Exhaust Leak Diagnosis After Header Install With a Persistent Tick
A customer installed long-tube headers and a catless mid-pipe on a V8 themselves. They now report a rhythmic tick that is loudest cold and fades somewhat when hot, plus a faint exhaust smell in the cabin at stops. Visual inspection shows: header flange bolts at the head appear tight, the collector-to-mid-pipe joint uses a supplied gasket and two bolts, one mid-pipe hanger is missing, and the rear O2 sensor is zip-tied to the frame rail with the harness stretched. The tick frequency rises with engine speed. A smoke test at the tailpipe shows smoke escaping at the collector joint within 20 seconds.
1. Distinguish the likely causes of the tick and the cabin smell, and rank them by probability given the evidence.
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The smoke test is decisive: smoke at the collector joint confirms a leak there, which explains both the tick (pulsing exhaust escaping at a high-velocity joint) and the cabin smell (leak under the floor draws into the cabin at stops). The tick fading when hot is consistent with thermal expansion partially closing a gasketed joint. Ranked causes: (1) collector joint leak, confirmed by smoke; (2) missing hanger allowing the mid-pipe to sag and load the joint, reopening it; (3) header flange at the head may still be weeping even if bolts feel tight, because a warped flange or reused gasket can leak without loose bolts. The stretched zip-tied O2 harness is a separate safety/reliability issue, not the tick source, but must be corrected.
2. The customer wants to just tighten the collector bolts and add a hanger. What is your recommendation and what would you verify before returning the truck?
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Tightening alone may not seal a joint that has already been heat-cycled with a missing hanger, because the gasket may be crushed or the flanges distorted. Recommend replacing the collector gasket, checking flange flatness with a straightedge, adding the missing hanger with rubber isolation, and re-torquing to spec in a cross pattern. Before return, re-run a smoke test at the collector and at each header flange, verify the O2 harness is rerouted with slack and secured away from heat, and confirm no codes for the rear sensor. Note that removing the cat may make the vehicle non-compliant for on-road use depending on jurisdiction; flag that to the customer in writing.