The issue is not so much to do with the EGR itself but the passage ways that lead from it. Most manufacturers bleed metered amounts of exhaust gas from the EGR into the common plenum of the inlet manifold. Honda does things differently in that they use a passage way assembly to feed the exhaust gas from the EGR into each runner of the inlet assembly close to the intake valve. Over time these passage ways become blocked with sooty carbon deposits, but not all simultaneously. This means that some cylinders run as they should and others run lean with the overall effect that the engine runs unevenly and will misfire on those cylinders to which the passage ways are blocked. Two types of exhaust gas feed systems were used, one with a removable lid and one that consisted of a complete casting with blanking plugs. You will need to access this passageway assembly, it lies beneath the fuel rail and on top of the inlet manifold; the process is quite involved for the casual DIYer. The internals of the exhaust feed assembly need to be cleaned out. Those assemblies with the removable lid (bolted on with a gasket) are pretty easy to clean out with a screwdriver, brush and carb choke cleaner spray. Those with the single cast unit with blanking plugs are much more difficult. The blanking plugs need to be removed and new ones will be needed to replace them. The best way is to drill a pilot hole in the centre of each plug and then screw a heavy duty threaded, self tapping, dome topped screw. The plug can be removed by applying leverage to the screw head. To clean the passageway use a a frayed brake cable fitted in the chuck of drill. The cable can be eased in through the plug holes and along the passage ways, the rotation imparted to the cable by the drill will loosen any obstruction. Spray liberally with carb. choke cleaner and wipe clean. Fit the new blanking plugs and tap home. Replace all the fuel rail assemble etc and the engine should be good for another 100k, no more EGR and no more misfire and no more speed restriction. Note the safe-home mode imposed by the ECU on the engine is due to the knock sensors detecting the misfire events. It is just a safety precaution to prevent any damage and will be lifted when the computer is cleared.
I changed my EGR valve and have had no problems with the light coming back on. The Acura fix is best left to the dealer and may very well be permanent, but I chose a $60 rockauto part and a little carb cleaner. The misfire may be plug wires? My Cl has 175K and it was due.
2004 Marauder and 2003-2004 Mustang vehicles built before 12/19/2004 equipped with 4.6L 4V/5.4 4V engine may exhibit a runs rough, lacks power, and engine misfire, prompted by a MIL light and DTC codes P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, and P0316.
ACTION
Diagnose engine for engine misfire concern. If diagnostics determine an engine misfire which is characterized by leakage through exhaust valve(s), only replace the affected cylinder head(s).
SERVICE PROCEDURE FOR VEHICLES WITH RUNS ROUGH/MISFIRE CONDITION:
1. Perform relative compression check on all cylinders. If abnormal, check cylinder leakage and actual compression for "low" cylinders refer to Workshop Manual (WSM), Section 303-00.
2. If leakage/compression check indicates a valve train concern, per valve train diagnostics in WSM, Section 303-00, replace cylinder head and cam assembly, pipe plugs and timing chain tensioner, per procedure outlined in WSM, Section 303-01.
3. If cylinder leakage and compression tests are inconclusive, perform misfire diagnostic, per TSB 05-22-8.
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