Engine will not stay running?

ANDIWARD76

MEMBER
1999 GMC ENVOY
4.3L
V6
4WD
AUTOMATIC
185,000 MILES

Okay, to start with this is going to be kind of drawn out just so you know what I've done that has ultimately left me still sitting where I'm at. So, I apologize for that ahead of time. Several weeks back my fuel pump went out. I replaced the fuel pump in the fuel filter. At which time the truck started and ran but ran really rough. A few days in it started running normally and a couple days after that the fuel pump went out again. I again pulled the fuel pump took it back returned it they diagnosed as a faulty fuel pump gave me a new one, I replaced that again fired up ran fine for a few weeks I drove to a friend's house and went inside when I came back out went to fire up my truck it would not start. It would crank it with fire, but it wouldn't turn over. I have since then changed the spark plugs, the spark plug wires, the distributor cap, the rotor cleaned the MAF sensor, the air filter and replaced a couple of weather rotted airlines. Now the truck has strong power but still all it does is cranks fires start and then it shuts off after a few seconds.

9 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The first things I need you to check are ignition fuses B and C. Both fuses are located in the under-hood fuse box. Once the vehicle starts, the key is released and power travels through the IGN B fuse. (See pic 1 below)

When you check these fuses, make sure there is power to and from them as well.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Let me know what you find.

Joe

See pics below. Pic shows fuse locations.

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Wednesday, May 31st, 2023 AT 10:22 PM

ANDIWARD76

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10 POSTS

Both fuses have power to and from.

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Saturday, June 3rd, 2023 AT 1:01 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Okay. I just read through your original post. When you try starting it, does the starter engage, the engine start and then shut off right away or does it just crank?

I realize you installed a new fuel pump, but have you checked the fuel pressure as well as the ignition spark at the plugs?

If it just cranks, see if it starts using starting fluid. If it does and then stalls, it is a fuel-related issue. If there is absolutely no change, I need you to check for spark at the plugs.

Here is a link explaining how that is done:

https://www.2carpros.com/articles/how-to-check-for-ignition-spark

Let me know what you find. Note, if it starts and shuts right back off, first check the fuel pressure.

Here is a link that explains how that is done:

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

I'm suggesting this because the heading indicates it won't stay running. However, the post says it won't start. If we have power at both fuses, this is the direction I suggest going.

Let me know.

Joe

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Saturday, June 3rd, 2023 AT 9:30 PM

ANDIWARD76

MEMBER
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Hi Joe,

My apologies for the confusion in my explanation. So, it does crank over and start. But then shuts off after just a couple seconds.

Yes, I replaced the fuel pump and yes, there is good fuel pressure.

I also replaced the spark plugs and wires. However, I did not check for spark. I assumed there would be due to new plugs and wires. Am I incorrect in that assumption?

I also replaced the distributor cap and rotor.

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Sunday, June 4th, 2023 AT 1:10 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

No problem whatsoever. I felt bad asking again. LOL

As far as ignition spark, if it starts, you have spark. However, that doesn't mean it continues. When you did the work, was the ignition control module replaced? (See pic below)

Also, have you checked for diagnostic trouble codes?

Let me know.

Joe

See pic below.

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Sunday, June 4th, 2023 AT 9:17 PM

ANDIWARD76

MEMBER
10 POSTS

Hi Joe, no the ignition control module was not changed when I did the work. I've never had to change that in the past doing the work that I've done on other cars. But who knows maybe I missed something along the way. LOL I have ran a scan on it and it was throwing a code for the MAF sensor. I cleaned the MAF sensor and reinstalled it and it has not thrown the same code again. I do have screenshots of the live data info it threw up though. Would you like me to screenshot that to you? Also, it has been suggested that maybe changing out the crankshaft position sensor in the camshaft position sensor might be an issue. What is your opinion on this?

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Sunday, June 4th, 2023 AT 9:51 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Interestingly, a faulty crankshaft position sensor may or may not set a code. However, I'm not one for replacing parts without confirmation.

Also, yes, send me the freeze frame data screenshots.

Take care,

joe

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Sunday, June 4th, 2023 AT 10:10 PM

ANDIWARD76

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Sorry I wanted to run a new live data scan. These images are kind of blurry so if you have a hard time reading then please let me know.

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Tuesday, June 6th, 2023 AT 2:28 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Things appear normal for an engine not running. However, we still have the 99% on the downstream sensor. I can't think of anything that would cause the 99% other than the PCM.

At this point, it may be a good idea to replace the crankshaft position sensor. I attached the directions below specific to this vehicle. Note that it says you need to perform a variation relearn after replacing it, but that will not prevent it from starting and running.

Take care,

Joe

See pics below.

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