Match the ending symptom before buying more parts
A cart that slows to a stop needs a different test from one that crashes, tips over, or reaches an obstacle. Reproduce the ending once before changing the setup.
If it stops early, test fuel first. If it is consistently slow, test one engine. If it becomes unstable, keep the counts and test cart order. For obstacle or zombie reports, verify the current game behavior before assuming a turret is the fix.