This is a standalone from a 2003 Yukon 6.0. It had a 4l60, but I installed and segment swapped to a 2wd 4l80. The engine internals are all stock. Exhaust manifolds are Camaro that I cut off the flange and welded 3? exhaust to, air intake tube is 4? to stock (new) Delco MAF, two 90?s with 14? total straight between them and 10? straight before MAF. I don?t have a wide band connected currently, working on it, but have a non-log able fuel pressure gauge that I can view while driving. At idle, fuel pressure is at 52* and under acceleration pressure rises to around 58-60*. The stock truck intake/fuel rails are used and there is a vacuum line connected to the stock regulator; there is a return line on this fuel rail. No cats. Car idles great and as long as you don?t give it much throttle, drives fine. Under throttle, engine stumbles bad, and it seems it may stumble less with harder throttle. Log ?3rd drive? is partial throttle acceleration, while ?4th drive? has harder throttle acceleration and didn?t stumble as much. I did test drive this engine prior to the standalone swap, and engine had no noticeable issues. I made sure wires to the MAF are connected to the ECM correctly and tested that it has power and ground (at least when tested, it did). I checked for vacuum leaks using carb cleaner, and didn?t find any; stock (new) truck PCV is used. One DTC set is P0102.
What I have noticed in the logs is, timing is being pulled dramatically in some cases, also in ?4th drive? log, at time 2:53, the MAF jumps high to low multiple times, but throttle, RPM and MAP don?t change. I?m thinking I have a MAF issue as it reads very low sometimes and figure that?s why it set the P0102, but not sure if that?s the only issue. When timing is pulled, the engine appears to be running lean sometimes according to the stock O2s. Fuel pressure seems low to me, I?m thinking is should be 58* at idle, but maybe the vacuum regulator adjusts for that. When I disconnect and plug the vacuum line, pressure stays at 59* at idle; didn?t test drive without the vacuum line. I had the injectors refurbished, entire fuel system including tank, is new, 3/8 feed and return.
I?ve been using HP Tuners for years now, but mostly just for standalone operation, disable VATS, adjust fans, disable unused DTCs, etc. I can log any info that?s needed (usually), but don?t know how to interpret the information that I gather. Should I force this engine into SD mode and see if I still get the stumble, drive without the vacuum line connect to the fuel regulator, both? I?ll keep poking away at this and researching, but any help identifying what?s going on is greatly appreciated. Thanks!!! B