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Old 04-20-2013, 08:42 PM   #1
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Default Starting issues Please Help!!

i have a 1993 trans am. The car has been sitting for awhile, and now seems to be acting up. The car will start some times and then will shut right off. However sometimes the car will start and idle and then when i give it gas it will rev up and then shut off. Once it shuts off i try to start it and it just turns over and wont start or it will start up and shut right back off. I have had the car running multiple times and have drove it around the block and it ran fine and i could shut it off and start it right back up but then it will act up again and shut off and not start up....?

It sounds to me as if it could be a bad ground maybe? Is there anyone who has had this problem or any idea what i should try and look at/for.
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Old 04-20-2013, 09:19 PM   #2
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You should begin a systematic troubleshooting approach to your problem. Get a spark tester, the kind that puts a load on ignition system simulating compression pressure, and a fuel pressure gauge.

Also check for codes, the 3 ignition biggies dtc's 16, 41, & 42, don't light the check engine light but will keep car from running. On your 93 you can use a paperclip on the dlc to check for codes. Connect terminal A & B of dlc turn ignition on and codes should flash.

When car won't run, first test for spark. If good spark, attach fuel pressure gauge and check for 41 ps1 or more at key on prime.

If no spark, go to sticky threads of this section and open the diagnosing the optispark tread. Watch the video and run the tests. shbox.com also has opti testing, as well as coil testing.

and yes, use wiring diagrams in service manual to check grounds, power supplies, connectors, connector pins, etc. Opti wire harness, which runs from opti to passenger side of intake manifold, is a prime candidate.

Service manual, in wiring diagrams, will have component location listed to help you find those pesky grounds.

Go to 4th gen section. Look for thread titled "GM service manuals". Open it, click link, download 93 factory service manual. It will have wiring diagrams, troubleshooting help, a ecm connector symptom chart, driveability and emissions section.

So your task is to find out if spark or fuel pressure is missing when car won't run. When you find which one, report back and we can take it to the next level.

Last edited by cocobolo95; 04-20-2013 at 09:27 PM.
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Old 04-21-2013, 05:07 PM   #3
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Originally Posted by cocobolo95 View Post
You should begin a systematic troubleshooting approach to your problem. Get a spark tester, the kind that puts a load on ignition system simulating compression pressure, and a fuel pressure gauge.

Also check for codes, the 3 ignition biggies dtc's 16, 41, & 42, don't light the check engine light but will keep car from running. On your 93 you can use a paperclip on the dlc to check for codes. Connect terminal A & B of dlc turn ignition on and codes should flash.

When car won't run, first test for spark. If good spark, attach fuel pressure gauge and check for 41 ps1 or more at key on prime.

If no spark, go to sticky threads of this section and open the diagnosing the optispark tread. Watch the video and run the tests. shbox.com also has opti testing, as well as coil testing.

and yes, use wiring diagrams in service manual to check grounds, power supplies, connectors, connector pins, etc. Opti wire harness, which runs from opti to passenger side of intake manifold, is a prime candidate.

Service manual, in wiring diagrams, will have component location listed to help you find those pesky grounds.

Go to 4th gen section. Look for thread titled "GM service manuals". Open it, click link, download 93 factory service manual. It will have wiring diagrams, troubleshooting help, a ecm connector symptom chart, driveability and emissions section.

So your task is to find out if spark or fuel pressure is missing when car won't run. When you find which one, report back and we can take it to the next level.
Car is still acting up.. i checked the fuel pressure and it is fine, also i went over and checked all of the connections and replace some grounds that looked like they could be redone. The car is still running for a couppe mins and then i wil rev it up and the rpm needle will go a little crazy and then shut off. Sounds to me like the opti... i replaced it like 3 years ago however the car has been sitting for like two years. Think it could have went bad again?
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Old 04-21-2013, 05:53 PM   #4
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Yes opti could be the offending part, but check for codes and see if you have the dreaded dtc 16- opti low resolution pulse. Could have icm related codes 41 & 42 also.

That's what the diagnosing the opti video will tell you when you run the tests.

Which brings me to the point where you should get the icm tested at an auto parts store. Make them run several test cycles to get it good and hot. Thats when it likes to fail.
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Old 04-21-2013, 09:17 PM   #5
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Yes opti could be the offending part, but check for codes and see if you have the dreaded dtc 16- opti low resolution pulse. Could have icm related codes 41 & 42 also.

That's what the diagnosing the opti video will tell you when you run the tests.

Which brings me to the point where you should get the icm tested at an auto parts store. Make them run several test cycles to get it good and hot. Thats when it likes to fail.
They only problem is I can't drive it long enough to get it to a store. Can they test it if I take it out?
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Old 04-22-2013, 08:17 AM   #6
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The icm must be out of the car to do the test, so yes carry it with you. I'd put it in a metal container and carry it under the hood, in a place where it won't fall out on the trip. That way it will be hot when the test begins.

Call the store first and ask if they can test the lt1 icm, as some stores don't seem to be able to do our icm, even though they have testing equipment.
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