Odd backfiring between 2500 and 2900 rpm - 4ZE1 2.6

[96RodeoTF]

Hi everyone,

I've been lurking in the shadows reading posts and completing repairs on my 1995 TF 4 door 2.6L (Australian model) but I'm bamboozled by this odd backfiring issue it has.

Issue - While under slight load/soft acceleration it backfires when between 2500 - 2900 RPM. At no other revs does it backfire.

Setup - 2.6 4ZE1, 5 speed, Redback header, 2.25" exhaust, no cat or 02 sensor. I think this truck was produced just before the cat/02 was mandatory?? The vehicle has 310,000km on it thus far.

Maintenance/troubleshooting thus far - Timing belt/tensioner, valve lashing, MAF clean, plugs, wires, cap, rotor, ignition coil, air filter, done at 300,000. All vacuum lines, rear main seal, fuel filter done at 280,000km.

History - The truck pulls hard and responds to throttle well. I drive 70ish km each day to and from work over a small mountain pass where I spend most of the time in 3rd gear between 3-4000 RPM. I average just above or just below 12L/100km. I have only owned the truck for a few years and it has always had this odd backfire issue.

Any thoughts or advice is greatly appreciated.

Many thanks,

Phill

[geeves]

Double check the no 02 sensor. The efi should be using this to set mixture even without a cat. Engines of that vintage often had air pumped into the exhaust to control emissions. (I think the only effect was more gas out the back diluting the nasties) Normally I would suspect spark but that should be worse at higher revs or load