No Start & loss of power

I've been having this problem for some time now and can't seem to track down whats causing it. The truck is an 02 B4000. The issue started out as a no start whenever the truck was cold and had sat for a while, like over night. The problem has since grown to not starting every time the truck is off, even if only off for 10 min.
Over the past year I've replaced the plugs, fuel pump, fuel filter, TPS, and MAF sensor. I also put a new PCV valve in it last night.

When revving the truck over 3k rmps the truck seems to sputter, it also has this problem if I try and leave in first gear under 1500 rmps.

If anyone has any suggestions I'd love to hear them, this thing is getting the best of me...

To add to that

The only way I get the truck to start when its cold is if I unplug the MAF sensor. If the MAF sensor is plugged in the truck will bog down, I have to wait till the truck is warmed up to plug the MAF back in.

Welcome to TRS


Because of the 3 timing chains on this 4.0l SOHC engine and the possibility of one 'slipping'(not uncommon) I would do a compression test to either confirm that is the problem or take it off the table as the problem.
Compression is mechanical so either is OK or not OK, black and white
Without this test you could just be wasting time, and money, on non-fixes

Spark plugs are hard to get at on this engine in a Ranger but there are shops that can do electronic compression tests, laptop, software and about 10mintes time for setup and test.
And for this purpose it will give you the info you need to see where to go next.
Short video on E-test here: www.youtube.com/watch?v=YDX83bWu3Vg

Compression is needed to heat up the gasoline so it vaporizes, liquid gas can't be ignited by a spark, only gasoline vapor can.
You need compression above 100psi on a cold engine to get vaporization, 4.0l SOHC should have 170psi.
So low compression makes for very hard starting especially cold, and even warm if it gets too low.
Compression is also Power, there is a rebound effect as compression ratio increases, giving higher compression engines more power, so if compression drops...........so does power

You can also try a Vacuum gauge($20) to test engine vacuum at idle, 18-21" is expected(at sea level), lower could mean low compression, but not definitive for compression issue.
Vacuum gauge can also detect clogged exhaust, which limits power as back pressure builds up in partially clogged exhaust system
Good read here on using vacuum gauge: http://www.gregsengine.com/using-a-vacuum-gauge.html

There is a REV Limiter in the computer(PCM) and it is set for about 3,000rpm, so in Park/Neutral(clutch pedal down) PCM will limit fuel to engine when approaching or above 3,000rpm

Unplugging MAF sensor could fit the low compression scenario, PCM has factory preset air/fuel mix tables these are offset by MAF air flow readings, which would be low if vacuum/compression is low, removing MAF input would cause PCM to stick with Factory air/fuel, no offsets

Do you have a manual or automatic trans?

2WD or 4x4?

I was going to check the plugs today to see their condition anyways so I guess I can knock out the compression test as well.

Thanks for all that info, I have a 2wd with a manual transmission.

Compression Test

Ok so I checked all of my plugs, they all looked good. No cracks, all had a light brown color on the end with some white.
I also did a compression test and every cylinder but cylinder #2 hit 180 psi. Cylinder #2 hit 178 psi.

The truck will start if I spray starter fluid into the intake, but it will die immediately.

The truck isn't throwing a CEL either.

Good compression numbers.

50/50 test shows spark is good, correct timing(manually adding fuel to intake)

And since it does start eventually, you are getting fuel injector pulses.

So best guess is your fuel pumps check valve is failing, or pump itself

Computer has no fuel pressure sensor, it assumes 60-70psi, but has no way to check it, so no CEL for fuel pressure

Fuel pressure on 1998 and up Rangers/B-series should be 60-70psi at the injectors.
This pressure will hold above 50psi for MONTHS, not hours, days or weeks......MONTHS
Inside the fuel pump is basically a flap on the OUT port that is pushed open when pump is on, and then snaps closed when pump is off, to hold pressure in the system.
This is called the Check Valve or Backflow preventer valve

Since you are not reporting any "smell" of gasoline(leaking fuel line) or big Drop in MPG(leaking injectors) the check valve in fuel pump is mostly likely place to lose fuel pressure when engine is off.
And the fact you report losing power would also mean fuel pump itself maybe getting weak.

The fuel pump only runs for 2 seconds when you first turn on the key, this adds about 10psi pressure, so tops up the 50psi to 60psi for starting, once Computer sees RPMs above 400(engine started) it will turn on the fuel pump full time.
This 2 second thing and 400RPM is a Safety feature, if there should be an accident and a broken fuel line, you wouldn't want the electric fuel pump to keep pumping out gasoline

Most fuel injected engines have a test port on the fuel rail(feeds injectors) to test fuel pressure, it looks like a tire's air valve, because that is what it is, a schrader valve, will often have screw on cap just like tire's air valve.
But not all years of the 4.0l SOHC engines had the test port

For now you can try priming the fuel system multiple times before starting.
Turn on the key, count to 3, turn key off
Repeat 3 or 4 times then try to start engine
Each time key is turned on fuel pump will run for 2 seconds, so you are trying to build up pressure in the system for starting
Listen for the fuel pump to run each time, it isn't quiet.

There could also be a break in the fuel line going from the pump to the top of the tank, this would leak fuel and pressure both but inside the tank so same result.

Even though you weren't helping me Ron, thanks. Lots of good info in a little space!

Sent from my QMV7B using Tapatalk

Ok so since the fuel pump was under warranty I went ahead and swapped it out for a new one. The truck ran great for a day then when I went to start it the next morning I checked the fuel rail for fuel and sure enough there was maybe a few drops that came out. No where near 35 psi at the rail. It seems like I have a leak somewhere along the fuel system that is allowing this drop in pressure.

Do the seals in the hose connections go bad or should I look for this leak elsewhere?

If gasoline was leaking from a fuel line, fuel filter or fuel rail you would most likely smell it.

That leaves 3 places for a pressure leak
1. Fuel injector, you would notice this in much lower MPG and Rich running if an injector is leaking.
When engine is cold remove the large air tube from upper intake, cycle key on and off 4 times.
Open throttle plate manually and smell for gasoline, if an injector is leaking it will drip fuel into the intake so you should be able to smell it.
You need to cycle the key to build up pressure in the system so gas can drip

2. FPR(fuel pressure regulator), on the fuel rail, it is connected to the Return fuel line, if it leaks, or bad spring, then fuel just flows back into the gas tank, no smell.
It also has a vacuum hose attached, remove it to see if there is fuel in it, if there is then FPR is leaking and it would be sucked into running engine, lower MPG and Rich running.
No fuel in vacuum line doesn't mean FPR is good just means diaphragm isn't ruptured.
You can remove the Return line and cycle the key on/off one time, no fuel should come out as long as pressure stays below 30psi.
FPR is actually set for 40-45psi before being pushed open and allowing fuel to flow back to the gas tank.

3. Gas tank lift tube or fuel pump check valve, no gas smell because leak is in the gas tank.
You just swapped out the pump, but did you do the whole assembly?
Check valve/backflow preventer is basically just a flap in the pump that is pushed open when pump is on, and then snaps closed when pump is off to hold pressure from there to the Fuel rail.

So you have:
fuel pump/check valve-------------fuel filter------------fuel rail--injectors---FPR

Between Check valve and FPR fuel pressure should hold above 25psi for a few MONTHS


Each time key is turned on fuel pump will run for 2 seconds, that adds about 10psi of pressure

Ok so I checked the intake after priming the pump several times. There was a very faint smell of fuel before I ever primed the pump and the smell didn't get any stronger after priming. If I had a leaking injector would it show on the plug(s)? None of my spark plugs showed any indication that I was running rich, they were all light brown and white at the tips.

As for the fuel pressure regulator, I was under the impression that my truck did not have one but had a fuel pulse damper. I could be wrong and if so I'll look along the lines for an FPR.

I purchased a new fuel pump from autozone, this one to be exact http://www.autozone.com/external-engine/fuel-pump/delphi-fuel-pump/342563_472304_20966
The part number is DFG0873
I'm assuming it was the whole assembly.

yes, 1998 and up used 60-70psi fuel pressure and no return line so no FPR.

Any help on where I can find the fuel pressure damper? If there's no return line and I'm not seeing symptoms of a leaking injector on the plugs, I'd imagine the loss of pressure is coming from the damper.
If I'm wrong someone let me know please.

Damper will be at the end of the Fuel Rail, it will have a Vacuum hose attached to it.
Check that vacuum hose for gasoline or gasoline smell, that would indicate it is leaking.
If no gasoline in the vacuum hose then Damper is OK.

Checked the damper and even swapped it with another from a running truck and saw no difference in symptoms. Its been a while since I really messed with the truck but today when I was trying to get it to start it only started after I let out some fuel from the schrader valve. I'm leaning towards a leaking injector that's just flooding out the cylinder.

If you had pressure at the schrader valve then you don't have a leaking injector

Push down on the gas pedal all the way, and hold it down, before starting, this will SHUT OFF fuel injectors, and give a flooded engine maximum air.
It is called "Clear Flooded Engine" routine, all fuel injection computers have this
Key on
0 RPMs
TPS(throttle position sensor) above 4.5volts, throttle Wide Open, foot to the floor
Computer will shut off fuel injector pulses until gas pedal is released, TPS under 4.5volts

I use this daily on my older high mile engines, get some oil pumping thru the engine first, then I release the gas pedal to let engine start