• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

Low fuel pressure?


ratdude747

ratdude747

Member
Supporting Member
Article Contributor
TRS 20th Anniversary
Joined
Aug 10, 2014
Messages
503
Reaction score
22
Points
18
Age
31
Location
Madison, IN
Vehicle Year
1995
Make / Model
Ford Ranger
Engine Type
4.0 V6
Engine Size
4.0L
Transmission
Automatic
2WD / 4WD
2WD
Tire Size
215/70R15
My 1995 4.0 seems to have low fuel pressure. I was measuring around 20psi or so (no longer have fuel pressure gauge)

I have replaced:

  • fuel pump
  • fuel filter
  • pump strainer
  • fuel pump relay (from parts truck)
  • fuel pressure regulator
  • (unrelated?) alternator

I also checked the inertial cutoff switch. All looks good there. Fixed some battery issues, no change.

Getting exactly 12v at the fuel pump connector when the key is turned on (no load). Not 12.4v like I'd expect... Indicates a bad wire?

I also tried feeding power directly to the pump via the inertial switch connector. No change.

I'm running out of ideas... Suggestions?
 


chewy012

chewy012

New Member
Joined
Jan 31, 2016
Messages
427
Reaction score
1
Points
0
Location
Colorado Springs, CO
Vehicle Year
1992
Make / Model
Ford
Engine Size
4.0 OHV
Transmission
Manual
Leaky injectors? That's about the only thing I don't see on your list.

Try the clear flood test and see if she tried to fire. Warm engine, turn off, WOT and crank. No fire is what you want.

Sent from my XT1254 using Tapatalk
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,363
Reaction score
8,369
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Alternator?

Battery voltage, engine off, should be 12.3 to 12.8volts
Battery voltage engine running should be 14.5 to 14.9volts just after start up, then drop to 13.5-13.7volts after 5 minutes or so of running

Yes, could be dirty connectors or bad wires are causing a voltage drop at fuel pump
Ground wire is as important as 12volt wire.
If a device needs 10amps to run and Ground wire is dirty or bad and can only pass 5amps then thats all the amps that can flow thru, DC power is like a hose from battery terminal to battery terminal, doesn't matter where you "kink" that hose flow is reduced for the whole thing.
 
ratdude747

ratdude747

Member
Supporting Member
Article Contributor
TRS 20th Anniversary
Joined
Aug 10, 2014
Messages
503
Reaction score
22
Points
18
Age
31
Location
Madison, IN
Vehicle Year
1995
Make / Model
Ford Ranger
Engine Type
4.0 V6
Engine Size
4.0L
Transmission
Automatic
2WD / 4WD
2WD
Tire Size
215/70R15
RonD said:
Alternator?

Battery voltage, engine off, should be 12.3 to 12.8volts
Battery voltage engine running should be 14.5 to 14.9volts just after start up, then drop to 13.5-13.7volts after 5 minutes or so of running

Yes, could be dirty connectors or bad wires are causing a voltage drop at fuel pump
Ground wire is as important as 12volt wire.
If a device needs 10amps to run and Ground wire is dirty or bad and can only pass 5amps then thats all the amps that can flow thru, DC power is like a hose from battery terminal to battery terminal, doesn't matter where you "kink" that hose flow is reduced for the whole thing.
Click to expand...
I checked most/all of that (not to brag, but FYI, I am an engineer with an electrical engineering technology degree, but sometimes even basic stuff knocks me on my ass once in a while).

---

Redid a pressure check, at cold start after a key cycle (no start) it read 40PSI, dropping to 35PSI after start attempt. So maybe fuel pressure wasn't the only issue?

I will do a clear flood test before I leave for a long trip (yay rental cars :( )...

I'll start a new thread with a better title.
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,363
Reaction score
8,369
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Yes, that fuel pressure is normal(30-40psi), and if it held for a few minutes then injectors are OK as well.

Do 50/50 test if there is a no start
Spray gasoline or starting fluid(ether) onto intake and try to start
If it starts up and dies then yes fuel is the issue
If it doesn't start then spark is where to look
50/50
 
You must log in or register to reply here.

Sponsored Ad


Sponsored Ad

Members online

No members online now.
Total: 728 (members: 0, guests: 728)

Today's birthdays

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Latest posts

Truck of The Month


Shran
April Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

Latest Album Photos

Hunters
20240409_190831.jpg
20240409_190818.jpg
20240409_180824.jpg
20240409_182648.jpg
20240409_181010.jpg
20240408_175026.jpg
99 Ranger
20200706_161414.jpg
20240207_155117.jpg
20240207_155111.jpg
20240207_154537 - Copy.jpg

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top