Here's the scenario:

The car: 1988 RS, former 305 TBI car, now running a 4bbl 600cfm Edlebrock with a mallory fuel pressure regulator (return style) at 4 psi. Roughly 120,000-130,000 miles on the stock fuel pump.

Over the winter the fuel pressure regulator would 'skip' when the fuel pump was running and the engine was off (never did this before). Watching the fuel pressure gauge (on the regulator) I could see the needle go up to 4psi, skip down to 0, then back up to four, all the while making a "click" noise as the pressure regulator opened-closed-opened etc. I mis-diagnosed it as a dead battery providing too little juice to the fuel pump.

Today the weird part happens. On the way home two full-throttle rips sees the car fall on its face as soon as I hit the secondaries (i.e - after I place a serious demand on the fuel system). After I park the car I can hear what sounds like bubbling / boiling water (with the car turned OFF). Removing the gas-cap had no effect and neither did unplugging the line to the charcoal canister.

With the car off I turn the key to start the fuel pump (its hot-wired to come on before the "Start" position on the key) and it groans noticeably then goes back to its skipping described above. I can still hear the bubbling noise. I let the car sit for 2 hours, go back and turn the key to start the fuel pump, it sounds normal, but again, the regulator is skipping, suggesting poor pressure / flow.

It sounds to ME like I have a dying fuel pump. It builds pressure, slows and then picks back up in unison with the regulator opening, closing, and opening again. Considering the change in tone of the pump motor as well, I think that only supports my conclusion. That does NOT explain the bubbling sound from the fuel lines, but perhaps if the pump is too old it will run hot causing the fuel to boil and / or the tolerances being too loose are now causing cavitation, allowing air into the fuel.

I'd love some feedback / experiences on this one. My plan of attack is:

1. Check carb fuel filter and chassis mounted fuel filter for obstructions.
2. Re-check fuel pump behavior and flow OUT of regulator (is there ANY flow going to the carb? etc)
3. Install a mechanical pump in-line with the electrical and let it suck through the electrical.

Thoughts please?

 

Quick question: why are you running that carb at 4psi? You should be at 5.5-6.5psi.

Although the symptoms to me either sound like a dying pump (which happens, these electric ones werent made to last forever), or vapor lock maybe? Where are your fuel lines in proximity to the exhaust headers?

 

Well...they're edlebrock TES headers which run around the same place as the exhaust manifolds from GM. I don't think thats the cause tho.

I'm thinking that I either have a plugged up filter (so the pump is working WAY too hard, gets hot, and the fuel bubbles) or my pump is dying, getting hot because its old and tired, and causing the fuel to bubble. Either way the heat / bubbling is DEFINITELY in the back of the car.

I'mna pull the filter this weekend and see what I find. Hopefully its just that. But knowing my luck its a filter.

Does anyone know if its OK to run a mechanical sucking through the running (but assumedly tired) stock in-tank pump?

Tyler

 

The vets on here discourage going that route, from what I have read.

 

I'm a moron. Started diagnosis today - apparently I DIDNT replace the fuel filter. Punch me in the junk.

Thanks for trying to help guys

Tyler

 

Sweet, if only all of our problems were that easy all the time. I envy you.