This article deals with solving the problem of missing, loss of power and backfire in my 1946 Packard Straight 8 282 CID. This problem happens when the engine is held at high revs. Idling is fine. The car is an evolving project car (sort of my Harley Earl's Y-job) with the drive train rebuilt. When we rebuilt the engine, the distributor was mistakenly set one tooth off. Number 1 timing plug tower on the distributor cap was at 6 o'clock instead of the correct 7 o'clock. This is a problem on "vacuum advance" cars because it changes the degrees of advance. This does create high rev problems and has been there since the rebuild, but the problem was getting worse, so we knew something else must be going on.
We only start this car about every three months, always with fresh gas and a little Marvel Mystery Oil down the carburetor. Even so, straight 8's are known for sticky valves, so that was the first place we looked. We removed all of the spark plugs and filled the cylinders with MM Oil, also removing the side covers (valve covers) and sprayed down the valve train with MM oil, then let everything soak for a week. At week's end, with the plugs removed, I turned the engine over, laying rags over the open cylinders as the MM oil blew out. Then, using air, I blew into the cylinders to dry them, and installed a new set of AC M-8 10mm spark plugs gapped at .028 and started the car. Same problem.
To test further for sticky valves, using my tablet I shot video of the valve train as the engine ran. Looked good. Then I removed the 1/4" pipe plug from the intake and connected my vacuum gauge to check vacuum at warm idle. It was a perfect 20 inches. As I revved the car, the gauge moved to different readings, but they were all okay. Next, I put an inline fuel pressure gauge right before the carburetor. The engine idled at around 450 RPM's and had 5 PSI fuel pressure, and when held at approximately 1500 RPM's, the fuel pressure dropped to 2 PSI. Even though the engine had been rebuilt, I decided to check the compression. It was 90 PSI on all cylinders (acceptable) and a good indication of no stuck valves. I could now be pretty sure that the problem would be in the fuel or ignition systems.
With the fuel pressure dropping so low at high revs, I decided to go through the fuel system first. The manual fuel pump runs off of the cam, and a worn cam can cause the fuel pump pressure to be erratic, but the cam was checked at the time of rebuild, with almost no miles on it since that time, so a bad cam wasn't likely. But I put an electric fuel pump on to eliminate that possibility. I made a steel plate and capped off the old manual fuel pump opening in the block. The electric pump I installed is a Carter #P-60430, as recommended by our buddy Ron at Daytona Carburetor. This pump is a 6/12 volt, positive/negative ground. At 6V, fuel pressure is 4-5 PSI; at 12V it is 5-6 PSI. These pumps are gravity fed and should be mounted below the fuel tank and pointed toward the front of the vehicle. I have seen electric fuel pumps mounted above the tank in the trunk as in our '67 Jaguar Mk II. However, we ran out of gas once in the Jag and had to prime the pump by blowing air into the gas tank. Not much fun out on the road! To completely bypass our old fuel system, we put a 5 gallon gas can (full) on a stool above the fuel pump, then new gas line to the front of the car to the carburetor. We wired a manual switch to the electric fuel pump so we could cut it on and off while testing the system. It is recommended to run it through the ignition switch, but ours is for testing only. If it didn't work, we would go back to the manual fuel pump.
Now with the new fuel system on, we turned on the fuel pump and almost immediately the fuel pressure test gauge went to 4.5 PSI. As I started the car, the fuel pressure dropped to 4. As it warmed up, I held up the throttle. Pressure dropped to 2 PSI with the same missing and backfiring through the tail pipe.
The only thing left in the fuel system was the carburetor. A bad accelerator pump can cause our problem. With the engine turned off, I pushed the butterfly open and throttled the carb, and was able to see two squirts of gas go into the throat. That told me that the accelerator pump was working, but not how well, so I replaced the Carter carb with a rebuilt one from our longtime Packard buddy David Moe, then started the car.
S-s-s-same problem !!!
The fuel system was all ok. It was now time to go to the ignition system. Before remedying our distributor-one-tooth-off problem, I checked the timing. We hadn't touched it since rebuild, so it should be on spec of 6 degrees before top dead center (BTDC). The Packard 1946 motors manual specs timing at 7 degrees. Motor's Manual specs 6 degrees, and another motors manual says 5 degrees. The car runs best at 6 degrees. I have a 6V and a 12V timing light, but decided to use the 6V to be in period with the car. To do this, you have to turn off the garage lights to see the timing mark on the harmonic balancer. With the lights off I could see fire jumping around the spark plug wires at the cap and the timing was now on 8 degrees. How did that happen? It was time to straighten all of this out. First, to set #1 plug on my distributor cap from 6 o'clock to 7 o'clock. I set the harmonic balancer pointer to top dead center, and using a paint marker, I put a dot on the distributor cap and a dot next to it on the engine block, then dots on the rotor and distributor plate where the rotor pointed and carefully pulled out the distributor. I noted the position of the end of the distributor shaft (oil pump side) was at 9 o'clock and I moved it to 10 o'clock, which would move my rotor to point at the correct 7 o'clock on the distributor cap. The distributor runs off of the oil pump on the other side of the engine, so I went to the right side of the car and pulled the oil pump, marking the pump to the engine block for reference. After removing the oil pump, I turned it around to check the drive gear to see its position. It was at 9 o'clock, the same as the distributor had been. I moved the drive gear's shaft to 10 o'clock, marking reference marks on the gears (front side) so the gears wouldn't be moved when I put it back in. This would make the oil pump's drive blade parallel with the cam when installed in the engine. The oil pump has a shaft with a blade that inserts into the distributor shaft groove. After doing this several times out of the car, I reinstalled them both. They fit right together (the oil pump has to be rotated about one quarter turn to go in and come out of the block.)
I had cleaned up the distributor while it was out, putting in new points, condenser, rotor, cap and spark plugs and wires. I found the reason that ignition fire was jumping at the cap. The wires' insulation was cracked on most of the wires (we use the stranded, lacquer cloth covered wires). When the distributor was out of the car, it was easy to see the vacuum advance and how it connects to the distributor. This is an Auto Lite system, and the vacuum advance moves the distributor body as the advance kicks in (over 500 RPM's) as opposed to the Delco centrifugal type, also used by Packard, that moves the distributor plate inside the distributor, not the distributor body. At first look, the advance hookup is genius. The vacuum control arm attaches to the distributor calibration plate (octane selector) with a #10 cam screw that goes down through the vacuum advance control arm, through the calibration plate and through to the bottom side, where a pointer with downward tabs on each side keeps the nut below it from turning. When the desired timing is reached, the pointer shows the degrees on the distributor calibration plate and you turn the screw inward, thus locking down the whole assembly. Here's what's wrong with that:
When the distributor is in the car, it is so low on the engine that the cap covers the pointer and the pointer/lock nut spins when you tighten it down, even though the pointer has two tabs that face downward to keep the nut in place, and a tab on the back of the lock nut that is supposed to push up against the distributor body to keep the nut from moving. I didn't appreciate how comical all of this was until Jason was holding the timing light as I moved the distributor to get my 6 degrees with my left hand (rubber gloves on, of course) then with my right hand I tightened down the lock screw, not realizing the lock nut was turning, then I turned the car off and restarted it. Back to 8 degrees! After doing this five times, I realized I was doing the same thing over and over again, expecting a different result. This is one definition of insanity. So I made my own distributor lock down. I used the same cam screw, passing through the vacuum arm and distributor calibration plate, then on the bottom side I added a star washer, deleted the tabbed pointer, used the threaded lock nut from the old assembly and added a thumb nut at the bottom to double-nut it. Packard changed to a very similar setup as evidenced on the cover of their Ignition Training Booklet dated April, 1947 (see next page).
To base time an engine, #1 plug is removed, put your thumb over the hole and crank the engine over (coil wire off) to bring #1 piston up on its compression stroke. You will feel the air from the cylinder pushing out against your thumb. Stop when the pointer points to TDC on the harmonic balancer and the rotor points to #1 plug (ours is at 7 o'clock. If it had been at 1 o'clock we would have been 180 degrees out.) Also, to confirm, #1 piston's intake and exhaust valves will be closed (down on our straight 8), which is correct for the compression stroke.
To static time using a test light, put one lead on the distributor's primary terminal (the wire from the coil's + side [ours is a positive ground car]) and the other lead to a ground on the engine. Turn the distributor until the light goes out (points closed). Then turn the distributor toward #1 firing plug (clockwise on our car; this is opposite of cam rotation). Turn until the instant the light goes on (points open). Lock down the screw and you're done.
To time with a timing light, warm the car to operating temperature with low idle and disconnect the vacuum advance and cap off the carb end of the line. This will keep the vacuum advance from kicking in and advancing the timing. I backed off the #10 lock screw and advanced my timing (this distributor advances clockwise and retards counter-clockwise), setting the timing to 6 degrees on the harmonic balancer using the timing light, then locked down the screw. When I started it, it idled nicely, no miss, 20 inches of vacuum, 5 PSI fuel pressure at idle, 3.5 PSI at "snap" throttle, then back to 4.5 PSI at fast RPM's. (I found that fuel pressure drop can be caused by bad ignition timing, causing the engine to shut down as engine speed decreases.) When I brought the revs up. 500, 800, 1000, 1500. No missing, no loss of power, no back fire! The old straight 8 was back! One thing about these old L-heads is, I've found they love to idle and be throttled, but not to just hold them up at 3,000 RPM's with no load. They were not designed for that.
Now, what exactly caused my problem? Here's how the clues add up. Most every time we started the car over the years, we removed the distributor cap to file the points because of oxidation (Georgia's wet climate!). We would unclip the distributor cap and hold it back toward the spark plug wires. This cracked the insulation on the spark plug wires causing cross-firing, and this moved the ignition timing itself. And the distributor being off one tooth with a vacuum advance secondarily contributed. Next time we file the points, the cap will be carefully moved to the side with no stress on the wires. This fixed the chronic after-fire problem when the engine was raced, but on occasion when the engine revs were held up with no load, it might occasionally backfire through the tail pipe. That's the way the article ended back in march of 2015. The only thing that wasn't done was to rebilt the distributor. Out distributor was sent to our good buddy Ron Carpenter. He is a specialist on these old Packards and has the knowledge and equipment to go through the distributor. After we got the distributor back totally rebuilt including a new vacuum advance, we dropped it in. The idle was now smoother and never any after fire through the tail pipe! I would suggest having your distributor tested and rebuilt before going through the carburetor and othe rparts of the ignition system. As for us, we wanted to go through all of our systems to ensure many more years of dependable service from our old friend. Keep 'em driving!
Our thanks to Ron Carpenter, California Packard restorer
David Moe, Packard Seattle Company
Odell Hancock, restorer
Danny and Daniel at Chatt-Town Radiator
Keith at KIR Custom Car Creations
Max Merritt Packard Parts
and the SW Restoration Team: Woody, Jason, & Wayne