Hi all, new here.

One of my two 1968 Imperials is suffering from fuel starvation. This is a mostly stock engine, but it probably has a cam upgrade close to an HP cam, given the engione's urge at high rpm's (this is normally a great high speed car, and can hold its own very nicely against modern machery at high speed).

The problem I have had is fuel starvation. I recently replaced the 630 cfm AVS with a 750 cfm AFB, and I can see that the engine seems to have more upper end urge, until the starvation hits (this engine used to nicely rev up to 5000 rpm with the 630 cfm, but now, even in cold weather, it missfires at higher engine speeds, and the missfire is worse the more you open the throttle). I have installed a pressure fuel gage through the firewall, and I can read the pressure while driving. It starts around 4 psi, but when you hit it hard, and starts revving up, it slowly drops down to 2 then 1 psi, and then missfire starts.

I had replaced the fuel pump, nothing. I removed the sock filter in the tank, nothing. I have blown air through the lines, no improvement. I recently installed an electric fuel pump between the tank and the mechanical fuel pump. This seemed to help, but the cheapo fuel pump does not have enough flow rate. On a short trip I had made to San Antonio last spring during a very hot March day, the electric fuel pump did seem to help keeping the fuel pressure a bit higher. But in the afternoon return trip, when the ambient temperature was high, you could not exceed 3,000 rpm cruising (speedo reads 97 at 3000 rpm, true speed is 90 mph).

I suspect that a high flow electic pump will solve the problem, since I have the electrical side already installed. but this is very puzzling. My other 68 Imperial has no such issues (that car actually has an 850 cfm Rochester, which seems a (bad) copy of an AVS, but seems to work well and provide good airflow to that 440). I suspect that may be the push rod of the fuel pump is worn out.

Any thoughts? Anybody else faced such problems?

Thanks

D

 

The fuel pump shouldn't be starving it fuel until well above 6k RPM IMO... I have a high volume mechanical pump and its good to about 7k rpm..

I would suspect something with the carb.. I'd say put a holley double pumper on it and see what happens...

 

id say its a carb too, holley is a good carb but so is a carter, the rotten chester is also a good carb,

id sat it has to do with the jets, most carbs are roughly set out of the box. but all carbs need to be adjusted (even holleys) be for they are right.

search the web, read what carter says for trouble shouting,
good luck

 

Hey guys, I may have forgotten to say that the same thing used to happen with the 630 cfm AVS. THen, I changed to the 750 cfm AFB, with no improvement (in fact, things got a bit worse because the new carb lets more air in, so it needs even more fuel). I also said that the fuel pressure goes to nothing when the engine starts missfiring. So, it seems to me, that the problem has to be fuel delivery. In fact, the electric fuel pump does help.

So, do you still think it must be the carburetor?

Thanks

 

if the pressure drops to zero then there could be a hole in the line sucking air into the fuel line,

 

Thanks 66 Sports Fury. But if there was a hole in the line between the new electric fuel pump and the mechanical pump, I would have had a fuel leak with the electic pump on and the engine off, and I would smell gas. None of that has happened. Good suggestion though ....

At some point, I had also installed a new temporary fuel line from the tank to the fuel pump (before I had installed the electric pump). That had not made any improvement. All that was taking place last summer.

That's why I tend to believe that may be the pushrod that activates the mechanical fuel pump is somehow worn out. I am also not ready to dump the mechanical fuel pump, as electric fuel pumps are not as reliable, and I do not want to get stranded. Imperials are not meant to be pushed around !

 

Take a gas can, run a line to the mechanical pump bypassing the tank lines.

If it runs good, you know its something from behind the pump.

If it runs bad, it could still be anything. But most likely something from the pump - carb

 

you can suck in air with out leaking gas,

 

Measure the push rod first. Spec is 3.242"

 

The pushrod, that's it.

How do I measure it? When I remove the fuel pump, only a portion of it is exposed. Sorry if this sounds damn, but I have not messed with the pushrod before. I do have the shop mannual, I can look into that, but any info as to what is involved to remove it, measure it, or replace it, will help.

Thanks Scotts