Interesting fuel pressure observation
 

So I just got my car put back together and have put about 100 miles on it this weekend. Twice on slightly longer drives I noticed that I started to get a slight hesitation at light/part throttle. First time it happened, I caught a glimpse of the fuel pressure gauge which read only 2.5psi. I tried adjusting the fpr, but nothing happened. Instead of further diagnosing I parked it. Later went for another ride and fuel pressure was back to normal at 6.5psi. Today, same thing happened. This time I shut it off for a minute then restarted it and the pressure was normal again. I checked my fuel filter which seemed ok. Does this sound like a pump issue? I am running a Holley blue pump. Anything else worth checking?

If the fuel you're using has 10% ethanol in it like most pump fuel has these days,that very well could be causing problems with the Holley "blue" pump,as those specific pumps are'nt recommended for use with fuels containing alcohol,and as a result they seem to have corrosion related issues in the cast aluminum lower pump housings.

That often includes problems with gumming up the pumps bypass assembly.

The Holley pump(s) to use with alcohol fuels is either the Holley "black" pump,or their HP line of billet gerotor pumps.

Could also be a faulty gauge too,,,what sorta FP gauge are you using on this???

HTH

Bret P.

My blue did the same thing on Saturday. So I ordered a new blue and now I have to refuse it and I ordered a black one now.

maybe since it's for ethanol you should get a green one... :poke::clap3::Peace:

hahaha

I just had a fuel presure reading problem like yours, after a drive the gauge read 1-2 psi. The gauge was in the fuel line next to the carb. I removed it hooked the gauge up to another and put 6 psi of air to it, all good. Stuck the gauge in a coffee mug of hot water, again 6 psi of air, only read 1.5 psi, when it cooled back to 6 psi. The gauge is temp sensitive.

The hesitation may be something other than fuel presure.

I have the Holley HP 150 billet gerotor pump and really like it. one year and going and not so much as a burp.

never will i buy a mallery gerotor again. went thru 2 in one year. cheaper built than the holley billet. poor tolerance settings on the gerotor to. weaker motor.

have had several holley blues, they were good but the vanes get out of tolerance quickly and wear. sometimes would quit working and could tap the pump and it would work again.

Good info guys, thank you.

To clear up a few things....

- I only run non-oxy
- Gauge is a non-liquid autometer attached at the carb fuel rail

JT, interesting that you seem to have found fp gauges to be heat sensitive.... I'm not sure if I can believe that or not, aren't the mechanical ones simply a diaphragm? What gauge do you use?

I will almost have to drive the car a bit more to figure out the hesitation I can feel. Maybe it's with the timing. In all honesty it feels too good for the fuel pressure to be too low and for the pump being weak. Matter of fact, yesterday when I noticed the slight hesitations at light/cruising throttle, I tried flooring it and didn't feel any miss or stumble.... Seems odd if it were in fact a fuel problem??

I have a shelf of Holley blue pumps that have failed in years past (seal failure mostly). I have installed over a dozen Mallory 140 pumps in my cars and my friends cars without one failure - so to each his own. I do like the Holley gerotor pump, and have the 150 model on the cruiser.

No vane or gerotor fuel pump will stay happy in very hot weather feeding into a deadhead regulator. Fuel recirculates inside the pump, and quickly increases in temperature until it flashes into vapor. At that point, fuel pressure dives. Give the pump and fuel a little time to cool off, and things go back to normal. Just today I finished up installing a by-pass regulator and return line into the Cruiser because even the H150 pump would start to buzz up in RPM when stuck in traffic (sure sign it is spinning in vapor and not liquid).

interesting. I suppose I should look a little closer to how the lines are routed too then? I know my feed and return lines are only a few inches away from the tail pipe over the rear axle. Like you mentioned, shut it down, let it cool and things are back to normal... that seems to be what I noticed the other day. Is there a different/better pump to use to avoid this?

Also to clarify, I do run a return fuel line.

Steve

I know mine is the fuel pump and it is no sucsion at the pump and the motor was cold.

If you have a functioning return line, that pretty much throws my idea out the window. The return should always allow a fresh supply of fuel to the Holley pump, and prevent the fuel in it from flashing into vapor. What size of return line? Maybe check for kinks in the lines?

I have a friend that was experiencing an intermittent fuel starvation problem after the engine warmed up. He finally pulled the tank to check the interior and found a piece of plastic bag inside. It was a perfect 8" circle and it looked like maybe someone had cut it out and used it in place of the gas cap, and it got sucked into the tank. Probably plagued the previous owner also. The plastic would sometimes block off fuel flow, but other times stay out of the way as it traveled around the bottom of the tank. When it did get sucked up, it came loose when he shut the engine off and floated off around the tank again.

I recently had what looked like fuel pressure problems, similar to what you outlined here. But worse yet, my '70 GTO was dying when driving around in hot weather.

I had a little autometer fuel pressure gauge under the hood that was also giving me very, very low PSI numbers, like from 1psi to 3 psi vs. 5psi to 7 psi that we need

I thought that my mallory 140 pump failed so I had that rebuilt and then I reinstalled it.
Failed again!

Then, I bought a new Holley HP 150

Long story short, the new HP150 dies on me also! Shortly after that happened, it started working again. What was different ? Heat! I realized that what I was experiencing was likely a form of vapor lock. I am running a factory fuel line and I figured that it was no longer cutting it, even though it worked OK for years.

I took the car out of service, bought a new RobbMc sending unit (half inch), RobbMc regulator (bypass mode) and put in twin -8AN lines, including a return line.

Problem solved. I should have done this years ago ;)

READ ALL MY PROBLEMS I HAD HERE IN THE PY FORUMS, all because the way pump was mounted!! Fuel tank sumped??? Only way to go.