Been chasing misfires on all cylinders since I put the new build in back in December. No other codes.

Other than rough idle, the engine runs extremely well. Its a new TWS build with 4.0 pistons on a 4.6 rotating assembly, performance cam, and ported heads with bigger valves. I also have a new Magnaflow Y pipe, O2 sensors, and a different muffler. Plenty of smooth power, deep sound (not loud), and fantastic oil pressure and running temps (inline t-stat).

So far I've replaced the plugs (NGK BPR5EIX), the wires (STI), The coil packs and Crank Position Sensor were changed about 2 years ago with Bosh. Rebuilt injectors 2 years ago too. Just cleaned the MAF. At a loss...

Starting to think that the engine just runs a little lopey with the new cam and heads...

 

Could be, but unlikely. Any codes other than random misfire? What do the fuel trims and 02 sensor voltage charts look like?

 

No other codes at this time.

Started with a Cam Position Sensor code. New sensor, no more code.

Had some purge flow codes, took the charcoal cantier off and drained it of the goo - that code is gone now too.

O2 sensors gave me some trouble. replaced them, no more codes.

Just the misfires at this point.

O2 voltages look good and consistent.

I think I know how to look at the fuel trims - but what would I be looking for?

Thanks!

 

Misfires are detected by the CKP sensor by timing between the reluctor teeth for each cylinder power stroke. So it is possible a lopey cam would appear like a misfire at idle, particularly if all cylinders are involved, because the actual rotational speed of the flywheel is not completely smooth. Maybe try a higher idle speed to see if the misfires are eliminated. Might need to reset (programmed value) TPS idle position to do that. Fuel trim values should be near the middle, not to extreme limits (+/- 25%), with some short term variability while driving. Real time STFT and O2 sensor voltage should correspond at idle. Hope this helps. Sounds like you are almost there with a nice build on the motor!

 

I would start by plotting the fuel trims and 02 voltages with an analog device recording the fuel trims. I would recommend the Torque app with an elm327 on an android device but there are others will record the data and display it for you on a chart. 02s should cycle smoothly from around .15 v to .8v in a sinusoidal pattern and fuel trims should steady out at idle and not move much. A little variation would not be bad but too much could indicate a problem. Also, open the hood on a dark night and look at the spark plug wires for some arcing to surrounding metal. 90% of the time random misfires are spark related.

 

Thanks for all the helpful replies.

I’m going to have to start self teaching on the monitors, fuel trims, and O2 voltages. Thanks in advance for your patience - I’ll be asking a lot of questions.

Also, while I did see misfires on almost all cylinders in the past, after changing the spark plug wires, I’m consistently seeing misfires on 3, 4, 7, and 8. I don’t think that is coil related. Also checked the coil connectors when I had everything apart. No corroded or pushed out pins and all wires look good - coil side looked good too.

 

I used dialectric grease on all spark plug wire boots - coil and plug ends. Always have. Any concerns?

 

Using OBD Fusion app with a Veepeak scan tool. Not sure the Fusion app will chart the fuel trim data.

 

Generally no, unless you really packed each boot full of grease.

 

No, but I’m tempted to go clean two of the four cylinders giving me issues and monitor.