VS V6 missfire problems

[VX L67 Getrag]

Has anyone had experience with VS-VY Maf style PCM's having a missfire issue when hot but not throwing codes?

When logging the car & you can drive it for over 40 minutes if free flowing traffic, but once driven for more then 25 minutes in stop/start traffic there is a bad missfire & eventually cuts out but when missing the wideband shows around 20, where as before this was completely normal 13.5 to 14.5!
There is no fault codes being logged (expected 18x or 3x), I have put a complete dfi with coil pack assy on it & is the same, I'm hoping cause it happens with log it may show something but not sure what to look for does the 18x & 3x signal get logged & what would you expect to see?

[vlad01]

have you checked the spark at the lead ends when it does this?

On my nephews car the CAS was physically stuffed and cross fired so bad it would reverse the engine. No codes were logged at all. So I wouldn't dismiss it just yet.

Also worth checking fuel pressure when it does this to check if its is or not a possible pump issue as the fuel temps in the tank go up with recirculating hot fuel from the rail.


Another thing to consider is possible mechanical issues, like sticking lifter or similar keeping valves open.

[delcowizzid]

sounds like cas issue pore cold water on it and see if it runs again.they tend to fail a lot in traffic as they heat up that little bit more when stationary

[VX L67 Getrag]

Yeah thats what I thought, it does have a new balancer on it & CAS looks new too, but thought I'd be able to see in the log when the fault happens too.

[antus]

Yeah the computer cant see problems on the output side of the dfi. Too far upstream.

[MAGP]

You would think it would see a drastic change in afr though and log a fault on that.

[antus]

But no, it logs electrical problems on the sensors it is connected to.

[VX L67 Getrag]

Looks like it "MAY" be the CAS as it happened twice on drive home & both times poured water over the CAS & was good for another 5 to 10minutes depending on flow of traffic.

I would have thought you could see a wave in the 3x or 18x with the CAS pick-up, fair enough about the DFI not sensing anything.

It also had me doubting just because AFR's were going leaner I thought they would have gone richer from not igniting properly, but then now thinking about it there'd be no inj pulse too I guess.

[vlad01]

no its will go lean as the WB only sees available o2 in the exhaust. No combustion means all o2 is free and not bound up in co2 and co

[VX L67 Getrag]

Well I went to replace the CAS & then noticed the 3 wires for the cam sensor are bare & partially broken through, it's still not throwing any codes but what would the cam sensor not getting a clean signal cause for issues?