HELP...1986 C20 5.7....smog removed,,,Check engine light???

[72freak]

I dont have any experience with this crazy pre-87 emissions stuff. I dont have another one close by to compare it to.......We picked up this crew cab a few weeks ago.....running great. It looks like there may have been a smog pump at one time that was cut off??? A few tube things up top on each side and two plugs that go no where. It will throw a "check engine" light when on the highway. I am sure it has something to do with the unplugged stuff.

1) any pictures of what is should look like?
2)Will the plugs that arent hooked up effect this check engine light?
3)If so can they be jumped off?
4)Where do these pinched off tubes up top go to?
5) CHECK ENGINE LIGHT....are you kidding me...WHY? Whats it supposed to be telling me?

Im sure I will eventually change the intake, carb and exhaust, but for now Id like to make sure its right.

Thanks for your help!

[CaliDude76]

Depending on your state, I don't know if you are required to take and emmisions test.. but if you don't... I would just unplug the bulb to the "check engine light",... most of these lights were hooked up to the emmisions system anyway (mine is)... seeings that yours was all hacked to peices (do you need it all back together?)... could be anything setting it off..... I have an 84 with all the smog stuff hooked up (strict smog laws here in Cali)... would show you pics.. but I'm pretty sure the plumbings different between 84's, and 86's..

[72freak]

Originally Posted by CaliDude76

Depending on your state, I don't know if you are required to take and emmisions test.. but if you don't... I would just unplug the bulb to the "check engine light",... most of these lights were hooked up to the emmisions system anyway (mine is)... seeings that yours was all hacked to peices (do you need it all back together?)... could be anything setting it off..... I have an 84 with all the smog stuff hooked up (strict smog laws here in Cali)... would show you pics.. but I'm pretty sure the plumbings different between 84's, and 86's..

Yep...bulb is coming out. No...we dont need a smog test on it here because of its GVW. it came from Texas so I dont know if the under hood would be the sameor not.

[CaliDude76]

Originally Posted by 72freak

Yep...bulb is coming out. No...we dont need a smog test on it here because of its GVW. it came from Texas so I dont know if the under hood would be the sameor not.

.. yeah, you should be good!.. good luck with that

BTW.. Dude.. how big of a garage you got?? geez.. you got some rides LOL

[Slonaker]

The C10 in 1986 didn't have a check engine light unless it was a California emissions model. Your C20 may be a CA emissions model.

Slonaker

[rfmaster]

Originally Posted by 72freak

I dont have any experience with this crazy pre-87 emissions stuff. I dont have another one close by to compare it to.......We picked up this crew cab a few weeks ago.....running great. It looks like there may have been a smog pump at one time that was cut off??? A few tube things up top on each side and two plugs that go no where. It will throw a "check engine" light when on the highway. I am sure it has something to do with the unplugged stuff.

1) any pictures of what is should look like?
2)Will the plugs that arent hooked up effect this check engine light?
3)If so can they be jumped off?
4)Where do these pinched off tubes up top go to?
5) CHECK ENGINE LIGHT....are you kidding me...WHY? Whats it supposed to be telling me?

Im sure I will eventually change the intake, carb and exhaust, but for now Id like to make sure its right.

Thanks for your help!

In the Photos it looks like some one really hated AIR system - (air injection) - the two plugs were used for AIR diverter valve which by-passed air from the AIR pump when not commanded to inject air into exhaust manifolds. As for check engine light I have to assume that you have CCC (computer controlled carb). Take a look at you carb it should have a model cast into it - probably M4MED or ???. Inside cab, look left of the steering column for ALDL connector.



If you have one this also means that you have ECM controlling carburetor. To determine what is causing SEL to be one - short pins A&B with a paper clip and turn ignition on, but do not start engine. SEL should blink code 12 3 times followed by the offending DTC.

//RF

[Jonboy]

Just unplugging the smog will not set a CEL. You have something else going on. Pull the codes like RF said, and report back. I bet it is something else entirely.

[72freak]

Thanks for the informative info!!! I will run out in a sec and look...HOWEVER last time I checked I DID NOT see a plug in under the dash. It was the first thing I looked for when that crazy check engine light came on. ill check to make sure it has not been unscrewed and tucked up in the dash.

[72freak]

There is NO OB port under the dash and NO electronic carb.

No port=no codes to repot.

Lots of smog stuff, Check engine light and I cant remember if i mentioned it before....it also has a stupid CHOKE light that glows now and again. What was GM thinking?

[CaliDude76]

Originally Posted by 72freak

There is NO OB port under the dash and NO electronic carb.

No port=no codes to repot.

Lots of smog stuff, Check engine light and I cant remember if i mentioned it before....it also has a stupid CHOKE light that glows now and again. What was GM thinking?

ehhh.. it was the 80's,... they were trying to be all "sophisticated" with the computer controlled stuff.. but bombed apparently.. I mean look at the early 80's Caddy's with the 4,6,8 HT electronically controlled engines that failed miserably.. Got a hand it to em for giving it a shot. They got better with time though....

[72freak]

Any other ideas why it would be throwing a check engine light?
If unplugged smog wont do it and it does not have a computer.....what throws the light?

[CaliDude76]

.. I could be spit-ballin here... but if it had smog stuff,.. and a check engine light.. it has to have a brain(ECM) somewhere?...no? Did you check under the dash,.. behind the glove-box? I know that's where mine is located...

[motornut]

now i'm curious........not up there?

[72freak]

I cant tell what I am looking at......is that behind the glove box?

[87 chevy silverado]

yes that is

[clinebarger]

My 85 3/4 ton Suburban had the same emissions equipment, Dual smog pumps, No catalytic converters, No EST, No feedbak Quadrajet, Dual exhaust, Leaded gasoline compatible.

There is a "smog pump control module" on the firewall. Heres a pic of mine, The circle is where it used to be. It grounds the "check engine light" bulb when a fault is detected in the "Air Diverter solenoid" curcuit. Unplug the module, the light should go out.

[motornut]

yup it's my 85

[72freak]

Originally Posted by clinebarger

My 85 3/4 ton Suburban had the same emissions equipment, Dual smog pumps, No catalytic converters, No EST, No feedbak Quadrajet, Dual exhaust, Leaded gasoline compatible.

There is a "smog pump control module" on the firewall. Heres a pic of mine, The circle is where it used to be. It grounds the "check engine light" bulb when a fault is detected in the "Air Diverter solenoid" curcuit. Unplug the module, the light should go out.

WOW.....great info...I had just gotten back from some more picture taking and research and took a picture of that little box on the firewall to find out what it was and if that could be the culprit....I plan to give it a shot next time I drive it. As far as mine goes here is some more info......

Stock true dual exhaust with no Y pipe, no cats and no O2 sensor. It is very obvious this is the original exhaust by the shields all over the pipes.

Absolutley no computer behind the glove box.

[clinebarger]

Originally Posted by motornut

now i'm curious........not up there?

The shiny aluminum box with the rusty strap holding it up is your ECM.

[motornut]

my fuel pump relay is there on my firewall,whats all the wires on the right?looks like fun there

[HOGDADDY]

Originally Posted by motornut

now i'm curious........not up there?

That box above the heater/ac box is the computer (ECM). You will need to change out distributors to an older pre-81 HEI and if carb has wires for mixture it will need to be changed.

Also in pic looks like your heater/ac diverter valve is broken.

http://67-72chevytrucks.com/vboard/s...diverter+valve

[kristian_dancer]

Ihave been haveing exactly the same problem,

I have an 86 c20 dually converstion. Check enginelight would come on on when I went over 55 then off every time i turned ignition off.
Now it stays on.
I have no plug for code reading under dash.
No obvious smog equipment under the hood.
Trucks runs fine other than needing a break seal replacement on the dually rear end.
All I want to know is that im not killingthe truck and that the check engine light is not coming on for a good reason like trans temp or oil pump failure etc.

[clinebarger]

Originally Posted by kristian_dancer

Ihave been haveing exactly the same problem,

I have an 86 c20 dually converstion. Check enginelight would come on on when I went over 55 then off every time i turned ignition off.
Now it stays on.
I have no plug for code reading under dash.
No obvious smog equipment under the hood.
Trucks runs fine other than needing a break seal replacement on the dually rear end.
All I want to know is that im not killingthe truck and that the check engine light is not coming on for a good reason like trans temp or oil pump failure etc.

Did you see post #29? Do you have the "smog pump control module" on the firewall?