ecm problem? need help!

[ron85C10]

Hi guys im new to the forum also as a chevy owner i have an 85 C10 shorty with a 305CID stock everything. Well atleast thats what i think. I think i might have a problem with the trucks computer because as soon as the key is in the ignition in the on position, the check engine light doesnt stay on and when i try to get a code read, it doesnt even give me a code 12. Ive been driving it for about 1 month and noticed its giving me bad gas mileage. I think i might have an ecu or ecm whatever problem. Any feedback would be appreciated. Oh one more thing, when im driving, sometimes the check engine light flashes pretty fast???

[VileZambonie]

Do you want to keep it stock? You can increase your performance inexpensively and eliminate the ancient technology you're going to attempt to fix. Where do you live and what are your emissions requirements?

[ron85C10]

I live in cali and i plan on trying to just get it running right. Im on a budget thats why im trying to fix it myself.  Im only getting about 6 to 7 mpg and from what ive heard i should atleast be getting 12 to 14mpg. What do you think i should do? Only thing ive done to it so far was a carb rebuilt done by a chevy mechanic. $#*() had the nerve to charge me 700 bucks. So i dont plan on going back to him.

[87454westernhauler]

I live in cali and i plan on trying to just get it running right. Im on a budget thats why im trying to fix it myself.  Im only getting about 6 to 7 mpg and from what ive heard i should atleast be getting 12 to 14mpg. What do you think i should do? Only thing ive done to it so far was a carb rebuilt done by a chevy mechanic. $#*() had the nerve to charge me 700 bucks. So i dont plan on going back to him.

WOW!! thats more than ive paid for most of my trucks... is the carb a quadrajet?

[ron85C10]

Yeah its a quadrajet.

[bake74]

     $700.00 is a little steep for a rebuild on a carb. good call on not going back.  I don't know where in Ca. you live but I know several shops in Sac. if you are close that I trust.  My Q-jet guy locally is top notch and only bills $200.00 for a complete rebuild, and he is willing to show you or at least let you watch the rebuild so you can learn something.

[ron85C10]

Thats cool but the problem is not the carb since i already paid for the mechanic to fix. I took it back and i told him i was getting poor mpg and he said that he tuned the carb and thats not the problem. He said it might be the computer and since i dont want to give him anymore of my hard earned cash im trying to fix the problem myself. He did point me in the right direction though because I tried putting the truck in diagnostic mode (sticking a paper clip in the OBD) and it doesnt even make the check engine light flash at all. So im assuming that there has to be something wrong with the computer. Any feedback on that would help thanks.

[thirsty]

Oh one more thing, when im driving, sometimes the check engine light flashes pretty fast???

I'm not a computer guy but doesn't that mean misfire on the older stuff?
I may be wrong, just noticed it in the thread. I'm sure somebody that is up on that stuff will clarify.

[frotosride]

The good thing for you is that you don't have a '87 or newer truck because no TBI means less thing for the ECM to control so less to check. Here is a pin-out chart of all the things that you ecm controls...This should give you an idea of what to check and make sure is functioning properly just obviousely omit the pins that your truck isn't equipped with.
http://www.chevythunder.com/fuel%20injection%20ecm%20pinouts.htm#1985 pinouts (ecm #1226870)

This may be an obviouse answer but you never know so thats why I ask. Whan is the las time you replaced the plugs, wires, distributor cap and rotor button. Also, have you checked you distributor's ability to advance timing and take it away as needed. I'm not sure if the dizzy on '85s are completly computer controlled or if you still have a vaccum advance.

[frotosride]

Your ecm isn't actually throwing any codes if all you see is code-12. Code 12 is a delimiter or marker code to show where the error code string begins and ends. So if it were a real problem/code like say code-44 (exhaust too lean) then it would loge each instance proceeded by 12 and ending in 12. So if the exhaust went lean 6 times it would look like this 12 44 44 44 44 44 44 12. The reason for the 12 is say tou have two problems at once. it will seperate the codes, ie... ehaust lean and oxygen sensor circuit(code 13) it would look like this 12 44 44 44 44 12 12 13 13 12 12.

[bd]

OBD 1, Code 12 = "No tach signal"

With key ON engine OFF, code 12 signifies a properly functioning diagnostic mode.

With key ON engine ON, code 12 will not flash.

Any given code will flash three consecutive times - long pause - then flash the next numerically higher code three consecutive times - long pause - and so on, until all codes have displayed.  At that time, the sequence will start over, beginning with the lowest numerical code.

Before you condemn the ECM, make sure you are "shorting" the correct ALDL terminals: with the key ON engine OFF.  Refer to the following links for an image of the ALDL and code specific definitions:

http://troublecodes.net/GM/

http://www.gmtuners.com/OBD1_DTC.htm

Other common issues are poor ECM grounds and poor ECM connections.  Check both!

[bd]

Do you want to keep it stock? You can increase your performance inexpensively and eliminate the ancient technology you're going to attempt to fix. Where do you live and what are your emissions requirements?

Vile, finish your thought....  What do you have in mind??

[ron85C10]

Ok guys thanks for the feedback the only thing ive done so far was spark plugs, oil change, radiator flush, i havent done anything with the distributor. Ive tried putting the computer in diagnostic mode and i know it should flash code 12 (3 times to be exact) but it doesnt give me anything the service engine light doesnt even stay on with the key in the on position. As far as driving the truck its pretty good no backfire so my guess is that theres nothing wrong with the timing. Im still gonna doulbe check grounds and ill get back to you guys and thanks alot for the links.

[bake74]

I took it back and i told him i was getting poor mpg and he said that he tuned the carb and thats not the problem. He said it might be the computer 

     You gave him $700.00 to fix your carb.  you do not want him to do more work for you because you think he ripped you off.  So now you believe him on this issue ?
     Take it somewhere else and have someone else give you a second opinion.

[VileZambonie]

Do you want to keep it stock? You can increase your performance inexpensively and eliminate the ancient technology you're going to attempt to fix. Where do you live and what are your emissions requirements?

Vile, finish your thought....  What do you have in mind??

If he's subject to visual inspection that requires factory equipment in tact functioning I won't even go there.

On another note: post a few pix of your carburetor, your VECI label, The data link connector and the engine compartment so we can see exactly what your set up is. Change the wires cap & rotor.