Does trouble code mean automatic check engine light on?

[92470]

I have an 87' V10 and when I turn the ignition switch on, the check engine comes on briefly like is supposed to. My question is if my truck had registered a trouble code, would my light automatically come on? When first started, it idles rough and the motor really shakes. It also surges, like it's trying to breath, but it has never died. If you gently give it gas, it really starts to sputter until you put your foot into it a bit. After you drive it, it really idles and drives pretty decent.
Vaccumm lines look good, EGR is fine, new plugs, wires, cap, rotor. No light, but I'm convinced something is not right. Just wondering if it did register a code, would my light have to go on. Thanks

[STOCKISH]

If it had a stored code in it the light would come on and stay on. Since it is not OBD2, once you turn the key off and re-start your truck, the code is erased. Sounds like your throttle body may be leaking down causing a flooded situation that clears up once run for a minute. When you turn the truck off, remove the air cleaner and look down into the throttle body (dont move throttle) and see if there is fuel dripping. Could also be a faulty coolant temp sensor for the ECU. Good luck and hope you get it fixed.

[72 CustomCamper]

My blazer does something similar to that. I had a friend check it with his scanning equiptment and found out mine needs a O2 sensor. It could be something for you to look into at least...


Chuck

[92470]

When your Blazer did this, did it throw a trouble code? I guess I was wondering if someone hooked a reader to mine, would it show codes for any problems, if I have no light on? I heard there was a diagnostic mode on the readers. What does this do?

The coolant temp switch looks like the P.O. just installed it before I bought it. I've also been told to look at the idle air valve. I guess I can start disconnecting these sensors and see what happens? If it runs worse, I'll assume their good. I figure this way is better than throwing money into replacing sensors that aren't bad.

[72 CustomCamper]

It didn't show any codes and the light doesn't come on, at least not for that reason, but the reader showed that the O2 sensor is stuck in open loop...

Chuck

[clinebarger]

A non-heated oxygen sensor (one wire) has to be at least 600 degrees for it to work. so the computer will go in to open loop at idle or if the engine is cold.
Thats why they came out with heated oxygen sensors to get closed loop faster and stay there. Check your MAP sensor vacuum line, fuel pressure (9-14psi) you got to have a tee that goes where the filter is. check TPS voltage 0.20-1.25vdc closed throttle to 4.50-4.99 full throttle. check the grounds on the themostat housing and intake bolts. check for vacuum leaks. hope this helps

[92470]

Originally Posted by 1972SuperCheyenne

If it had a stored code in it the light would come on and stay on. Since it is not OBD2, once you turn the key off and re-start your truck, the code is erased. Sounds like your throttle body may be leaking down causing a flooded situation that clears up once run for a minute. When you turn the truck off, remove the air cleaner and look down into the throttle body (dont move throttle) and see if there is fuel dripping. Could also be a faulty coolant temp sensor for the ECU. Good luck and hope you get it fixed.

Tonight I am going to start the truck as suggested and then after turning it off, check for dripping fuel. If it's dripping, it would be dripping on top of the valves right? What I did last night though was just open the valves by hand and look down in the bottom of the intake. There was fuel pooled at the bottom. Not alot, but pattern of the intake bottom looked like the element on a stove (circular pattern), and the fuel was standing in those grooves. Should it be dry? It hadn't been started for 24 hours. I'm also going to do as someone in another post suggested and put a timing light on the injectors when it's running and see what the pattern looks like. Currently, white smoke when it starts for the first time, and a really heavy gas smell always. Coolant temp sensor and idle air valve both new.

[Captkaos]

Turning the truck off doesn't erase the codes, disconnecting the battery for at least 30 seconds will erase the codes.

If you want to see what codes are stored, find the ALDL connector (to the right of the parking release) and put a paper clip in the A and B terminals (top right 2 holes) turn the key to on and count the flashes.

It will flash the code 3 times and 12 is always first. The way is lights is light.....pause..... light, light, 3 times. If yours flashes 12 the whole time you have no codes.

you can decode them here;
http://www.troublecodes.net/GM/

44 or 45 would indicate a problem with the O2.