Fuel pressure regulator question

olddog · #1 (**permalink**) 10-15-2007, 07:39 PM

My fuel pressure regulator is the type that has a vacuum line connected to it. It is a Mallory model 4305M. It is supposed to lower the fuel pressure 1 psi for every 2" of vacuum.

I put a hand vacuum pump on my fuel pressure regulator. The pump is the type that you can use to bleed your brakes. The regulator will not hold vacuum for more than a second. Pumping as fast as I can, I can only pull up to 15". Pump is good. Plugged the line and it will pulled 22" in one pump and held it for 5 minutes.

Is it normal for a fuel pressure regulator to bleed off vacuum quickly like this?

bobcowan · #2 (**permalink**) 10-16-2007, 10:06 AM

As I understand it, that's for blown motors only. It raises fuel pressure as the boost goes up.

rick50 · #3 (**permalink**) 10-17-2007, 08:18 PM

Quote:

Originally Posted by bobcowan

As I understand it, that's for blown motors only. It raises fuel pressure as the boost goes up.

That's correct

Aussie Mike · #4 (**permalink**) 10-17-2007, 10:54 PM

Just leave the port open and a to atmosphere on a naturally aspirated motor and set your pressure. Then at least the regulator will equalise pressure with altitude changes.

You only really need that port for blown motors to equalise the difference between manifold pressure and fuel line pressure. That manifold pressure is trying to push that fuel back into the injector and reduces the flow. The reg will deliver more pressure when on boost to ensure the injector flow rate stays the same.

Your ECU will have a MAP (Manifold Atmospheric Pressure) sensor that it will use to adjust injector flow in conjuction with TPS (Throttle Position Sensor)to deliver the right ammount of fuel for the specific load point.

I've got mine bolted to the fire wall with a liquid filled pressure guage attached. Easy to set and check the pressure.

Cheers

olddog · #5 (**permalink**) 10-18-2007, 05:55 PM

I have a Mass Flow system, that is designed to look like a carb. It is very similar to the picture Aussie Mike posted. I have the fuel gauge and firewall mount as well.

In talking to Mass Flow technical support. I am told that the pressure should be set at 40 PSI with the vacuum line disconected. Also that the fuel pressure should drop 1 psi for every 2" of vacuum. Indeed the fuel pressure does drop from 40 psi to 33 psi with 14" of vacuum.

On a cold start the rpms start at 1200 and drops down to 500 rpm or less. Vacuum is 14" at 1300 rpm, 10.5" at 900 rpm, and 5" when bellow 500 rpm. So as the rpms drop the fuel pressure goes up. Cam has quite a bit of overlap. Exhaust smells very rich when cold. My theory was that a stock cam would give 18" vacuum or 31 psi fuel pressure. My cam's low vacuum is allowing more fuel pressure than the ECU map is expecting and therefore is dumping too much fuel. My plan was to pull 18" of vacuum with the hand pump and start it cold, to see if it would idle propperly at the lower fuel pressure.

Aussie Mike · #6 (**permalink**) 10-18-2007, 11:25 PM

Sorry, I'm not much help there olddog. I'm running the factory LS1 ECU. They are designed to run with a fixed fuel pressure and I've just had it all re mapped to suit my mods.

Is there any software with your Mass flow setup to adjust your tune?

Cheers

olddog · #7 (**permalink**) 10-20-2007, 11:38 AM

Mike,

Mass Flow Tech support told me that the ECU is pretty much a late 1980's to mid 1990's Ford factory computer. Mine is an older system. They do rechip the factory computer now and can do mine if I like for about $250.

They have been very helpful to me so far and I do not want to bad mouth them. However when I asked what information they needed to do a custom program for my engine they basically said all they needed was the cubic inches, injector size, and the Mass meter along with the ECU. Cam, heads, and compression wasn't needed. I'm sure they know more than me, but it seems to me that they are only going to get the tune in the ball park. So I am looking for someone who can re-chip my ECU and tune it on a dyno. However before I do that I want to get everything working properly, at least to the best of my ability.

hookedonford · #8 (**permalink**) 11-24-2007, 11:55 PM

Olddog,
I have Mallory 4305 regulator with Mass Flo setup and have the same problem. I actually should notify Mallory because this is the second unit with the issue. It is bleeding off through the top and threaded pressure setting rod. I put a little thread sealer on the rod and nut and adjusted to 39-40PSI. Good luck, Jim

olddog · #9 (**permalink**) 11-25-2007, 05:38 PM

Has your ECU been chipped and tuned or is it still factory?

What engine and how radical is the cam?

I would like to compare notes.

hookedonford · #10 (**permalink**) 11-25-2007, 06:13 PM

My ECU has a moates.net chip from Mass Flo, not tuned on Dyno yet.

418W - 4.100” Stroke
Custom cam designed by Panhandle Performance - duration 290 Int 298 Exh
10.1:1 Compression
Victor JR. Intake ported by Panhandle Performance
AFR 205 heads with Ferrea valves & MEI roller rockers

It runs strong and smooth, but I plan to get it fine tuned at Panhandle Performance in next few weeks.

olddog · #11 (**permalink**) 11-26-2007, 03:50 PM

My engine is a 5.0 stroker to 347 cid.

Edelbrock performer rpm heads and Victor Jr intake.

Cam is 236/242 intake/exhaust duration @ 0.050" lift - advertised is somewhere up in the 280 range.

Off the top of my head, it seems like the compression was 10.4 but I'm not certain.

My intake gaskets are leaking and causing problems when the engine is cold. I plan to pull it in a couple of weeks, while I'm on vacation. The engine has never ran right cold sense the day I purchased it. Once the O2 sensors heat up and it goes into closed loop control, it idles great. So, I'm still sorting things out.

I had oil sucking into the intake ports and it coated onto the flow sensor. When I cleaned the wires up, it felt like I picked up 80hp. Still the engine should put out 400+ hp based on the parts, but I don't think it is there.

The ECU is still factory stock with no chip added to it. I've got a guy lined up to add a chip and dyno tune the car this spring.

I am mostly interested in how well does your engine run cold and hot. I would also be interested in your before and after dyno tuning results, when you get that done.

bobcowan · #12 (**permalink**) 11-26-2007, 04:01 PM

You can't reliably clean an O2 sensor. Once you get it all fixed and tuned, replace it.

olddog · #13 (**permalink**) 11-26-2007, 05:36 PM

Quote:

Originally Posted by bobcowan

You can't reliably clean an O2 sensor. Once you get it all fixed and tuned, replace it.

Bob - I didn't make it clear. I meant I cleaned the mass air flow sensor. The throttle body looks like a carb, with flow sensor sitting on top. With the cam and the low rpm cold idle it tossed oily fumes up on the sensor. At least that is my theory.

hookedonford · #14 (**permalink**) 11-27-2007, 06:41 PM

Olddog,

I tried using the plain 1262 intake gaskets a couple times on 302's & 351's, but will not use again. You can research how the 1262 gaskets crush and they caused me some intake port leaks. The newer 1262S-3 (Ford Racing #M-9439-A50) gaskets with steel core worked much better.

Cold or hot it runs very smooth, but it is chipped. One important part about a Mass Flo upgrade install if there are any EFI problems before Mass Flo is added, the problem just moves over with the Mass Flo installed.

I would suggest getting the intake leaks stopped first step. Then you can set all your base settings and make sure you disconnect IAC motor per directions.

Let me know how you progress.