Timeing and Motor Mounts HELP!!

[JapanL81]

I just got my 1981 im sure something is offf with the timeing i have a mechanical fuel pump new other than that it is stock. it shruggles to idle and as it idles it shutters when it does there is a tapping noise from the passenger side of the motor underneath the car. i think its a timing issue and then the tapping is a bad motor mount. i have a living room full of parts new brake lines front and rear all and i mean all the interior new new T Tops air filter and assembly, optima battery alternator, master cylinder, brake booster, and many more parts but i want to get this timeing issue and motor mount if that is the case

So any advice would be greatly appreciated, who knows i could be way off about the mounts and timeing.

 

[Antz81]

Welcome, great to see another vette rescued.

There's a few thing that could be causing your rough idle.
A common problem is vacuum leaks.
Have you checked to see if there are any stored fault codes in the ECM?

 

[JapanL81]

Welcome, great to see another vette rescued.

There's a few thing that could be causing your rough idle.
A common problem is vacuum leaks.
Have you checked to see if there are any stored fault codes in the ECM?

I havent dove to much into the motor yet, nor do i have much experience with older cars. Since the C3 is Pre OBD how do you pull codes from the ECM i found a very indepth (but confusing) process about the ALDL? Is there a thread here on checking for Vac leaks. Would it be easier to just replace all the vacum lines? I need this thing up and running quick fast and in a hurry she is going into paint and body in Aug. i would prefer to have everything buttoned up before then.

Thanks for your response
Nate

 

[GerryLP]

I havent dove to much into the motor yet, nor do i have much experience with older cars. Since the C3 is Pre OBD how do you pull codes from the ECM i found a very indepth (but confusing) process about the ALDL? Is there a thread here on checking for Vac leaks. Would it be easier to just replace all the vacum lines? I need this thing up and running quick fast and in a hurry she is going into paint and body in Aug. i would prefer to have everything buttoned up before then.

Thanks for your response
Nate

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 could be anything in the engine bay and even the headlight switch inside the cabin. The best way is by using a vacuum pump (and they have a gauge attached to them). However, due to temperature in the engine compartment over a long period of time, the plastic connectors also suffer from heat and become brittle.

1) Spray WD-40 or similar product on the hose ends and fittings before attempting to disconnect the hose segment.

2) Follow the emission's label and start with those hose segments to check for vacuum leaks. Cap/plug the opposite end of hose being tested. Remember that perhaps the opposite end of hose could be disconnected already (thus causing the vacuum leak).

3) Exercise extreme caution and care with solenoid connectors (passenger side and slightly forward of distributor). Spray WD-40 to ease disconnection the hose segments (do one at a time). Twist the hose segment to aid in breaking the seal or grip the hose segment has on the plastic fitting. The top solenoid one is red in color. The bottom one is white. THEY ARE NOT REPRODUCED, SO SLIGHTLY DIFFICULT TO FIND IN eBay.

4) with vacuum pump and other end of hose segment capped/plugged begin creating vacuum signal inside hose segment. If it does not build (like the needle move from 5 in-hg to 10 in-hg) AND does not hold the vacuum after you stop pumping, then there is something wrong with that hose segment.

5) you could try to get 4-5 foot segment of hose of each diameter of hose most common in the engine compartment, but I would only do that if I found a lot of the hoses dry-rotted.

6) after you have checked the emission's hoses, check the head light pop-up mechanism hoses. If the head lights are slow to rise, then you have a leak somewhere (it could be the actuator seals, which are not terribly bad to change, but not available locally -only specialty corvette parts supplier like Corvette Central, Mid-America Works, Ecklers, Corvette Doctor, ZIp, etc.

7) the rough operation could be your positive crankcase vent valve (PCV). If it is sticking open, it basically causes one serious vacuum leak.

Good luck.

 

[JapanL81]

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 could be anything in the engine bay and even the headlight switch inside the cabin. The best way is by using a vacuum pump (and they have a gauge attached to them). However, due to temperature in the engine compartment over a long period of time, the plastic connectors also suffer from heat and become brittle.

1) Spray WD-40 or similar product on the hose ends and fittings before attempting to disconnect the hose segment.

2) Follow the emission's label and start with those hose segments to check for vacuum leaks. Cap/plug the opposite end of hose being tested. Remember that perhaps the opposite end of hose could be disconnected already (thus causing the vacuum leak).

3) Exercise extreme caution and care with solenoid connectors (passenger side and slightly forward of distributor). Spray WD-40 to ease disconnection the hose segments (do one at a time). Twist the hose segment to aid in breaking the seal or grip the hose segment has on the plastic fitting. The top solenoid one is red in color. The bottom one is white. THEY ARE NOT REPRODUCED, SO SLIGHTLY DIFFICULT TO FIND IN eBay.

4) with vacuum pump and other end of hose segment capped/plugged begin creating vacuum signal inside hose segment. If it does not build (like the needle move from 5 in-hg to 10 in-hg) AND does not hold the vacuum after you stop pumping, then there is something wrong with that hose segment.

5) you could try to get 4-5 foot segment of hose of each diameter of hose most common in the engine compartment, but I would only do that if I found a lot of the hoses dry-rotted.

6) after you have checked the emission's hoses, check the head light pop-up mechanism hoses. If the head lights are slow to rise, then you have a leak somewhere (it could be the actuator seals, which are not terribly bad to change, but not available locally -only specialty corvette parts supplier like Corvette Central, Mid-America Works, Ecklers, Corvette Doctor, ZIp, etc.

7) the rough operation could be your positive crankcase vent valve (PCV). If it is sticking open, it basically causes one serious vacuum leak.

Good luck.

Sooo the head lights(which turn on but do not pop up) is probably the issue, Thanks alot i would have never thought headlights would cause a problem with idle. This corvette blows my mind daily. Im sure i will be hitting you up in the future Thanks again for your very detailed and easy to follow troubleshooting tips. Im an A/c Tech so i have a vacumm pump i just hope this doesnt pull to hard and cave the hoses.

 

[Antz81]

I havent dove to much into the motor yet, nor do i have much experience with older cars. Since the C3 is Pre OBD how do you pull codes from the ECM i found a very indepth (but confusing) process about the ALDL? Is there a thread here on checking for Vac leaks. Would it be easier to just replace all the vacum lines? I need this thing up and running quick fast and in a hurry she is going into paint and body in Aug. i would prefer to have everything buttoned up before then.

Thanks for your response
Nate

Pulling Codes is very easy.
The ALDL connector is located below the ash tray. its a 5 pin connector.
turn the Key in the run position, but without starting the engine.
You should now have a check engine light on.
Now short pins A + B on the ALDL connector (a paperclip works well for this). These two pins have a slot between them making them easier to short.
Your check engine light will now start to flash the codes, and the mix control solenoid will cycle.
Each code is two digits.

The first digit of the code will be flashed followed by a short pause then the second digit will be flashed followed by a long pause.
After the long pause the code will be repeated twice before the next code is flashed. Once all the stored codes have been shown the codes will start again from the beginning.

A list of all the codes can be found here:
Corvette Action Center Knowledgebase :: 1981: ECM Codes

Note Code 12 is normal. You should get this code every time you check.

I hope that makes sense.

Yes if your headlights are not popping up when on that could be your problem.

 

[JapanL81]

Pulling Codes is very easy.
The ALDL connector is located below the ash tray. its a 5 pin connector.
turn the Key in the run position, but without starting the engine.
You should now have a check engine light on.
Now short pins A + B on the ALDL connector (a paperclip works well for this). These two pins have a slot between them making them easier to short.
Your check engine light will now start to flash the codes, and the mix control solenoid will cycle.
Each code is two digits.

The first digit of the code will be flashed followed by a short pause then the second digit will be flashed followed by a long pause.
After the long pause the code will be repeated twice before the next code is flashed. Once all the stored codes have been shown the codes will start again from the beginning.

A list of all the codes can be found here:
Corvette Action Center Knowledgebase :: 1981: ECM Codes

Note Code 12 is normal. You should get this code every time you check.

I hope that makes sense.

Yes if your headlights are not popping up when on that could be your problem.

And im sure that you are in the same boat when it comes to replacement parts as i am locally it is impossible im on a small island oj japan we have a Chevy Nova, Trans am, and a Mach 1. thats about it for american muscle on this island everything else runs on motor cycle engines.

 

[Antz81]

And im sure that you are in the same boat when it comes to replacement parts as i am locally it is impossible im on a small island oj japan we have a Chevy Nova, Trans am, and a Mach 1. thats about it for american muscle on this island everything else runs on motor cycle engines.

NZ isn't too bad when it comes to parts. We have a large number of american cars here, so most common parts can be obtained overnight. We even have a supplier that specializes in Corvettes.
On saying that, i need a rear wheel bearing done on mine and that's going to be a two week wait for parts.

 

[GerryLP]

Sooo the head lights(which turn on but do not pop up) is probably the issue, Thanks alot i would have never thought headlights would cause a problem with idle. This corvette blows my mind daily. Im sure i will be hitting you up in the future Thanks again for your very detailed and easy to follow troubleshooting tips. Im an A/c Tech so i have a vacumm pump i just hope this doesnt pull to hard and cave the hoses.

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 engine and see of it idles better. It won't mean that another hose is not leaking, but at least you can see if the engine runs better (less shaking; it smooths out).

 

[JapanL81]

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 engine and see of it idles better. It won't mean that another hose is not leaking, but at least you can see if the engine runs better (less shaking; it smooths out).

Thanks Gerry, i get off work in about 30 minutes this will be the first thing i try out.

 

[GerryLP]

Thanks Gerry, i get off work in about 30 minutes this will be the first thing i try out.

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. Follow the hose, and if it heads towards the left fender and forward, then that is the one.

 

[Peer81]

Welcome and enjoy your stay overhere! I see Gerry is coming to the rescue
Good luck, I'll shime in later after Gerry did all the hard work! :L

Greetings Peter

 

[JapanL81]

You guys have been my savior i disconnected the vacuum hose from the manifold last night and plugged it..... idles PERFECT at 650rpm i mean smooth its like a brand new motor no shaking no shuttering nothing. Thank you to all of you who replied hearing her run smooth last night was like watching one of my kids being born .

 

[JapanL81]

You guys have been my savior i disconnected the vacuum hose from the manifold last night and plugged it..... idles PERFECT at 650rpm i mean smooth its like a brand new motor no shaking no shuttering nothing. Thank you to all of you who replied hearing her run smooth last night was like watching one of my kids being born .

 

[GerryLP]

You guys have been my savior i disconnected the vacuum hose from the manifold last night and plugged it..... idles PERFECT at 650rpm i mean smooth its like a brand new motor no shaking no shuttering nothing. Thank you to all of you who replied hearing her run smooth last night was like watching one of my kids being born .

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 each size of hose going to the lights. Then, replace each segment one-at-a-time. Before you know it, it will be all done ready for driving at night.

congrats!

p.s.

I noticed your description of your L81..."faded red..." Reminds me when Gail's paint job was faded. Here is a pic when the CAC gathered in Colorado Springs in 2007.