAP. As I accellerate there is no (that I can tell) backfiring.
I am going to check plugs and timing aswell, but any advice would be appreciated, or people with the same situation's experience.

While I'm at it, there are tons of these threads, but I have the infamous decellerate -> stall problem. This may also be my BOV, but I wouldn't say so. Anyways, if I'm good and warmed up, I have to slow allllll the way down in 2nd gear before I can finally put it in neutral - we'll say 10 or less mph. otherwise, I'm stalled. Often when I'm slowing down and finally inch my way to neutral I notice the revs barely miss hitting dead, and then my idle finally kicks back in and they go up.

I'm going to adjust my new SAFC-II settings for DEC-air and am wondering what are some recommended settings. And if you have had this problem -- which is obviously quite common on tubrocharged vehicles -- what fixed it?

And last - shifter issue. I had a new tranny put in my car by a great shop and my shifter is loose. The mechanic had told me that the bushing and C-ring that hold the shifter in place may need to be replaced from being worn down. I don't know about this - It's not expensive I can get a bushing and C ring for a dozen bucks from a dealer but prior to being put in my shifter was perfectly stiff. Now it is quite loose - I can shake it a good deal and hitting gears feels nothing like it used to, however with some getting used to it it's not bad, but I'd rather have the feel I had before. No B&M or short shifter here, good old stock, but could use some help or opinions.

420sx
08-05-2005, 04:39 PM
well i used to have stall problems but i adjusted my atmosph. bov - apexi to stiffer setting and it runs GREAT takes like 5 min to do while the car is running.

now backfire, i have similar issue. i found that its just my cat since the gaskets dont fit that great (need to get a straight pipe). s14 "cat" is just a guted resonator, it allows for backpressure to build up a lil thats why it pops for me on decel around 2k rpm. also i need to regap my plugs, it could be the case. other than that its really not that bad.

not to stall just downshift or when slowing down leave it in gear and dont release untill almost at idle (and still rollin a lil). hope this makes sence

Ess14
08-05-2005, 04:44 PM
what cat do you have? And I was trying to make it clear that i do put it in second and coast untill I'm going really slow and then finally put it in neutral - But it is very agravating especially in stop and go traffic and it's so sensitive that often even if I'm going really slow it just may have been a hundred rpms too high before I hit neutral and bam I'm dead. Just makes me look like a dumbass.

Flybert
08-05-2005, 07:36 PM
Seeing as you are running an open BOV, backfires are pretty normal, especially if you aren't running a cat.

Since you have an SAFC, set that thing properly to cope with the stalling issue. Read Hugh's post on the proper way to do it. http://forums.freshalloy.com/ubbthreads/showflat.php?Cat=&Board=UBB9&Number=67772988&Forum=All_Forums&Words=dec%20air%20settings%20cold&Match=And&Searchpage=0&Limit=25&Old=allposts&Main=67772932&Search=true#Post67772988

S14DB
08-05-2005, 07:54 PM
Is it the ECU De-fuel or an actual backfire. Like pops or a loud boom.

junkilo
08-05-2005, 10:10 PM
S14
S13 blacktop

My blacktop backfires as a decellerate, most commonly inbetween downshifting. It may happen when in any gear but is most common when slowing down to a stop going from 3rd -> 2nd I get a backfire. Sometimes it will not, sometimes it will be subtle, but ussually it backfires. It is also more common after I'd been spooling and afterwards slow down. Now I found that my BOV diaphragm is busted, I just ordered a type RS and am putting it on ASAP. As I accellerate there is no (that I can tell) backfiring.
I am going to check plugs and timing aswell, but any advice would be appreciated, or people with the same situation's experience.

While I'm at it, there are tons of these threads, but I have the infamous decellerate -> stall problem. This may also be my BOV, but I wouldn't say so. Anyways, if I'm good and warmed up, I have to slow allllll the way down in 2nd gear before I can finally put it in neutral

too hard to troubleshoot with the broken bov in the equation. with a broken bov that is leaking lots of air you will be pushing less air into cylinder than the engine is expecting, and underboost that will be larger than at less vacuum pressure. fix the bov and check back. also with the excess backfires it 95% confirms a overly rich mixture pointing at a post maf boost leak.

Ess14
08-05-2005, 10:14 PM
loud is subjective but I would say it can be a loud boom -- it varies. When I decellerate from 5th - 4th or 4th to 3rd -- if it does backfire then it would not be a loud boom, it seems small. It's only loud when I'm slowing from 3rd to 2nd. Not every time, but sometimes it is a loud boom. I am familiar with my lawn mower backfiring and that is loud as crap -- Sounds just like that but definitely more subtle and not ear shattering.

Ess14
08-05-2005, 10:20 PM
too hard to troubleshoot with the broken bov in the equation. with a broken bov that is leaking lots of air you will be pushing less air into cylinder than the engine is expecting, and underboost that will be larger than at less vacuum pressure. fix the bov and check back. also with the excess backfires it 95% confirms a overly rich mixture pointing at a post maf boost leak.

Thanks, my BOV should be here tomorrow, I'll give updates as soon as I get it on, in the mean time, what else should I check if this doesn't fix it. If it makes any difference, I have a brand new maf.

junkilo
08-07-2005, 12:51 AM
Thanks, my BOV should be here tomorrow, I'll give updates as soon as I get it on, in the mean time, what else should I check if this doesn't fix it. If it makes any difference, I have a brand new maf.

I'd check things in this order after the bov: boost leaks, test o2 sensor, test injectors. When the similar issue happened on my ka it was a leaky injector.