Mechanical Fuel Pump Issues

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enio45
Posts: 826
Joined: Wed Jul 02, 2003 6:56 pm
Location: Gilbert, AZ

Mechanical Fuel Pump Issues

Post by enio45 »

After reading Kerry's thread with his fuel issues, i decided to post mine here as well - not to hijack his thread. Although the two issues are different - there are some fixes that could help both issues.

On a slightly different issue with fuel delivery, I have been fighting this problem on a GTC that we recently had rebuilt. This issues was with the car, before the rebuild and a variety of patches were discovered when we did the rebuild. ISSUE: The mechanical pump cannot provide sufficient fuel pressure without the electric pump. After pulling the pump on and off 20 some times check various things - we are able to get 2.4 lbs of pressure on the carb side of the regulator.

We did the measurements on the fuel pump cam rod and we have 2.4 MM of stroke. The max or recommended should be 3.0 mm, so possibly I'm a little light on stroke. Then we experimented with various thicknesses of gaskets, and phenolic blocks, trying to fine tune the stroke to maximize the diaphragm movement. We rebuilt the pump several times, using both the orig reed valves and tried the replacement generic valves.

After multiple iterations - the 2.4 was the max press with can get with the mechanical pump. Incidentally in discussion with Bill at GT Car Parts - he said the electric pump should be 4 -5 pounds, which ours was only 3 pounds, which is another issue ill pursue. Our elect pump is aftermarket by FAUCET (i believe) . There are numbers on the bracket of the pump that translates to the pump pressure. I have not checked ours yet - BUT, i like the idea of adding a shield to insulate the pump from the exhaust pipe heat.

Back the mechanics side - when we rebuilt it, the new valves do not seat in the cavity like the old ones and the springs also don't have a place to seat as well - so this may be an issue of alignment when you screw the top cover back on and get some movement of the valve and spring.

Additionally - the diaphragm today is the single layer type, where the past they used a two layer one and originals were 3 layer, which i don't know if there is a difference in performance. Also, GT car parts had another diaphragm that had a slightly longer shaft that Bill gave me to try to see if it made a difference in the volume of flow, thus greater pressure.

Having said all the above with trail and error, including breaking the arms of the pump lever due to too tight of thickness between the block and the pump, out of frustration, i went home and took my 330 GT pump off my car which is orig to the car and rebuilt (about 6 yrs ago) and never run. Looking at the pump, i notice my diaphragm had the 2 layer style and it also had the orig valves, phenolic etc on the pump. I installed my pump on the GTC and 'Walla" we got pump pressure 6 lbs on the pump regulator side and 3 lbs on the carb side. !!!!!

At this point, I'm not sure what the issue is with the orig pump on the GTC, especially after multiple swapping of parts, gaskets etc. For now i put the issue on the shelf and will get back to it after Monterey Week - but if anyone has any suggestions - I'm all ears - we can talk about it at Tom's party thursday nite!
Ed Montini
330 GT 2+2 Series II - 8289
58 Ellena - 0855GT - orig drivetrain
87 El Camino SS
Steve Meltzer
Posts: 982
Joined: Mon Sep 06, 2004 10:31 am
Location: with Barney the Beagle boy and Enzo 8995

Re: Mechanical Fuel Pump Issues

Post by Steve Meltzer »

you probably know this, but at least on my e-pump (Facet as well), it must be mounted vertically, upright. Not sure if that would answer your pressure problem on the e-pump side of things or not. s
steve meltzer,
"I've spent all of my money on wine, a beautiful woman, and stunning cars. Then, squandered the rest."
330Jim
Posts: 85
Joined: Thu Oct 21, 2004 3:24 pm

Re: Mechanical Fuel Pump Issues

Post by 330Jim »

Were you able to check the spring to verify it is the right spring rate? Checking it in the installed condition and comparing it to your good pump would be the best bet since that will take into account any installation differences. The spring rate has a direct correlation to discharge pressure.

Cheers Jim
enio45
Posts: 826
Joined: Wed Jul 02, 2003 6:56 pm
Location: Gilbert, AZ

Re: Mechanical Fuel Pump Issues

Post by enio45 »

Jim, i have that on the list to do now - when we get back from CA.....
Ed Montini
330 GT 2+2 Series II - 8289
58 Ellena - 0855GT - orig drivetrain
87 El Camino SS
Don Micheletti
Posts: 13
Joined: Sun Sep 26, 2004 7:59 pm
Location: Menlo Park, CA

Re: Mechanical Fuel Pump Issues

Post by Don Micheletti »

When I rebuilt the mechanical fuel pump on my GTE, it drove me crazy because no matter what I did I could only get about 2-1/2 psi out of it. I could tell that the inlet check valves were leaking because I could blow back through them with the pump disassembled. The checks were new.
In the end, it turned out that the gasket between the check body and pump top was leaking. I had to machine that body sealing surface smooth and use a square cut "O" ring as a seal. After that I got 6-1/2 psi out of the pump.

Don
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: Mechanical Fuel Pump Issues

Post by John Vardanian »

How well these little gaskets seal makes all the difference. After years of screwing around with it, I learned the best results came from cutting these out of 1/16" stock gasket paper. The same goes for the heart-shaped gasket on top. The paper seals well, it's indestructible and most importantly it's oblivious to the current formulas that attack the elastic materials.

john
PF Coupe
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