1998 Mercury 150 EFI

[SoFloStone]

My engine started running badly towards the end of the last time out, and I have narrowed it down to fuel. (spark and compression are good on all six).

When priming the bulb, I can hear air escaping somewhere around the VST housing, but cannot locate the exact area.

Is there a check valve in the external fuel pump that may be the cause?

The weird thing is that there is no fuel that leaks when the engine is running, so it seems to be an internal leak somewhere that I am hearing.

Any help would be appreciated.

 

[CharlieB]

Re: 1998 Mercury 150 EFI

ALWAYS carry a spare set of spark plugs.

Many drivability problems are caused simply by worn or fouled spark plugs, they will start, idle and run OK at low throttle settings, but mis-fire under heavier loads.

K.I.S.S.

 

[hkeiner]

Re: 1998 Mercury 150 EFI

When priming the bulb, I can hear air escaping somewhere around the VST housing, but cannot locate the exact area.

The sound of escaping air does not sound like a good thing. You might try lightly spraying some soapy water onto the general area where you hear the air (while squeezing the bulb with the motor off) and then look for some bubbles. Avoid damaging or shorting any electrical parts by letting the motor dry before starting it up. Just my thoughts...

 

[SoFloStone]

Re: 1998 Mercury 150 EFI

ALWAYS carry a spare set of spark plugs.

Many drivability problems are caused simply by worn or fouled spark plugs, they will start, idle and run OK at low throttle settings, but mis-fire under heavier loads.

K.I.S.S.

Thanks for the reply, but this is not a spark plug isssue, this is a fuel related issue.

Compression test and spark test + new plugs was the first thing I did.

 

[SoFloStone]

Re: 1998 Mercury 150 EFI

The sound of escaping air does not sound like a good thing. You might try lightly spraying some soapy water onto the general area where you hear the air (while squeezing the bulb with the motor off) and then look for some bubbles. Avoid damaging or shorting any electrical parts by letting the motor dry before starting it up. Just my thoughts...

Did that, but no luck..

I will be taking it to the place I purchased it from on Tuesday, adn see if we can get to the bottom of this. Although used, the engine came with a 45 day warranty, and the Seller seems to be standing by this even tho he is closing shop.

Thanks for trying to help

Rick

 

[hkeiner]

Re: 1998 Mercury 150 EFI

I can hear air escaping

Since you can hear the air escaping but can't locate the exact spot with your naked ear, you might try using a mechanics stethoscope to find the exact spot. This tool is not expensive and is available at most automotive parts stores. Or, you can do a search on the internet using terms such as "mechanics stethoscope" or "automotive stethoscope". Just my thoughts...

 

[SoFloStone]

Re: 1998 Mercury 150 EFI

Since you can hear the air escaping but can't locate the exact spot with your naked ear, you might try using a mechanics stethoscope to find the exact spot. This tool is not expensive and is available at most automotive parts stores. Or, you can do a search on the internet using terms such as "mechanics stethoscope" or "automotive stethoscope". Just my thoughts...

Got one, but the sound seems to reverberate off the VST housing. the closest I get to hearing the sound, is from the external fuel pump.

I am stumped on this one...

 

[CharlieB]

Re: 1998 Mercury 150 EFI

Try using the stethoscope on the fuel pressure regulator.

If the diaphram wears thru the fuel will leak back into the VST, no external leak. That COULD be the hiss.

Test by checking fuel pressure at the port provide, test under load, in gear, watch to see if the pressure falls off as the throttle is opened to WOT.

 

[CharlieB]

Re: 1998 Mercury 150 EFI

Addendum

If the fuel pressure regulator diaphram has a pin hole then it could leak (hiss) into the small hose leading to the intake manifold.

Pull the hose off the regulator at an idle and look for any fuel.

 

[SoFloStone]

Re: 1998 Mercury 150 EFI

I took it to the Mechanic last week, and it seems that one of the recirculation hoses that takes the excess oil in the cylinders back up to the pump failed, and required replacement.

Thank you all for your help.

Rick