WTF???? backfiring into boost

[WhiteNgold]

ok so i feel like a complete failure and am now at the point to ask you guys. ive done my tuck and finished all the motor work. fires up and idles nice first time, revs real smooth, sounds amazing. back it out of the shop, drive it real easy for a few minutes (stayed out of boost). decided to watch my wideband and punch it from about 5mph. it squats and hooks, then BAM!!! sheared bolts off the driveshaft near the carrier bearing and popped off a coupler. push it back, fix it, try again. now as soon as i hit boost it backfires and breaks up way to bad. i cant even stay on it long enough to watch the wideband. it shoots flames like 3 feet and lights up the night. my nismo fpr is set at 37 at idle and fuel pressure stays strong the whole time. idle is awesome and it revs great w no load. but if i rev it rapidly it back fires and spits black smoke out (really rich like). at idle wideband says 13.7.

new bkr7e plugs at .28
tried z32 maf(neo tune) and sr maf
fuel pressures are good
all coils firing
3 different ignitors

im thinking timing isnt being pulled when boost comes in. just wanted to see if any of u guys have had somthing similar happen. im sure its something stupid and its the only thing keeping me from dropping it off to the paint shop. i wont be able to fuck with it for a few days but i cant stop thinkin bout what it could be.

[Epstein]

Boost leak. Recheck your couplers.

[WhiteNgold]

got -20 vac..... all couplers good. to be more specific, from a dig, wot, just before boost it bogs and as soon as it reaches 2 or 3 psi it hits a wall and starts throwing 3-4 foot fireballs

[4wheeldriftS13]

Under load this was the same problem I had.
I had a bad coilpack and driving it would be fine, when I got into boost it would backfire

[greenman100]

got -20 vac..... all couplers good. to be more specific, from a dig, wot, just before boost it bogs and as soon as it reaches 2 or 3 psi it hits a wall and starts throwing 3-4 foot fireballs

Vacuum has nothing to do with boost leaks. Vacuum is measured between the throttle body and the engine. What happens on the other side of the throttle body doesn't matter.

[jizmogloben]

along with everything everyone else has said check your voltage running.......
when my alt took a shit it made enough power to keep the lights, radio, boost controler, turbo timer and all that stuff on but didnt have enough juice to keep the car going under boost and it would cut out and back fire like your talking about

[WhiteNgold]

alt at 13.5-14.2v. i did use a different set of coils and harness. ill switch them back and see what the deal is. thnx for help guys

[Epstein]

Vacuum has nothing to do with boost leaks. Vacuum is measured between the throttle body and the engine. What happens on the other side of the throttle body doesn't matter.

Exactly! The only place in the system that has vacuum is the intake manifold itself. The rest of the system is basically at ambient pressure. You could have a decent sized hole in your IC pipe and it wouldn't hardly affect your AFR's and would not touch idle vac. With the pressure in the pipe and the outside pressure being the same, no air would really flow through the hole. Pressureize that pipe with 2-3psi and all the air come shooting out -> dead rich -> fireballs.

Bad coilpack could do it too, but you're usually not going to get 3-4ft fireballs like that. The lead-up scenario also tells me that it's probably boost leak.

[mewantkouki]

A wet 300zx maf gave me 3-4 ft fireballs at qsl one time... it wasn't fun.

[WhiteNgold]

fixed..... open in wire knock sensor harness grounding out the signal. rewired and it runs fucking mean. gonna need a new one soon though. now onto the dieseling after i shut it down lol

[Epstein]

now onto the dieseling after i shut it down lol

injector o-ring leaks.

[WhiteNgold]

lol.... thnx. where to get some new o-rings?

[WhiteNgold]

actually, now i have a new problem. it takes a bit to start and i have to give it gas and keep tapping the throttle to keep it alive for a min before it idles right. still diesels after shut down even tho i replaced the o rings

[silviaivlis]

So it doesnt want to start and doesnt want to stop? Typical moody SR.

Check CTS (coolant temp sensor) harness/plug. Tweek pins as nessesary. Do the same with the MAF. At least make sure you got good terminal connections. Ive fix many many KA/SRs running issues with just a tweeking of a few terminal pins and rechecking connections. Add a second (or third, or forth, etc.) ground to MAF. Always helps.

Sounds like two seperate problems to me. the hard start sounds like CTS(look for dark smoke from exhaust under boost and (warm) startup, or check your wideband for that matter. Check both hot and cold starts (i dont know if the issue is both/either conditions), excessive fuel consumption, or wet/gas-smelling plugs.

As for the Dieseling, could be running so rich as to no burn all the fuel out of it. Check your oil and see if its kinda green and gassy smelling and not very viscous.


I dont proclaim to be a SR god or anything, these are just the things i would check first.

Good Luck.

-Joe