Fuel Pressure for 7.4L vs 5.7L

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Crazydavez28

I'm Awesome
Joined
Feb 12, 2018
Messages
109
Reaction score
47
Location
Kansas
I have an El Camino with a Vortec drivetrain in it and already suffered thru the high mileage damp hard starting issue. Now it just won't start without a shot of starting fluid in the PCV hole in the TB hat. Once running it does run but stumbles around and if shut-off will not restart without the ether.

Before loading the parts cannon I got a fuel pressure gauge from the harbor and it tested 43psi pulling 6.8amps, immediately went to zero once powered off.... Now I have a new fuel pump in the mail. FYI it showed 52psi once running. I'm amazed it actually ran. Everywhere I read this should be 60-65psi

Then I went and tested my 7.4L and it was showing 43psi pulling 7.3 amps and sounded much healthier but I have some starting issues if ambient is over 90 degrees. This still seemed low to me and my thought is the regulator isn't working right. What should this actually be a for the 7.4?

7.4 has Five-O Motorsports Ford injectors and 0411 swap. I also changed the regulator out 2 years ago but stupidly used an Amazon cheapo one.
 

someotherguy

I'm Awesome
Joined
Sep 28, 2013
Messages
9,784
Reaction score
14,138
Location
Houston TX
Vortec 7.4 fuel pressure spec is 58~62 psi. They will often start and run at considerably lower pressure due to the injector design; the small block Vortecs are the ones notorious for not starting when fuel pressure falls even just a little bit below spec because the poppet valve setup is very picky about pressure. (small block Vortec spec btw is 60-66 psi though it seems the MFI updated injectors operate at somewhat lower pressure)

Your cheapo regulator could very easily be the source of trouble. Also the vacuum line leading to it...

Richard
 

Crazydavez28

I'm Awesome
Joined
Feb 12, 2018
Messages
109
Reaction score
47
Location
Kansas
Vortec 7.4 fuel pressure spec is 58~62 psi. They will often start and run at considerably lower pressure due to the injector design; the small block Vortecs are the ones notorious for not starting when fuel pressure falls even just a little bit below spec because the poppet valve setup is very picky about pressure. (small block Vortec spec btw is 60-66 psi though it seems the MFI updated injectors operate at somewhat lower pressure)

Your cheapo regulator could very easily be the source of trouble. Also the vacuum line leading to it...

Richard

I have noticed fuel mileage even farther in the toilet than normal. I was reliably getting 9-10 (double digits!!!) and it has dropped to 8 recently.

I will start here and ordered a FPR The pump seemed strong and I could hear flow in the return line. Vacuum line was questionable 2 years ago so that will be new this time around.
 

Schurkey

Supporting Member
Supporting Member
Joined
Jan 14, 2018
Messages
10,963
Reaction score
13,741
Location
The Seasonally Frozen Wastelands
That's what I was getting at. Test the gauge,

Harbor Freight sells bottom-feeder junk. They just recalled the jack stands they gave you when you turned-in the previously-recalled jack stands.

For the record, I test my compression tester gauges now 'n' then, too. I make sure they read the same as each other, and the same as the gauge on my compressed air regulator. This is why micrometers come with standards to measure against--A person HAS to be able to trust his diagnostic and measurement equipment to be accurate and repeatable.
 

Supercharged111

Truly Awesome
Joined
Aug 20, 2015
Messages
12,612
Reaction score
15,233
Vortec 7.4 fuel pressure spec is 58~62 psi. They will often start and run at considerably lower pressure due to the injector design; the small block Vortecs are the ones notorious for not starting when fuel pressure falls even just a little bit below spec because the poppet valve setup is very picky about pressure. (small block Vortec spec btw is 60-66 psi though it seems the MFI updated injectors operate at somewhat lower pressure)

Your cheapo regulator could very easily be the source of trouble. Also the vacuum line leading to it...

Richard

I know you're talking 454, but just to be clear the 350 doesn't have a vacuum line. Also, the 454 line is easy to forget to hook up for some reason. :banghead: OP how old is the regulator in the 350? They're known to fail like the 454 and cause starting/running/idling issues.
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
3,410
Reaction score
4,348
Location
Dallas, TX
I have an El Camino with a Vortec drivetrain in it and already suffered thru the high mileage damp hard starting issue. Now it just won't start without a shot of starting fluid in the PCV hole in the TB hat. Once running it does run but stumbles around and if shut-off will not restart without the ether.

Before loading the parts cannon I got a fuel pressure gauge from the harbor and it tested 43psi pulling 6.8amps, immediately went to zero once powered off.... Now I have a new fuel pump in the mail. FYI it showed 52psi once running. I'm amazed it actually ran. Everywhere I read this should be 60-65psi

Then I went and tested my 7.4L and it was showing 43psi pulling 7.3 amps and sounded much healthier but I have some starting issues if ambient is over 90 degrees. This still seemed low to me and my thought is the regulator isn't working right. What should this actually be a for the 7.4?

7.4 has Five-O Motorsports Ford injectors and 0411 swap. I also changed the regulator out 2 years ago but stupidly used an Amazon cheapo one.


So what's the cause of the "damp cranks but won't fire?"

I've got a 4.3 that has been doing this for about 2 years, maybe 3. I'm about to yank it and do a V8 swap because of low oil pressure, but would like to figure this out. Fuel pressure is good, about 58 psi on mine. I thought it was electrical?
 

someotherguy

I'm Awesome
Joined
Sep 28, 2013
Messages
9,784
Reaction score
14,138
Location
Houston TX
I know you're talking 454, but just to be clear the 350 doesn't have a vacuum line. Also, the 454 line is easy to forget to hook up for some reason. :banghead: OP how old is the regulator in the 350? They're known to fail like the 454 and cause starting/running/idling issues.
Absolutely, no vacuum line to the regulator in the 5.7 Vortec. But OP has a 7.4, as far as I can tell..

Richard
 
Top