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Peter, in the early 70's I remember folks rigging the headlights so that they can be turned on, and not pop up (call it a poor man's dog light setup lol), but I think that is how I messed up the by-pass switch. :chuckle

The reason I asked is that my by-pass switch stopped working like it should. It is like it developed an internal leak, and it is not working as it should. You can mark the hoses at the switch (to remember where they go), and connect them in a direct way or plug them, and see if that helps.

The sensor was the culprit in my Vette. It would be operating correctly at idle, but at power, it would close the flap doors and cause a rich condition ([sorry, closing the flaps would NOT be a lean condition] Dyno proven). The mixture ratio would fatten.

When you say backfire, do you mean from the throttle body or from the tail pipe? If throttle body, the backfire is caused by a lean condition. If from the tail pipe, it will likely be timing related. :)

Keeping them the way they are is one option, but restoring would also be good. Nowadays, everything gets restored. ;):D

Is the by-pass vacuum switch pulled (beneeth dash aligned with steering column?

Ok, so if the Thermac is not working properly, then disconnect and plug the hose that goes to the stuck-open vacuum motor, and that way you don't loose vacuum signal. You could perhaps just leave them open, but the problem is that they are spring-pressure closed, so the passenger's side may...

Peter, First of all, she is looking sweet! :) Secondly, you are much better at the electronics than i would ever be, but I wonder if it would still doing the problem if you were to disconnect/swap the O2 sensor to stock one and only one O2 sensor as in stock. My premise is that if you are...

Tator, I hope you are not ready to throw the towel. It perhaps improved mileage, but just as illustration, I bumped Gail's compression ratio to 9.5:1, and around town I get 14.5 MPG....albeit with a 4th automatic gear. Nevertheless, I was never getting 12's MPG when stock. You should be able...

Rough operation and no codes seems to be vacuum leak. But it could be ignition related. A bad oxygen sensor could would cause a problem, but it should trigger a code.

The 81 Vette uses a plate between the manifold and the EGR to avoid contacting the valve cover (in fact, it will not install flush if using stock valve covers or unmodified). The plate is basically in the same shape profile of the EGR's base. It takes a gasket between the plate and the manifold...

No need to warm up engine. Just turn the ignition key to on, and then with a multi-meter, check voltage from green wire to ground. It should read 12 VDC +/- 0.5 volts. If you do get 12 VDC, then start engine and watch the chock plate. Kick the gas pedal, and see if chock carb plate opens. If it...

Alright, Nate! Good news! I am glad it is only the headlights, although it means you can only enjoy it during the day until you can fix the headlights. If you can, order the actuator seals for the headlights. And Dr. Corvette offers a complete set, but you could just order about 10 feet of...

Nate, presuming that the vacuum fitting is the one used on an L81 with auto transmission, the fitting has three ports. The top port is for your transmission modulator (a manual transmission does not have a top port for this fitting). The driver side port should be the one for your headlights...

Alright, Nate. You will find many helpful folks in here. Since your headlights are not popping up, one easy way to isolate the vacuum leak is to disconnect the hose for the headlight mechanism at the manifold fitting (between carb and distributor), and plug it at the manifold. Then start...

Nate, There are several threads concerning vacuum leaks throughout this site, but the following link will get you in touch with the L81 Registry: L81 Vette Registry Forum - Corvette Action Center - Corvette Forum : CorvetteActionCenter.com Corvette Forums Concerning vacuum leaks, yes, it...

Hammer,I have an L81. Going from memory alone (warning!!! lol :L ), the black wire went to one post of the pressure switch, a shorter white wire went from the remaining post to the other pressure switch post, and the other long wire went to the remaining post on the second pressure switch. I...

do you see that plug to the right (on the image) to the pressure sensor? That's where the other one goes. However, I am not sure if both are rated to the same pressure. I am still searching my photos for the image of my transmission.

I'll look to see if I still have images of my transmission's wiring, but the two tangs you have are supposed to be one per pressure switch. The switch itself grounds to the valve housing and completes the circuit. If you look at the shop manual's page 7A3-15, figure 7A3-36, lower right-side...

Hammer, did your transmission valve body had one or two pressure switches? The wired it for second and third gear to lock up. Mine had that extra wire for the additional lockup.