1990 isuzu trooper

my trooper has been giving me starting problems for about a year. it has plenty of crank (new battery). the problem starting is hit and miss. it may not start first thing in morn. other times it will start first thing in morning but after vehicle has run awhile and has been shut down, on quick restarting it will but let to rest awhile it may not. Trooper has never stalled during driving. Some times if i shoot starting fluid into fuel injector body it will start but not always. some times forcing injector body flapper slightly ajar it will start while spraying starting fluid. If i park trooper on hill and after trying unsuccessfully to start it, it will always start on rolling jump. Trooper does have engine ping when approaching 55 to 60mph when on road with upgrade. Parts changed out so far are battery, distributer wire harness,ignition switch assembly, and fuel pump relay. Any suggestions would be greatly appreciated. this has been very frustrating. Even though trooper has 150,000 miles on it, the engine is very sound. It also has new clutch, shockes, brakes, and above mentioned parts. so in a nutshell i don't want to give up on it yet. plus i would rather be able to use its four wheel drive through at least one more winter than use our new pontiac g6 to get through snowy conditions. thanks, Ted

i think that you must check the fuel pressure

I just acquired a 1990 isuzu trooper II and I was experincing similar problems. Sometimes it would start just fine. Other times it would not start at all. I replace the alternator and has not happened since. I got the alternator for $135 at Advanced Auto. Hope this helps