I have a 2007 S40 T5 giving me a OBD2 code P0305 Misfire Detection. All Cylinders are misfiring. The tool I am using is the Innova 3040 RSv1 and once I erase the DTC and get a computer restart(I guess because I hear a click) the vehicle runs great for 3-4 days then I get the P0305 again. So every 3-4 days I plug in the Innova 3040 RSv1 get the misfire reading and erase DTC and everything runs well again. 3-4 days later the misfire codes show up again.

What is going on with this vehicle and how do I fix this?

 

P0305 indicates only cylinder 5 misfiring. Generally clearing codes won't affect misfires. You really need a tool that allows you to dig deeper. But I'd start with a close look at cylinder 5 (unless you really have a P0300 code instead)

 

habbyguy,

I am getting P0300 thru P0305. P0300 is the random misfire and P0301 is cylinder 1, P0302 is cylinder 2 upto P0305 which is cylinder 5. This time around the car did not want to start. Like we are draining the battery or something. Once I got the car to start it was running terrible. The whole car was filing pretty shaky(because the engine misfire I guess). RPM are around 2000. I erased the DTC from the Innova 3040 RSv1 twice and the car shakiness went away. RPM were down to right below 1000. Drove the car about 100 ft and the car felt fine. No engine light.

I am so confused.

 

nothing really confusing here - just a need for further diagnostics. Keep in mind, when you start up, the engine is cold so by nature, it wants a richer mixture and a hotter spark. Long cold cranking can be due to any number of things - low fuel pressure (ie a leaky injector or pressure regulator can require pump to run longer to build pressure), weak coil(s), weak spark (what do the plugs look like? gray/tan=good or black/oily=bad? Low compression can also make for misfires long cold cranking (does the car consume more than 1 qt per 1000 miles?). Reading or clearing OBD codes won't fix anything in how the engine runs - that's just a report created by the ECU when any of the sensor signals fall outside a targeted range or when the knock sensors detect too much noise. Once the engine warms up a bit, it won't need as rich a mixture or as hot a spark.

Also, not all codes are immediate. Misfires and some of the fuel trim codes are cumulative or averages over time so I wouldn't expect the CEL to return right away after clearing the code.

 

So P0300 is still happening but down to codes P0304 and P0305. This is after changing all spark plugs and coils. I am about to change the fuel filter but not sure that would help.
Any other suggestions?

 

hope you kept your old coils - swapping out parts as a diagnostic approach can get expensive. Things to check: 1) fuel pressure at the rail 2) intake air leaks/ vacuum leaks 3) compression/leak down test 4) engine temp sensor resistance values 5) collect run time fuel trim/sensor input data. Any other symptoms ie cold start/warm start cranking? stumbling at idle or wandering idle or surging (could suggest an ETM issue)?