Packard Forum Index » Post-War (1946-54)

Whats strange is that the problem didn't manifest itself until the motor swap. Will try the gas cap trick tomorrow, and if that makes no difference, try to see if i can get any debris out of the line from the tank or come up with any evidence of a clogged intake.

I can get it to lose pressure in the driveway running for a bit, which may point more to a cap problem.

Also, it really reared its ugly head after a fill up...i had been working on it with a near empty tank.

Yup, that is how it started with me. Lots of crap on the underside of the roof of the tank. Worked great when the fuel was low, but as soon as I filled it, all the crud broke loose from the roof and the nightmare began.

It wasnt large pieces I was getting, it was very fine rust/varnish silt that was clogging the filters.

Ended up have the tank media blasted inside and out, and renu'd. Not exactly cheap, but guaranteed for life.

A thought on venting: you have the problem worse with the tank full. When the tank is full there is little air and when a small amount of fuel is used that empty space expands say 100% and a high vacuum is created.
With the tank near empty and the same amount of fuel used the empty space expands say 10% and a much lower vacuum is created. EZ to test, when the problem occurs remove the gas cap, you should hear a whoosh air going in and the starvation problem should stop.

Then again when a tank is filled the crud is stirred up.

Good Luck Sherlock

Removing the cap didn't help much, although it didn't seem to be knocking as much.

Backed it out today, no gas cap, and car dead cold and drove it up the road. Literally about a mile away as the car was warming up i could hear the tell-tale knock. Drove about 2 miles, turned around, came home. The knock was worse as it warmed up and you could change it's pitch with the throttle, part throttle cruising was worst. It was so that it was tapping lightly at idle when i got home. Gauge showed little or no fuel pressure again, and was idling a little rough. The knock/rattle seems to be coming from the front at idle, and seems different than the spark knock that comes and goes with throttle.


Maybe the noise is in the fuel pump and gets worse when warming up? I wouldn't think a new pump would be bad but i've seen crazier things...i don't really know how to go about troubleshooting it though. Maybe i can run a fuel line from the pump inside the car to a gas can and see if it does the 4 mile trip fine that way to rule out the pump and focus on the tank/lines?

Oil pressure is great, even when warm about 20-25lbs at idle with fresh 30 wt in the car. I don't really thing it's a rod knock or anything like that, or i think i'd have fuel pressure and it'd run great with correct timing, just knocking and loud.

Edit: As a note, if you just back it out of the driveway cold and go WOT, no noises or issues, just no real power, but i'm sure that's because the timing is so far retarded.

Random googling turned up this in regards to a packard straight eight:

" I just read the response to the question about the engine knocking even after rebuilding. I would suggest checking the fuel pump. If the bushings are not used the arm can clear the cam and cause a knock. It sounds a lot a rod knock. Also check the correct pump number the arms differ slightly"


I did put a 1950 pump in the 53 motor, after MM tech said that there really shouldn't be any difference.

Also, i can't at all think of what bushings they would be talking about here.

it might be the thin gaskets between the pump and the engine block. mine had 2 instead of one when the engine was originally disassembled

John

The mounting holes in the pump are much larger than the bolts that go through them. This space was taken up by little insulator bushings to cut down heat transfer. In additiion, there were insulating washers under the washers on the bolts. Often, all of this stuff is missing.

When the bushings are missing, I cut a strip of thin gasket paper and roll it around a bolt to make a tube and then stick it in the fuel pump flange. I make the insulating washers from a couple of disks of gasket paper cut with a punch.

Without the bushings it is possible to put the pump on either crooked or too high or low.

I did have those little bushings that went in the hole, i just hadn't thought about how that could cause it to knock. Maybe i'll warm it up so it's tapping lightly at idle, take the fuel pump off and start it. have to make a block off plate though.

Turning out to be quite the PITA to chase down! I still think it's detonating too though, which is more troubling as i haven't found any solid reason yet.

If the knock is at IDLE or just off idle then likely a wrist pin is loose.

Remove one plug wire at a time to see if knock changes significantly.

Put a scew driver to chain cover and listen for loose chain (if it has a chain).

Sometimes on very bellmouthed cylinders the top ring will come up thru the side of piston and cuse a knocking noise but that usualy never goes away.

PULL one plug wire ata time to see if noise changes.

I've pulled the full pump off and run the motor, it doesn't spray at think out of the hole. So you wont need a block-off for a short test. Also a carb bowl full of full with run for a little bit at idle.

Are you sure you fuel filters are clean, tank clean, and the fuel line doesnt have any pin holes to create a fuel starving situation?