Well done in providing both the codes and their descriptions.
Misfires are caused by Electrical and Mixture problems:
Electrical (tends to be cylinder specific)
Mixture (tends to be multiple cylinders)
- Plugs and coils. Swap with another cylinder to see if fault follows
- Harness. Dirty connectors, damaged wires, faulty coil earthing resistor, missing coil earth straps (cylinders 1 and 6)
- DME. Inspect the 2 sets of 6 MOSFETS (Black boxes) around the outside of the DME PC Board for damage. Inspect for PC Board track damage. Any damage will be obvious.
- Too rich. Too much fuel, not enough air. Faulty MAF or Pre-Cat sensor fooling the DME into thinking 1 or the 2 prior causes is happening, blocked Cats, O2 pilot mod on CCV, if the problem is bank specific, a leaking injector.
- Too lean. Too much air, not enough fuel. Faulty MAF or Pre-Cat sensor fooling the DME into thinking 1 or the 2 prior causes is happening. Vacuum leaks (see first tip)
- The DME has a performance tune. The DME tables may not match the MAF or injectors fitted. The Air/Fuel tables have been incorrectly altered. Put the DME back to its original tune and see if the problem is fixed.
As your problem is with multiple cylinders, start with the mixture.
With a hot engine at idle, look in the “Live Data” section of your scanner and record the 4 fuel trims, 2 short term and 2 long term. If any are >8% then you likely have a vacuum leak.
Rev the engine to 3,000 rpm for 30 seconds and watch the short term trims.
What this test is doing
- If they reduce significantly, might even go negative, then it is confirmed that you have a vacuum leak to find. Smoke test the engine to find the vacuum leaks. Read: How to Smoke Test
- If they increase (larger positive numbers), then you have a fuel supply issue. Fuel pump or fuel filter.
When you have a vacuum leak, there is air entering the engine without going through the MAF. This is un-metered air. The volume/ratio of un-metered compared to metered air is highest at idle and lower under high rev’s.
This test is using the 4 fuel trims to firstly identify the likelihood of there being a vacuum leak present (any fuel trims >8%). It then uses the short term fuel trims to see if the ratio of un-metered to metered air changes significantly under high rev’s to confirm the presence of a vacuum leak.
When you have a fuel supply problem, the short-term fuel trims get more positive as the engine starves of fuel and the DME has to put extra in so that the engine runs correctly.