1997 7.4l - At my wits end with an irregular miss.

[Alex_M]

All right yall, I need some help. 97 Suburban 7.4l 4l80e 4wd 185k miles. Irregular miss starts at 3k rpm and gets worse with engine speed. Load is not necessary - it will do it in neutral. No codes. Previous owner (buddy of mine) did injectors, fuel pressure regulator, plugs, wires, throttle position sensor, fuel pump. I changed coil, ignition module, distributor (found it had been replaced by the owner previous to my buddy in 2019 - had play in the shaft), ecm (I damaged the original when I opened it to inspect), MAF, O2 sensors, upper and lower intake manifold gaskets, crank position sensor, fuel pump (was a cheap universal, I installed a delphi), and replaced the catalytic converters with a universal converter. There was a lean code for a time - I found that the oring in the fp regulator had been pinched and the screen broken. I replaced the oring and screen, those codes have not come back. I think I'm remembering all the parts that have been replaced. I'm not normally the parts cannon type, but I'm at my whits end on this one.

It is making about 60# of fuel pressure. The injectors installed are the yellow ford style injectors. They do not appear to leak and the spray pattern looks ok by my eye (checked installed with the upper intake off, cranking with the coil unplugged).

I will note - sometimes you can get a clean run out of it up to 60mph without missing. It will do it after that first pull 100% of the time. The miss seems to get worse the more it happens, as though something heats up and then starts to progressively get worse.

I would love any kind of input on this. I am about to throw in the towel and drop a 5.3 in it that I have, or carb swap it, but really I got the thing to haul a camper with my family. It would be nice to get the 454 sorted and retain the factory efi. Thanks all!