94 Truck dilemma

[EFISYSTEMS at aol.com]

 Hi People,
          I have spent an entire day trying to diagnose a problem, to no 
 avail.  When the engine starts it runs fine for approx 10 seconds,then 
starts 
 running extremely rich.....I then rev it up to "clean" it out and block 
 learns and integrators are reasonable (123-125) then gradually returning to 
 idle all numbers stay within reason and again will idle fine now for about 
 3-4 seconds then whammo rich again, I was fortunate enough to have the exact 
 year and truck to start swapping parts with.....here is a list of what I 
have 
 checked or changed....
 Fuel Pressure      steady at 13 when problem is occuring or not
 TPS voltage         steady, no intermittent highs or lows
 Map Voltage        steady, no intermittent highs or lows......even tried 
 another
 Coil                     coil was tried from other truck....supply voltage 
13+
 Tach lead disconnected from coil to verify no shorting of tach
 Throttle Body and injectors were exhanged for the other truck
 BHMX (matching)computer chip tried from other truck
 Computer tried from other truck
 Distributor tried from other truck
 EGR checked for leaks and even blocked off at one point to verify idle 
problem
 Temp sensor checked on scanner to verify no intermittent jumps
 Knock circuit checked on scanner to verify no intermittent jumps
 Timing verified and verified 10 degree jump with rpm(wire pulled) still 
 changed dist later
 Spark plugs changed....compression checked ,all within 20 lbs of each other.
 Another shop had already replaced cap, rotor, wires, and plugs... to try to 
 fix problem.
 Customer had just come from muffler shop and had new o2 sensor, y pipe and 
 cat back system installed since previous shop had told him he had a plugged 
 cat.
 Stored data on the scanner of 75 frames prior to engine stumble and 25 after 
 ....looked at every frame and compared all data points to see what voltages 
 had moved or even if vss had somehow gone crazy......
 All this and no codes on the scanner (unless you let it idle poorly so long 
 it sets the high map voltage code)
 The above is not in the order of which things were changed...just trying to 
 recall from a very frustrating day.
 At the end of the day I got the idea it has to be some sort of a grounding 
 problem and the only grounds I know of on the engine are the two small ones 
 near the thermostat, the two on the passenger rear of engine(one goes to the 
 chassis from the engine and one goes to the frame)and the main battery 
ground 
 cable......All seems ok.....but maybe there's more I am missing here......I 
 then unhooked the battery for a few minutes (last ditch effort) and truck 
 started and ran normally this time for 7-8 minutes,,,not 
seconds..........One 
 last thing is this truck has had lots of stereo put in it and lots of 
 capacitors for noise......if anyone can give me a spot to look tomorrow I 
 would sure appreciate it and get back to the group with my 
 findings......Thanks in advance.
 -Carl Summers