Backfire/misfire

[kbollaert]

Cranking motor after a five minute cooloff after a 120 mile drive. Nothing out of the ordinary noted.
Engine cranked over normally about 3 revolutions (or so), when BOOM!! and a big cloud of bluish smoke came out of the rear of the car. 
Thinking that there was pissibly an induction fire (a la airplane piston engines), I continued to crank for a period of time to put out the possible fire. Very strong misfire, with minor pops for appx 1 minute.
Let the motor cool for 2 hours, pulled the air filter. No damage (lots of leaves though). No oil behind the butterfly noted. Pulled the MAF (carefully) and inspected with no damage noted. Reassembled everything and tried to start the motor with the MAF disconnected. Durametric codes of P1602 and P0102 pulled and cleared. Disconnected the battery for 30 minutes.
Instantly tried to go full throttle. Probably got up to 5000 rpm before I could react.
Shut down, inspected the throttle cable, with no defects noted.
Reconnected the MAF connector. Tried another start. Serious misfire, minor backfiring. Will not accelerate much beyond 1000 rpms. 
No further codes came up, no indications from the Durametric-which I had to uninstall, reinstall and install another Windows driver.
BTW I borescoped around the intake runners, and didn't see anything unusual.
Any ideas?
Fuel delivery seems ok, based upon the rapid rise in rpms with the MAF disconnected. Don't understand why that happened, though.
Background: 16k miles after overhaul. No detritus noted when I removed the oil pan for a repair last week.
Normal cranking/operation since overhaul. 
New AOS, Oil filler cap seal/tube all filters, etc.
More than half full of fresh fuel.

[JFP in PA]

Year and model is always helpful in these situations.

[kbollaert]

99 996c2 thanks

[JFP in PA]

OK, P0162 indicates a power supply interruption, usually a battery disconnect or a wiring issue.  It can also occur it the DME momentarily loses power.  P0102 is a fault that happens when the MAF looses power due to a wiring issue or short.  I would say that you had a backfire, caused by a momentary lose of battery power.

 

You need to check the primary leads (battery cables) for voltage drop, tight connections, etc. I would also load test the battery to make sure the problem does not start there.  You can get all sorts of faults and problems with low battery voltages.

[kbollaert]

Followup: This problem was caused by a fuel injector that apparently stuck open, dumping a lot of gas into the intake. A warm start a few minutes later was enough to ignite the fuel, causing an explosion in the intake system. Replaced the injectors, gaskets, an intake runner tube, my shorts, and all is well.