Hi all,
So a couple years ago I decided to replace the tach gear that runs off the distributor. In the process of doing so the engine fell out of time. I had her running very well but recently she has not been running well at all. I'll give a walk through of the car and what I did in hopes for some insight. Please excuse the excruciating detail but I did not want to leave anything out that could be important.

She's a 1970 454 LS5. All stock.
After changing the gear off the distributor I needed to time and tune the engine. I did so based on the specs located under the hood (decal near the fire wall) and the shop manual.

This included:
1. Setting the timing (standard timing gun, and marking the pulley to locate the correct degrees advanced)
2. Setting the carb idle mixture (seating and backing out the set screws, and checking with a vacuum meter)
3. Setting the idle (I did this with a multi-meter)
4. replacing and gapping plugs
5. replacing condensor
6. replacing and checking the dwell angle on the points (i did this with a mutli-meter)
7. Replacing the temperature sensor in the engine block (the pin connector snapped off the original).

When all this was done the car was running great but the fast idle was very slow so I unsuccessfully attempted to set the fast idle.

8. Setting the fast idle. The shop manual instructs to disconnect the electrical lead to the transmission control solenoid located near the carb. I broke the wire off when I tried to do this and she ran terribly. No power at low rpm's and poor performance in general. I removed the trans control solenoid and re-soldered the wire. After reinstalling she seemed to run pretty well but I didn't have a chance to drive her much
(during a test drive i had to lock up the brakes because someone cut me off and now there is a noticeable disturbance in the ride, it feels like a flat spot on the tires and I'm assuming it is since it increases and decreases with the speed of the wheels, whether the brakes are applied or not and regardless of engine RMP. The tires are old, slightly over a decade but low mileage on them).

All the parts I replaced (plugs, condenser, points, and temp sensor) are from local auto parts stores and are supposed to match the original parts. However, the temp sensor has a different end (instead of a pin it has a circle connector) and the points are constructed slightly different.

The car sat over the winter and when spring/summer came I rebuilt the ebrakes. After completing the job I took her out for a test run and she was running quite poorly as described above (no low end power, breaking up occasionally around 3500 rpms), the motor did not reach operating temperature (the gauge barely budged) and the disturbance to the ride as described above.

I'm thinking that perhaps the wire came off the TC solenoid again, and may be causing the poor performance (I'm pretty sure this solenoid effects vacuum at low idle and at certain r's in certain gears, but I'm not sure which), and perhaps the thermostat failed in the open position not allowing the engine to warm up fully, along with flat spots on the tires causing the disturbance in ride, but I wanted to run these symptoms by you guys and see what you thought.

Could a failed thermostat cause the engine to not reach operating temp, and could that cause the car to perform poorly? Or could a bad TC solenoid cause the poor performance and not allow the car to warm up fully? Is there anything else I'm missing?

Thank you very much for any and all help!
Bob

 

a thermostat stuck in the open position would cause the low temperature and may effect the running of the engine. Remove it and check with a thermometer and a pot of water being heated or just replace it. Did you set the dwell before the timing? Did you adjust the carburetor after the dwell and timing with the engine fully warmed up? If the tires are over 10 years old regardless of mileage replace them. The solenoid provides vacuum advance in top gear only.

 

First check that the cooling system is working properly and allowing the engine to warm up quickly. As already suggested, check the thermostat.

Second, check that TCS is working properly. Connect a vacuum gage in the hose between the solenoid and distributer. You should have full vacuum when the engine is warm and with the transmission in 3rd or 4th (4 speed tranny) or high gear (auto). You should have no vacuum if engine is cold/cool, or the tranny is in lower gears. TCS won't work properly unless the thermostat is working (step 1).

FYI, the temp sensor for the TCS is in the right cylinder head (two flat connector blades); the temp sensor for the gauge is in the left cylinder head (single "round" connection).

Third, check the dwell, THEN ignition timing. Be sure to disconnect vacuum advance while doing this. Is the distributer in good shape? A worn distributer can cause erratic timing; Lars has a good post about this in the forum.

Fourth, adjust the carburetor. Make sure the PCV system is ok as well.

Tires over 5-8 years old are prone to failure regardless of mileage.

 

Thank you for the reply. I'm getting new tires put on her today. After reading some of the Willcox posts I tested the temp sender and that seems to be the issue. Am going to replace and see if that fixes the issue of the gauge not showing the car as warm. I believe I set the dwell after the timing. Is this problematic? I adjusted the carb after the dwell. The car was warm for adjusting the carb, timing, dwell, etc. I jumped out the vacuum from the TCS solenoid and it performed much much better. But could there still be an issue because I set the timing before the dwell?
Thanks for the help!
Bob

 

Thanks for the help!
I ran a couple of the Willcox tests on the temp sender at that seems to be the issue. I'm going to replace the sender and see if that fixes that problem.

I also jumped the TCS out of the vacuum lines and the running improved significantly. There appeared to be a vacuum leak between the carb and the TCS and also the solder job appeared to have failed. I'm going to replace the TCS eventually, but for now she is running ok.

Unfortunately I did adjust the dwell after the timing. Can that cause issues? Should I recheck the timing?

I set the carb after the dwell, and did all of these steps with the car warmed up.
Thank you again!
Bob

 

You got the dwell and timing reversed, dwell is always first it changes the timing. Make sure the vacuum line to the distributor is disconnected when setting the timing. Make sure it is connected when adjusting the carburetor.
The TCS is there for emission purposes only, if that is not an issue run a manifold vacuum source directly to the vacuum advance on the distributor and forget about the TCS.

 

Thank you very much! Right now I have the TCS vacuum running from the carb to the distributor. Should I find a vacuum from the manifold and plug all the vacuum lines from the TCS?

 

Bobby also post in the 70 LS5 thread in the general section.

 

I'm going to go back and check the dwell, and then the timing in that order. If I change them, then I will also check the carb.

One question tho. When checking the dwell, does it matter if I have the vacuum line connected to the distributor? Should I disconnect it?
Thanks again for all the help!

 

Thank you. Will do!

 

Changing timing (vacuum or mechanical) does not affect dwell. But changing dwell can affect mechanical timing. That's why dwell should be adjusted first.

 

If you changed just the cross gear and not the main shaft, you're going to be repeating the whole job some time soon. The main shaft gear is damaged and worn and will destroy the new cross shaft.

 

The dwell is not effected by the vacuum line but since the next step is to recheck the timing you might as well disconnect it right away.

 

Thanks Mike!
I did change the gear off the main shaft so hopefully I will not have to do that job again anytime soon!

 

Thanks again for all the help Mark!
I just wanted to give a quick update:
I replaced the temperature sender to the temp gauge and now I can see that the car is warming. It warms up fairly quickly, not reaching 210. What temp should it be warming up to?

Also, I changed the tires which fixed the shudder in the suspension.

I also replaced the TCS-solenoid. I tested it hooked up and jumped out. When it is jumped out it performs a little better, particularly in low gear and starting off, which is to be expected since it is receiving vacuum in low gears with the switch jumped out. I'm going to test the vacuum on the switch as well to be sure the new one is functioning properly.
But, either way (connected or disconnected) it is still performing a little poorly. It feels like it is missing, or not burning the fuel adequately.
What do you think of this approach?

I am going to pull a plug and check it to see if it is running rich/lean. Also I'm going to order new points and condenser. Replace these parts, set the dwell, time the car, set the carb and see how she runs.
Does this sound appropriate?

Also, I found an exhaust leak right before the passenger side muffler and another in the drivers side muffler. These are pretty far back on the exhaust system and I'm not sure if leaks that far back can impact how the car runs. Should I fix these before doing anything else?
And while I'm posting, the clutch is starting the chatter (which I'm sure can impact the low end power, but hopefully not this much). I hope changing the clutch isn't something I have to do imminently.

Thanks again for all the help!
Bob

 

Thanks for the help! To give a quick update:
I replaced the tires which fixed the shudder in the suspension. I also replaced the temperature sender and I can see the car is warming up now. What temp should it reach? It is warming up above the second tick mark on the gauge but not reaching 210. Is that ok?

I also replaced the TCS-solenoid and it's running a little better but still a bit poorly. Lack of low rpm power, and it feels like it's missing or not burning all the fuel.
I was going to check the plugs to see if she's running lean/rich. Then I was going to clean them if necessary and order new points and condenser that are the exact match for the car.

I was going to install the points and condenser, set the dwell, time the car and set the carb. Then see how she is running. Does this sound good?

Also, I found an exhaust leak right before the passenger side muffler and another in the drivers side muffler. These are pretty far back on the exhaust system and I'm not sure if leaks that far back can impact how the car runs. Should I fix these before moving forward with anything else?
Also, the clutch is starting the chatter (which I'm sure can impact the low end power, but hopefully not this much). I hope changing the clutch isn't something I have to do imminently.

Thanks again for all the help!
Bob

 

Are you sure you when you replaced the gear on the distributor that you dropped the distributor back in onto the correct gear on the cam. Seems like you might be one tooth off.

 

What's the best way to check? Move it over and see how it runs? I tdc'ed the engine and the rotor was advanced of the first plug, ie it would be firing before top dead center. Is there a better way to check?
Thanks for the help!
Bob

 

The 'one tooth off' idea is a misconception held by people that don't fully understand the ignition system. If the timing gun shows that it's firing at the right spot, you're all set.

 

Thanks Mike,
I've fixed the exhaust leaks and now it's time to install new points and condenser, set the dwell and then the timing. I know the car should be at normal operating temp to set the timing, but should it also be at normal operating temperature to set the dwell?
Thanks again,
Bob