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

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!

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

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..

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

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.

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

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

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

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

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

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

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.

http://z.about.com/d/autorepair/1/0/..._connector.gif

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

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

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.

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

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.

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

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?

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

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....

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

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?

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

If it doesnt have the electronic carb and the rest of the stuff associated with that. If you cant find a diagnostic port and theres no computer just take the bulb out of the dash so it doesnt light up anymore.

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

Thats what is going to happen but I am one of those "figure it out" types so the search goes on!

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

Theres probably nothing to figure out. If theres no computer and no sensors to read. The light is simply lit because it has power to it from somewhere. trace some wires under the dash. If the choke light acts up too there could just be a wiring issue behind the dash or cluster.

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

It comes on only at higher speeds/longer drives (normally on the interstate)
It will go back out when you shut the truck off and it will stay off untill you are back on the interstate. It never comes on driving around town.

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

another possibilty could be the O2 Sensor... just a thought...

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

I will look and see if I have them and report back. Any thoughts where they would be other than the exhaust? Thanks!

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

Theres only going to be one and it should be near the exhaust manifold in the y pipe. You said you have no computer though. If thats true theres nothing for the o2 to send signal to.

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

My thoughts exactlt!

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

The signal for the light should come directly from the computer. Like I said I think your chasing a ghost and theres a short or electrical problem in the dash itself.If theres for sure no computer then the light shouldnt be lit.

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

.. 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...

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

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

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

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

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

yes that is

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

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.

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

yup it's my 85

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

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

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

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

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

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.

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

That doesnt look like a 85, Looks like a 87-91? But to answer your question that is the main harness to your ECM.

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

mine or his dosn't look 85

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

I think he means yours....with that fuel pump relay I believe it should be a throttle body that started in 87....Thats probably what he is talking about.

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

Well i was told it was a diesel when bought new.but vin says 454 2 wheeler and it's C20-4X4

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

http://67-72chevytrucks.com/vboard/s...d.php?t=416576

FYI is another 85 not sure if he's tbi too tho,i just asked him

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

I have never seen a 85 chevy/gmc C/K/S/T/M platform have TBI. Even the 85 4.3s had feedback Quadrajets on them.

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

Can you post a photo of your 'fuel mixer' please - suspense is killing me!!!

//RF

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

I'll get prettier pics this weekend if you want,but the 85 tbi etc was all matching my 87 that i had.I've only since finding this site i've explored rpo's and vin #s,and yes as you say it shouldn't be(just read to do it u have to shave bolts and other stuff?)........So when i turn the key i shouldn't hear the fuel pump humpin,before startin, should be manual pump?And no wires in there either.hmmmm

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

would i have the computer above the glovebox with out tbi,as it would seem it was born with a 454 but sadly it was removed.replaced with a 350........i am asumming the puters don't interchange....i figured the 2x to 4x4 frames/driveline were changed.........but to change the rest?Got any ideas how i would check/know........i posted/started some pics in a build thread...........16 inch tires if i read right?

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

The CCC (computer controlled carb) used ECM - which is located above globe box. It possible to take later 87+ TBI 350 with ECM and harness and swap it in place of CCC without great deal of effort.

//RF

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

Have you run your VIN to confirm its year?