91formulaSS

can anyone explain this one? first off I swapped a holley 4150 for TBI, used a Mallory 4309 FPR with stock in-tank pump. when I set the pressure to anything over 4 psi the pressure gauge needle fluctuates wildly, the more pressure the more swing in the needle. If I try and set it to 6 psi the swing is from 3-9 psi and it's very rapid. The pump starts making a ticking noise that coincides with the swings in the needle and the lines actually start to move with it too. Once I lower the pressure to 4 psi or below the needle doesn't move at all. This happens regardless if the engine is running or not. Do I have a bad FPR? any and all comments welcome.

CamaroRider

Sounds like a 'resonance' is being made in your fuel 'system'. The pressure increases then something dumps the pressure and then it stops dumping so the pressure builds again, over and over. It would probably make any flexible joint stiffen then relax. That is probably what is making your fuel pump clink in sequence. Maybe you better tell us exactly what your in tank setup is and what kind of connecting hoses and lengths you are using.

I would also be curious to know if your Mallory regulator is actually returning fuel to the tank in spurts and/or if your in-tank fuel pump system is leaking and dumping fuel back into the fuel tank.

Are you using any hard line or is it all rubber hose or what ?

91formulaSS

stock TBI pump. stock hardlines to engine bay. stock rubber flexlines to the regulator. I cut the connectors plus few inches off the stock hardlines that go to and from the TBI and had them flared for compression fittings so I could go to 3/8 male NPT for the regulator feed and return and maintain the stock flexline fittings. Then rubber hose to the carb. I'll post a picture tomorrow.

CamaroRider

Does the TBI carburetor still have a functioning Fuel Pressure Regulator ?
If so, do you detect any fuel being returned to the tank from the carburetor during the pulsating you noticed ?

Do you have another fuel return line from the Mallory Adjustable Fuel Pressure Regulator ?
If so, do you detect any fuel being returned to the tank from the Mallory Adjustable Fuel Pressure Regulator during the pulsating you noticed ?

Just trying to get a very clear picture of what could be contributing to the pulsating pressure. Sort of sounds like one thing is bucking against another and making the pressure resonance. The proper term is probably ''hydraulic resonance''.

91formulaSS

The TBI unit is not installed on the motor. I'm using a Holley 4150 carb and a Mallory 4309 regulator. I just spoke to a Mallory tech and he stated I need a return line equal to or larger than the feed line. I know many people are using stock lines and not having this problem though. You would think that if the return was too small, at low pressure you are returning more fuel and the problem would we worse than at a higher pressure. but the opposite is true. The Mallory tech basically said that what I am telling him does not make sense. He reccomended that I should disconnect the return from the tank and let it dump into a big gas can and see if the problem goes away.

CamaroRider

Interesting. I would suggest that when you are dumping fuel directly into the large gas tank that you go through the various fuel pressure setting and try to keep track of where you are at the time (like ONE turn in, Two turns in, etc.) From what I read hydraulic resonance can be induced from the interaction of the PUMP and the REGULATOR. There are various combinations that will work and others that will NOT work. The style impeller contributes, the speed of the impeller contributes, the length of the pipe between the two contributes, the material with which the pipe is made contributes, etc.

If you do what the tech suggests you are dealing with only ONE criteria. So there might be other surprises when you make the final assembly for your vehicle.

Keep posting what you find. This may be of interest to others in the future.

91formulaSS

here's some pics of my setup. Anyone have any thoughts?



http://s464.photobucket.com/albums/r...t=DSC01557.jpg

http://s464.photobucket.com/albums/r...t=DSC01559.jpg

CamaroRider

Pictures are each worth 1000 words ... nice.

The only thing I can think of is to try a hard line between the regulator and the engine. That would remove any possible 'rubber flex' in that area.

And the tech suggesting a larger return (I.D.) hose is valid but I do not know if it is necessary in your case.

dctrumpet

iTrader: (10)

From my experience I see no reason why a larger return line is necessary, but it's worth a shot. I would do a temporary fix and run a larger "rubber" return line to the tank to see if that solves the issues at hand. If it does then you can run a more permanent line.

With our typical TBI setups the the supply line is 3/8" o.d. hard-line and the return out of the TBI is typically 5/16" o.d. The fittings are usually 16 mm (supply) and 14mm (return).

Good luck and keep us posted
----------
The pictures look great! Nice job

91formulaSS

so I ran a 1" rubber hose from the return side of the FPR to a gas can and all pulsation ceased. I guess my next step is to look for kinks or obstructions in the retun line. Do you think I could use compressed air to blow it out? maybe there is something in there causing an obstruction. Last thing I want to do is have to drop the tank to run a larger line.

CamaroRider

Hey wait a minute. Am I thinking correctly? You stated you had a 'stock TBI fuel pump' installed. If so then 'dctrumpet' is 'spot on'. Your return line is large enough for this setup. If this were not so then there would be lots of people having a problem !!!

If you have a STOCK TBI FUEL PUMP then the current feed and return lines, if clear of obstructions, ARE capable of handling the volume expected.

I would expect that you should be allowed to set your new regulator to 11.5 PSI and NO FUEL would be returning to the tank UNLESS your pump was delivering MORE PSI than that. If so then your regulator should be 'returning' ONLY the volume that will drop your PSI down to the 'regulated' value of 11.5 PSI. That would NOT have to be much in my opinion.

Are you sure you do not have a higher PSI pump installed than what is typical for a TBI? A pump appropriate for a TPI system would attempt to provide a VOLUME and have this pressurized to about 40 PSI. Now that would HAVE to return a large volume of fuel to your tank CONTINUOUSLY to bring the pressure down to 11.5 PSI. That probably WOULD cause the return line to look 'too small'.