Engine Checkup - Part 1 - 10/23/2013

After having driven the car over 600 miles on the freeway, then putting another 400 or so on general around town driving, it was time to see if the engine could use a tune up or check up. Vintage vacuum lines have a way of causing problems, so it's best to check all of this out before going any further.

Engine in as-bought state.

Engine carb and vacuum hoses. Every single line except one (grey on right side to air cleaner) is ribbed and marked, just like done at the factory. This probably means they ARE factory hoses... EGR is plugged off with a dowel pin.

Engine idle solenoid as part of TCS system. Note original distributor delay orifice still intact.

Distributor Spark and EGR Thermal Vacuum Valve. Per the factory manual, this item is designed to allow operation of EGR when the air-fuel mix temperature is above 62F, and allow spark advance in any gear only when same mixture is below 62F (otherwise no spark advance unless in high gear or cold feed switch above 140F or 155F). This is kind of complicated. The valve is in the #1 intake runner.

Another view of same item. Note all hoses with ribs are numbered to where they go. The factory diagrams call for stripes with colors and not numbers, but I see zero evidence of color striping left. Even after 40 years you would expect to see a hint if the colors were ever present. Interesting to see a factory clamp was on the charcoal cannister to carb connection... Indentation is still visible.

Carb number is a 7044262. That translates to a 455 Firebird carburetor, which seems a little odd that this car would have rather than the California emissions variety. Remember, this was an old couple's car so the chances of it being hot-rodded were practically zero.

The cold feed switch was disconnected and the pins bent back. I hooked it back up. It appears to function properly (open when cold, closed when hot).

Engine hot switch was an interesting character. It was bent over backwards and not able to be plugged in. I plugged it in after bending it back properly. The purpose of this switch is to provide vacuum advance at all times when the coolant temperature reaches above 240F (to which the manual warns "CAUTION: DO NOT ALLOW COOLANT TO REACH ABOVE 240F!"). The manual indicates that this switch will provide a ground to the solenoid in this condition (so a simple test is to look for a high impedance between the tab and ground when cold).

Thermostatic air cleaner valve actually works! Can't say I've ever seen this happen on any car I've ever owned. Since it was cold outside when I tested all of this (55F per the thermometer), it was always closed. The valve is designed to keep the air coming in at all times to 115F, except under high load conditions (no vacuum).

Factory diagram for vacuum hose routing. Matches this car spot on.

Electrical diagram for how the TCS is wired up. Solenoid does work (clicks).

Overall total vacuum diagram.

More electrical diagrams. Annoyingly enough, NONE of these diagrams were included in the factory service manual. There is a special supplement for 1974 that details how the emissions system works. Sounds like mid-model year document finalization. Since this car was built in the very first few weeks of production it may have been slightly different.

So, I do know that I have vacuum advance in all gears, but then when I was doing the testing it was chilly and below 62F, so I'll have to wait for it to warm up to figure out if it's truly working. When the EGR is hooked up and you mash the gas, it pops through the exhaust quite loudly, indicating it is going super lean. I left the EGR disconnected as a result because no one needs that nonsense...

I also took advantage of this time to check out the timing settings with my timing light. All numbers are measured on the crank balancer.

Initial: 10
Vacuum advance: 18
Mechanical advance: ~20 by 2000RPM
Idle vacuum: 18inHg
Idle speed: ~700RPM

Not bad, seems that the initial is set right at the factory setting, the vacuum advance seems to be slightly higher than expected and the mechanical advance is working and returning to 0 like it should. All things that can really mess with a car's timing & fuel economy. Need to do more research and driving to see how it behaves under all conditions and if there are any items to change or benefits to be had...

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Last updated October 23rd, 2013