Why does my 6.0L LS swap crank but not start?
Work through the swap-specific causes first:
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- 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.
- 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.
When a 6.0 swap cranks but won't start and it has been sitting, stuck injectors are the first thing we check; the telltale sign is that it fires on starting fluid but not on its own. What we've seen work is tapping each injector with a small rubber mallet, soaking them in Seafoam, and bench-testing each one with a quick tap of 12V to feel for the click (12V to the prong closest to the clip nipple, ground on the other). Only pulse it for a moment; a steady 12V feed can cook the coil. Also confirm the engine ground you may have missed during the swap, check fuel pressure (about 55 psi is typical, like on a Walbro pump), and use a noid light to confirm the injectors are being pulsed. You don't need the alternator or MAF hooked up just to get it to start.
Check this first:
- Try starting fluid to see if it fires
- Check fuel pressure (~55 psi)
- Use a noid light to confirm injector pulse
- Verify the engine ground
Careful: Don't boil stuck injectors to free them; it can melt the insulation on the coils.
Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead shop tuner (over 20 years of LS and LT tuning experience). Every combination is different, so use at your own risk and check our safe tuning limits before any wide-open pass.
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Every option we know of
| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| Generic (parts stores) Noid light set | varies | GM Multec/EV1/EV6 injector connectors | about $20-40 | Harbor Freight, Amazon, parts stores | Current production Confirms PCM is pulsing the injector; doesn't confirm fuel delivery |
| Injector service shops (e.g. Fuel Injector Connection, local) Injector cleaning/flow-testing service | n/a | LS truck/car injectors | about $20-30 per injector | mail-in services | Ongoing services Worth it for a set that's been sitting years |
| ACDelco / GM Replacement LS injectors (OE) | varies by application | Match to original application for injector data | varies | RockAuto, dealers | Current production Copy injector tables from the donor vehicle |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.