Bypassing emissions computer (1 Viewer)

[Advent]

Somewhere in the jumbled bunch of wires going to the emissions computer, one has fried. It took the fuse for the fuel cutoff solenoid and voltage regulator with it.

I'm thinking of wiring up a setup where each device has it's own fuse. That's all well and good, but one of the wires for the emissions computer is still toast.

How hard would it be to hook the secondaries up so that they're only controlled by vacuum, not vacuum controlled by the emissions computer?

The HEI is already running straight vacuum. I'm running a late '77 or '78 carb (can't remember which) on a '76 2F, all other smog components stock. It seems to me like I can just bypass the computer and make the engine run well, basically shutting off the emissions components. I'm pretty sure I could pass a sniffer with them shut off, but I won't pass if they're removed.

Has anyone done anything similar? It's basically a desmog without actually removing anything. But I couldn't find in any of the diagrams where to run the vacuum for the secondaries. I assume this way that the 'full throttle switch' would be unneeded as well?

 

[Pin_Head]

Everything on the emissions computer is fed from the 10A engine fuse, so there should be no possibility of burning a wire. Either one of the wires shorted to a non-fused wire or somebody wired it incorrectly bypassing the engine fuse. Dig in to the harness and find out what happened, then replace the wire. Make sure that nothing is connected to the non-fused ignition wire.

 

[Advent]

I'm honestly just guessing that that's where it shorted. I thought when the fuse blew that it was just the charging fuse. I replaced it with a 30a (closer to the output of the alternator I thought) and saw smoke come from under the dash.

But it just makes me want to move along with my project to eliminate as much smog crap as possible and still sneak through inspection.

 

[Pin_Head]

I replaced it with a 30A (closer to the output of the alternator I thought) and saw smoke come from under the dash.

.

That would explain it. The alternator output doesn't go therough the engine fuse or any other fuse. It is fused by the fusible link between the alternator and battery.

You really don't want to put in any other fuse than the recommended size or you run the risk of frying your wiring.

No matter, you still have to check all the wires in the harness to make sure that they are not shorted or replace the part of the harness that is burned. It is a bigger problem than just bypassing the smog computer.

 

[Mark W]

How hard would it be to hook the secondaries up so that they're only controlled by vacuum, not vacuum controlled by the emissions computer?

The emissions system has nothing to do with actuating the secondaries. That is all internal to the carb and is affected only by the throttle linkage position and the vacuum in the intake.


Mark...

 

[Advent]

If I run the fuel cutoff and voltage regulator to switched +12V, then unplug the computer, I've basically done a ghetto desmog?

I've already decided I'm blowing my PFD on re-wiring it correctly...Just trying to figure out how to get the emissions wired (ideally just cutting the wires out and leaving them out).

If the computer has nothing to do with the secondaries, what is the full throttle switch for?

 

[Pin_Head]

If the computer has nothing to do with the secondaries, what is the full throttle switch for?

The full throttle switch tells the engine control computer to open the power valve, which is an auxiliary main jet used only during WOT situations.

W/O the computer, the power valve won't work properly. If you leave it disconnected (open all the time) it will run rich. If you disable the coputer, hook the power valve line to intake vacuum so it will be closed when the intake has vaccuum.

You are better off just fixing all the wiring so that everything will work properly.

 

[Advent]

I think I'll connect it to the manifold vacuum. That's really what I wanted to know, how to remove the computer controls from the carburetor.

I'm going to fix all the wiring but I don't trust the emissions controls to keep from dying on me again...and again...and again...

Is there a way to control the EGR and smog pump without the computer? A particular way to plumb them to vacuum? I'd like to make things as simple as possible.

 

[Mark W]

The full throttle switch tells the engine control computer to open the power valve, which is an auxiliary main jet used only during WOT situations.

W/O the computer, the power valve won't work properly. If you leave it disconnected (open all the time) it will run rich. If you disable the coputer, hook the power valve line to intake vacuum so it will be closed when the intake has vaccuum.

If you disconnect the powervalve from the emissions system and simply plug the port, it will operate normally. That is to say it will open when the intake manifold vacuum drops. All the connection to the emissions system does is prevent it from opening in some cases, sacrificing power for reduced emissions in some limited situations.


Mark...