Logo
FULL SITE MENU

Air in fuel line???

P

pinkhippo72

New member
Hello,

I have a 1997 Mercury 175 EFI. I have been having some issues with it to include running rough at idle, stalling at idle, and difficulty starting. It has new gas and we have replaced all the filters, checked and replaced lines, installed new pulse pump, checked vapor separator float and tank as well as electric pump, and had the fuel injectors sent to Brucato for cleaning. After the injector service it ran much better but there is still an issue. Also we have done quite a bit of troubleshooting on the ignition system to include new plugs and spark confirmation. Also checked the timing and its fine.

Today after it wouldn't stay running for me I removed the fuel line going into the water separating filter and it just blew pressurized air out with a "whoosh" sound, not a drop of fuel going into the filter. With the line removed still I pumped the primer ball and out gushed fuel as its supposed to. Reconnected the line and still wouldn't start for me.

Any ideas what might be causing the air in the line? Thanks for any advice!

Meg
 
Bad/clogged tank pick-up, bad connector at the tank, toasted anti-syphon valve. Start at the watersep filter and work back towards the tank. Sounds like you have done the work from that point through the motor itself..
 
Thanks for the reply galamb... I tried running the motor off a remote tank and still nothing. So that should rule out any tank or tank line issues. Tomorrow I am going to work my way through each section of the fuel line at the engine and see if I come up with anything. I just don't understand how air is getting in the system. Do you think I could have a vapor lock issue? Thanks again for any advice.
 
Just got back in from tracing the fuel flow... I did a cranking flow test from a stand alone gas tank and removed the primer bulb line and also the engine fuel inlet connector from the equation...

Turns out I am getting no fuel flow through the pulse/mechanical pump. I ran a short line right from the remote tank to the pump and removed the pump outlet line... cranked the engine for several seconds and got no fuel flowing into or out of the pump.

This makes sense for the symptoms I am having, because when I prime the engine initially it is forcing fuel through the system and filling the vapor separator tank. The electric pump works and the motor will start and run for a short period of time and then die out as if it is being starved of fuel. So it is running of the primed fuel but the pulse pump is failing to replenish the supply and it dies.

My problem now is that we already rebuilt the pulse pump so why isn't it working??? It was a pretty simple job and we followed the mercury manual we have so I'm confident it was done correctly. Also, when rebuilding it the original pump appeared fine but we rebuilt it anyway since we already tore into it. Being that the pump is run off crankcase pressure from piston travel, do you think I could have an internal motor issue that is causing the pump not to pump?

Another thing I found odd was that fuel would gush out of the water separating filter (in the opposite direction of fuel flow) when I had its inlet line off and cranked to test for flow. So basically there was no fuel being pumped into its inlet (from the pulse pump) but fuel would gush out of its inlet connector back towards the pump. Any ideas what that is about?

Thanks again for all the input!
 
Back
Top