BLK87Z

Hey guys, just got done doing a 305 to 355 TBI swap on a 92 Caprice. The 305 ran great no problems no missing no hiccups whatsoever. Ok I get the 355 installed, used a knock sensor for a flat tappet truck (92 C1500) since I'm using a 1977 010 block. I had to have some tuning on a new prom chip to because I went with a small comp XE256 cam and Vortec heads with carb manifold and TBI adapter plate and Long Tube Headers. Added heated O2 as well. Running Vortec truck fuel pump EP381 a/c delco and 18 psi fuel pressure, and 65 lb hr 9C1 injectors. This thing is a beast up to 3800 where it studders and goes on till 4000 rpm or so then it clears up and pulls strong on up to 5500. I think this rules out valvetrain issues?

I have already, installed new distributor, new A/C Delco ignition module, new plugs (R44LTS6's gaped at .035, new plug wires, cap and rotor button even though they were already new, swapped throttle bodies with another known good unit to eliminate injectors or TPS, even put a factory 350 prom in it, it does the same thing, though it runs much better with the tuned prom for the vortec heads. Any ideas? Seems electrical to me, sounds like a studder box on a drag car when it does it.

BLK87Z

No ideas anyone? I even called Ken Casey, and picked his brain on it. we decided to unhook the knock sensor and retest (because I used a 350 knock sensor but kept my 305 esc module), same thing....I'm at a loss on this one.

RFmaster

If you have ruled out mechanical and fuel delivery issues this may be related to what your ECM is doing at that RPM range. Before pointing any fingers lets have the usual listing of ECM type, EPROM mask and what mods were done to EPROM. Since you have a B-body you're probably running some version of $62 mask specific to B-body. Plotting VE and timing tables of your EPROM would be my starting point. Getting some dataloging is also required to rule out unknown RPM related gremlins.

//RF