Fuel pump problems

[BLP]

I am having some fuel pump issues. I have a blueprint 496 crate motor in my 1971 suburban C20. I have been having this issue with the fuel pump not pumping when the engine gets up to temp. about 190’. It is all good when it is cool, good flow and 8psi. But when it reaches 190 the pressure tapers off and I can see the fuel filter start running dry. I had a Holley mechanical fuel pump that I now replaced with a new edelbrock pump. I removed the gas tank and made sure everything looked good inside there. I also removed all the fuel lines and blew them out with compressed air. I replaced all the rubber hoses with new. I thought that maybe what I was seeing was water in the fuel filter so I put 2 bottles of heat in the tank after inspecting it again. I have now replaced the fuel pump push rod with a new high quality one and still after each thing I did it does the same thing. My current thought is when the block is warm that passage for the push rod tightens down not allowing the rod to pump the pump. I have run a hose from my fuel pump to a jar of gas and it did the same thing. The engine only has a few 1000 miles on it. I don’t really want to go to an electric pump but that seems my best option. Does anyone have any ideas on anything I can try? Thanks for any input. Sorry for being so long.

[watash]

Might be a dumb answer but can you "polish" the rod to reduce the O.D. or could you have the wrong rod, if that is possible.

[BLP]

I thought that I had the wrong rod or sub par so I bought good quantity with the same results. I thought about turning it down but I am afraid to make it too thin and damaging something.

[cadillac_al]

Two different fuel pumps and the same problem. I have never seen a fuel pump rod failure myself and I think it would be pretty rare. I just had an issue with my truck where it had a pin hole in the fuel line. I couldn't see it and it didn't leak but my mitivac couldn't build any suction in the fuel line. My fuel pump was having a hard time sucking fuel too. Try a mityvac on the fuel line to make sure there are no leaks.

When you ran a hose to a jar of fuel, the fuel pump really should pick that up. If you really have a bad lobe for the fuel pump, you should be able to turn the engine over and see how far that rod moves. Don't stick a finger in there unless somebody is turning it by hand. If you bump the starter, maybe you can use a stick or screwdriver to hold it against the cam. Good luck.

When I have fuelpump problems I always threaten to put an electric pump on the vehicle but that isn't too popular around here. Reliability questions I guess. I haven't had to resort to that yet.

[BLP]

I was thinking a bad cam lobe but then it should not pump at all and i have good flow and pressure until the engine gets warm. The last time I took the pump off the rod was sticking down like it should.

[cdowns]

does it do it with the gas cap off of the tank? non venting gas tank will lot let gas flow

[BLP]

I did try it with the gas cap off also and it made no difference.

[geezer#99]

So how does it run thru the gears at 6000 rpm?
Does it quit or just keep crankin'?

[storm9c1]

Do you have a fuel filter before the pump? If so, try bypassing it to see if the problems go away. Mechanical fuel pumps do a better job at pushing than pulling.

[BLP]

When it gets warm while i am driving it will just die. If i can keep it cool, about 185, it does fine but any warmer and it dies.My fuel filter is between the carb and the pump. Thanks everyone for all the feedback. It seems like a weird problem but it is a pain in the butt.

[Blue Rat]

Does it stops all of a sudden or just dies out slowly?

[GASoline71]

Might not be fuel related at all. I had a module in an HEI distributor that worked great until it got warmed up. Then it would click off, and the truck would die. Once the engine cooled down, it would fire right back up again.

My dad and I removed the module and hooked a multi-meter to it. Then held it over a burner on the stove with a pair of tongs, and when it got warm, it clicked to an open circuit. So the module in the HEI was bad. What we figured was happening, was that when the body of the module heated up and expanded, it was somehow messing with the internals of the unit by spreading a circuit apart. Then when it cooled back down and contracted, whatever was "seperating" from the expansion inside was now making contact again, and it ran perfectly.

Not sure if you have an HEI... just thinkin' outside the box.

Gary

[bama63]

sounds like vapor lock, insulate your fuel lines from pump to carb and any line close to the exhaust, also make sure no part of the fuel lines are touching the engine anywhere causing a heat soak condition and vaporizing the fuel.

[BLP]

I do have HEI but I can physically see it running out of fuel. I was thinking vapor lock but i ran the hose from the tank to the fuel pump and no where near heat and it did the same thing. The hose from the pump to the carb is not near a heat sorce either. I will see what I can do though. Hopfilly it will make a difference.

[Blue Rat]

Some blocks I have learned have the adjustment nut to hold the fuel pump push rod up for easier fuel pump install. Check an see if yours is to tight if it has one? Just a thought. Those rods are hollow you could take it an have it turned down a few thousands?

[BLP]

I thought about the bolts that hold the push rod but for some reason I thought just the small blocks had them. When I installed both rods it slides up in the hole real smoth. I also thought about having the rod turned a little, just need to find someone to do it.

[Blue Rat]

I know you don't want too. But sounds like a perfect reason to go to a electric pump.

[BLP]

I know. Its like a never ending money drain. Why can't I be into like exercise and not cars and trucks?

[geezer#99]

What carb?
What's the fuel line size?
Do you have a fuel regulator on it?
Do you have a vented gas cap?

[BLP]

I am running a holley street avenger 870 with 3/8 fuel line. My gas cap is vented and I have another good vent on the tank. I am not running a fuel regulator just the mechanical pump. I have checked the fuel issue with the fuel cap off with the same resultes.

[geezer#99]

Got a heat plate/spacer between carb and intake?

[BLP]

no, no heat plate.

[geezer#99]

Heat plate/ spacer would likely help if not eliminate your problem.
Ones that are phenolic (plastic) work well.

[storm9c1]

Originally Posted by geezer#99

Heat plate/ spacer would likely help if not eliminate your problem.
Ones that are phenolic (plastic) work well.

Agreed!

3/4" or 1" space for best results. Been there, done that many times. If you have hard fuel lines, this will mess with the geometry and throttle linkage, so be prepared to mess with those when you add the spacer. As I mentioned in another post recently, the "winter" gasoline has a lower boiling point than "summer" gasoline. This can uncover these types of problems rather quickly and become a headache.

[cadillac_al]

How are all these vapor lock fixes going to get fuel into the fuel filter? It sounds like some kind of tank restriction to me. On a normal vehicle that filter is usually completely full with maybe a little bubble on the top.