Truck misfiring?

TRAVIS2121

MEMBER
1997 CHEVROLET 1500
5.7L
V8
4WD
AUTOMATIC
216,000 MILES

So, my truck has a strange issue where if I'm driving on the freeway or above 50 MPH for a semi long period of time (15+ minutes) my truck will throw a cylinder 6 misfire code. I've changed the plugs, cap, rotor, and wires. Not sure what would be causing it. The other interesting thing is it doesn't happen every time. What usually happens is when driving on the freeway and get off for some period of time then about 5-10 minutes after getting back on the freeway it'll throw the code. If you have any ideas I'd greatly appreciate it.

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
48,397 POSTS

The first thing I would do is a compression test on #6 and if over 125 PSI you are okay, next look at the spark plug to see if it is black with soot, if so, the fuel injector is not spraying correctly, and the spider injector will need to be replaced.

https://www.2carpros.com/articles/how-to-test-engine-compression

This could help as well:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

REMOVAL PROCEDURE

CAUTION: Use care in removing the fuel injectors to prevent damage to the electrical connector terminals, the injector filter, and the fuel nozzle.

NOTE: The fuel injector is serviced as a complete assembly only.

CAUTION: Also since the injectors are electrical components, these injectors should not be immersed in any type of liquid solvent or cleaner as damage may occur.

1. Disconnect the negative battery cable.
2. Relieve the fuel system pressure. Refer to Fuel Pressure Release Procedure.
3. Remove the Upper Manifold Assembly. Refer to Engine Mechanical.
4. Remove the Fuel Meter Body Assembly. Refer to Fuel Meter Body Assembly.

INSTALLATION PROCEDURE
1. Install the fuel meter body assembly. Refer to Fuel Meter Body Assembly.
2. Install the upper manifold assembly. Refer to Engine Mechanical.
3. Connect the negative battery cable.

I have also seen the EGR valve not close all the way which can affect the cylinder misfire as well so remove it to see if it needs to be cleaned.

Check out the images (below). Please let us know what happens.

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Thursday, January 12th, 2023 AT 5:05 PM

TRAVIS2121

MEMBER
2 POSTS

I've checked the spark plug its looking good, I'll have to do a compression test next.

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Thursday, January 12th, 2023 AT 6:34 PM

KEN L

MASTER CERTIFIED MECHANIC
48,397 POSTS

Yep, let me know if it's okay, the fuel injector can be bad. Also, we should check for a vacuum leak. Please use this guide when the engine is cold only.

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

Please go over this guide and report back.

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Friday, January 13th, 2023 AT 12:19 PM