Loss of power and backfiring

[AeroNautical]

I’ve done some performance mods to my 98 high output 4.0 running a 93 obd1 wiring harness. The throttle body is bored, it has the horseshoe intake, volvo 4 port injectors, banks header with a zj cross pipe, newish catalytic converter, and high flow muffler. For mostly stock parts shes a torquey girl, but I’ve got some weird characteristics. She seems to lose power briefly when hitting the throttle hard at about 2-3k rpm. And she backfires on occasion when either engine braking or shifting (ax15), sometimes a “rumbling” backfire. These computers are adaptable, but maybe a tune is in order? Fuel rail reads correct pressure and no check engine. Maybe it just can’t supply enough fuel to the rail, causing a lean condition. Thing is, I would think the check engine light would show up due to a bad O2 reading. Thoughts? 

[thecodemonk]

Computers adjust to a certain level, but you might be running beyond how much adjustment it has. I would think you'd need a tune after all of that. Do you have any way to check your own air fuel ratio? That would probably tell you what's up. (Have you had those injectors bench tested?)

The fact that it mostly happens when you try and suddenly accelerate makes me think it might be a bit lean and the sudden intake of air leans it out a lot farther before it catches up.

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[AZJeff]

Backfiring is usually a sign of a lean mixture.

[75sv1]

What size if the TB bored to? Has the O2 been changed? What brand? They do make adjustable MAP sensors. Or I should say an item to make the MAP sensor adjustable. The Stroker guys use them. 

[AeroNautical]

The injectors were recently taken off by me, and cleaned with pressurized sea foam and a 9 volt battery. They all work perfectly.

 

I believe the TB bore size is 62mm. The O2 is new, replaced when I did the obd1 conversion, don’t remember the brand, about $70. That is a good idea on the adjustable map sensor, if that’s enough for a stroker guy to run an engine right, it ought to be enough for some stock mods. I’m also going to inquire about a tune, but chances are that it will be more money than it’s worth. Might even pull the valve cover off to make absolute sure I don’t have a sticking valve or cracked rocker. Thanks guys. 

[AeroNautical]

This is an older thread, but I did end up fixing the issue. 24 pound mustang single port injectors did the trick. No backfiring, bogging or torque loss at all with these. I figured the volvo 4 ports would do the trick, but I was wrong. Good insight to anyone trying to do the same mods as me.