81 Rough idle and surging

[LT4man]

The lead is a green connector and does not come directly off of the M/C solenoid plug. The lead is spliced in the wire that goes to the plug a few inches back and sticks out through the black wire loom. Follow the 2 wires from the M/C solenoid back to the loom and look for a green connector sticking out of the loom that is not connected to anything.

Connect the Dwell Meter lead to this connector and the ground the Dwell Meter ground wire to a good engine ground.

If you do not find it there, it might be lying between the air pump and the A/C compressor in a wire loom. It can be wrapped in electrical tape. Look for a bulge. Unwrap the tape and you should be looking at the connector!

SAVE THE

 

[GerryLP]

Ok Bill,

I found a dated image of my engine before going in into the Vette...

The connector is near the lower right corner of the image...

The Dwell green wire connects to this one, and the Dwell ground wire goes to ground. Again, first you connect the green Dwell wire to the green connector on the image, and then the ground to ground. To stop using the Dwell gauge, disconnect the ground (place it biting on a rubber hose), and only then, disconnect the Dwell green wire.

The Dwell needle should hunt small distances on the scale. If it does not, then wait until the engine is nice and warm. You only use this to set the air valve. Reference some of the images that I uploaded for precise instructions. You could also buy this book, and it has all the instructions...

http://www.factoryautomanuals.com/ProductDetails.asp?ProductCode=75408

GerryLP:cool

 

[GerryLP]

Gerry: No can do on the TPS plug. I can see the top of the adjusting screw and thats it. there is metal around the screw and nothing to pry against. I worked on it for a long time with no results..... I must hope it is within range by the factory settings...
Bill

Are we talking about the same thing???

 

[Bills money pit]

Gerry:
Great photo and info. I will attempt to locate the green connector after work. Thanks for taking the time to help me.
Also, we are talking about the same TPI adjusting port. I drilled a small hole and tried to thread a screw to pull it out. The plug was in so tight the screw would pull out. After many tries, I drilled the plug until I could see the top of the adjusting screw. I thought I could dig the remainder of the plug out. Now there is nothing I can do to remove the remains of the plug.
Bill

 

[Bills money pit]

Let me get this straight. Using the three wire TPS connector, jump each of the three wires, wiring harness three wire connector to three wire connector on carb. (male to female setup) Assuming the top wire is A, second is B, bottom is C. Do I put one lead of the volt meter on B and the other on C to get a reading?
Thanks!
Bill

 

[GerryLP]

Let me get this straight. Using the three wire TPS connector, jump each of the three wires, wiring harness three wire connector to three wire connector on carb. (male to female setup) Assuming the top wire is A, second is B, bottom is C. Do I put one lead of the volt meter on B and the other on C to get a reading?
Thanks!
Bill

Correct!!!!!

p.s. Like it says on page 6C4-9, par. 6, of the L81 shop manual, "With ignition on..."

Check-out this cartoon...

 

[GerryLP]

Gerry: No can do on the TPS plug. I can see the top of the adjusting screw and thats it. there is metal around the screw and nothing to pry against. I worked on it for a long time with no results..... I must hope it is within range by the factory settings...
Bill

Bill you drill (5/64" drill bit) a small hole into the aluminum plug. Screw in a #8 screw. Using a flat screw driver, pry between the head of the screw and the adjacent surface. The plug is perhaps 3/8" - 1/2" long.

 

[GerryLP]

Bill,

We both need to know if the factory anti-tamper plugs are still installed on the idle mixture adjustments screws. The way to remove them is shown on page 6c4-9, figure 6c4-10a. The reason for this is that if the dwell check does not check-out, the procedure tells you to re-adjust the idle mixture screws.

So basically, you want to start the idle mixture screws at the maintenance setting given in page 6c4-33, figure 6c4-45.

Then, you check the rich screw for the mixture control IAW page 6c4-20. In essence, the float setting is +/- 1/16" of this eye-ball check. That gage shown on the figure, is the same one part of Thexton tool kit 370. You could make one out of a short metal ruler graduated with 1/32" increments, for what matters is that you get approximately 4/32" when you lightly plunge the float (of course, you don't do this with the engine running!!!) by pushing onto the ruler (again, lightly until you feel where it stops plunging).

For the air valve check, follow the steps on the shop manual on page 6c4-7, "Idle Air Bleed Valve Adjustment". The tools part of Thexton 362 and 370 are mostly needed if you do an overhaul of the carb. But if you just want to make sure that the settings are as required, then the adjustment procedures are sufficient. That "J" hook looking gage on the link I posted on the first page (post #10) of this thread is used for setting the air valve screw to the initial point during build-up of the carb or before starting the air bleed valve adjustment procedure.

Good luck!

 

[Bills money pit]

Gerry:
Your help is most appreciated. The TPS adjusting screw is exposed, but has metal around it from plug. Cannot get it out, nothing to hold...
Also, the wire to use for the dwell reading was tucked in the loom. It is the only green wire not connected to something. I thought it was at one time connected to the choke, but there is now another wire going to the choke cover. Due to the fact the green wire did not have a green connector, I was not sure it was the one to use for the dwell check. The previously mentioned green wire is without the green connector. Seems some one cut off the connector and put a crimp spade connector. I do believe the wire is the correct one to use as it is not connected and there is no other green wire not being used. The idle mixture plugs have been removed.
Thanks!
Bill

 

[GerryLP]

Gerry:
Your help is most appreciated. The TPS adjusting screw is exposed, but has metal around it from plug. Cannot get it out, nothing to hold...
Also, the wire to use for the dwell reading was tucked in the loom. It is the only green wire not connected to something. I thought it was at one time connected to the choke, but there is now another wire going to the choke cover. Due to the fact the green wire did not have a green connector, I was not sure it was the one to use for the dwell check. The previously mentioned green wire is without the green connector. Seems some one cut off the connector and put a crimp spade connector. I do believe the wire is the correct one to use as it is not connected and there is no other green wire not being used. The idle mixture plugs have been removed.
Thanks!
Bill

Bill,

If it is loose metal chips from the drilling, then use a vacuum hose and reduce the adapter opening to about a 1/4" size, and the suction should be strong enough to pull the chips.

If it is the leftover plug in place, then use a drill bit that will fit all the way to the top of the screw for the TPS , and measure the depth of the screw head. Mark this depth on another drill bit which is slightly smaller than the size of HOLE where the TPS screw is, and carefully (with minimal force and low speed on the drill) drill-off the remainder of the plug.

On the idle fuel mixture screws, Lisle has a tool (looks like a screw handle with a long flexible shaft) that contains adapters for adjusting some of the more common carburetors. The Rochester has the double-D shape idle screw heads. The tool is very convenient and it is reasonably priced at around $12 -$17 dollars. The flex shaft is worth its weight in gold!!!

 

[GerryLP]

Gerry:
...Also, the wire to use for the dwell reading was tucked in the loom. It is the only green wire not connected to something. I thought it was at one time connected to the choke, but there is now another wire going to the choke cover. Due to the fact the green wire did not have a green connector, I was not sure it was the one to use for the dwell check.... Thanks!
Bill

Bill,

See if it is that turquoise-green as the one in the image.

The choke's green wire is more like a regular green color, and it originates on the wire bundle running forward of the left fender inside the engine compartment, so I am confident that the one you found is the right wire.

 

[iamfine2]

I judt did a hand test on my 1981 EGR valve, I could move the diapraghm, but it was very stiff.
THen under idle I took off the cavuum line and there was no change in idle speed. Is the EGR bad?Also, there are NO vacuum lines hooked up to the EGR vacuum solenoid.
Is this the source of my slightlu rough idle and feeling of missing?

 

[GerryLP]

I judt did a hand test on my 1981 EGR valve, I could move the diapraghm, but it was very stiff.
THen under idle I took off the cavuum line and there was no change in idle speed. Is the EGR bad?Also, there are NO vacuum lines hooked up to the EGR vacuum solenoid.
Is this the source of my slightlu rough idle and feeling of missing?

fine,

The solenoid helps control when hydrocarbons are burned IAW the computer logarithm. But if you do not have them connected at one point, and depending where that location is, perhaps the solenoid is venting (i.e. opening to atmospheric pressure), and that would have the same effect as removing a vacuum line off the intake manifold, so yes, it could make your engine run rough. However, if none of the ports for the solenoids are connected to anything, and the manifold-side ports (manifold or carb) are capped, then that would not be the cause.

Look at the smog label under the hood, and see where the diagram has the hoses connected, and follow them to that point, to verify that they are either open or capped.