Prob with my LO3
07-11-2007, 02:13 PM
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Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Prob with my LO3
Hey guys, just finished a plug/ wire job on my 91 firebird with the LO3 5 spd. When you first start the car, no matter how warm or cold the engine is, it runs really rough like it has a big cam, then after a minute of struggling to stay running the computer kicks the idle up a bit and it smooths right out, then the idle drops back to normal (~700). Now after the computer fixes the rough idle, the SES light immediately comes on. Before the tune up, the SES light NEVER came on and it didn't run rough. I'm assuming it's a sensor problem right now. A friend told me it could be the o2 sensor but I have no idea. Any help would be great. Thanks in advance.
07-11-2007, 02:48 PM
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Car: 1984 Z28 Hardtop
Engine: 383 Carb
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Axle/Gears: 3.54 Dana 44
Re: Prob with my LO3
Read the codes and find out why the SES light is on.
07-11-2007, 06:24 PM
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Car: 89 Firebird Formula(Totalled), 91 C
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Re: Prob with my LO3
I agree with ape, but are you sure you put the wires on right?
07-12-2007, 01:58 PM
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Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Re: Prob with my LO3
Well I had already planned on reading the codes, but I was wondering if any sensors are prone to making the car do things like that. As far as wires go, i'm pretty positive I put em on right, but i'll go and check again as you never know what could happen.
07-12-2007, 10:16 PM
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Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Re: Prob with my LO3
Well, I went over the firing order 3-4 times and everything is where it should be. So looks like it's time to check out the codes. Thanks for the replies.
07-12-2007, 11:52 PM
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To be honest with you, it was time to check the codes the first time the light came on.
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07-15-2007, 08:35 AM
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Re: Prob with my LO3
You should take a close look at all the plastic vacuum lines to see if you might've broken one while changing the wires, especially the vacuum line that runs to the MAP sensor. Those plastic lines are real easy to break when you're doing the plug wires. If your MAP vacuum line is broken, it can cause the motor to run rough until the computer compensates for it by going to a set parameter, but it'll also trigger the check engine light since you essentially just went into "limp home" mode.
07-16-2007, 11:40 PM
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Re: Prob with my LO3
i had the same problem with my LO3. it was the coolant temp sensor connector.
Last edited by mystikkal_69; 07-16-2007 at 11:43 PM.
07-16-2007, 11:50 PM
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Re: Prob with my LO3
yeah thats all well and good that you got the plugs in the right order and all but that doesnt mean they are on the right posts that also needs to be checked and make sure they are all properly seated... new wires can sometimes be a pain to get snapped into place especailly with all the contorsions required to get your hand to some of them
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