Not my Nova, my **** works.
This is on the Wagon I tune.

We put 1600cc injectors in this turd and were immediately past 100% duty cycle. Not right.

The pump it the Magnafuel 4303.
-8feed, -6 return.
Holley regulator. Same one I use.

I finally put a FP sensor in that I can log. Fuel pressure barely rises with boost.
System voltage falls apart every pass dropping to batt voltage or lower.

I set base pressure just like my car. Pump on, engine off.
On my car, this works perfect.

His car, here is what happens.
Set pressure to 50psi, start the car and pressure goes up to 58.
Vac/boost line from the intake manifold connected to the reg.
With vacuum applied to the reg, I expect the pressure to drop. Mine does.

Ok, so shut his car off and connect a Mity Vac to the reg. Pull 15" vacuum, the pressure drops as expected.
Apply boost to the reg and pressure rises 1 for 1, just like it should.

Start the car again and apply boost and it does not rise 1 for 1.......more like .5 for 1.

I'm stumped.
The Magnafuel pump must be really voltage sensitive!

I checked volt drops throughout the wiring. By the time it gets from the alt back to the batt and back up front it drops .4v with the pump working hard with simulated 20psi applied to the reg. This is fairly normal.

Ideas?

So on to the system volts during a run.
The reg tries to increase fuel pressure, but with the volts dropping like a stone, the net result is low fuel pressure and lean fuel.......
Damn truck alternator.
I did a test with the car idling and pulled the plug from the alt. Has only the L term in the harness. Alt quits charging.
So for whatever reason, I believe the PCM turns that terminal off during a run. I'm going to hard wire this with a bulb to the batt term where it connects to the starter and where it powers the pcm and rest of the car.

So you smart guys chime in! The voltage thing isn't unusual for the truck DR44 alt and I'd like to find a solution for others that see the same thing.

Ron

 

I've got the DR44 alt on my Nova. Haven't had any issues, but it was a brand new gm take off. Not sure if you're dealing with a reman or not. I hooked up, not only my idiot light, but also the "s" terminal wire. This is the "sense" wire that increases the output of the alt based on electrical load. I believe normally this comes from the ecu, but I run the Holley system, so mine comes from the fuse box. I never see less than 13.8 volts on a complete pass. That's totally loaded, fan, lights, both pumps, etc. The gm alts will charge with just the battery cable hooked up, but it's not the best. As far as the fuel pressure going up when you hook up the vacuum line....you got me on that one! If there's vacuum there, it should go down (obviously). I'd fix the voltage issue, then prepare to can the regulator.

 

Hmmm.. sounds like something I need to do to mine. My PSI harness only came with 2 inputs to the 4 wire alt plug. I am only pulling 12.8 volts with everything going on the big daddy 145amp truck alternator.

You hooked the s terminal to a 12v accessory source right?

 

Yes. You can pull it from anywhere on the fuse box. Some say go right from the large terminal on the back to the "s" terminal, others say it's not the same. It definitely helped on my car. Wasn't having issues, just made the charging better.

 

It's a reman alternator.
PSI harness. Just the L and F terminals are connected.
I wasn't aware we can add a sense wire. I'll have to research that.
I believe though that theslt shuts off and we go batt volts.

 

I never liked vac/boost to the reg, I always just run boost. Usually a min of 10/8 to and from the reg. I know people use a 6 for return, seems like it needs to be free of bends, etc.
I ran 3 wires to the alt plug, +12, idiot light or rest., and one to the large term.
That's just what worked for me

 

Always set base pressure with engine running, alternator charging, and vac removed from the reg.

Given you've proven the regulator is capable of working as expected....stick a pressure gauge onto the line close to the reg as possible...to ensure it is actually seeing a manifold pressure signal. ( not a gauge on the fuel pressure side, although of course the two should mirror each other to a degree )

And IMO a 0.4v drop at the pumps is fairly large. Probably not the cause of your issues, but wiring could be upgraded.

 

I think he needs a bigger return.
I bought a pigtail for the alt so I can add a sense and remove the pcm from the equation like you guys need to do with the Holley EFI.

 

The drop at the pump is more like .2v. It's .4v by the time it gets back up to the starter.

With the engine running, pressure is 58 with the line to the Reg disconnected. If I pressurize with 20 psi simulated boost, it doesn't go much past 70 psi.
Repeat with the engine off and pressure tracks 1:1
Ill fix the volt issue first.

 

What regulator?

 

Holley dominator just like I have

His buddy built the car. They both use the same pump, Reg, lines and both have the same deadheaded rail setup.
Its not how I would have done it.

 

So where is the regulator, how is it installed, and where are you measuring pressure ?

 

Reg is in the engine compartment.
Feed in one side, return out the bottom.
The other side feeds a T located between the backs of the rails. The rails are plugged at the front end.
Pressure is measured from the tap on the side of the Reg.

 

I always wondered about the diff in starting fuel pressures-with the Holley HP I ran a base of 43, boost ref up from that. Others I see start at a higher starting pressure, in your instance 58. Not sure what the controlling factor is, if you can start at a lower pressure, and keep the tune, seems more in reserve for higher pressures. Is it injector size, etc

 

all sounds perfectly functional to me

 

I couldn't turn this setup down to 43. I tried.
Perhaps this Holley regulator isn't the right choice. Orofice size might be too small for the Magnafuel pump volume

 

Agree, it should work.

 

I want to thank you guys for your thoughts and ideas.
Its hard enough managing my own car trying to sneak it into the 8's much less trying to solve issues on my buddies car that I tune but didn't build. Although by the time I sort out all his issues, I'll have rebuilt most of it!

 

Dont know if this applies to you or not but using a 4 post shutoff switch I measure a .5 volt difference using the little posts for the fuel pump. I am using a microsquirt ecu. Thought this was interesting as my voltage to ecu and all other items was only .2 different. I am using the sense wire back to fusebox

 

Thanks. He has just the two pole switch. It drops less than .05v.
My old switch dropped .3v, was over 20 years old so I bought the mondo switch with 1/2" terminals and didn't use the little ones.
I chased every .1v drop.