after it has been sitting all day, it starts, then bogs down and sometimes dies?

Hi,

The EVAP leak can cause a rough idle and stalling, but I don't think it would cause a delayed start. Based on your description, it sounds like low fuel pressure.

Try this.

1) Turn the key from off to run (engine off). Count to 5

2) Turn the key if and repeat step one, four more times.

3) See if the vehicle starts normally.

If it does, check the fuel pressure. Here is a link that explains how it's done.

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

You will need a fuel pressure gauge, but most parts stores will lend one to you.

Let me know what you find.

Joe

After cycling the key, I had the same symptoms and possibly even worse than normal. The truck hesitated and shut off immediately, then on the second try it bogged way down before bringing up the RPMs.

Hi,

Interesting. I wonder if we have a leaking fuel injector or fuel pressure that is too high. What I would suggest next is to check the fuel pressure. In addition to checking pressure, pay attention to see if the pressure drops quickly when you turn the key off. Rather than not getting enough fuel, we may be getting too much.

Here is a link that explains how to test pressure:

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

I attached the manufacturer's pressure specifications below. You will need a pressure gauge, but most parts stores will lend one to you if you don't have one.

Also, if you have a live data scan tool, check two things for me. See what the short-term fuel trims are at operating temperature and before starting it in the morning, see what the coolant temperature sensor signal indicates. It should be close to the ambient temperature.

Let me know what you find.

Take care,

Joe

See pic below.

I will need to pick up a fuel pressure gauge, but I did run the live data on my scan tool. I am not sure what all of it means but it looks like it is out of spec.

I did not realize ECT was the coolant temperature right away so I missed the initial temp reading, however, it seemed to rise as expected while warming up. After warming up, I collected data in Park and in Drive (Not Moving).

Park
STFT B1: 1.6%
LTFT B1: -9.4%
STFT B2: 1.6%
LTFT B2: -10.9%

O2S values fluctuated but were regularly above 0.5V on B1 and B2, below is an example of B1 data but B2 looked similar.
O2S B1S1: 0.610V
STFT B1S1: -0.8%
O2S B1S2: 0.760V
STFT B1S2: 99.2%

I then shifted the vehicle into Drive and looked at the data while holding the break.
STFT B1: -2.3%
LTFT B1: -6.3%
STFT B2: -1.6%
LTFT B2: -7.8%

O2S values fluctuated but were regularly above 0.5V on B1 and B2, below is an example of B1 data but B2 looked similar.
O2S B1S1: 0.240V
STFT B1S1: -0.8%
O2S B1S2: 0.760V
STFT B1S2: 99.2%

Let me know what you think. Thank you!

To follow up on my previous reply, I was able to get a pressure gauge on the truck and run some tests.

Key On: 56-58lbs
Idling: 61-62lbs
Revved up: dips to ~60lbs
Under Load (Reverse and holding the break): dipped to ~60lbs

What does this mean along with the scan tool data?

Hi,

The fuel pressure is perfect, no problem. The readings are all good as well except the short-term fuel trims. You indicated bank1 sensor 2 is 99%. Do you mean bank 2 sensor 1?

If that is accurate, the computer is dumping fuel to that side of the engine. The odd thing is it isn't happening on bank 1. Do you have an exhaust leak at the exhaust manifold?

Let me know.

joe

Okay, I went ahead and started the truck (its been sitting all day) and looked at the live data for the O2 sensors again. Here is a snapshot of the full data for bank 1 and bank 2 while idling, and the motor was still cold.

O2S B1S1: 0.570V
STFT B1S1: -3.1%
O2S B1S2: 0.810V
STFT B1S2: 99.2%

O2S B2S1: 0.795V
STFT B2S1: -1.6%
O2S B2S2: 0.790V
STFT B2S2: 99.2%

Does that clarify the confusion?

Also, I am not certain about the exhaust leak. Is there a way to know for sure that I do or do not have an exhaust leak at the exhaust manifold?

Hi,

When you checked the trims and sensor voltages, the engine should be at operating temperature.

The purpose of the downstream (sensor 2) oxygen sensor is primarily to monitor the efficiency of the catalytic converter and not to actively adjust the fuel mixture like the upstream oxygen sensor (sensor 1). As a result, the short-term fuel trims at sensor 2 are typically maintained near zero, indicating that the catalytic converter is functioning properly. I suspect the 99% indicated is caused by the engine not being warm.

If you get the same reading when warm, the computer is maxed out trying to compensate for a lean mixture by adding as much fuel as possible.

Let me know.

Joe

This time I allowed the vehicle to reach operating temperature.

Additional data from the scan tool
ECT: 190 degrees
STFT B1: Range ~0.0% to -3.1%
LTFT B1: Stayed at -10.9% (even during warm up)
STFT B2: Range ~0.0% to -3.1%
LTFT B2: Stayed at -11.7% (even during warm up)

O2 Sensor Data
O2S B1S1: Range ~0.080V to 0.795V (jumping up and down)
STFT B1S1: Consistently around -3.1%
O2S B1S2: Consistently around 0.770V
STFT B1S2: Stayed at 99.2% (even during warm up)

O2S B2S1: Range ~0.070V to 0.785V (jumping up and down)
STFT B2S1: Consistently around -2.3%
O2S B2S2: Consistently around 0.770V
STFT B2S2: Stayed at 99.2% (even during warm up)

Hi,

The idea that the oxygen sensors are correct and the STFT are so far off leads me to think we have a different kind of problem. I'm starting to think the PCM is failing because what you have as far as readings shouldn't be. If it was correct, I would think you would see dark gray or black smoke from the exhaust and smell a rich fuel mixture, and the O2 voltages would be pegged.

Let me know your thoughts.

Take care,

Joe

It's strange since it does not show any DTCs related to these readings being out of spec, and the truck runs well once it gets past the initial start up struggles. It may smell a bit rich but I'm not certain, and the exhaust is not pouring out dark grey or black smoke.

As far as the PCM, is there a way to test it's function?

Are there other things I can check to continue to narrow down the scope of the problem?

.

Hi,

As far as testing a PCM, it is done the same as sensors, codes. When there is a failure, there should be codes specific to the PCM. In this case, there aren't any, but the readings don't make sense. In some cases, the PCM may require a software update or calibration to address issues related to sensor readings. However, I checked for technical service bulletins and didn't find any related ones.

I am going to mention this to the site owner to get his input. Let's see what his thoughts are related to the issue.

Take care and hang in there.

Joe


Update: He already got back to me. He said the same thing. So, although I can't guarantee it, you have about 70 years of experience suspecting that is the issue.

Thanks for the update, Joe!

Which data points are the ones that show the PCM is failing? (Just trying to further my knowledge and understanding.)

Are there any other tests I can do to further confirm the PCM is failing since I don't have any codes showing? (Since the data I sent was at idle, should I check numbers while driving/revving the engine to compare values?)

What's the process to swapping out the PCM?

Hi,

Unfortunately, in many cases, we determine a PCM issue when impossible readings are present. I wish I had an easier answer for you. There are codes that will point directly to a faulty PCM, but there aren't many. In this case, you have sensor 2 @ 99% which I don't even think is possible. Sensor 2 is really there to simply determine if the converter is working. Being that sensor 1 is accurate and sensor 2 is that far off makes no sense. If the converter was an issue, you would likely see a code, P0420 or a P0430.

Are there any new codes?

As far as replacing the PCM, physically it is easy. However, what I am going to recommend is this. Find a site online that provides remanufactured ones. They will request your VIN number and program it before you receive it. At that point, they are plug and play. In many cases, they request your old one be sent back as a core.

Please understand, what I am saying is a theory. This is what is making sense to me. Also, I did bring your post to the site owner and he indicated the same thing. Can I guarantee this is the problem, no. Do I feel it is, yes. Not being there with you makes it difficult, but the sensor readings are too far off.

Let me know your thoughts,

Take care,

Joe

No new codes, just the same pending EVAP code P0446.

Thanks for the help!

Hi,

I went through the diagnostics for the code you have. Although I don't see how it would cause the sensor reading, it could cause a bog and stalling if there is a loss of vacuum. If you take a look below, I attached the diagnostics related to the code. Take a look through them and let me know if that is something you are comfortable performing.

Let me know.

Take care,

Joe

See pics below.

Joe, Thanks for the information. Unfortunately, I don't have a scanner that allows me to see the fuel pressure sensor data or a smoke machine to hook up. For step two, I replaced the purge valve and EVAP canister vent solenoid and filter. The EVAP canister itself, I have not pulled out and tested. That was my next thought if I could not get the code to go away. Along with blowing out the EVAP lines if the canister was bad, and the carbon pellets were spilling out.

Hi,

Okay, by chance have you installed the new canister and other parts? If you have, did it make a difference?

As far as the light going out, it may take a few drives for that to happen.

Let me know.

Joe

I installed those parts because the gas tank was not filling well. They seemed to help, and the tank did fill better but still not able to fill with the pump on maximum.

I actually cleared the codes with the scan tool and the check engine light is out. However, I have a pending code that won't go away when I check using the scan tool. I've driven the truck a five or six times since replacing the parts, and the code is still pending when I run the scan tool.

Unfortunately, they did not help as far as fixing the stuttering when starting the truck.

Hi,

A pending code is caused by an intermittent fault. The PCM needs to see it happen during two consecutive warm-up cycles to set the code. If the fault doesn't occur again over a period of 40 warm-up cycles, the code is automatically deleted.

The stuttering is a tough one. Most times, it is a fuel pressure issue, a faulty coolant temperature sensor, or an engine vacuum leak. An overdue tune-up can cause it as well.

Let me know your thoughts.

Joe

Thanks Joe, I will not worry about the pending code for a while.

Looking at the list of possible causes for the stuttering at startup, the coolant temperature was functioning correctly, and fuel pressure was good. How can I test for vacuum leaks?

What all should be done to tune up this motor?

Hi,

Engine vacuum leaks can be difficult to locate. However, if you use carb cleaner, it makes it easier.

Here is a link that explains how it's done:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

As far as the tune-up, things like spark plugs, air filter, PCV valve, fuel filter, ignition cables (spark plug wires), and so on.

Let me know.

Joe

Sounds good! Thanks Joe!

Joe,

I have been running the truck now for a few weeks and the stutter has resolved itself. Maybe I just had some bad gas, and it took a couple of tanks and a can of seafoam to clear itself up. Will be replacing the EVAC canister in the next week or so to hopefully resolve the check engine light since it came back on.

Thanks again for your help!

Hi,

That is certainly possible. Let me know if anything changes or if I can help in any way.

Take care of yourself and feel free to come back anytime in the future.

Joe