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eng. sometime start, sometimes won,t
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guy allen
New User
Jan 30, 2012, 1:48 PM
Post #1 of 2
(1966 views)
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eng. sometime start, sometimes won,t
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1991 chevy silverado, 350 v8. Start up drive about 20 miles,let sit about 6hrs.coil won,t fire.coil has power when turn key on but just won,t fire.Let sit overnight,will start.Drive short distance,sit short while start right up.Replaced coil,checked in dist. nothing loose,broken or burnt. Thanks, Ya,ll pass a good time
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 30, 2012, 2:26 PM
Post #2 of 2
(1938 views)
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Re: eng. sometime start, sometimes won,t
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All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.
Every engine requires spark, fuel and compression to run. That's what we have to look for.
These are the basics that need to be tested and will give us the info required to isolate a cause.
1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.
2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.
3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.
4) If all of these things check good, then you would need to do a complete compression test.
Once you have determined which of these functions has dropped out,
you will know which system is having the problem.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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