Hey everyone,
So I have been researching and looking through alot of different forums out there to see what people are saying about this issue I am having.
I wanted to ask my fellow Club Lexus members and see what they thought.
so here it goes:
1995 Lexus SC300 original 5spd
swapped 1JZ GTE and swapped R154
stock twin turbo and stock tranny
Running a AEM 320lph for fuel pump, stock injector etc all stock (except for FMI and custom downpipe)
Also had a buddy of mine who is wiring expert to extend my wiring harness 3ft (He checked every single wire before finishing the harness).

SO.......I am having massive backfiring when i start to get on the gas and spool up the turbos
Now the top 3 solutions I have read is ECU, coil packs and tps
I have changed the ECU, checked my coil packs and readjusted my tps......stick backfiring...
Oh and I just ordered a stock 1jz fuel pump to downgrade from the 320lph AEM ( I went overboard with the fuel pump cuz I got a good price on it).

NEED HELP! OR ANY OPINIONS/THOUGHTS/FEEDBACK IS GREATLY APPRECIATED!

 

first, 3 ft extension is way too long.

second, does it break up (what you're calling back firing) in neutral if you free rev it?

Check your timing. Make sure that when the crank mark is lined up at 0, that the cam pulley marks are facing straight up towards their respective marks on the timing cover backing plate.

You didn't go overboard on the fuel pump, you wasted your money buying another one. AEM pump is perfect.

 

Has the backfiring always been present with the AEM?

 

Yea realized that a 2 1/2 ft extension would of been just fine, but thats least of my worries..
Also even in neutral it still backfires/pops

i bought the oem fuel pump one for 20$ from a buddy of mine ...(he had two)
....gna check the timing today and crank mark..
had the swap done at the a proffessional shop I work at...so I would hope they would have gotten that right the first time around.

 

Never drove the car with the OEM pump cuz I got the engine and AEM one at the same time.
havent really heard any problems with the pump either on other forums

 

OK! SO....I just realized I am running NGK Iridium plugs! Im gna change them to regular non iridium plugs and see what happens next....

 

it wouldn't be iridium plugs ve regular plugs. sounds like an ecu or map sensor issue.

 

Sounds like a map sensor to me... stock map?????

 

Timing, ecu or bad map sensor.

What's the gap on your plugs?

 

For some reason I keep reading on different forums that the 1JZ does not have good luck with Iridium plugs and some people who have had similar problems have solved it by using stock oem plugs for some reason...

 

-Yea stock map
-checked the timing today and spot on, already changed the ECU and stock map sensor
- Gap on plugs in car currently (iridium) is 28, gna gap them to 26ish with the new non iridium plugs

 

I also checked the coil packs today and removed the boots to inspect them...they looked good and not cracked. I even cleaned them before putting them back in.
AND I bought a new TPS installed that too

 

If your running the NGK BKR6EIX, thats not the issue.

Now with the wiring, did your friend use shielded wire when he extended the cam/crank sensor wires? Just asking to cover all the bases.

Have you tried a different ignitor?

Do you have a wideband installed? What is it reading?

 

Does it do it at the same rpm regardless of driving or in neutral free revving? Do you have a boost gauge? Does it build boost when free revving in neutral?

Are there any check engine lights?

You're gap is way too tight, .032 should be fine. Especially if there aren't any cracks on the coil packs under the boots.

Are you sure about timing? Because its either that or fuel delivery.

Try bypassing the fuel pump ecu, try another map sensor.

 

You need to verify the fuel pressure and volume is correct. what your experiencing could be a lean back fire. and its important to verify volume. just cause the pressure is there doesn't mean that when you go to mash the throttle, enough fuel is flowing thru the rail and thru the injectors. just did a single turbo build on my 02 gs430 and while self tuning myself before going to tuners, I was not enriching the fuel enough on my fic 8 so when I'd punch it it'd pop and backfire that sounded hollow. that's a lean misfire. maybe check your rising rate fuel pressure regulator if you have one. also, whoever installed the fuel pump might not have installed it correctly and it could be leaking onto itself if the oring wasn't installed correctly between the top of the pump motor and the fuel pump housing.