Why does my 6.0L LS swap crank but not start?
Work through the swap-specific causes first:
- VATS: a donor PCM that hasn't had VATS deleted will crank but not start (or start and die). This is the #1 swap no-start (PSI Conversion).
- Reluctor/PCM mismatch: a 24x PCM or harness on a 58x engine (or vice versa) won't sync. Check the crank sensor color (black 24x, gray 58x).
- Fuel pressure: an LS needs about 58 psi. A carb-era pump, a wrong regulator or pinched hose won't do it.
- Wiring basics: PCM power, grounds, fuel pump relay and ignition feeds on the standalone harness.
- Tune mismatch: injector data or a transmission calibration from the donor can also cause problems.
Confidence: medium — sources disagree or are limited; check the sources below.
Community discussion
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Sources
- Squarebody LS Swap Guide | 73-87 C10 Parts List — Speedway Motors
- LS Swap How-To Guide — Speedway Motors
- What Every LS Swap Builder Needs to Know About the PCM and Harness — PSI Conversion