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jmichaelre 07-14-2010 08:27 PM

Fuel Delivery Problems
 
Rebuilt 355 with 600cfm Holley
New Stock Mech Fuel Pump
Both Primary and Secondary Floats adjusted to Holley specs
Inline clear plastic filter

Heres the deal.......I'm running out of fuel or thats how it seems with anything more than light throttle. If I'm at medium or heavy throttle I hit a void and if let all the way off it will gradually accelerate.

When Idling or free reving the engine sounds strong and doesnt miss at all.

Heres one thing I noticed today: I had a small air bubble at the top side of my filter and another thing when I turn the truck off the fuel drains completely out of the filter.

I unhooked the fuel line from the carb and put the line inside a 2 liter bottle and it filled it about a half inch short of the bottom side of the label in about 20 secs of continuous cranking.

I've checked and reched all of my hose clamps and lines from the fuel pump all the way back to the tank and did not find any leaks.

Any ideas?

techinspector1 07-14-2010 08:34 PM

You'll be shooting in the dark until you determine what the fuel pressure is at all engine speeds and load conditions.

Tee off at the fuel line where it enters the carb inlet and run a line off that back to the firewall, then up past the lip of the hood and up onto the cowl of the car. Temporarily mount a mechanical fuel pressure gauge (0-15 psi) onto the cowl with tie wraps, duct tape or whatever means you can arrange (it's only temporary, so it doesn't have to be pretty). Observe fuel pressure through the windshield as you drive the car. Determine your course of repair from that info. Holley carbs will tolerate a max pressure of about 6 1/2 psi before the pressure blows past the needle and seat. Shoot for 6 psi with regulator, different pump, return line, or whatever.

jmichaelre 07-14-2010 08:39 PM

Tech

What exactly should I be looking for? Like what psi should I be getting?

lmsport 07-14-2010 08:43 PM

4-6psi continuous.

One time, I had a customer use a clear filter that had a plastic element. After a short while, the plastic element had swollen and was restricting fuel flow.

jmichaelre 07-14-2010 09:08 PM

I'll give it a try tomorrow and get back with you guys.......THANKS!

cobalt327 07-15-2010 10:25 AM

The filter won't stay full, so don't worry about that- unless you orientate it straight up and down. That way it'll stay the fullest.

But there is a check valve at the inlet and outlet to allow the pump to operate, the filter shouldn't drain itself empty- at least not immediately.

kleen56 07-15-2010 10:48 AM

I've had new mechanical fuel pump not work on a few occasions. The symtoms your describing sure sounds like the pump is not delivering fuel when it needs to. The fuel gauge like the other stated will tell you what is happening. If you have another fuel pump that you know is good, try switching it and see if that changes anything. Sometimes you have to go by process of elimination.

jmichaelre 07-15-2010 11:18 AM

I have the filter sitting vertically and after shutting the engine down about 2 to 3 minutes later it drains down to about half full and then within 10 minutes its empty.

I'm going to pick up some extra fuel line hose so I can check the psi tonight. I'll let you know what I get for readings.

jmichaelre 07-15-2010 12:45 PM

Went home over lunch and hooked up the gauge, but never took it for a drive. With the truck idling I was getting between 9 and 10 psi which is crazy high I pinched off the line a little between the filter and the carb and got it down to 7, 6, and then 5.

Is this reading possible with a stoch mech fuel pump. I do have to mention that all of my drivability problems have been in drive the worst in 3rd gear.

If I drop it into first or 2nd I dont have any problems. Is it possible that this reading is right and that my needle isn't being able to withstand the pressure?

cobalt327 07-15-2010 01:08 PM

Quote:

Originally Posted by jmichaelre
Went home over lunch and hooked up the gauge, but never took it for a drive. With the truck idling I was getting between 9 and 10 psi which is crazy high I pinched off the line a little between the filter and the carb and got it down to 7, 6, and then 5.

Is this reading possible with a stoch mech fuel pump. I do have to mention that all of my drivability problems have been in drive the worst in 3rd gear.

If I drop it into first or 2nd I dont have any problems. Is it possible that this reading is right and that my needle isn't being able to withstand the pressure?

In first or second, the RPM is higher, that usually means more fuel is being used, so it is possible for the carb's needle and seat to be more overwhelmed in high gear than in the lower gears.

But if the gage is accurate, that is likely the problem- TI for the win! lol

jmichaelre 07-15-2010 01:11 PM

Should I throw on a regulator and see if it fixes everything?

cobalt327 07-15-2010 01:13 PM

Quote:

Originally Posted by jmichaelre
Should I throw on a regulator and see if it fixes everything?

My only concern w/this, is the fuel pump is draining the fuel from the line and filter quickly- and I just don't think it should. Combined w/the too high pressure (provided the gage is accurate) makes me think the pump's faulty.

jmichaelre 07-15-2010 01:20 PM

got me puzzled too.....one thing to note is that the filter is always full when its running....

techinspector1 07-15-2010 02:34 PM

Quote:

Originally Posted by jmichaelre
Should I throw on a regulator and see if it fixes everything?

A regulator will likely bring the pressure into line, although it is not the ideal fix because fuel is dead-headed against it, heating the fuel and working the pump harder. If I were going to do this, I would want to use a bypass regulator and return line to the tank to bleed off excess pressure.

Alternately, you could install a stock pump. What is on the motor now is NOT a stock pump. Here's an example of what I might install....delivers 5 1/2 to 6 1/2 pounds pressure, no regulator needed....The Holley carb needle and seat can handle 6 1/2, whereas an Edelbrock or Carter AFB could not.
http://www.summitracing.com/parts/CRT-M6624/

jmichaelre 07-15-2010 02:58 PM

Bought this pump at Oreilley Auto Parts told them it was for an 86 Silverado 4x4 with a 350. I paid 34.99 for it....here's the link

Fuel Pump link

The pump has a return so it won't be deadheaded right?


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