fuel pump problem today.. figure THIS out

[Zedyone_kenobi]

Okay, configuration... I am running triple webers on an L28, fueled by a Mallory Comp Pro Series 70 (P/N 4070LP) fuel pump set at 4 psi. I was getting 2.75 psi to the fuel rail under the hood. This setup has worked flawlessly since 2010, and the webers loved it. Well I finally finished getting the dash back in the roadster and took her out for a pleasure drive for the first time in 4 months, and had to back up the Z.  I just drove the Z 2 weeks ago and I swear she was running better than ever.  Car has been rock solid for years.  However, the thing would not start, and smelled like it was getting way too much fuel.."How can this be I thought, I have everything dialed in!" Still smelled like fuel. 

 

I got out and noticed a STRONG fuel smell and my fuel pressure gauge on my fuel rail, which is normally happily at 2.75 or so reading, well it was not reading anything as the needle was pegged past 18 psi and my beautiful webers were streaming fuel out at an alarming rate. Guess I know the floats cannot stop 18+ psi.

 

So I took the pump out and pulled off the bottom off to see the seal and expose the gear. I cannot see anything that would lead to this happening. I have never touched the tensioner spring inside the bottom of the pump.

 

Any ideas?

 

 

[Zed Head]

Just went over this pump with jxq.  That pump uses a bypass port to regulate pressure.  I'll bet there's something blocking it.  Not sure exactly where the passages are but the instructions describe screwing a bolt in or out to get some variation of pressure, probably by shrinking or enlarging the port.  I'd remove that bolt and see what's in there. 

 

Here's the instruction sheet - http://www.jegs.com/InstallationInstructions/600/650/650-4070LP.pdf

Edited April 8, 2016 by Zed Head

[Zed Head]

By the way, older floats are basically just tin bubbles.  High pressure can bend/crush them, I think.  Carb people went to plastic in later years.  Hope you're not at the start of a trail of fixes.

[Zedyone_kenobi]

No my webers are only about 5 years old. They are not vintage italian ones....rather the ones made in spain.  They have plastic bowls.

[Zedyone_kenobi]

May have found it.

I undid the locking nut and the allen bolt and the spring loading the bypass plunger onto the seat in the body just fell out. This piece moves to regulate the pressure output by the pump. Very simple design. However, the brass cylinder was stuck against the fuel body and would not move a bit. I had to pry it out. Apparently a piece of sludge or something got in there and held it up hard.  I took it out and ran a brass 9mm gun cleaning brush through it and it slides in nince and falls out easy.  It actually operates.  I would be willing to bet this was my issue.  I will install it back into he car and see what I can get.  It may be time to install a new filter in there. I have been running the same one for years.  

 

 

[Captain Obvious]

Well that's not cool. Did you lay eyes on said sludge gumming up in the pressure regulator?

I'd be concerned that without knowing the origin, it could happen again?

[Zedyone_kenobi]

Yeah, it could, but it was on the bottom of the cylinder bore horizontal to the ground.  I think it was accumulated junk from the fuel and the fact the car is not driven enough. Either way, I am going to replace the fuel filter as it is a few years old, Just to be sure.  I would hate to have this happen while I am driving.

 

 

[Captain Obvious]

Yeah, that would be really bad for that thing to stick while driving. You might not even know about it until it's too late.

What kind of fuel filter are you running? The ubiquitous G3, or something different? Seems weird that anything "visible" could make it through a filter like that, even if it was a couple years old.

How about a liquid contamination issue maybe? Ethanol in the fuel reacting with the aluminum or the brass inside the pump? Water maybe? Something like that?

[siteunseen]

I just have pulled all the old gas out of the two I don't drive much.  Plenty of lawn mower gas for this summer.  

I have a cheap low pressure pump with a glass filter at the end of the output hose, fortunately it was nice and clear.

[Patcon]

Zedyone

Do you have a fire extinguisher in your Z? At 18 psi, blowing fuel everywhere above the exhaust, it might be a good idea....

[Zedyone_kenobi]

Cleaned out the pump and eureka 3 psi 

wonderful to solve a problem like this but truth be told 

It's time to address the filter 

[Captain Obvious]

One of my engineering mentors beat into me... "If you don't completely understand the true root cause, it's likely to happen again."

That, and "You shouldn't have told the company president that he has Recto-Cranial Inversion. He's smart enough to figure that one out."