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One of the guys I work with has an '05 GS430 with 105,000 miles that has a perplexing intermittent problem. He's getting a code for #4 and #6 coil misfires (P0354 and P0356) under acceleration. It doesn't do it all the time, and it will fail when cold or warm, but it only throws the codes when accelerating. When the car misfires, he can shut the car down and restart it and it runs fine again. After 4 cycles, the CEL goes out and the car is happy, until he accelerates again, and it may or may not fail again..
He swapped coils 3 and 7 with 4 and 6 on the engine, and it still shows up with the code for #4 and #6 coil misfire. So, we know it's not the coils. Looking at the schematic, those 2 coils share a feedback signal to the ECU, so I wonder if it's experiencing an ECU failure?
He's ready to get rid of the car because of the problem, but I have to believe it's something simple..
I had a similar problem. My problem was from leaky valve cove & oil spark plug seal. Once I changed it my problem went away. Try changing the plugs they might be fouled up if you say it's not the coils.
Take off your engine cover and check your hoses and inspect for oil seepage. As mentioned right around 100k is when the valve cover gaskets begin to deteriorate so check those as well. If you are not sure please don’t throw money at the problem - take the car to a mechanic that understands the 2GS. More than likely it’s something they’ve seen before.
Guys thanks for the input and suggestions. After some serious trouble shooting yesterday afternoon (finally decent enough weather to spend a little time on this...) We found a broken wire in the engine harness, just outside of the ECU. The feedback wire for #4 and #6 coils had a crack in it and the only thing holding the wire together was the conduit. Putting an OHM meter on the wire ends (Coil connector and ECU connection, we found the wire would open up at the slightest movement of the loom. Once the ECU saw the open condition, it would kill the signal to those 2 coils. Oh, and the plugs and VC gaskets were done within the last 5-6,000 miles.
So, this takes care of the problem and he's finally good to go..
04-19-18, 05:17 AM
2005 GS430 Misfire under acceleration - Not Coils
