Emissions quest/question

[Jsmay]

hello, recently a new member here.. I picked up a very well maintained 1992 chevy c1500 with 305. It was a one owner truck, the only issue I have is here in TN I have to pass emissions. Basically for this year just a visual (catalytic convert) and tail pipe test. Well the owner told me, just unplug this wire(tan/black) because with it connected it won't pass. Seems to run rich.. ok, I disconnect and it passes.. then I wondered.. what's that wire. Well I found out it's the timing bypass.. now I've gotta figure out why that's being done.. so I had it scanned and got a code 42.. is it simply the ignition control module in the distributor? Can I be that lucky?? Any help would be great. Thanks Jason

 

[Breakdown]

The wire you disconnected is the electronic timing control from the computer. By disconnecting it you locked your advance to 0 degrees (or should be at 0 degrees if your base timing is set correctly). The only reason I can think this would have been done is he might have the advance set to a different baseline that the computer pushes, which gives a bit more power, but at the expense of running a tad rich. Again, just guessing. Disconnect the wire, and hook a timing light up and see if its sitting at 0 on the timing tab with the engine running.
The only time Ive ever heard of pulling it is when setting initial timing. After setting the initial, turn the truck off and re-connect the wire, you will see the timing has jumped a good amount.
Someone else chime in on this and throw some more ideas out there.

How does it run with the wire connected? Wonder what the smog shows when its hooked up....

 

[Jsmay]

The wire you disconnected is the electronic timing control from the computer. By disconnecting it you locked your advance to 0 degrees (or should be at 0 degrees if your base timing is set correctly). The only reason I can think this would have been done is he might have the advance set to a different baseline that the computer pushes, which gives a bit more power, but at the expense of running a tad rich. Again, just guessing. Disconnect the wire, and hook a timing light up and see if its sitting at 0 on the timing tab with the engine running.
The only time Ive ever heard of pulling it is when setting initial timing. After setting the initial, turn the truck off and re-connect the wire, you will see the timing has jumped a good amount.
Someone else chime in on this and throw some more ideas out there.

How does it run with the wire connected? Wonder what the smog shows when its hooked up....

I did check that and it is set correct. It runs fine connected and I don't get any check engine lights.. but it doesn't get great gas mileage... just want it right lol. Thanks

 

[Breakdown]

Great gas mileage? Buy a Volkswagen lol. I know the feeling on wanting it right. Previous owner had bypassed or disabled almost all the emissions except the charcoal canister on my 95.. I replaced a good portion of the things he bypassed, not because I had to, but because I cant stand seeing crap bypassed or not hooked up, especially when the things he bypassed were 30$ parts and took ten minutes to fix. Now by not so great gas mileage, what are you referring too. Heck, the EGR valve alone if bypassed actually lowers your mileage unless you program it out of the chip (actually noticed almost a 2mpg difference in mine when I undid the bypass and put a new valve in)
A couple things Ive found that helped me so far with mileage (was getting 10-12 mpg, now getting 16-17) were full tune up (wires, plugs, cap, rotor, pcv, and filters) and believe it or not, a 12 dollar AC-DELCO throttle body rebuild kit. Came with everything you need to completely tear down and rebuild the entire throttle body, minus the spring for the fuel pressure regulator, and the injectors. If you go that route, fill a small bowl with seafoam, and let your injector tips sit in it while your cleaning and rebuilding everything else. Saw a big improvement in the spray pattern on the injector.
Heck replacing the old thermostat and the Coolant temp sensor actually showed some improvement as well.
Just my two cents.

 

[Jsmay]

Ha yeah I guess I should have worded the gas mileage better. I just want the thing to run efficient. I'm gonna start with the ignition control module. Seems like that has come up in other searches and is related to that code. I'll check the plugs and also inspect the cap and rotor for corrosion. Like I said it seems to be running fine, no idiot lights, just the idea of unplugging the timing control is weird to me. Why not fix it right.

 

[Blackwater]

I was getting 17 on the highway, now get 19. Then again I redesigned my whole drive train. Pulls like a mule and gets good mileage.