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#1074595 07/25/22 08:01 PM
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I was able to hook up my fuel gauge in-line to car today before carb. I’m not familiar with readings for the 305 v8 but does this look correct?
https://vimeo.com/733369238

Last edited by 83Monte305; 07/25/22 08:05 PM.
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From the looks of it that's too high, what does it read say at 2000 r.pm.?
From my little bit of knowledge which is not much I would say 4.5-5 psi, no more than 6. Quadrajets do not like much fuel pressure at all.

Last edited by 88ssBrent; 07/26/22 12:51 AM.
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That was at kicked down idle, but honestly it didn’t change throughout. I showed a guy at Napa who prob worked on these cars in the 80s told me it
Looked fine, and I don’t need a new pump, but I saw it going to 10psi and got a bit concerned… plus the fuel coming out sometimes, but he also mentioned should be a bad floats causing that

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Factory manual states 7-9 psi. Its not uncommon for mechanical fuel pumps to output too much pressure, especially with the low quality of today's replacement parts. Might need to install a fuel pressure regulator.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
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Well I installed this pump in the late 90’s so I guess it wouldn’t hurt to update it - they’re not too much money so may be worth it

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As buick said quality control is horrible on fuel pumps these days. Even if one is advertised as 5-7 psi or 4-10 psi or whatever number the manufacturer states its probably not going to be that. If you spend any time at all on numerous forums the problem comes up a lot about new fuel pumps. To me nothing looks wrong with your fuel pump except for too high of psi. If it was mine I would probably plumb in a regulator and set the psi to what I want. If you buy a new pump you might get lucky but more than likely you will still be in the same boat.

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I agree, the carb/engine problems you are having may, could, and probably are related to high fuel pressure. As said Qjets do not like fuel pressure over 6 at idle.

And buying a "factory" replacement fuel pump is a crap shoot these days. Any mechanical fuel pump produced today should be using Viton for diaphragms, not rubber, and any internal parts subject to touching ethanol gas. When a rubber diaphragm gets harder from age or possibly ethanol it's like adding spring pressure to the pump spring, the output pressure is increased.

A Monte SS with A/C will have a return fuel pump, three connections on the pump, input from tank, pressure output to carb and a return back to the fuel tank. A return line is used in an effort to insure the fuel in the input line from the tank doesn't sit in the supply fuel line and soak up heat at any one of several sources. Vapor lock in the fuel line is the product of excessive heat soak causing the fuel to boil, change into a vapor, a pump can't suck vapor. What a return system does is not allow the fuel to sit in any location allowing the temp of the fuel in the steel fuel line to increase.

Point is an operating fuel return is a huge plus for most any car, A/C or not. A stock replacement pump would be a return style pump. No high performance pump is a return style pump. So you are stuck with one of the box store stock type pump which you roll the dice and hope you win the fuel pressure game.

It's possible the return fuel hard line in the car is compromised. Stock is a steel 1/4" tube back to the tank with three rubber hose sections.
One runs from the pump to the 1/4" line, located at the hole in the frame where the feed and return exit the frame.
Second rubber hose is under the sheetmetal shield directly above the rear end, left side. Three rubber hoses there, a 3/8" feed from the tank, a 5/16" which is the vent from the tank to the canister under the hood. The third is that 1/4" return.
Back at the fuel tank there are three more short rubber hoses that connect those lines to the fuel tank pickup/float.

With the age of these cars and the fact all those line are steel and rubber, and we've been run junk ethanol for decades now it possible the insides of those steel line have decayed and became restrictive. We've seen this in the 5/16" steel vent line. Air and condensation can become stagnate and cause damage.
The return fuel line may have the same issues on the vehicle that sits most of it's time. The 3/8" fuel feed line I think not a problem to diagnose, any stuff in the line ends up in the fuel filter and we find it quickly if, when, the engine won't start, starved of fuel, filter clogged problem.

If the 1/4" return hose was removed from the 1/4" hard line where it exits the frame and a low pressure air supply was attached to the hard line, and the gas tank cap was removed, and you had someone stand at the filler cap area with an ear to the tanks's inlet they would be able to hear the air in rush the tank. A good ear could qualify the sound/flow, good or bad. The return line into the tank's pickup/sender unit dumps the fuel into the top of the tank so there would be no bubbling. Just be aware the air coming out of the tank is gas vapor. For you kids you always got to throw up the safety nets. Warning: don't breathe the fumes or smoke any stuff while doing this test.
This method would also work well for testing the troublesome 5/16" vent lines on these cars.
Just a few psi is best, less than 10. Any more than that and you have a problem if it doesn't flow.

A working return line system will reduce the fuel pressure. How much, lots of variables, but safe to say 1 maybe more psi. On the same token a blocked return will increase pressure to the carb.

I saw the video of the pressure test done. You need to use a gauge with a 15 psi range or less, a FI 100 psi gauge is inaccurate at 8-9 psi. In the old days when we had 3" diameter vacuum gauges to test engine vac those gauges usually had a 10 psi fuel pressure gauge feature on the same face.
Also didn't like that way the psi jumped around. Should be a lot steadier, revving engine should show gradual steady change.

Yes a new needle and seat in the carb, and adjusting the float level just a tad lower than the factory spec may help a carb that isn't controlling the fuel level very well. But with a Qjet you need to control the inlet psi. This makes it easy for the N&S and float to control the fuel level in the carb, which is critical to a good running Qjet.

See if you can get a better idle psi gauge reading that is reliable, insure the carb filter is clean.
From there need to see if lower psi will make the car run better.

Pittsburgh, grew up nearby, been out there dozens of times since. It seems the steel mills demise was why we left and the steel mill's burial grounds are where we go back occasionally. Go figure.
Bob

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Good stuff as always Bob!

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Nice write up Bob and others! So what is a good regulator to add to the system? Any links would be great - thanks!

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Again the fuel needs of the car dictate parts of a system. If stock and only ever a mild up tick in power expected and using a stock pump with recirc and "less expensive" dead head regulator may be the ticket.
Something like this:
https://www.summitracing.com/parts/aaf-all40290
It would need to be installed close to the carb.

less expensive again would be a Holley Fuel Pressure Regulators 12-804.

I run a dead head on a 100% upgraded system. It's a now discontinued, Mallory 4207M
https://www.summitracing.com/parts/MAA-4207M

The 1/4" return steel line was removed. The stock steel 3/8" feed line is now used as the return. A new 1/2" Cunifer line is the feed to a large volume RobbMc pump. A Tee in the pumps outfeed line supplied fuel to the regulatory at the carb and also the Tee supplies calibrated fuel returned to the tank via the old 3/8" feed line. And the fuel tank is the FI Spectre tank with a Robbmc 1/2" tank pickup.

A constant 6.0 psi is supplied to the Qjet carb and a constant return flow to the tank keeps the fuel cold.

The system was build so IF anything that required large amounts of fuel was installed the lines and their flow could handle the chore. At a meager 500hp the engine never starves for fuel. The car vapor locked one day at the drags on a 90+ day and the new system was the result of that. Has never had a fuel delivery problem since.

Nozzle drip should be another topic of discussion. Several possible causes and may be want you are experiencing with this engine.
Bob




Last edited by mmc427ss; 07/27/22 06:12 AM.
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Nozzle drip in Qjets is often caused by having the throttle blades open too far at idle.

Also GM used to offer a emission legal 350 swap kit for LG4s and L69s for F bodies. Part of the kit included an elecrtic in tank fuel pump and a return type regulator than bolted to where the mechanical fuel pump used to go. This is the same kit that the ZZ4 Proms came from.

Last edited by Buick Runner; 07/27/22 10:53 PM.

SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.

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