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Engine misfiring?

Tiny
CHILLYDYLLY9
  • MEMBER
  • 2000 OLDSMOBILE BRAVADA
  • 4.3L
  • V6
  • 4WD
  • AUTOMATIC
  • 191,000 MILES
I just bought this vehicle and it’s been misfiring since the day I got it. So, I switched the plugs wire and distributor cap and it’s still misfiring but no check engine code for it. So, I thought it could possibly be the temp gauge sending the wrong temp to the computer causing it to run rich. But I tested it to see if it’s getting power and it is. So now I don’t know if the gauge is causing this issue or if it is in fact a gas issue.
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Saturday, April 1st, 2023 AT 1:15 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,164 POSTS
Hi,

A misfire can be caused by several things. Is the engine original? Also, the idea that it has a misfire, and no codes is odd. That should set a code. When you connect the scan tool, does it function properly?

Also, when testing the coolant temperature sensor, did you use a live data scan tool to see the temperature signal to the PCM?

Let me know.

Joe
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Saturday, April 1st, 2023 AT 5:55 PM
Tiny
CHILLYDYLLY9
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  • 5 POSTS
I believe the engine is original but it not 100% sure. It has 190xxx on the dash. I have plugged a code reader on it and it shows engine codes and tags all. No ABS codes and says emissions testing not ready. It actually did throw misfire codes before I changed the plugs and wires. My buddy has a computer for it and when it’s driven down the road you can see it misfires on all cylinders. Also has ABS light on and just recently it pops atc fuses left and right not too sure if they’re connected but no matter what I do I can’t seem to get those lights off the dash.

Yes, we have that’s why I switched because it was originally stuck on 113 degrees, so I switched it, and the gauge goes up but only to 120 and fluctuates from 100 to 120.
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Saturday, April 1st, 2023 AT 8:30 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,164 POSTS
Hi,

The idea that it isn't emission ready tells me that the PCM hasn't completed the full drive cycle for all components. If the battery has been disconnected or the codes were cleared, we need to wait for all monitors to be reset.

By chance, was the battery disconnected, or were the codes cleared recently?

Let me know.

Joe
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Sunday, April 2nd, 2023 AT 5:52 PM
Tiny
CHILLYDYLLY9
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Yeah, they have yesterday actually. Would that cause it to run the way it is running? And how long would it take for the emissions to be ready?
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Sunday, April 2nd, 2023 AT 6:31 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,164 POSTS
Hi,

That would explain why one of the monitors hasn't reset. However, in and of itself, a monitor not being complete won't change how the vehicle is running.

By chance, do you have a live data scan tool? If you do, I need you to check the short-term fuel trims for me. When you do this, the engine should be at operating temperature and the vehicle at idle. Drive it a bit before doing this.

As far as the temperature gauge, you could have a thermostat that is stuck open, or someone could have removed it.

Let me know,

Joe
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Sunday, April 2nd, 2023 AT 7:15 PM
Tiny
CHILLYDYLLY9
  • MEMBER
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I don’t have a live data scan tool; I only have a code reader that connects to my phone and displays all the code via Bluetooth.

I’ll take a look at the thermostat tomorrow when I get a chance.

If I can happen to find a friend that has one, what would I be looking for when I check the short-term fuel trims?
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Sunday, April 2nd, 2023 AT 11:11 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Short-term fuel trims are a parameter used by the engine control module (ECM) of a car to adjust the amount of fuel delivered to the engine. They represent the deviation from the base or target fuel delivery rate, which is set by the manufacturer. The short-term fuel trims are typically displayed as a percentage value, which indicates the percentage increase or decrease from the base fuel delivery rate.

With this information, I can determine if there is too much, or too little fuel being injected into the engine. If the trims exceed the parameter at either end of the scale, it can cause a misfire. Additionally, I can use this information to determine if there are issues such as exhaust leaks, a faulty fuel pressure regulator, an engine vacuum leak, and many other things.

Let me know what you find.
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Monday, April 3rd, 2023 AT 7:36 PM
Tiny
CHILLYDYLLY9
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Oh, all right, I gotcha. Still haven’t been able to check it yet. But as soon as I do, I’ll let you know.
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Tuesday, April 4th, 2023 AT 10:15 PM
Tiny
JACOBANDNICKOLAS
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Hi,

No problem whatsoever. When you have a chance, let me know. I'll be here.

Take care,

Joe
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Wednesday, April 5th, 2023 AT 5:55 PM

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