engine and drivetrain Fuel Pressure Problem - Electric Pump

[brianstj]

This may go a bit long cause I am going to try and throw everything I can remember in here to describe the issue...

I am running an electric pump mounted in the trunk with a Holley regulator and gauge up in the engine compartment. I have run this with a 38/38, and now with 40 DCOEs. Pressure is set to 3.5 PSI at idle.

I noticed at various times when I had the car running with the hood up I would look down at the gauge and see it was sitting at 0. I thought maybe the gauge was messed up or something - tapping on it did nothing, but the car stayed running and seemed to drive just fine.

When I switched to the DCOEs I put in a wideband O2 sensor to help with tuning. I noticed one day when I pulled in to my driveway the O2 sensor was reading way lean at idle. I popped the hood and found the fuel pressure gauge sitting at 0. So probably NOT a faulty gauge since I am also seeing a lean condition when the fuel pressure drops. But the car still drives fine - even under a load with the DCOEs, and the O2 sensor has not shown any leaning out when under load.

All this time I was running a Carter pump, but I had a Summit unit laying around, so I swapped it out to see if the pump itself was acting up. Same story - but I was able to gather a little more info and test a few more things after the pump switch. So when the fuel pressure gauge is reading 3.5 the O2 sensor is showing good mixture at idle. When the O2 sensor starts showing a lean idle I can jump out of the car, open the hood, and find the gauge reading 0. The O2 sensor readings still look the same once I start driving again and even when doing some hard pulls it doesn't look like I am going lean. I also have a voltage gauge and it is staying over 13.5 when this happens at idle.

I pulled in to a gas station and I was seeing the lean idle, popped the hood and saw 0 PSI. After I filled the car I started it back up and still saw the lean idle, 0 PSI. But I also noticed I didn't hear the LOUD pump buzzing away in the trunk. I popped the trunk and found that it was actually still running, but very quietly (not typical), and the motor casing felt warm to the touch. Driving away I could hear the pump start buzzing louder and then quieting down. It also seemed that when I came to a stop that if I could hear the pump buzzing loudly then my O2 readings at idle would be normal, but if things were quiet I would be registering lean.

Sooooooo....any ideas on this? I am finding it strange that it looks like I am starving for fuel at idle, but I can still take off and blast down the road just fine. Anyone ever experience anything like this?

[gracer]

You may have a fuel pickup problem. Make sure there is no place in the suction line that will cause a leak. G

[TobyB]

yup, i was thinking air, too-

or junk in the tank bottom.

If you can't find any air leaks, try a

filter before the pump to catch

crud...

t

[Guest]

If your car is running fine either at idle or under load, dont believe the gauge throw it out we never ran a bloody pressure gauge in the old days.

[KFunk]

I don't know about the Summit pump, but the Carter is actually supposed to be self regulating. It must be based on demand or something, but that could explain your change of humming. I noticed mine was always way louder when you first start the car cold, which is when it needs the most fuel, but I have no idea of the mechanism how the pump notices that.

And yes, its possible to run an engine even without any fuel pumping action at all. Our 24 Hours of Lemons E30 would sit and idle all day if you turned off the pump switch, and even rev a little. It weirded us out at first, but I guess some siphon action must take place or something. This was on a EFI/Megasquirt car, but an engine without load can run on an extremely small amount of fuel.

I would try pitching the regulator and see what happens. I don't have the gauges that you have, but I've been running fine without one for years (With 32/36, then 40DCOEs, with a Carter, and now an Airtec pump). I'm wondering if the regulator actually impeding your flow at idle. It'd be interesting to prove this point once and for all, but I've never had a good regulator, wide-band o2 sensor, and fuel pressure guage to check myself. My car just keeps on runnin strong/cheap, and the plugs look good when I check them.

[rover1]

mine does the exact same thing i dont use a pressure gauge or 02 sensor i do use a carter mounted under the relay panal inside the engine bay i gets noisey then silant 38/38, schrick, JE etc.etc. runs fine. Dont wake the dead.

[brianstj]

I do have a filter before the pump. I should check it and see if there is any junk in there. I am thinking that if the gauge is reading 0 PSI, then there is either a problem picking up the fuel, or the regulator is shutting off the flow almost completely. Everyone seems to be adamant about running a regulator with Webers, so I don't know if I want to remove it. Maybe I will try another one. It wouldn't bother me if the O2 sensor was consistent at idle.

[KFunk]

Everyone seems to be adamant about running a regulator with Webers, so I don't know if I want to remove it.

No, certainly not everyone. There's plenty of us out there running them without regulators. We're just tired of arguing it everytime somebody brings it up. It comes up all too often.

Here's an explanation on a website:

http://www.racetep.com/webfuelspark.html#webfuel

with respect to the Carter: "This pump DOES NOT and SHOULD NOT use a Pressure Regulator for any reason.....The Regulator is just a restrictor that inhibits flow. "

With respect to the much quieter Airtec pump that Ireland Engineering sold me, Ireland told me himself that it does not need a regulator with the Webers. So, I'm trusting their word, and it works fine for me.

[kbmb02]

Question: Is your Holley regulator installed such that the gauge outlet is oriented upwards? I ask because I've occasionally / intermittently seen "0" psi on the gauge that's installed on my regulator, even as an inline gauge installed between the regulator and the carb read the proper psi . . . makes me wonder about those Holley regulators (though I still use one).

[brianstj]

I think I will go back to the Carter with no regulator and see how that goes.

To answer the other question, the pressure gauge is mounted straight up right at the outlet of the regulator. You can see it in this picture when I had the 38/38.

[Emyers]

To second KFunks comments, I have run the Carter since 1994 with no regulator, first on a 40/40 DFAV and now on dual Mikuni 44PHH carbs. Took the folks I bought it from at their word and the pump carb combinations have done fine.

Snakedriver

74 02Lux

02 M Roadster

72 Volvo 1800ES

[KFunk]

Oh, and I'm pretty sure StaceyG has a wide-band O2 sensor and has been running his Carter unregulated for a while into DCOE 45s. So, he's probably got the data to back it up that its running OK. I haven't talked to him for a while though, and don't think he posts that often.

[TobyB]

I do have a filter before the pump.

oh... then yeah, try changing it and also the suction lines.

The problem with doing this is that the filter tends to

collect air, and then can let big bubbles into the pump.

What happens then is that the pump can suck air, and while it doesn't

'lose prime' as such, since it's trying to push against

a pretty- much static (at idle) load, it simply can't develop pressure. Once it passes

its embolism, then it regains pressure. I actually went to a recirculating

system to solve a different problem, and it cleared this up, too.

Having a regulator in there exacerbates this...

You might be able to create a restricted return line from the

pressure side of the pump back to the tank. If you made a 'bleeder'

(1/16") plug to restrict flow, it wouldn't hurt anything (that pump can

power a big block at WOT) and would let air bypass. It'd also cool the

pump. I did this for the roadster, and it made a big improvement.

Incidentally, while the cause is different, the effect of air in the system's

the same as the old 'vapor lock' problem, where the fuel would vaporize

and then the pump would be unable to move much of it.

As to the regulator, there seem to be a bunch of different pressures coming

out of these pumps. I bought a pair for the race car, and they delivered 6-7

psi reliably. Which overpowered the floats in my older brass- float DCOE's.

BUT some Weber carbs MAY be able to handle pressures that high IF you

tune 'em for it. You'll need to set the float level by the fuel in the carb, tho...

And others have the exact same pump (usually older) that delivers about 3

psi. So they run fine without regulators.

The GAUGE is indispensible. Full stop. I have firsthand experience with

motor explosion due th exactly this symptom- the thing ran, even though

the gauge read zero, so off we went. The lean condition caused #3 exhaust

valve to overheat, lose its head, and turn a perfectly good 4- banger into

a 3- rattler. So I'd try to resolve it one way or another.

that's me.

hth

t

[KFunk]

You'll need to set the float level by the fuel in the carb, tho...

That's exactly what I do... never had good luck with bench measurements, don't trust them anyways... just don't seem very reliable. The fuel level is what matters the most.

It's pretty easy to do, and yeah I have Italian DCOEs w/brass floats. Just pop the little hat off a carb while the engine is idling (or shortly after shutdown if your engine is too bouncy to get a good measurement), then remove one big main jet assembly. I just put a wooden stick down in the hole until it hits moisture, then measure that distance from the top of the carb. I can't remember the exact spec right now (edit: found it, 25mm plus or minus 1mm). If its just a millimeter or so too high, then it will spill over during acceleration and cause a huge stumble that feels like its running out of fuel, when essentially its flooding itself (had that puzzle me a while recently, but reset the floats and now its fine).

[TobyB]

If you find that measurement,

please post it! It would be a worthy FAQ to

have known good fuel levels for Weber carbs.

t