Need to know compression pressure on a gm 3.1 liter v6

Place a spark plug tester in your number #1 ignition lead and confirm spark.- No spark = possible ignition module failure if spark from coil is present.

Test the fuel line pressure for 12 PSI.for throttle body fuel injection systems on 1987 to 1995 - If reading is low replace fuel pump. If reading is zero lbs check relay.

Compression test for acceptable compression.

If you have spark, fuel and compression, static time the engine and try again to start the vehicle.

PS: If your vehicle is a standard shift you have a clutch safety switch and a column mounted ignition switch that should also be considered.

Here is some more info that may help:


How to Test the Fuel Pump on GM TBI Fuel Systems How To Check Engine Compression GM 3 5L 4 2L

Do you mean p0303? And on a gm 4.3l V6? If so this is a cylinder 3 misfire. Cylinder 3 is the back drivers side cylinder. You will need to check the plug and wire. A compression test to rule out any I ternary problem would be advisable as well. Compression test needs to be done on all 6 cylinders. The results should fall in a range of +/- 10%. There are tons of causes for this from ignition module, wire, plug, injector or fuel delivery, bad map/maf sensor, valves problem, ring problem etc.

Pull the number one sparkplug, and hold your finger or thumb over the hole while the crank is being turned. As the crankshaft comes around to the zero mark, you will feel a slight pressure buildup on the compression stroke. If you are on the exhaust stroke and approaching TDC, there will be no pressure buildup. But even turning the crank by hand, you will feel a slight pressire on your finger on the compression stroke. When at tdc of compression stroke, rotor will be pointing to number one plugwire tower-if you have a distributor, that is. But feel for the compression on number one as the crank approaches the zero mark (tdc).

Interpreting the Results
of the Engine Compression Test.The idea behind the Engine Compression Test (in the case of a Misfire Condition or Rough Idle Condition) is to find out if any one engine cylinder is not contributing 100% of its power to the overall engine output. If only one cylinder has lower than normal compression, your GM 4.3L (or 5.0L, 5.7L) equipped vehicle will run rough or cause a Misfire Code to set and turn on the Check Engine Light.
So then, to wrap things up, the individual cylinder compression readings of each engine cylinder can not vary more than 15%... and this is how you can find out:

1. 1Grab a calculator and multiply the highest compression reading that you recorded by .15.
   
   So, let's say that cylinder #4 gave you the highest reading of 170 PSI. Well 170 X .15 gives you 26 (25.5 rounded off).
   
2. 2Now, the next step is to subtract 26 from 170... which gives us 144 PSI.
   
3. 3So then, 144 PSI is the lowest possible compression reading that any one of the rest of the engine cylinders can have. Any compression reading below this.. and that engine cylinder will misfire..
   

injector and fuel pressure is the indicated problems
have a compression check an look for uneven compression pressures
check for cam followers/ hydraulic followers for a mechanical failure

fuel pressure regulator it is located on the spider pump behind the throttle body

Normal compression will be between 185 to 205.
Minimum compression is 180
Lowest compression reading should not be less than 70 percent of your highest compression reading. None of the compression readings should be less than 100 psi.

All cylinders should be quite close to each other and if you know from the manual (or other online resources) and multiplying it by atmospheric pressure of 14.7 lbs per square inch (air pressure of the atmosphere) will give you the nominal compression.
For example: a 10:1 compression ratio which is fairly common on small engines would yield ~ 147 lbs of pressure.

Do you mean oil pressure or A wet compression test? Oil pressure should be at lest 10 psi warm at idle.

It will vary too much between gauges to give you a definitive answer, probably between 150 and 175. The key thing you should be looking for is consistency. Crank the engine for the same amount of time for each cylinder, about 3 seconds. The readings should all be very close to each other, within about 15%.