backfiring/bogging/shutter - only at 3k rpm at heavy throttle

[bryan767]

recently ran into a few problems with my sc300 1jzgte:

the main concern is that it bogs at 3k rpm only.. like it hangs there for a few moments then itll accelerate past it. at which time ill hear a pop,pop,POW.. (itll also start to shutter sometimes, and try to learch forward) and then ill accelerate throughout the rest of the gear. HOWEVER if i accelerate slowly, as if a cop were behind you, i dont have any bogging throughout the power band.. say anything past 25% throttle and itll bog and miss.

i recently replaced my clips on the coil packs which made alot of the missing sounds go away (i had a low, very fast, thumping noise at the same time as the louder pow pow BANG).. but this one purists!

mods:
stock 1jzgte
fmic
greddy type s
12v fuel pump mod
3" cat back
relocated battery

im thinking its either the coilpacks, fuel filter, fuel pump, tps, map or fpr.

what do you guys think it is? i thought about putting another fuel pump in but a stock 1jz shouldnt need that right?

 

[TripleC]

Check your Plugs and make sure they are gaped around .028 (My recomendation) Let us know what happens after that.
Do you have a boost gauge?
If so does it spike up or Down.
Also do you have a AFC?
If you do what is it showing for fuel.
Fuel Pressure could be anothe thing, Fuel Filter/fuel pump could be plocked.

 

[bryan767]

plugs - ngk iridium .27 - brand new
boost gauge - spikes to 14psi, but i have a boost cut eliminator so its not boost cut
and i have a wideband but i havnt welded the bung on yet.


i think its the fuel, either the fpr has gone bad or the fuel pump isnt getting enough power in the lower rpm range (i have the 12v mod)

 

[mkiiichip]

Do you know what your boost cut eliminator does? I would take it out, and turn the boost below 14, or go standalone.

 

[bryan767]

yeah i know what it does, thats why i have it lol.

im thinking its the 12v fuel mod that everyone does, supposedly some people have the same issue.. its like how the supra needs a direct power cable because the stock wiring is shit.

 

[mkiiichip]

nm, good luck

 

[enjoi.this]

yeah i know what it does, thats why i have it lol.

im thinking its the 12v fuel mod that everyone does, supposedly some people have the same issue.. its like how the supra needs a direct power cable because the stock wiring is shit.

Im having the same "popping" issues as you, but with my 7M-GTE right now. I changed out the plugs and turned up the fuel pressure and it seems to have helped a lot from where it was but its still there.. Whats the issues with the 12v pump mod through stock wiring? I have noticed that the pump does run harder sometimes after Ive been driving for a while.

 

[bryan767]

yeah, i believe its just the stock pump not getting enough power. i read somewhere that mk4 guys run a thick power wire straight from the battery to fuel ecu or something.. idk ill have to research it more, but essentially the wires deteriorate after awhile and possibly lose the conductivity. idk just a guess.

 

[enjoi.this]

A way to run power to your FP is just run new wiring with a relay so once the key is tuned on the fuel pump is ON! This is what Im going to do since I will be demanding performance and dont want a lean out related failure.

 

[CanadianLurch]

I recently ran into similar issues with my 1j. Even after heat shrinking my coil packs thebhairline cracks have now got the best of a few of em. I swapped my back up set in and everything is working a ok. I had a slight hesitation / misfire at 2k rpm until the car had warmed up. Try to find some 1.25" heat shrink and check for hairline cracks. Also irridium plugs to my knowledge arnt the best for these engines, try some copper ngk bkr7e which also come pre gaped for our application .028 I believe. Hope his helps

 

[bryan767]

so heat shrink the blue bottoms of the coil packs? because i have about a foot left thats 1.25" from a project awhile ago