1980 FI acts like it is starving for fuel

[mkassing]

Okay, I am at my wits end with this. I have a 1980 FI that has been acting up. History: parked for a few weeks and was running well; turned on the key and dead fuel pump (voltage at pump no pump); replaced the fuel pump with OEM Fiat; running for test drive; bogged after running for a few minutes; replaced the fuel pump with after market fuel pump; ran better and then started doing the same thing.

Problem: runs fine when started; runs fine when driving for 3 minutes; bogges down like it is starving for fuel after driving with load; pull over and the fuel system seems to catch up; pull into drive way and idles fine; bring it up to 3000 rpm for 30-50 seconds and it duplicates the feeling of starving and it drops down to 500 rpm and almost dies; bring it back up to 3000 rpm and hold for 30-50 seconds and it does it again.

I have check all of the electronics and they seem to be in the good range for the ohms. The fuel lines are all clear and the filter has been replaced. What in the world is causing the fuel issue? The afm is now setup perfect so the pump only runs when the car is started; the idle sensor clicks only when the gas peddle is pushed and the ohms read correct.

And the fuel pressure at the injectors is around 40. Although I have not seen what it is while the starvation issue is happening. It would likely be next to zero. I have also pinched the AAV and nada, same issue.

HELP!

[Foster48x]

I had the same symptoms with my 80FI but it ended up being a vacuum leak on the main air intake hose. Before you go crazy dealing with a fuel issue I would check all of your vacuum hoses.

Rick

[mkassing]

too late, already went crazy!

It acts like a leak but I checked everything I know to check. Which vac line did you have a leak in?

I also just did a fuel pressure check inline while I drove. Took it awhile to act up but I saw my pressure go from 30ish to 20ish to 10ish and then when it did it did not go back to the 30's. If I let it sit for a few it will go back to the 30's and stay there for awhile before going to 10 again. Here is what I find hard to believe, that I put in 2 different fuel pumps that just so happen to have the same issue? I really don't think it is the pump.

Could it be the voltage to the pump is dropping? I was under the understanding that the voltage was the voltage was the voltage; on or off. Am I wrong? If so what controls the voltage to the pump?

Thanks Michael

[mkassing]

Crap, does this mean the Fuel Pressure Regulator is bad? Vac leak to the regulator? How does one test?

[rlux4]

A line goes to the fuel pump from the dual relay on green with black stripe wire. The dual relay makes the contact for the fuel pump when the flap in the AFM opens.
Your fuel pressure should be up around 38 lbs. Pressure is regulated by the pressure regulator, which needs a good vacuum line to it. That's where I'd check.
Ron

[So Cal Mark]

the dual relay supplies voltage to the pump. Put a voltmeter on the pump terminals to see what you have
How is the integrity of the supply hose to the pump? Any cracks in that hose can lead to starvation. The pickup screen in the tank could be an issue or your tank may not be vented and creating a vacuum so fuel can't flow. Try driving the car and loosen the fuel cap when the condition arises

[mkassing]

Ron,

Strange thing, when I remove the vac line my pressure goes to high 30's low 40's. When I reconnect it it goes back down to low 30's. Stranger thing, when I pinch the return line my pressure goes to zero, I expected it to go up.

To be clear, the only thing that has changed form a great running car to a poor running car has been the fuel pump. But what if I have the return line and the main fuel line crossed? I have the return as the bottom of the two and the main as the top, just like it has always been. But the drop in pressure when the return is pinched troubles me.

[mkassing]

Mark,

Thanks for the reply! I have 12.2 volts at the pump and the lines while old do look okay and not pinched. There is one line that I am confused about that does not look like it carries fuel, it is by the tank on a short hose with some sort of filter or regulator inline. It looks like it comes out of the tank and back in, it was unhooked and I hooked it backup last week and it did not solve the problem, but I dont know what it does.

"The pickup screen in the tank could be an issue or your tank may not be vented and creating a vacuum so fuel can't flow. "

When I use to open my cap I had hissing, now I dont. I will try the cap off thing in about 10 minutes but what else should I look for on this, I did note that when I was changing the pump for the second or third time that the flow was slower.

THANKS!

[mkassing]

Strange!

Took the gas cap off and it happened again.

Took the vac line off the pressure reg and it runs GREAT (idle a bit high) with NO drop in pressure. WTF?!? I could drive it to New York the way that it is running now (I fixed a few things while tracing down the issue). So what gives, do I have a dead regulator or do I have a line crossed? With the vac line off I am getting a rock steady 37ish pressure with my foot slammed down or coasting like a baby.

What should I test next?

[rlux4]

The fuel pump will put out more pressure than is needed, the regulator's purpose is to, uh, regulate the pressure. So, it's sounding like you either have a failing regulator or restricted vacuum line/source. Check your vacuum line and make sure the orfice it's plugged into on the plenum is not plugged with gunk.
Ron

[So Cal Mark]

I did run across a Spider with the two fuel lines reversed. The car was really hard to start, and barely ran after being primed.

[mkassing]

Ron,

I will check the vac line but I am almost sure now that the regulator is DOA. I drove it yesterday with the reg vac line disconnected and got it to 110 mph with plenty of room on the pedal. Drove it at 35 mph today and it started to starve. On the bright side, I now know what EVERY component of the FI systems does and that everything else is good to go.

@Mark, good to know and it turns out that I was crimping the intake line (ya ya ya, stupid mistake).

Thanks,

Michael

[mkassing]

Okay, got the new fuel pressure reg in and guess what? Didn't fix a damn thing! So here is the story, start the car fine pressure, drive the car and the pressure fine, drive the car for 5 minutes and the pressure goes bad. By bad I mean that the pressure starts doing the inverse of what it should; I press on the gas and rather than getting a rise I get a drop in pressure. If I turn the car off for a second or two it is fine.

As near as I can tell everything is fine except that I am getting some sort of weird load up or cavitation in the fuel. Any suggestions?

[Foster48x]

too late, already went crazy!
It acts like a leak but I checked everything I know to check. Which vac line did you have a leak in?
Thanks Michael

The big black one coming off the AFM. It was a small (very small) crack in the nipple that comes off the side of it. Just that very small crack sucked in enough air to reek havoc on the FI system causing the same symptoms your encountering.

Yours situation may not be as easy of a fix as mine was but it wouldn't hurt to replace all of your vacuum lines and hose clamps If your not 100% sure that they're good. It's a cheap fix and will at least eliminate it as a variable.

Good luck.
Rick

[majicwrench]

This is not a vacuum line issue.
So do you have a pressure gauges "T"d into the fuel line coming into the rail?? And you are watching the pressure drop on accelleration??
keith