my 86 NA has been running like a champ for a while and now when I give it heavy throttle when it gets past 3400 RPM it goes to 10:1 AFR.

I thought it was a sticking injector so I switched them out with an extra working pair and ohmed out all 3 pairs of them and they all came out within spec and switching them around a few times still didnt fix it.

under light load I can get up past 6krpm and get normal AFRs in gear, the car revs past 3400rpm under heavy load/wot but its 10:1 afr to maybe 11:1, its not like it bucks and wont get past 3800 like a hesitation issue, which my car does not have.

the fuel pump is only 2 years old, the previous owner installed a walbro 255lph fuel pump.

my grounds are clean

I have new spark plugs

I checked the TPS and its in working order

all my sensors are fine according to my code checker

02 sensor is my 5 wire bosch that is part of my AEM UEGO

I have a feeling it might be the injector driver within the ecu (but I dont have a spare to test) or it might be the FPR but the FSM wants me to test fuel pressure with a multi line tester

but is there a way to test it without that fancy tool, like just a regular fuel pressure tester.

help?

 

oh and I forgot to mention when unplugging the secondaries the 3400rpm 10:1 afr still occurs.

 

I dunno if this is normal or I am just noticing it now but when I let off the gas (like 0% throttle) it goes richer before it goes lean, if that helps at all.