All these threads about fuel cells have been poping up. Ive been getting contrasting info about which engine uses what for fuel pressure.

TRS lists the 3.0 to need 30-40psi.
3.0 specs

TRS also lists the 4.0 OHV to be 30-40psi, while the SOHC is listed 64-75psi.
4.0 OHV and SOHC specs

So who wants to join in and clear this up if these numbers are correct or not.

 

The 30-40 psi specs are for Fords that use a conventional "return" fuel system.

1998+ Rangers use a mechanical "returnless" fuel system regardless of the engine. Mechanical returnless fuel systems have the following characteristics:

(1) there is no return line running back to the fuel tank from the fuel rail;

(2) the fuel pressure regulator is now in the fuel tank with the pump, not on the fuel rail;

(3) theyare designed to operate at higher fuel pressure (64 +/-8psi for gasoline engines, 55psi +/-8 ps for FFV);

 

the 4.0L SOHC engine has a pressure regulator on the drivers side fuel rail on the very back. i found it on mine in class

 

What you are describing is the fuel pulse damper, which the Ford Manual describes as follows:

 

Thanks, Rockledge, for your clarification, it's important to note the difference. Do you happen to know on a 2007 ranger 4.0 if this also has the fuel dampener on the drivers side rail towards the back? I am having fuel pressure attaining 55ish PSI and then dropping off to 30ish and slowly bleeding down from there. No apparent leaks and replaced fuel pump.
Thanks, David

 

Fuel damper is just there to stop pressure waves from building up in the fuel rail, pressure waves form when injectors open and close, the damper at the end of the rail/tube absorbs the waves so they don't reflect back into the tube, its just a rubber diaphragm, the vacuum hose is for safety, if diaphragm should leak it would drip on HOT exhaust, a BAD thing, lol, vacuum line would suck any leaking fuel into the intake and cause Rich codes

Fuel pump assembly, the whole unit, has the fuel pressure regulator(FPR) as part of the assembly
So did you change the whole assembly or just the pump?

And with key off fuel pressure may bleed off, but not while engine is running, so please clarify when pressure is dropping

 

Hey Ron,

Thanks for jumping in on this. This goes back a ways, and you and I exchanged a number of messages and I'm sticking with your 50/50 test which led me to establish low fuel pressure @ rail (0-20psi). We have most recently replaced fuel filter and pump/ assembly (the entire unit.. pulling the bed BTW is far easier than dropping the tank IMO), and we now get 55+PSI @ rail but then it quickly drops off to 30 and then slowly bleeds down (engine isn't running so goes down after cranking). Also while there drained and cleaned tank (nasty, gas turned orange/ yellow) and put new gas in. So, we've made progress. But still not there (running) yet. I am as interested in checking the vacuum line on the dampener JIC.

To review briefly:
- 07 4.0 Ranger purchased as 'salvage'
- Ran initially though briefly but had loud knocking in "upper end"
- spark was orange so we replaced coil, plugs and wires; blue spark now
- compression 120+/- on all cylinders (not optimum but should suffice)
- adding starting fluid to carb seems to get it closer to firing and on occasion has started briefly 'almost going' (after which died) but not consistently

Since then I've run down the various lists some appropriate and necessary, some not.
- verified PATS not activated
- checked inertia switch (though I am almost at the point of bypassing JIC)
- swapped corresponding relays/ checked fuses
- disconnected MAFS

Probably other things I've checked (mostly based on your input) but not resolved yet, most appreciative of your thoughts, insights, etc.
David

 

Knocking at top end and compression of 120psi reads like valves are out of time

Was average compression in all 6 cylinders 120psi?
You need to test all 6 with no spark plugs in the engine, and battery voltage at or above 12.4volts, so you get good crank speed

4.0l SOHC runs 9.7:1 compression ratio so expected static compression(cold engine compression test) would be 175psi
If compression is 120psi then you may be chasing your tail with spark and fuel issues
Ether(quick start) might get it to fire, but compression that low would be marginal for gasoline and carb cleaner

Spark can't ignite a liquid fuel, yes the movie guys take liberties with that fact, lol, spark can only ignite fuel vapors
The point of higher compression is to heat up and vaporize part of the fuel so a spark can ignite it, when that happens the ignition will quickly vaporize and ignite the remaining fuel in the cylinder
Without the initial ignition point then no start
Ether becomes a vapor at a lower temp than most fuels, which is why its used to start cold engines, gasoline or diesel engines

 

Thanks Ron. When I tested compression it was one cylinder at a time and I replaced each plug after doing it so never with all 6 out. Battery is new and has been on tender so although I didn't verify voltage (I can) I suspect it was sufficient but will if you feel it's necessary.

But given what you said, given low pressure and other items attended to/ checked, is it your opinion that I should pursue troubleshooting valve timing?

David

 

Test all 6 cylinders again, spark plugs out
write it all down
Add up the 4 cylinders that are in the middle, don't use the lowest or the highest number
Divide total by 4, and that will be the average compression number

If its under 150psi then valve timing is most likely off
If one bank/side of the engine are all lower than the other side then that one cam in that side is out of time

 

Thanks again Ron. They were all within 5-10#s of one another but I will rerun the test under the conditions you've indicated. If I understand you correctly, if they are in fact all ~120 and given the other information, I should then look into valve adjustment next as a means of getting the engine running, correct?
David

 

There are no valve adjustments, just valve to crank timing via the timing chains