Check gauge light comes on and voltmeter shows low voltage

SOURCE: obd1 scan tool will notaccess

A couple of ways to check and see if the computer is ok first:
check engine light must come onwith they in on position
The fuel pump must run for two (2) seconds with the key ON
There must be a 5 volt reference at sensors like map, TPS
Must communicate with scan tool
The ORANGE wires at the computer are you power input wires one has 12V all the time this is your KEEP ALIVE MEMORY
one is 12 with the Key on you MUAT HAVE VOLTAGE AT BOTH
Check the computers Ground most are out under the hood and are brown wires
Try the GM TAP TEST this is a factory authorized test with the computer connected and you verified all of the above SLAP the computer with the open hand firmly not too hard but firm see if anything changes,
Do not disconnect the battery you will erase all the codes!
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SOURCE: 1992 Ford F150 shows 12 trouble codes and all say

Put on a TPS switch for the starting problem and the rich mixture problem.

Low voltage on all sensors would mean a bad battery, voltage regulator in the alternator or bad primary wiring.

The bad primary wiring would also mean the battery and chassis ground wires as well as the hot wires.

The sensors can work on a lower voltage and the resistance is variable. The variations is what makes them work properly. You would blow out some sensors with 12 volts.

Remember to disconnect the battery for 10 minutes to wipe out old error codes. They stay in memory and you may have fixed something 20 starts ago and not know it.

Also it is good to clean under the airhorn and replace the gasket. This area will cause EGR errors and flow errors if it is dirty.

SOURCE: throwed a code po335 crank sensor , i changed the

Are you sure it was the crank sensor that you replaced? The cam and crank sensors look identical. Was the engine hard or slow to start? If so, this will sometimes set this code.

SOURCE: GMC envoy after I filled gas tank the low fuel

You will need to replace the fuel level sensor which is in the fuel tank.They have a lot of problems because the metal fingers on the sensor wear off and gives you the incorrect readings.This will also cause the check engine light to come on.You will probably have a level sensor code.This will be a lot easier if the fuel level is down to about a quarter tank or less.Also you should be able to get just the level sensor and not have to get the complete fuel pump module.Good luck.

SOURCE: low oil pressure 93 GMC P/U w/350 motor w/205,000 miles gauge

While engine is running, open the cover where you add oil to engine and see if you see a good flow of oil, if good flow, could be as easy as replacing oil sending sensor. got to realize that if poor maintenance history your engine may not be building enough pressure at iddle to move your hydraulic operated valves, only when you rev it up it will pump enough to run smooth. if running engine too long, you may cause more damage to other engine components such as crankshaft and cam shaft bearings. if you can spare a few bucks, have a good mechanic check your oil pressure with a mechanical gauge. another cheap option is to replace oil pump. last resort if you love your truck as much as we do,replace engine or rebuild it. At 205,000 this is a normal symptom, other than timing chain problems, most engines don't make it that far. hope this helps!