jason86/2.8

The only time I ever get an SES light is when I've been on the interstate for 20-25 miles. It'll come on and stay on for maybe a minute then go off and then come on maybe 2 more times b4 the trip is over. This almost always happens at night too as it's only happened twice during the day. Anybody know what this might be?

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1986 Berlinetta, 2.8L, newly rebuilt 700R4, 3.42 Posi. 127,000 miles and counting.
I've come to realize that I'm gonna have this car till it pukes for good, b/c I'll never be able to bring myself to sell it.

TomP

You'll have to pull the code out of the computer for that one.. I believe instructions for that are detailed in the tech section of this website.

-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

Kevin91Z

iTrader: (1)

If you get an SES light while driving on the freeway like that, its probably code 32, EGR.

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Vader

I told you guys earlier (forget which post) that this is EGR week at ThirdGen.org...

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Vader
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IROC-ZTWENTYGR8

Yeah Vader, it really is, I even think I need another 1!!

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jason86/2.8

Should the EGR thing be a problem? When the light comes on I can't tell any difference in the car or the performance. I'll have to pull the code when I get a chance to make sure. I just have to do what it says on the FAQ to check it, right?

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1986 Berlinetta, 2.8L, newly rebuilt 700R4, 3.42 Posi. 127,000 miles and counting.
I've come to realize that I'm gonna have this car till it pukes for good, b/c I'll never be able to bring myself to sell it.

Vader

Jason,

If it is an EGR problem (as the concensus seems to indicate) it shouldn't cause any problems with your engine other than heating the chambers more than necessary. Once you find your paper clip and retrieve the error codes, you'll know with some certainty. The DTC is probably being set because the EGR is not opening when it should, not the other way around. If the EGr were stuck open when it shouldn't be, you would have a lot of other problems, like a poor idle and accelleration, low vacuum readings, etc.

Just in case the code is for something else, you should take ten minutes to check them soon. You don't even have to raise the hood, so it's no big deal.

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Later,
Vader
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jason86/2.8

I pulled my code for the SES light up a few mins ago. It wasn't the EGR thing. It ready a code 13 which says "Oxygen sensor signal stays lean during warm engine cruise" This sounds right since 20 miles on the interstate would be a warm engine cruise. I didn't figure it'd be an O2 sensor though. Don't you have bad mpg's when you have bad sensor, I get 22mpg on the interstate. And one more thing, what exactly does it mean that it stays lean during a warm engine cruise? Will this be a problem? I drive 400 interstate miles a week. Should I get a new O2 sensor or what? Any help is appreciated.

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1986 Berlinetta, 2.8L, newly rebuilt 700R4, 3.42 Posi. 127,000 miles and counting.
I've come to realize that I'm gonna have this car till it pukes for good, b/c I'll never be able to bring myself to sell it.

Vader

Jason,

Running lean generally means you'll be getting better MPG, not worse. There are several possibilities, including the sensor itself. If you haven't changed the sensor in the past 30-40,000 miles, you might want a new one. This may not solve your problem, but you'll have a known good sensor. A Bosch replacement sensor will be about $18.99 at an automotive grocery store. (Bosch was the O.E.M. supplier to GM for O2s. If you pay more for one in an AC/Delco box, it will still have a Bosch sensor inside.)

You could be sensing a lean exhaust from a stuck A.I.R. diverter, constantly dumping extra air to the exhaust manifolds. You could also actually be running lean, in which case you might have a vacuum leak which can't be overcome by the ECM fuel offsets, or you might have a TPS set a bit too low.

At least you now know which direction to look.

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Later,
Vader
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GMTech

Code 13 is one of the most mis-understood codes that I know of. I don't know where people get "lean during warm cruise", there is a different code for being lean (it doesn't matter when you are lean, LEAN is LEAN)

Anyway, code 13 is the O2 sensor circuit. The ECM supplies a 450mV bias voltage to the O2 sensor. A healthy engine will stay around the 450mV while in open loop. Once the vehicle is in closed loop however, the voltage will vary from 0mV to 1000mV very rapidly. This is a good sensor. However, when the sensor does not put out a signal, or the sensor is disconnected, the 450mV never gets pulled high or low, and the ECM sees that 450mV never stray, and assumes the 02 sensor circuit is bad. Usually, the sensor is bad, sometimes you get a chaffed wire or bad connection. But most of the time it is a bad sensor.

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dtpmike

I forogt the code, but i get a code when im on the highway at like 65 mph. Usually at night and when it is a constant speed. The car runs the same, smells the same and I get teh same gas mileage so i usually dont worry about it. I does get annoying seeing that light though.

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89 camaro 305 tbi, flomaster 3 chamber cat back, gutted cat, Edlebrock open element, 2 kicker comp 12"'s, polk for the rest. Phoenix gold xs2300 to subs, kicker impulse 404XI to 4 speakers, pioneer DEH- P7000R head unit, and finally a 12 disc changer. Full leather interior from MrMikes.com