Engine Stalls?

Have you checked for power to the MAF? Have you confirmed that fuel pump pressure is within the manufacturer's specs even though it is somewhat new?

These guides can help

https://www.2carpros.com/articles/engine-stalls

and

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Please run down these guides and report back.

This is the closest I could find for your vehicle. It will be very similar.

https://www.2carpros.com/articles/testing-a-fuel-pump-and-pressure-regulator-video

As far as the MAF, I need to know what code you found to give the proper directions. I have attached a schematic of the MAF wiring system. Take a look at check grounds and check for power as shown.

Do you have the trouble code that was found?

Hi:

You know, I feel the MAF and O2 sensor issues are related. Do you have access to a scanner that can read real time data?

If you have the actual code numbers, for example, P0137, that would really be helpful. I have pages of tests to go through and can't do it without the codes. Since you haven't replaced the MAF, it may be the issue. First, check the following:

Air intake - objects blocking throttle body inlet screen
Intake Manifold leaks
Vacuum leaks at throttle body
Air leaks at EGR valve flange and pipe
Crankcase ventilation valve faulty, missing, or incorrectly installed.
Also, check the brake booster vacuum supply for leaks.

IF they all check okay, then this is where I need to know what codes you found. For example, does it have a P0121? That would indicate throttle position angle is not near 0 and certain things need checked. If it is near 0, then I have to go a different direction. Without the actual codes, we could spend weeks going through things.

Let me know.

I will assume that you checked the items I listed. Also, that you have a real time scanner that you can look at how things are reacting.

The first thing I need you to check is for throttle position angle. It should be near 0. Let me know what you find.

Welcome to 2CarPros.

Rob, the idea that you have to press the gas indicates to me there is more fuel than is needed to start the engine. When you press the throttle on a fuel injected vehicle, it shuts the supply off.

I have a few questions. First, have you checked fuel pump pressure?

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Is the check engine light staying on when the engine is running? Do you have a live data scanner?

I'm questioning if the fuel pressure regulator is bad or if the engine coolant temperature sensor (ECT) is bad. The regulator is a vacuum operated component. Often times when they go bad, they draw fuel through the vacuum hose directly into the engine. A rich mixture is the result.

On the other hand, if the ECT is bad, it could be telling the computer the temps are extreme and the computer over compensates with a rich fuel mixture. If you have a live data scanner, you can check what the ECT is indicating. Also, if the check engine light is staying on, have the computer scanned. Most parts stores will do it for free.

If you could, let me know the answers to my questions.

Take care,
Joe

Welcome back:

I will provide directions for testing fuel pressure. You will need a fuel pressure gauge, but most parts stores will lend/rent one to you.

As far as a live data scanner, yes, it is an OBD2 scanner. However, it has the option for you to view specific components while they are working. In this case, I wanted you to look at the temperature sensor's signal. If it was saying -40°F and the actual temp was 80°F, the fuel mixture would be extremely rich and cause a hard start and rough running.

Okay, as far as the fuel pressure, the original link I included above shows how it is done in general. Here are the manufacturer's specs for pressure:

FUEL PRESSURE SPECIFICATIONS
FUEL PRESSURE
1. Ignition "OFF" for 10 Seconds.
2. With ignition "ON, " engine "OFF" and fuel pump running, pressure should be 385-430 kPa (56-62 psi).
For additional fuel pressure testing procedures,

Now, I attached a picture of the fuel pressure regulator for you to see what it looks like. The problem is its location. It is under the intake manifold. Based on what you described, I am questioning if the regulator is bad and allowing fuel to be drawn into the engine via the vacuum hose. If you can see the regulator and are able to remove the vacuum hose, do so. Check to see if there is any evidence of raw fuel in the vacuum hose. If there is, it needs replaced.

Please feel free to ask questions if you need anything. I'm not here 24 hour's a day, but a minimum of once a day for a few hours, so I will get back to you.

Let me know if this helps or if you have other questions.

Take care,
Joe

Welcome back:

It will affect how it runs because the computer won't know what is happening without an accurate reading from the oxygen sensor. It will most likely cause a rich fuel mixture to that one side.

If you have easy access, see if you can get an inexpensive universal cat that will work. Then cut the old one out and clamp the new one in place.

Let me know what you find on the fuel pressure. Also, feel free to let me know if you need help.

Take care,
Joe

Can you clarify the voltages? When is the battery at 12.86 volts? Engine off? Engine running? If the generator and battery are not at the same voltage, suspect a problem with the heavy wire going back to the battery.

14.75 volts with the engine running is perfect. 15.25 volts is a little high and suggests, along with some of your other observations, loose or corroded battery cables.

A running problem and a confused voltage regulator can also be caused by voltage spikes from the generator. The generator will keep the battery charged, but the spikes will confuse some of the computers on the truck.

Caradiodoc

Don't rely too much on the dash gauge for diagnosis except that you are familiar with what is normal. The voltage readings at the battery and generator seem fine. Those are what really count.

At 240,000 miles, I would guess the generator has been replaced a couple of times already. If not, suspect worn brushes causing an intermittent no-charge condition. You will have to make some measurements when the problem is acting up.

12.8 volts at the battery suggests it's in dandy condition although an intermittently shorted cell, (not common), could cause the symptoms you listed. If you see your dash gauge drop to 13 volts or less, jump out, (stop the truck first :)), and measure the battery voltage. If it is indeed below 13.75 volts, measure at the back of the generator too. If both are low, suspect a defective generator, but first measure the voltage on the small plug-in red or brown wire, (I can't remember the color). It must have full battery voltage on it while the engine is running. It should have around 2 volts with the ignition switch on and the engine not running. That is the circuit that starts up the generator and turns the battery light on the dash on and off. A resistor is used if you don't have a battery light.

If you can catch it not cranking again, measure the voltages at the battery while a helper holds the ingition switch in the "crank" position.

Caradiodoc