Devil in the details

Mazdarati3000 · Aug 22, 2018

I have a 1996 b3000 se.

I have put 5 new fuel pumps in this truck and keep getting 19-21psi of pressure.

-The pump is getting 13.5v while running

-pumps have ohm checked anywhere from .9-1.9 ohms. according to the Delphi tech this is acceptable

-new pressure regulator

-new fuel filter

-fuel pressure from pump 19, at filter 19, at reg 19

-checked all grounds to the pcm, pump,

-tested the pump with just the battery

-bypassed the inertia switch

-checked resistance from the pump connection on the hanger to the pump itself, 0 ohms

-checked we were getting min 12v through the pump connection harness as well

-fuel system holds pressure after key off.

I am fairly certain that there is no electrical issue getting power to the pump itself. And that there is no internal or external leak to the fuel system.

the only way we got 40+ psi at the shraeder was to make a restriction in the return side at the pump itself, bypassing just enough to create the 40 psi.

the 5 pumps have been various manufacturers from different part stores locally. bought as either full hanger assemblies or pumps that were swapped into different hanger assemblies.

I am at a loss for what this could be. Ford wants almost $600 for an OE hangar assembly, but I don't think this is going to fix it based on what we've already tested.

Someone, in the last 20 years of rangers has had to come across this?

Any help would be appreciated!!!!

Dirtman · Aug 22, 2018

Mazdarati3000 said:
the only way we got 40+ psi at the shraeder was to make a restriction in the return side at the pump itself.

This is how the pressure regulator operates, by allowing or restricting fuel flow to the return side. With low vacuum the regulator closes the return side for maximum pressure, at high vacuum it allows most of the fuel to return so low pressure. You essentially just did the pressure regulators job for it when you blocked the return line. Might be a good idea to pop the regulator off and see if its functional. Not uncommon for new parts to be DOA.

Mazdarati3000 · Aug 22, 2018

I completely agree with you on that.

Outside of checking that we are getting a change in pressure from altering the vacuum to the regulator, what other test could we perform on the regulator?

The Ford original regulator would alter psi by a grand total of 6psi. the new one we installed after thinking it was the a regulator fault did the same.

My thinking is that if one was bad, we would see different readings between the two. I can't imagine they would fail in the exact same manner?

Thanks!

RonD · Aug 22, 2018

Fuel Pressure Regulator(FPR) usually has its spring set for about 42psi

Engine OFF
Cycle key on and off, fuel pump runs for 2 seconds each time, it should take 3 or 4 off/on to get to 40psi, if starting at 0 psi
If pressure doesn't get to 40psi, pinch off Return line and see if it does, if so replace FPR

Getting to 40psi means the pump is not the issue it can produce 40psi pressure, but the FPRs spring can not hold 40psi, it is being pushed open too soon

The FPR vacuum setup pulls against the spring, so with engine running pressure should drop, bigger drop at idle, but should be 28psi or higher.

Yes, the 6psi change with vacuum is about right, but doesn't mean much

Also test Pressure gauge on a tire, same schrader valve fitting, to make sure it is accurate, same pressure ranges, 28-35psi

20psi should be OK for driveability, unless pressure drops farther at higher speed/demand
Below that might set Lean Code
Computer compensates for fuel pressure using O2 sensors, so there is quite a range for "working" fuel pressure, computer will set Lean codes, on both Banks, when pressure drops too low, which doesn't mean engine is running Lean, it just means Computer is opening injectors 15-20% longer than it calculated..........because of the lower fuel pressure

Mazdarati3000 · Aug 22, 2018

Thanks for the replies!

I completely agree with everything.

the whole reason we are going through this, is because the truck stumbles to the point of stalling on take off, then lacks enough power to accelerate to even 40mph.

If 19psi were the lowest it went I would agree, but that's at idle, no load on engine.

And this doesn't throw any codes.

We are checking the regulator as suggested.

Thanks again!!

fastpakr · Aug 22, 2018

As Ron said - are you sure the gauge is accurate? It would be awful to chase this problem ad nauseum only to have been on the wrong track.

Mazdarati3000 · Aug 22, 2018

yeah, without a doubt the gauge we are currently using is accurate.

My initial test was with an Actron that I have owned for years, the other two was a Matco and Cornwall I believe. Not saying that the big names are always better but in this case, they would read the same and the Actron was the one that was different.

The regulator that was suspect was 275k original, yet the one we replaced yesterday was new from Advance Auto.

We are still getting the same results with the new regulator. I reached out to Ford and am keeping my fingers crossed than an OEM unit will do what it should.

Thanks for the suggestions!!

RonD · Aug 22, 2018

Reach over and stick it(the gauge) on the tire's valve, see what pressure it shows, ease peasey lemon squeezy

.

Occam's razor-the simplest explanation, with the fewest assumptions, is usually the correct answer.

If not the pressure gauge maybe the schrader valve on the fuel rail is limiting pressure, so pressure is a moot point.

the whole reason we are going through this, is because the truck stumbles to the point of stalling on take off, then lacks enough power to accelerate to even 40mph.

I would use a vacuum gauge and check for exhaust blockage
18-21" vacuum at idle
Blip throttle(Open quickly and let it snap closed) should see drop to 0" then QUICK return to 18-21"
Slow drop and slow return = blocked exhaust

Mazdarati3000 · Aug 30, 2018

RonD said:
Reach over and stick it(the gauge) on the tire's valve, see what pressure it shows, ease peasey lemon squeezy .

Occam's razor-the simplest explanation, with the fewest assumptions, is usually the correct answer.

If not the pressure gauge maybe the schrader valve on the fuel rail is limiting pressure, so pressure is a moot point.

I would use a vacuum gauge and check for exhaust blockage
18-21" vacuum at idle
Blip throttle(Open quickly and let it snap closed) should see drop to 0" then QUICK return to 18-21"
Slow drop and slow return = blocked exhaust

I purchased a new gauge and verified it would at least sweep in the range I was needing accurately.

The exhaust blockage was another culprit that was tested and fixed before posting any of this. I had a bad cat, and was getting about 11" of vacuum. With the blockage fixed the vacuum increased to about 15". I understand this is a little low, but the longblock has 173k-ish.

The fuel pressure fix was by replacing the pump with a Delphi 0310.

In my ignorance, I assumed any pump from the 1996 3.0 ranger or mazda would be a direct swap. They all have the same power for that year and all require the same pressure at the regulator. This is just not the case. Electrically they all vary in load and pressure, and also gph.

That also brings be to ask again, the truck still has a stumble on take off and lacks power. Every fix, to include the new pump has helped but nothing is curing this. The only code currently displayed is P1443, evap purge.

When I checked compression I was at about 110-120 on all cylinders. I am still thinking it's fuel related, and with no codes or troubled electronics (to my knowledge) I'm thinking it's lacking volume. Could new tank straps cause a pinch in the plastic tank to the point the pump doesn't have the clearance to the bottom?I am also starting to think the issue just be that I am expecting too much out of this truck? Has anyone else had similar issues?

Thanks again!!

RonD · Aug 30, 2018

3.0l Vulcan ran 9.3:1 compression ratio, so expected static compression would be 160-165psi range, regardless of miles
The 110-120psi would explain the low Vacuum as well

General rule of thumb is Compression Ratio x 18 = expected PSI
9.3 x 18 = 167.4

If you wonder where the 18 comes from its air pressure at sea level(15) + 3 for mechanical movement of piston compressing the air in the cylinder, so general number, if you are within 10-15% then test is fine, you are not.

Compression = power, so low compression = low power, simple as that
If you are living in Denver, a mile high so lower air pressure, then you would expect a little lower compression or Vacuum at idle, but not that much lower.

Retest compression
All spark plugs removed
test a cylinder DRY, then add a teaspoon of oil and retest WET, write down both numbers
WET test will always be higher, but the amount of change can tell you if its rings or valves

When all cylinder are equally low then timing chain may be loose, tensioner failed, not a common occurrence on the 3.0l.

But compression is where you should focus your efforts, this is not a fuel issue any more

Mazdarati3000 · Aug 30, 2018

I know generally speaking power comes from how much cylinder pressure is being made. I didn't know about the rule of them for that test.

I was under the assumption that as long as the engine had consistent pressure across all cylinders it would be a turd but would run well, if that makes sense. The hesitation off idle is something I wouldn't attribute to low compression, but it's not fixed either.

Either way I will test as suggested and let you know.

Thanks for the help!!

RonD · Aug 30, 2018

Compression is needed for 2 reasons.
First is so the gasoline can be ignited by a spark.
Liquid gasoline can't be ignited by a spark, yes the Movie Guys take liberties with that one, lol.
Gasoline VAPOR(fumes) can be ignited by a spark, and compression is HEAT, that HEAT vaporized the liquid gasoline that comes out of the fuel injectors, so it can be ignited by a spark plug

Second is power, think rubber band powered airplane propeller, the tighter you wind the rubber band the more power is stored and released when you let it spin.
The higher the compression the more power is stored and released when that cylinder fires.
But there is a trade off because Regular Gasoline will ping/knock with compression above about 9.5:1
You get more power out of a 12:1 ratio engine, but you also have to run Premium Gasoline.

With compression of 120psi you are basically running a 6 cylinder lawn mower engine
6.6:1 compression ratio
Briggs and Stratton L engines ran 6.0:1 ratio they would read about 100-110psi on a compression test.

The Hesitation could be you are flooding out the engine on acceleration, computer dumps extra fuel in and retards the spark for the faster burn rate of Rich mix, but with the lower compression the burn rate is not as fast as it should be so engine loses more power, the hesitation you feel until a regular air:fuel mix returns.
But you would still have the overall sluggishness of 6.6:1 ratio

bobbywalter · Aug 30, 2018

compression testing and vac gauge with a hard look at the plugs are skills needed but in short supply these days as the efi systems run way past the point where a carb will...

Mazdarati3000 · Aug 31, 2018

Boy was I way off. HA!

I got 170-180 psi on all 6. Didn’t add oil since it was within range.

Double checked vacuum at idle 14”

All the plugs were not oil fouled or discolored. By discolored I mean any color, no golden brown or white (at least not visible), didn’t see any electrode transfer...

Timing could be too far advanced? Scan tool says 12-16degrees at idle. Wot gives me 40-46 degrees. I have no clue what this truck should be since it’s dis.

Your comment about the chain giving up in a sense got me looking for an out of tolerance spec. 6 degrees of crank to cam play?

RonD · Sep 1, 2018

Compression is right on for the 3.0l Vulcan,

It is possible to get good compression with poor timing chain tension, 5 or 6 deg of play is OK, i.e. you move the crank 5 or 6 deg before cam starts to move

1996 3.0l Ranger is distributorless so there is no spark timing adjustment available.
But it reads OK since it is advancing

Steady 14" of vacuum is too low, unless you installed a bigger Cam

I would have vacuum gauge attached, engine idling and then pull off PCV Valve hose from intake and then block that port, see if vacuum gets up to at least 17"
Do the same with Power Brake booster vacuum hose.
These are the two largest Vacuum hoses so can effect vacuum the most.

Then move on to the smaller hoses on upper intake, pull off and block intake's port with finger.
Smaller hoses shouldn't effect vacuum that much, i.e. 3"+

And I would expect Lean codes with intake vacuum leak as well

Test vacuum gauge on another engine if possible, 18-21" is expected on any gasoline engine

Devil in the details

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