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No code 12

Tiny
CHUCK921
  • MEMBER
  • 1989 GMC C1500
  • V8
  • 2WD
  • AUTOMATIC
  • 199,722 MILES
This truck has had the computer replaced with a new one(same prom) and it still doz this: high idle, pinging, dies check engine light is on and of the pinging is when you put your foot in it. And with the scanner reads no prob. Found. Can not get the light to blink code 12 if I could get the codes I could out of it then I could fix it HELP! And thanks. I cant afford to donate much to day.
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Tuesday, September 15th, 2009 AT 11:37 PM

10 Replies

Tiny
SERVICE WRITER
  • MECHANIC
  • 9,123 POSTS
Here is how you get the codes

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

The ECM incorporates a diagnostic program which, when activated, will flash codes stored in the trouble code memory through the "CHECK ENGINE" lamp. A diagnostic connector, located under the instrument panel, is used to activate the self-diagnosis system. The connector,allows access to system circuits and contains a test terminal which, when grounded with the ignition on and engine stopped, causes stored trouble codes to be flashed on the "CHECK ENGINE" lamp. The ALDL is under the dash on the drivers side near the e-brake lever.

You should check if the exhaust is plugged too.
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Thursday, September 17th, 2009 AT 7:06 AM
Tiny
CHUCK921
  • MEMBER
  • 6 POSTS
I have read the ans you sent me but. I do not get any codes, check engine light is on but no flash code 12 or any codes.
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Thursday, September 17th, 2009 AT 2:21 PM
Tiny
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What liter engine?

Pre-detonation cause be caused by various things including low octane, try going to premium fuel.

Il sent
you a chart.
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Thursday, September 17th, 2009 AT 2:48 PM
Tiny
CHUCK921
  • MEMBER
  • 6 POSTS
5.7
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Thursday, September 17th, 2009 AT 8:34 PM
Tiny
SERVICE WRITER
  • MECHANIC
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Did you get the chart? Sometimes the emails end up in the spam folder. It would be good to get the code problem solved.

Did you look at this page?
https://www.2carpros.com/first_things/why_does_my_engine_idle_high.htm

Are you losing any coolant? A head gasket can fail between 2 cyls and cause a ping.

Incorrect timing can cause a ping.

Excessive carbon build up can cause a ping.

A bad egr valve as well. try unhooking it and see if it changes.

bad knock sensor, unplug and see if it changes.
I believe that system grounds to the therostat bolt. These have a habit of corodeing where the bolt goes in the housing. You can have a good connection to the bolt but not the engine.

A lack of fuel volume or a restricted exhaust such as a plugged cat can cuase pinging, but would not explain the high idle. Premium gas would not explain the high idle, I retract my previous comment on that..

Let me know the progress on getting the codes.
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Friday, September 18th, 2009 AT 5:43 AM
Tiny
CHUCK921
  • MEMBER
  • 6 POSTS
I did get the chart and im at : back probe ckt 451. Witch one is that? Exhast good pressure and doz not smell like coolent the cat has been replaced. I think the ecm is cawzing the IAC. Valve to act up. And I did change the valve still the same I think this is the high idle prob. I want to send ya some more money do I start over with same title ( 1989 gmc code 12)?
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Saturday, September 19th, 2009 AT 1:35 PM
Tiny
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451 is the white/black wire. The connector is on the driver side near the ebrake lever.


https://www.2carpros.com/forum/automotive_pictures/30961_gmc_1.jpg



I'm not sure how the donation works, but keep this thread.
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Monday, September 21st, 2009 AT 5:08 AM
Tiny
CHUCK921
  • MEMBER
  • 6 POSTS
Well it looks to be the prom.I will replace the ecm with one out of the bone yard ( with the same part #) and try that. The new prom is 199. Oo, the bone yard ecm is 30. Oo. I will keep in touch with ya and let ya know if I fixed it > Big thankx to all who helped out. If I can help you out with some other car problem, you got my # thankx Chuck
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Tuesday, September 22nd, 2009 AT 9:48 PM
Tiny
CHUCK921
  • MEMBER
  • 6 POSTS
Hi guys remember me, well its still the same, with new prom and a new computer no code 12. Well ok 1 flash code 12 then the light goz out. When I get some money ill send you some. Thankx. Chuck
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Monday, October 19th, 2009 AT 11:17 PM
Tiny
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Hi Chuck.

Did you try unplugging the egr?

Have you tried any carbon removal procedures?

Paul
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Tuesday, October 20th, 2009 AT 5:52 AM

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