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Low/zero compression would explain faster than normal starter spin, but questionable root problem with "just cut out".
Are plugs wet with fuel? If not, verify carb bowl has fuel at proper level. If plugs are dry, pour a couple tablespoons of fuel down the carburetor and see if it fires. If it fires... its carburetor or no vacuum/compression. If it doesnt fire with raw fuel, then likely no spark, followed by low/no compression.
Recheck spark with a cheap spark tester, the kind with adjustable gap, and verify check actual spark.
Most people do not understand when it comes to buyer gasoline for your vehicle most vehicles run on regular. You will not get more power, cleaner fuel, or better fuel economy if your vehcile does not require a higher octane rating. If you ask most mechanics or fuel attendants they will most likely tell you that the middle or high octane fuels will net you more power, cleaner fuel or more milege on that type of fuel which is not true. The reason there are differant grades of fuel is because engines have differant compression ratios, depending on your vehicles compression ratio will depend on the fuel it needs. All fuels are clean otherwise your vehcilces fuel filter would clog prematurely and stop running. The lower the octane rating the faster the fuel burns or the lower its flash temp is. Compression creates heat and if you have a high compression engine and use low octane fuel the heat will cause the fuel to ignite before the spark from the spark plug thus causing a pinging "pre-iginition". So what ever your vehicle manufactutrers rec use that fuel you will not gain by upgrading to a higher ovtane rating.
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.
Loss of compression is something else. What you are describing is a fuel pump issue and it sounds like a relay. Since you did not post what the year make and model is, we have no way of knowing UNLESS it is a jeep.
A thumb is not test for compression as 10lb/sq " will blow your thumb off. Have a proper compression test done. Next although it is sparking the question to ask is it sparking at the right time and to the right cylinder. Pouring fuel into the cylinder is a waste of time as the air/fuel ratio will be too rich to ignite even if the spark was occurring on the compression stroke. So here are some simple steps to follow to get it going
Have a compression test done to determine if there is sufficient compression to ignite the mixture
2 check that the spark is occurring at the cylinder at the right time ( no 1 cylinder on timing mark on compression stroke.)
3 . If it is EFI engine then check that the injectors are actually squirting if carby engine check that the fuel is in the fuel bowl With engines you have to have a combination of 3 things for the engine to work They are compression -which you will be checking for--2 spark timing--- which you will be checking for and lastly 3 fuel into the cylinder at the right time ==which you will be checking for
you only have to be missing one of these and you had best take it to a professional mechanic to get it started.
Compression is what happens when the piston comes up and compresses the fuel/air mixture. Then the spark plug ignites it and the explosion drives the piston down in turn, turning the Crankshaft in turn making the car go. A compression leak is when this compressed fuel/air mixture is escaping from the combustion chamber.. This can happen 3 ways. 1. Bad piston rings, 2. Blown head gasket or cracked head or block, (usually caused by overheating), Or the least costly.. loose spark plugs.
Pull out # 1 spark plug and put back into plug wire, rest on motor block so that end of electrode is against metal. turn motor over and have a finger or compression gauge in # 1 cylinder, check to see if spark occur at same time as compression (compression will blow air past finger or raise gauge). When you say it has fuel do you mean gas tank has fuel? Are you sure fuel is getting to the cylinders? are plugs wet with fuel? Does it turn over but kinda thumps or backfire (Caugh)? Check the spark and compression first. if they don't happen at same time, the timing skipped or belt broke. if all is good pull plugs and inspect, could be flooded (WET) from fuel. either replace or spray with starting fluid and compressed air to dry them. spray starting fluid into air intake if starts then stalls, try again, if same thing happens then you have a fuel problem. try these suggestions first 1/2 hr time table, hopefully sucess, if not it sure indicates fuel.
did you check for fuel and compression? Check for compression either with a compression tester or pull the plugs and one by one stick your finger on the top of the hole and have someone crank it. whether there is compression or not you will easily be able to figure out your answer. Also make sure you are getting Fuel if im not mistaken the 85 had a carb. again while someone is trying to crank it see if you can see gas squirting into it if not i'd go the route of either a clogged fuel filter or bad pump... the 3 things a vehicle needs to run is compression spark and air/fuel mixture
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