1980 FI acts like it is starving for fuel

[mkassing]

I have recheck the vacuum a dozen times and will recheck again. I do have a fuel pressure gauge t'ed into line in for the rail. When I start the car and drive it for a varying amount of time (5-20 minutes) everything is fine. When driving fine I can watch the pressure rise as I step on the gas; when the problem hits the pressure goes down as I step on the gas. I have replaced the fuel pump twice with no change in the situation. I have replaced the pressure reg and the fuel filter. I have checked everything for the correct ohms. If I turn the car off for a second or two the problem goes away but comes back quicker than when I just start it up.

I also have tried driving with the fuel cap both on and off and the cold start valve pinched and unpinched. I have the feeling that it has something to do with the replacement of the fuel pump and the lines under the car but am stuck on what to try next (other than the shop which is admitting defeat).

???

[So Cal Mark]

what does the pressure drop to?
How is the fuel line from the tank to the pump?
what voltage do you have to the pump? Especially when the problem occurs?
The fuel pump ground is at the left taillight, is it tight and clean?

[mkassing]

Mark:

The pressure drops from mid 30's all the way down to 10's depending on how much gas I give it. I am not sure but it appears that when I get to about 90 on the temp sensor the problem hits. Everything running fine until driving for a bit so it is hard to tell if it is temp related.

The voltage at the pump stays steady at 12 volts.

I double checked and really cleaned the ground.

I also tried to get straight lines both to and from the fuel pump and filter. Lines look good but I am not above replacing them.

Nothing like getting your ass kicked by a 20 years old Fiat!

[mkassing]

Okay, found one more item to fix, there is a slight leak in the plenum allowing air in on the right side back. I do mean small, carb cleaner has a very slight effect on the engine.

[rlux4]

It's good you found the leak. It doesn't take much air to make a big difference in how the car runs, because it's air that the ECU isn't taking in account for. Take a look at your AAR when it's in the open position sometime, you'll be suprised how small the orfice is.
Ron

[Foster48x]

Okay, found one more item to fix, there is a slight leak in the plenum allowing air in on the right side back. I do mean small, carb cleaner has a very slight effect on the engine.

Did fixing the vacuum leak fix your problem?

Rick

[TeeCee]

I know this may be an old thread but I'm having a similar issue with my 82 2000,
I cleaned and checked every ground I have found on this car except for what may be lurking underneath.
I had a datsun that had rust in the tank that acted this way once. Never knew when it would do it. I used a portable compressor to blow it out and away I went. This approach had no improvement. The AFM works right as best as I can tell and from what I've read. I've sprayed carb cleaner every where and dont seem to be any vaccum leaks.
Can a bad vacuum advance do this? If so, how do you check it?
LMAO, i have too many issues. I wanna drive this dang thing so bad!

[GeorgeT]

Replace the fuel filter (just after the pump). After sitting that long, sludge in the tank may have been picked up and is clogging the filter.