Vacuum in fuel tank...

[Master-O-Turbonics]

so I have been having an issue with my 81 210 just randomly shutting off the engine and only running at low speed or even shutting off completely. At 70mph on the highway it cuts off and goes down to about 25mph.

 

 

Yesterday morning when I put 6 gallons of gas in the car, there was considerable vacuum in the gas tank.

Today the engine shut off for the most part after the top of 1st gear from a 4 way stop. I popped the hood and looked at the fuel filter and it was empty, and filled back up slowly as the engine was idling. When I first lookked I could hear the mechanical fuel pump sucking air through the lines...

 

The car has just the stock mechanical Nikki fuel pump, no electric pump at the back. Gas tank was recently professionally re-coated just before I bought the car.

 

Fuel pump is believed to be good. no gas spewing everywhere...

 

Ideas?

What is causing the vacuum in the gas tank that seems to be starving the fuel pump? Fuel consumption and a possibly not functioning atmospheric vent line?

[datzenmike]

Replace the gas cap on the tank.

[Master-O-Turbonics]

Replace the gas cap on the tank.

 

Isn't the cap supposed to seal though? this one seals great...great enough to hold a good vacuum.

[sinner720st]

if the setup is anything like the one on the 720 your tank should have a tube running up to the front that is supposed catch all the fumes in a charcoal canister then burned in the engine , try unplugging the line from tank to canister... if you do that you will prob have to disconnect and plug all vacuum lines

 

 

so according to this thing, at a glance it shows vacuum relief cap

Edited October 27, 2010 by sinner720st

[datzenmike]

I had this happen on a long trip to Ontario. Every time I fueled there was a big rush of air. I thought it was coming out, too much coffer, not thinking. Got within 60 miles of getting there whe the truck ran out of gas at 1/4 tank???? wtk???? I got out and noticed in the dark that the tank had collapsed. It was half it thickness!!!! Air pressure at sea level is almost 15 psi. that's over a ton per sq ft!!!! Leave the cap loose till you find out what's up.

[Master-O-Turbonics]

Running the car with the gas cap loose made no difference.

[datzenmike]

Well how is vacuum going to collect in a tank with a loose cap????? :lol:

[Master-O-Turbonics]

I thought the vacuum was bad. LOL.

 

I can drive the car as long as I want as long as I'm only on the primary circuit in the Carb. Going into the secondaries for any kind of time kills the engine and the fuel filter goes empty.

Tomorrow I'm going to pull the fuel pump apart to see if the diaphragm has any issues. (I have a like new L series fuel pump, are any parts interchangeable?