Pontiac Repair: 02 montana engine misfire/cuts out, brake torquing, pontiac montana

Question
2002 Pontiac Montana 3.4 ohv 139k, engine cuts out/ misfires at specific rpm depending on how warm engine is. When cold, engine will cut out at 5800 rpm, as it gets warmer the rpm point drops, eventually it will not rev past 1000 rpm when fully warm and has been driving a while. feels ignition related and not fuel related as engine does not "lay over" but cuts out and will relite when I get out of the gas. It is like a rev limiter but much harsher. If I give full throttle, the engine bucks and the tach needle bounces around but rpm will not go over a certain point. if I feather the throttle near the threshold it will stay running but go just over that point and it cuts out. Because it previously had leaking head gasket and an O2 sensor code, I decided to change front O2 sensor, do head gaskets and valve job (faced gasket surface, pressure tested, and replaced 4 "warped" intake valves - have old valves and they were not concentric anymore), replace plugs, coils, ignition module hoping these parts would fix cut-out problem. reassembled with new head bolts and locating dowels and condition still exists. checked fuel filter for clogging, disconnected head pipe from manifold to check for clogged cat, replaced both crank sensors and cam sensor all with no change. I can duplicate the condition anytime while driving - in any gear, while brake torquing (power stalling) if warm enough to cause condition below the 2500 rpm stall speed of the convertor, or by free revving if it is warm enough to cause condition under the factory GM cut-out point for neutral revving (35-4000 rpm?). I cannot think of any other ignition components to replace other than computer, have you ever seen this condition before? Condition is similar to how neutral rev cutout occurs but seems more violent and is very temperature dependent, let it cool and rpm point goes up again but immediately starts to drop as it gets warmer. I have not confirmed fuel pressure but lots of residual pressure when I checked filter and again, it does not feel like a fuel problem or an exhaust flow problem. It idles fine and runs without a misfire right up to the threshold where it then cuts out. While driving on highway I could maintain 2000 rpm due to constant airflow but in street driving I eventually ended up not being able to rev past 1000 rpm trying to go up a hill, went to get tow dolly and when I got back an hour later it was cool enough to rev past 3000 rpm and I drove it onto dolly. at this point I can only think it is the computer but I'm told its in the air box so it should have constant air flow to keep it cool.

Answer
Hi John:
ther are a few ways to look at this. #1 I doubt it's a engine control module. I think it's either a breathing issue when the engine gets hot like restricted exhaust from a bad cat converter you can just drop the converter pipe off at the raer manifold and try it or this has an issue with the crank sensor/crank sensor input to the ignition control module. being that his has been aprt chances at the the wiring between the crank sensor and the ignition module may have melted. it runs up the back of the engine and between the cross over pipe and the engine and if that harness contatced the manifold an the insulation is damaged corrosion may have set in. you can check the resistance of the crank sensor right at the igntion module with the engine cold unplug the harness at the module that has the yellow and purple wires and measure across the 2 terminals the resitance should be between 800-1200 ohms give or take a bit if it's much higher then take a long hard look at tthat harness if it far less I would suspect a bead sensor. if the harness looks good and the resistance is high I would also suspect a bad crank sensor. the only other thing I can thing of here is a fuel volume issue the pump may be wearing out or the filter is restricted and at the higher engine speed the fuel volume can't geep up with the engine demand. That is the last thing to look at here. good luck :-}