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OBD1 Diagnostic

 
Old 05-20-2018, 03:46 PM
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Todd Davis
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Default OBD1 Diagnostic

I have a 1984 corvette that I'm currently struggling with. This car has no power at all and backfires in the carbs and when you put it in gear it will bog down and die.
I have an OBD1 scanner but I'm struggling on understanding the check engine light codes as the thing just flashes and you have to decipher what the hell it means. I took a video of it but it is to large of a file to upload here. Would anyone be willing to help?
So far I have replaced plugs,wires,fuel pump as it was bad, fuel filter. Cap rotor. Running out of ideas.

Last edited by Todd Davis; 05-20-2018 at 04:07 PM. Reason: Adding a vid
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Old 05-20-2018, 03:59 PM
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1993C4LT1
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Upload that vid to youtube, and post it here. I don't how the codes work on those years, but 90 and up makes it easier. I'm sure someone will know.
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Old 05-20-2018, 04:02 PM
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Originally Posted by 1993C4LT1 View Post
Upload that vid to youtube, and post it here. I don't how the codes work on those years, but 90 and up makes it easier. I'm sure someone will know.
That I will! The obd1 just flashes the engine light in a mores code.
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Old 05-20-2018, 04:11 PM
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Old 05-20-2018, 04:14 PM
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Looks like 33 and 42 to me..
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Old 05-20-2018, 04:19 PM
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Originally Posted by confab View Post
Looks like 33 and 42 to me..
Thanks all for looking at this!
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Old 05-20-2018, 04:20 PM
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PS: If you don't know any of this and you are new to it all, one of the single best investments you can ever make in a corvette is either a Factory Service Manual, or a subscription to alldata dyi.

https://www.alldatadiy.com/

Cause there's tons of info in there..

C4's are horribly confusing. They have all the tech new at the time, and none of the advance diagnostics that came later.

You really, really need to do this if you want to work on your own car..

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Old 05-20-2018, 04:20 PM
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Originally Posted by Todd Davis View Post
Thanks all for looking at this!
Sure!!

Good luck, bro!!



If you have any questions, this forum can answer them.

These people know C4's inside and out, and upside down!
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Old 05-20-2018, 04:23 PM
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This thing backfires in the carburetor off and on when you pump the gas peddle. About ready to give up on her.
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Old 05-20-2018, 04:25 PM
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Originally Posted by Todd Davis View Post
This thing backfires in the carburetor off and on when you pump the gas peddle. About ready to give up on her.
If it is an 84, it should have a crossfire TBI unit on it.

Has someone replaced that with a carb? Do you have a picture if you aren't sure?
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Old 05-20-2018, 04:29 PM
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Originally Posted by confab View Post
If it is an 84, it should have a crossfire TBI unit on it.

Has someone replaced that with a carb? Do you have a picture if you aren't sure?
It's the original crossfire.
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Old 05-20-2018, 04:31 PM
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Sounds like timing.. Again, these things have all the tech that was new then, and none of the diagnostics.

I see one of your codes is the EST circuit. It's a single wire plug near the distributor that is disconnected to set the static timing. Then you plug it back in and the computer takes it from there.

You might check and see if it is plugged in. Also, if it looks corroded or varnished. and may be making a bad connection.

You can clean it if so. Put some oxygard on it or something similar.

Last edited by confab; 05-20-2018 at 04:34 PM.
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Old 05-20-2018, 04:36 PM
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Old 05-20-2018, 04:37 PM
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Originally Posted by confab View Post
Sounds like timing.. Again, these things have all the tech that was new then, and none of the diagnostics.

I see one of your codes is the EST circuit. It's a single wire plug near the distributor that is disconnected to set the static timing. Then you plug it back in and the computer takes it from there.

You might check and see if it is plugged in. Also, if it looks corroded or varnished. and may be making a bad connection.

You can clean it if so. Put some oxygard on it or something similar.

I'll take a look at that right away. Just kinda confusing.
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Old 05-20-2018, 04:38 PM
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STOP!!

I know a guy who lost his 84 like that.. It burned to the ground. Same reason - backfire and then caught fire.

(Almost did it inside my friend's garage, actually.)

Fix that timing circuit and try a MAP sensor on it before you continue.

Last edited by confab; 05-20-2018 at 04:40 PM.
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Old 05-20-2018, 04:43 PM
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Originally Posted by confab View Post
STOP!!

I know a guy who lost his 84 like that.. It burned to the ground. Same reason - backfire and then caught fire.

(Almost did it inside my friend's garage, actually.)

Fix that timing circuit and try a MAP sensor on it before you continue.
This is a pic I took before I changed the wires. This one cable had nothing to hook to
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Old 05-20-2018, 04:45 PM
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I have an 85 and they're TOTALLY different.. (This is where alldata or a factory manual would come in handy)

Last edited by confab; 05-20-2018 at 04:45 PM.
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Old 05-20-2018, 04:54 PM
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Old 05-20-2018, 05:33 PM
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Well the car is really doggy. I may just take it to one of the shops around here. The 84 is one confusing car...
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Old 05-20-2018, 08:02 PM
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I have an '84 as well. I would invest in a Factory Service Manual as mentioned above. I purchased a CD version on eBay. This one is searchable. It should also include the Electrical troubleshooting supplement.

https://www.ebay.com/itm/1984-Chevro...EAAOSwzgRWu9FH
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