Exhaust Manifold System — SOHC/DOHC
SOHC vs DOHC
- SOHC engines route the exhaust head pipe directly from the manifold; head pipe must be disconnected as part of removal prep.
- DOHC engines (our truck: 4A30 DOHC turbo) require the turbocharger removed first, since the manifold feeds the turbo housing.
Removal preparation
- DOHC: Remove turbocharger.
- SOHC: Remove air cleaner system; disconnect exhaust head pipe.
Component removal order
- Oxygen sensor (SOHC) — caution: do not damage the connector lead.
- Exhaust manifold cover
- Exhaust manifold
- Engine hanger (SOHC)
- Exhaust manifold gasket — discard and replace
- Installation is the reverse of removal.
Torque values (as scanned)
The exploded-view diagram on printed p.73 carries torque callouts alongside part-numbered balloons. OCR could not reliably tie each callout to a specific bolt/fastener position. Raw values recovered (kgf·m in parentheses):
| Engine | Value as scanned |
|---|---|
| SOHC | T=18 (1.8; 159 in-lb) |
| SOHC | T=44 (4.5; 32 ft-lb) |
| DOHC | T=29 (3.0; 21 ft-lb) — appears twice |
| DOHC | T=27 (2.8; 20 ft-lb) |
(verify printed p.73) — confirm which fastener (manifold nuts vs. manifold-to-head vs. cover bolts) each torque value applies to before use; the diagram’s balloon-to-value mapping did not survive OCR.
Oxygen sensor removal — SOHC
Use special tool MD998770 to remove the oxygen sensor.
Caution: Take care not to damage the wire lead. A damaged wire lead requires the sensor to be replaced.
