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Trying to chase down a weird fuel pressure drop after the engine has been running for a while. Running down the list of potentials.
Installed a Carter P4070 pump and a Holley 12-841 regulator for the Weber 45 I have installed. Pump is powered with a relay and getting a full 12v. The gas tank has been cleaned, all soft lines have been replaced and all hard lines have been blown clean. Fresh fuel filter before pump.
Turning on ignition has the gauge on the regulator reading 4.5 dead on. Start the engine and the longer it runs the more pressure drops. It goes all the way down to about half a psi.
I decided to drop the pump and take a look at it. Just inboard of the inlet on the pump it looks like some of the pump body has cracked and broken away. Looks like fuel can just run into the lower housing of the pump? This doesn't seem right to me. Looking in from the outlet it's smooth all the way to the center.
Can anyone else with this kind of pump confirm if this is how this is supposed to look?
True, I was also entertaining the thought that the gauge just isn't accurate, because it doesn't seem to stumble from fuel loss when it's reading such low pressure. Maybe the heat of the engine bay messes with the gauge.
Have you ever opened your pump and see if it looks like mine does on the inlet?
I'm not so sure about what damage there may be to the pump, but do you have a liquid filled gauge mounted in the engine bay? If so, it's common for the pressure reading to become inaccurate as temperature rises and the liquid in the sealed gauge expands. How long with the engine running does it take to reach ~0.5psi like you said?
If indeed you do have a liquid filled gauge in the engine bay, try just running the pump for a while and see if the pressure decreases. If not, keep the pump running but use a heat gun to raise it's temp. If that "decreases" the pressure, that's probably your issue. Perhaps you already knew that though, doesn't hurt to check. Anyway, those are my thought for now. I also have a P4070 with a Summit brand fpr in the engine bay and a non-sealed gauge. I'm not sure about the internal damage you're seeing, but I don't currently have any issues with mine besides perhaps cavitation (that's a separate issue). Hope you get this sorted out.
Yeah, the gauge is liquid-filled and mounted in the bay. I figured it was probably just the gauge not reading properly once warm.
The shiny surface just inside of the inlet on the pump seemed to me like something had broken off. Carter got back with me and they're saying everything looks as it should.
The issue liquid filled gauges have is that to the keep the liquid in, they inherently have to be sealed. This means that as the temp rises, the fluid inside expands and the internal pressure of the gauge rises. Since the reported pressure is relative to the interior pressure, it becomes increasing inaccurate (lower than true readings) as temp rises. Air filled gauges are rarely sealed and hence do not suffer from this issue - or at least that's my understanding.
I have the same setup and a 0-15 gauge hanging off the Holley regulator. I see the same thing and attributed it to the heat in the engine bay. My regulator/gauge is mounted on the firewall just to the passenger side of the hoodlatch. I wouldn't worry too much about it. Not sure about your pump, I use the same and have never taken the top off of it.
01-30-20, 11:41 PM
Carter P4070 Fuel Pump Potential Issue?
