Detroit Diesel — Locate a Misfiring Cylinder
Testing & diagnosis · Engine
From a Detroit Diesel service manual — check it applies to your exact model before use.
Before you start
- Do not crank the engine with the starting motor to check compression pressure.
Procedure
- Start the engine and run it at part load until normal operating temperature.
- Stop the engine, remove the valve rocker cover(s) and discard the gasket(s).
- Check the valve clearance (.009 in two valve head, .024 in four valve head).
- Start the engine and hold an injector follower down with a screw driver.
- If no difference in sound/operation the cylinder was misfiring; if there is a difference it was firing correctly.
- Repeat on other cylinders until the faulty one is located.
- If misfiring, check injector timing, compression pressure and install a new injector.
- If it still misfires, check the cam follower for a worn roller, camshaft lobe, bent push rod or worn rocker arm bushings.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Minimum compression pressure 430 psi standard / 540 psi N engine at 600 rpm, sea level
- Variation between cylinders must not exceed 25 psi at 600 rpm
Source: Detroit Diesel service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.