Air in my fuel lines, sources? how to bleed? (MFI system)

jkarolyi · 05-20-2005, 04:08 PM

Hi Al,

I'm so.... close to getting my long-time '73 Viper green 911E Targa project running! I have spark to each cylinder, but no fuel coming out of the injectors. Each injector line will squirt fuel into a bottle, but there is evidently not enough pressure to open the injectors.

The culprit seems to be air in the fuel line. You can see bubbles in the fuel tank (through the sending unit opening)

The return fuel line (from the MFI pump to the fuel filter holder) makes gurgling noises and you can feel the pulse of bubbles going through the line. This isn't evident in any of the other rubber lines.

Where can this air be coming from? Are you supposed to bleed the system, and if so, how?

I double checked that the fuel pump is installed correctly (new pump), there are no fuel leaks, and yes, the fuel tank has plenty of fresh gas in it.

jkarolyi · 05-20-2005, 05:25 PM

anyone?

silverc4s · silverc4s's Garage

No, I never bled a new MFI system, just cranked it up. Perhaps your injectors have been sitting too long dry and are somewhat stuck??

BK911 · BK911's Garage

Wow, just when you thought you've seen it all! I've never seen air bubbles coming from a fuel return line. The system should bleed itself after a little while. THe only line that is under a negative pressure, that could suck air in, is the fuel supply from the tank to the pump. Make sure those connections are tight. Also, make sure all you have all the lines installed correctly.

And as Bill suggests, maybe your injectors could use a sleep over in an ultrasonic cleaner. Send me your injectors and $10 and I'll soak them over night. The $10 is for return postage and a can of Berrymans. Email me if interested.

Good luck!
BK

jkarolyi · 05-20-2005, 11:05 PM

Thanks for the generous offer BK...I'll take you up on that. I already soaked them in Berryman's for about three days...your overnight soak is in an ultrasonic cleaner, correct?

Any bites on that 911S Targa yet? If it were in LA I'd buy it.

304065 · 05-21-2005, 03:28 AM

Are you sure you didn't plumb the filter console backwards? The factory diagram is WRONG, Grady posted the corrected diagram.

Do you have the silver can filter tightly screwed down? Sometimes when you attach the supply line to the bottom it can get loosened up, which could introduce air into the system.

BK911 · BK911's Garage

Yup, a sleep over in an ultra sonic cleaner. I've put rusty ones in there overnight and they looked almost brand new the next morning. Email bkolar at grgce dot com for my address.

Jay Auskin · 05-21-2005, 06:53 AM

Take a look at what John Cramer said. That could be your problem. My car gurgles and bubles immediately after key-on. Then the air is gone, and it's fine. I had my injectors ultrasonically cleaned, and the opening pressures checked.

jkarolyi · 05-22-2005, 11:26 AM

I checked the filter housing plumbing and tightness, and all is well. I've let the fuel pump run for a good 30 minutes and it still bubbles! The mystery continues...

tobluforu · tobluforu's Garage

There is a little screw on top of the fuel filter mount. Put wrags under fuel filter, start car, turn screw, watch gas come out, freak out a little, close it up, turn car off and clean up mess-which should not be to bad. Now the directions I just gave are for a 72. But I doubt this is the prob. but who knows.

jkarolyi · 05-23-2005, 02:25 PM

>But I doubt this is the prob. but who knows.

Just tried the bleeder screw you described, and it just continuously bubbles and froths. I began to "freak out" myself after a few minutes when the gasoline smell was strong (right next to the electrical CDI box and all) even though I had plenty of rags to absorb it.

jkarolyi · 05-25-2005, 03:40 PM

BK911...I tried emailing you and sent you a PM, but no reply. Could you email your mailing address to:

karolyi74@yahoo.com

Thanks so much. Still haven't solved my bubbly fuel...

Jay Auskin · 05-25-2005, 06:52 PM

I just re-read your initial post. I think you need to check two things:

1. your tank...is it dirty, and is the intake screen clogged? Mine was, and I was in denial about it. Grady Clay set me straight.

2. your injectors. Pull them and have them ultrasonically cleaned and tested. Find a diesel engine place. The gasoline guys can't test to the MFI injector pressures. If you need a copy of the factory instructions, PM me, I'll send you a PDF. It cost me $70 total at a local diesel fuel injection shop.

An MFI system doesn't need to be bled. There's a return line that will do this for you in about 5 seconds. You need to probe deeper in to your problem.

Good luck!