Runs rough, codes 24, 43

Tiny
CALEB POOL
  • MEMBER
  • 1993 GMC SONOMA
  • 180,000 MILES
Was running just fine then started running really rough and all of a sudden. Shows code 24, 43.
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Thursday, January 9th, 2020 AT 6:23 PM

10 Replies

Tiny
CALEB POOL
  • MEMBER
Also I can t find the knock sensor to save my life 4.3 v6.
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Thursday, January 9th, 2020 AT 6:25 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

As far as the knock sensor location, there are two. On the left side of the vehicle (driver's side) it is on the side of the cylinder head. See pic 1. There is also one on the rear of the right cylinder head. It is on the rear of the head. See pic 2.

The air intake temp sensor is front center (intake) see pic 3. I feel confident you already know the description of the codes, but here they are.

23 Air intake temperature sensor

43 Knock sensor

Let me know if this is all you needed or if you have other questions. I will tell you that a knock sensor issue will usually cause a valve noise or engine noise because they are responsible for maintaining proper ignition timing. The IAC, on the other hand, is most likely the cause of the rough idle, if you aren't hearing any engine noise.

Take care,
Joe
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Thursday, January 9th, 2020 AT 7:59 PM
Tiny
CALEB POOL
  • MEMBER
It s showing 24 and 43 on codes. It has no engine noise really but runs rough idling and driving and backfires. Cuts out when applied more gas.
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Thursday, January 9th, 2020 AT 8:08 PM
Tiny
CALEB POOL
  • MEMBER
And what is the IAC?
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Thursday, January 9th, 2020 AT 8:09 PM
Tiny
CALEB POOL
  • MEMBER
The knock sensor on the driver side between the two spark plugs? Also have no wire or nothing connected to it. Seems to have been that way for awhile?
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Thursday, January 9th, 2020 AT 8:12 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

IAC stands for idle air control. It is an electric motor that allows air to enter the engine at idle when the throttle plate is closed and is responsible for maintaining the engine idle speed.

Since you have a backfire, I would be checking the fuel pressure. It may be too high.
Take a look through this link:

https://www.2carpros.com/articles/engine-backfires-while-running

Here is a link that explains how to check fuel pressure:

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

Let me know if that helps and what you find.

Joe
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Thursday, January 9th, 2020 AT 8:44 PM
Tiny
CALEB POOL
  • MEMBER
Do you think it s the knock sensor? It s cuts out really bad too.
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Friday, January 10th, 2020 AT 6:02 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Anything is possible. The knock sensor is what fine tunes ignition timing to prevent valve knock. It is possible that it is throwing things off. However, I would think it is ore related to a fuel issue or the intake air temperature sensor.

Joe
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Friday, January 10th, 2020 AT 3:43 PM
Tiny
CALEB POOL
  • MEMBER
It backfires from the intake also? What should I change if it's getting to much fuel? I think that's the problem.
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Friday, January 10th, 2020 AT 6:30 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

If too much fuel is the issue, it can be one of three things, high fuel pressure, a bad coolant temp sensor, or faulty fuel injector.
Here is what I suggest. First, check fuel pressure to confirm it is high (beyond the manufacturer's specs). Here are the manufacturer's specs. Also, if you look at pic 1, I highlighted the test port for checking pressure.

1993 GMC Truck S15/T15 2WD P/U V6-262 4.3L VIN W CPI
Fuel Pressure Specifications
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Specifications Pressure, Vacuum and Temperature Fuel Pressure Specifications
FUEL PRESSURE SPECIFICATIONS
FUEL PRESSURE
1. Ignition "OFF" for 10 Seconds.
2. With ignition "ON, " engine "OFF" and fuel pump running, pressure should be 380-420 kPa (55-61 psi).
For additional fuel pressure testing procedures, See: A L L Diagnostic Trouble Codes ( DTC ) > Related Tests, Information and Procedures > A - E Charts & Related Test Procedures

___________________

If that checks good, then I need you to pay attention to fuel pressure drop off. Basically, you are checking to see how quickly fuel pressure drops when you turn the key off. It should maintain for a short period. It will drop off, but shouldn't go to 0.

_________________

Next is an engine coolant temp sensor. It is located on the front top of the engine. See pic 2. Now since this is an OBD1 system, you can check for diagnostic trouble codes, but chances are this problem won't show up. What can happen is the sensor indicates extremely cold temps. As a result, the computer makes the air / fuel mixture extremely rich to run the engine. Although the sensor sends an inaccurate reading, the computer doesn't know it's wrong, so a code may not show up.

With that, start with confirming the fuel pressure and let me know what you find.

I will watch for your reply. Note that most parts stores will lend / rent a fuel pressure gauge to you.

Joe
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Friday, January 10th, 2020 AT 7:37 PM

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