Boost Issues

[OBEEWON]

Whenever I try to boost past 11 or 12 psi I get some pop pop pops and some black smoke out my exhaust. It happens at WOT and above 3 or 4k rpm. Ive recently changed my spark plugs with the same misfiring. These are my modifications pertaining to engine and boost:

S13 Blacktop
3 in. Downpipe
Gutted cat
I think the exhaust is only 2.5 in (twas on the car when I bought it)
Voodoo MBC
Z32 fuel filter
Walboro 255lph
NGK Iridium plugs
Tial 55 BOV
XS front mount
Injen custom Ram air intake

Thats all I can think of. It misfires the same even on the highest available octane. Anyone have any ideas?

[OBEEWON]

no one has any ideas?

[S14DB]

1)Plug gap
2)timing
3)AFR

[cotbu]

I had a similar issue, WOT,minus black smoke. I was topping out the MAFS at .88 bar with T25. At .85bar it was fine, try a z32 mafs (or equivalent.) worked for me.

[Angel]

1)Plug gap
2)timing
3)AFR

In addition to what s14db suggested I would look for a possible boost leak.

[98ka24det]

Whenever I try to boost past 11 or 12 psi I get some pop pop pops and some black smoke out my exhaust. It happens at WOT and above 3 or 4k rpm.

Can u boost any lower than 11 psi..?? If u can, try it and see if the popping is still there..

The last time i had that popping sound was when my maf was flooded with oil from popping the # 4 ring land..

[jdm_s14_zenki]

Sr's tend to run very rich after 3-4k rpm and lean at and before 3k rpm. what do you have tuning your AFR, at least an AFC?? you can easily foul your plugs out, especially the iridiums when running too rich.

[OBEEWON]

right now I have the controller turned all the way down since I cant WOT with it turned up. The funny thing is that when I first got my MBC I could boost up to 20psi no prob(did not daily drive on 20). But then my hotpipe poped off my turbo one day at 20psi. Since then hi boost yeilds misfire. Which makes me not want to suspect my maf. Unless I somehow messed it up doing that(but if so wouldnt it misfire regardless of boost level?)

Checked and rechecked for boost leaks. Unless something is opening at higher PSI I dont see any leaks.

Im really suspecting my timing cuz I get backfiring under normal driving. Say if im coming to a stop while downshifting Ill get a backfire and a small flame out my behind.

Car is running rich, gas mileage is low.

[tchenku]

you have a leak somewhere. def. start looking at your pipings.

[OBEEWON]

ok im going to check again, but what about the backfiring? Its been doing that pretty much since i finished the swap?

[98ka24det]

ok im going to check again, but what about the backfiring? Its been doing that pretty much since i finished the swap?

The most common cause's of backfire is timming being off, and very rich mixture during shifts (like running an open bov on a maf equipped motor and the ecu is not tunned for open bov)

[Cashizslick]

The most common cause's of backfire is timming being off, and very rich mixture during shifts (like running an open bov on a maf equipped motor and the ecu is not tunned for open bov)


I was just going to suggest the open BOV + MAF scenario. I run just that and ocasionally get backfires @ low RPM's.




But backfires are JDM so :bite:

[R33GTS-T]

you should've PMed me on the boards....give me a call if you still can't figure out the problem

- Daniel

[OBEEWON]

Whats up Daniel, I didnt know you were on here too. Im going to call you soon. My bank card was stolen so my trip to your alignment guy is gonna have to wait till I get my replacement.

[Cashizslick]

you should've PMed me on the boards....give me a call if you still can't figure out the problem

- Daniel


Yeah but at the same time, if you keep tech info and suggestions inside of a private group (aka pm's) then people who search for this information wont be able to find it.

[R33GTS-T]

Whats up Daniel, I didnt know you were on here too. Im going to call you soon. My bank card was stolen so my trip to your alignment guy is gonna have to wait till I get my replacement.
i was starting to wonder what happened to you lol...damn your bank card got stolen?? hit me up when you get your new one for sure

Yeah but at the same time, if you keep tech info and suggestions inside of a private group (aka pm's) then people who search for this information wont be able to find it.
ah yes good point

[OBEEWON]

Ok I did my timing today. It seems a little bit better but i still get some misfire every now and then. I set the timing to TDC, since SR's run rich above 3k is this the ideal place to have it. I read somewhere else that I should set timing to 15bTDC, that is the second tick from the right instead of the left? My idle is a little rough to the point where my engine moves a little, and sometime the car bogs on take off, It feels like my maxima with VTC's(but I have no VTC S13blacktop) no power till 2 or 3k, sometimes it hauls bootang other times it just hauls.


Daniel I should have my bank card sometime next week. Life has been crazy with school and work, and women...so I havnt been out much. LOL

[OBEEWON]

Anyone? What timing setting is better for higher boost?

[Cashizslick]

Anyone? What timing setting is better for higher boost?


I have a similar setup to your's and i run completely stock timing with absolutely no problems. Just check the FSM and do what it says as far as timing goes.

[OBEEWON]

Did that but it still feels a little choppy. How much boost do you run and does the low range rpm feel a little boggy at all?

[R33GTS-T]

Did that but it still feels a little choppy. How much boost do you run and does the low range rpm feel a little boggy at all?
you are running an sr ;)

if your timing is set to original spec and your still having some issues you may want to talk to Matt....i'm going to see him tomorrow too

[Nizzan4u2nv]

Pressure test for leaks. Basically filling the piping with air till it reaches your set boost level. If it holds that amount of pressure, you know for sure if you have leaks. Just checking couplers, clamps and vac lines doesnt cut it if you wanna be sure.

use this for reference, its a very good homemade tool.
http://www.sr20forum.com/showthread.php?t=89947

[Cashizslick]

Did that but it still feels a little choppy. How much boost do you run and does the low range rpm feel a little boggy at all?


7-8psi daily, 1bar at the track/while racing.

Car feels fine normal. For comparison, its more throttle responsive than my old B16 Civic.


Drive any 4 cyl with a redline of 7k and tell me it doesnt feel sluggish/unresponsive under 2 - 3k rpm's.

[OBEEWON]

yeah but im talking more than usual. Oh well I guess ill figure it out sooner or later, at least it stopped misfiring for the most part. Thanks for the help though its much appreciated. This forum is much better than the other 240/silvia ones.

http://memimage.cardomain.net/member_images/1/web/2125000-2125999/2125653_102_full.jpg


bumper got ripped off coming out my driveway. Scares little children LOL
http://memimage.cardomain.net/member_images/1/web/2125000-2125999/2125653_108_full.jpg

[Cashizslick]

Just an opinion, this COULD all just be in your head . . . i mean, maybe you are just at the point where you are used to the way your car performs and you expect more out of it than is possible in its current config.

Your expectations of what it should do may be higher than reality if you have had the car for a while.


The only other suggestions I can come up with asside from checking for boost leaks is to do the following:

1.) If you run an EBC that can increase/decrease wastegate duty cycle (aka speed up boost response) then check to make sure the unit has not re-set itself or anything stupid. This could have been caused by a disconnected batt., or some other misc occurrence.

2.) How is the tension on your throttle cable? Make sure its nice and tight, it could have stretched/loosed over the last few weeks of driving.


Good luck!

[R33GTS-T]

yeah but im talking more than usual. Oh well I guess ill figure it out sooner or later, at least it stopped misfiring for the most part. Thanks for the help though its much appreciated. This forum is much better than the other 240/silvia ones.

http://memimage.cardomain.net/member_images/1/web/2125000-2125999/2125653_102_full.jpg


bumper got ripped off coming out my driveway. Scares little children LOL
http://memimage.cardomain.net/member_images/1/web/2125000-2125999/2125653_108_full.jpg
hahahaha....your driveway stuck to ya raw :boink:

[jdm_s14_zenki]

its not your timing, boost leak, plugs, coils, or anything like that. Its your MAFS! switch it with one that works and it will probably fix your problem.

Same exact thing happens with mine. I have the N62 Mafs and its not working correctly but it working enough to daily drive. When im taking off, it boggs until i throttle it more. And at about 4800 rpm, it starts missing. The Dyno tuner and I checked everything timing, spark, fuel related and we've singled it out to the MAFS.

[Josh K.]

It might have something to do with the fact you boosted to 20psi on stock FM? thats just crazy.

[Nizzan4u2nv]

It might have something to do with the fact you boosted to 20psi on stock FM? thats just crazy.

Wow, I just realized that too. What are you doing running 20lbs on a t25? Especially stock maf and 370s? Its probably missing because your maf cant read any higher. 370s at stock fuel pressure isnt enough for 15-16psi let alone all youre doing is blowing hot air with that t25 past 13lbs. Get a z32 maf, bigger injectors(555s at least, deatschwerks are pretty cheap), and some kind of fuel controller(SAFC if you know what youre doing, enthalpy tune if you wanna be safe, standalone if you got the flow and know what youre doing). With the upgraded fuel setup, youll have a lot more room to play with and wont have to worry about it when you get tired of little turbos.:D :blah:

[240sxworkinprogress]

I not sure this is it but one of my friends said that it could be rich poping. When you turn up you boost the computer is over corrects and dump to much fuel in the engine and killing the spark. He said all you have to do it regap that spark plugs. He said that sould fix it. You can always try it and see if it fixes it take you about 10 min to do. It allways worth a shot.

[OBEEWON]

Thanks guys. Im pretty sure its a combination of my MAF and rich poping. I only ran 20 psi two times. Kept it at 15 and below. With the controller turned all the way down it runs like 12. Im saving for a turbo uprgrade but for now Im going to do Z32 and injectors. I need another FPR too.