77 M20j fuel pressure fixed!

[Joe Larussa]

Been chasing a fuel pressure issue for weeks.  Unsteady needle with pressure going up and down.

Removed the fuel pressure hose at the back of the gauge. Then removed the restrictor. It was totally plugged with what looks like aluminum. Can't explain how it got there other than I hear of people

making a restrictor by filling with some kind of silver stuff and then drilling a small hole. Ran a small

drill bit through it and now it's perfect!

[jetdriven]

Pics?  Interested ! 

[Joe Larussa]

Here is a pic of the restrictor that was plugged.

[RobertGary1]

Have you seen much aluminum in your filter? Do you pull your sump screen?

-Robert

[Guest]

The fuel pressure gauge system is down stream of the servo finger screen.  Have you looked at the fitting in the servo body or the fuel pressure hose ends?  

Clarence

Edited September 10, 2015 by M20Doc

[Joe Larussa]

Well went flying after work and she's up to her old tricks. I just don't get it. The thing is I'm not really sure how big the hole in the restrictor is. For all I know it's as small as a needle and all that metal belongs there. I ordered a new one today and will see what a fresh new one looks like on Wednesday. This engine only has 50 hours on it. 

Thanks 

[jetdriven]

It's the fuel pressure not the oil pressure.  Why are there metal shavings in the fuel pressure line?

[Joe Larussa]

Ok so here's the thing. Apparently it wasn't a bunch of metal in the fuel restrictor. When they make these it's a modified AN fitting they fill with some kind of metal and then drill a tiny hole into it. I guess it wouldn't take much to fill a hole that's roughly 0.040. I'm going out to pull the gauge and restrictor and have it bench tested tomorrow. And so the fun continues.

[jetdriven]

How do you bench test a restrictor fitting?  what is it plugging up with?

[Joe Larussa]

Good question. You take it to the Gyro House in Auburn Ca. Just removed it and taking it over tomorrow. I'll let you know what happens.

[Nemesis]

Joe, why not just turn on the fuel pump with the fuel pressure line disconnected and draining into a jar or something? If there is something in the line maybe it will just blow it out into the jar - for you to find and inspect - and not clog up the gauge anymore.

Dave

[philiplane]

The orifice is normally very small, I will have to look but I think it's supposed to be .040". The correct fitting is not modified, they are made specially that way in one piece. The one you have is home made.

Edited September 10, 2015 by philiplane

[Joe Larussa]

Just received a new restrictor from Lasar. It's exactly the same as the one I thought was plugged. You can not see a hole and can't blow through it. Maybe mine was not plugged.

Had TGH open up the gauge and they said it has fuel contamination. Sent it off down south

to be tested and most likely overhauled . These units are very hard to come by.

[carusoam]

I'm glad you decided to seek some professional help for something that is difficult to understand and is intrinsically attached to your fuel system.  

Hangar elves have their shortcomings.

best regards,

-a-

Edited September 13, 2015 by carusoam

[Marauder]

Hangar elves have their shortcomings.

best regards,

-a-

Like not being able to reach things on top of the engine?

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[Browncbr1]

When you get it back together, I'd like to suggest removing the injectors from the fuel lines and running your boost pump so each line fills up a solo cup.  Do this while cycling the fuel selector back and forth.   Just to make sure anything that might be in there has a better chance of purging.    

[KSMooniac]

I have a MP/FP gauge from my 77 J for sale in case that is a better solution.

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[Joe Larussa]

Hey Scott,

Talk to me about your gauge. I'm interested.

 

Joe