Engine misfire

1996 CHEVROLET S-10
123,674 MILES • 4.3L • 6 CYL • 4WD • AUTOMATIC
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HUNTERRFERGISON
  • MEMBER
  • 10 POSTS
Hi, I have the truck listed above ZR-2 with a 4.3 v6. i put a fuel pump in it when i bought it and got it running, but when i first got it running it had a really bad misfire. I changed the rotor button, distributor cap, all new spark plugs and wires and put a new spider injector in it and it still has a small misfire only when accelerated full throttle. I don't know if it is something electrical or maybe a bad cylinder, but I would just like to have help figure it out. Also when i hook up my Snap-on computer to it it just says engine misfire it doesn't tell me anything else. thanks for the help in advance.
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Aug 23, 2021 at 11:30 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

It could be a few different things. Do you actually feel the miss? Also, there should be a code related to a "misfire." I'm not sure what scanner you have, but most of the Snap-on scanners will tell you how many times a specific cylinder has misfired.

Also, if you have live data on the scan tool, let me know what the fuel trims are and if possible, when the engine is cold and not started for the day, let me know what the engine coolant temp sensor is signaling.

One last thought. Have you checked for vacuum leaks and confirmed the fuel pressure is within spec?

Here are two links that explain how to test both:

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

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

Let me know. Also, the fuel trims will likely tell me if there is a leak or high pressure.

Take care,

Joe
Aug 24, 2021 at 1:17 PM
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HUNTERRFERGISON
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Hi Joe, yes I feel the miss at idle and acceleration also my scanner is a Snap-on modis and all of my vacuum lines are connected and tight and my fuel pressure is right where is needs to be.
Aug 25, 2021 at 1:07 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

If fuel pressure is good (regulator in new spider), and there are no leaks, keep in mind there could be a cracked vacuum hose.

Do me a favor. That scanner should read live data. Let me know what the short-term fuel trims are and before starting the engine (when cold), check what the ECT is indicating as far as the temperature.

Let me know.

Joe
Aug 25, 2021 at 11:34 AM
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