73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: ron85C10 on February 23, 2012, 09:06:30 pm
-
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???
-
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?
-
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.
-
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?
-
Yeah its a quadrajet.
-
$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.
-
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.
-
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.
-
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.
-
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.
-
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://troublecodes.net/GM/)
http://www.gmtuners.com/OBD1_DTC.htm (http://www.gmtuners.com/OBD1_DTC.htm)
Other common issues are poor ECM grounds and poor ECM connections. Check both!
-
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??
-
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.
-
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.
-
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.
-
The pictures Vile asked for would be very helpful. I also wonder about the check engine light not staying on when you turn the key on...what do you mean by that? Does it just flash on for a second or something more intermittent? That and the fact that it flickers while driving make me think poor ground to ecm or poor connection to the bulb socket in the dash.
-
Here you go im also
-
Yeah it doesnt stay on when the key is in the on position with engine off. Hope these are helpful. Where would i check for proper grounding? Also the bulb to check engine is new.
-
So key on engine off, the check engine light doesn't come on? Elaborate
The Assembly Line Communication Link (ALCL) is a diagnostic connector located in the passenger compartment (Figure 2). It has terminals which are used in the assembly plant to check that the engine is operating properly before it leaves the plant. Terminal "B" is the Diagnostic terminal, and it can be connected to terminal "A", or ground, to enter the Diagnostic mode.
If the Diagnostic terminal is grounded with the ignition "ON" and the engine stopped, the system will enter Diagnostic Mode. In this mode the ECM will:
Display a code "12" by flashing the "Check Engine"/"Service Engine Soon" light (indicating the system is now operating). A code "12" consists of one flash, followed by a short pause, then two flashes in quick succession. This code will be flashed three times. If no other codes are stored, code 12 will continue to flash until the Diagnostic terminal is ungrounded:
The engine should not be started with the Diagnostic terminal grounded, because it may continue to flash a Code 12 with the engine running. Also, if the test terminal is grounded after the engine is running, any stored codes will flash, but code 12 will flash only if there is a problem with the distributor reference signal.
Display any stored trouble codes by flashing the "Check Engine"/"Service Engine Soon" light. Each code will be flashed three times, then code "12" will be flashed again. If a trouble code is displayed, the memory is cleared, then the engine is run to see if the code is a "hard" or "intermittant" failure. If it is a "hard" failure, a Diagnostic Code Chart is used to find the problem. If it is an intermittant failure, the charts are not used. A physical inspection of the applicable system is made.
Energize all ECM controlled relays and solenoids (with some exceptions, as noted in "Component Systems"). The mixture control solenoid is pulsed for 25 seconds or until the engine is started, whichever occurs first.
-
CHART A-6 - WON'T FLASH CODE 12
This step checks for short to battery voltage in wire to Terminal "C" or faulty lamp driver.
Normal voltage reading is 9-11 volts.
This step checks to see if problem is related to the ECM or the lamp driver.
Normally, grounding Terminal "C" should turn lamp "OFF". If it does, the problem is related to the ECM and its wiring. If not, it is related to the lamp driver and its wiring.
Grounding Terminal "G" at ECM and finding light "ON" indicates an open in the wire to Terminal "C" of lamp driver. Normally, grounding Terminal "G" should turn lamp "OFF".
This step checks for open in wire from ECM to test terminal in ALCL connector. The lamp should flash Code 12 when Terminal "5" is grounded.
Checks for proper voltage supply to ECM. Both should read over 9 volts. Terminal "C" is ignition and Terminal "R" is constant battery for long term memory.
Checks for a bad ground to ECM - Terminals "A" and "U" are connected together in the ECM.
This step distinguishes between a faulty ECM and PROM. Normal response is for Code 51 to flash even though the PROM is not installed in the ECM. If it doesn't, it means that the ECM is faulty.
-
Nice thats some good reference im gonna try to work on it tomorrow and check the alcl under the passenger side. Also i took some other pics and found some wire that is disconnected and i dont know what its from. But here you go maybe you could ID this conundrum.
Oh also the check engine light does not stay lit when the key is in "on" and engine "off" and from my own understanding isnt it supposed to stay lit? And when i try to ground terminals A to B to place it in "diagnostic mode" the light does not flash any codes. Hope that kinda makes my problem a little clearer.
-
So the check engine light does not illuminate at all? Check the bulb
-
The bulb is new and flashes sometimes when i am driving.
-
the bulb could have a bad ground. that hapens to me all the time on my dash lights, and if u wiggle them or tap them they will start working again. it might be ok though, just another thing to check...
-
Well i finally gave up. It seems that the guy that igot the truck from had a really nice alarm with remote start so theres extra wires in the engine bay and all kinds of half way wiring. So i just decided to take the stock carb out and put in an aftermarket one. Any suggestions? I have a 305.
-
A rebuilt regular quadrajet is probably best. I love my Edelbrock 1406, though, and you can get them at most auto parts stores, slap it on, and be done with it. It will run pretty well out of the box, but as you drive it you may find that you want to get a tuning kit to get it just right. I did that recently and its much better than before.
-
Cool man thanks thats exactly what i want to do is to just be done with it. Im mainly going to be using my truck for work and right now the whole problem was getting it to not suck up so much gas. Im getting like 6-7 mpg right now and gas prices dont seem to be going down.