Engine misfires only slightly?

1995 FORD F-250
72,000 MILES • 7.5L • V8 • 4WD • MANUAL
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WJBARNICKOL
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95 ford 460 engine has injector fire pulse of 5us but with a 0.2 us flicker. engine misfires only slightly. Does not change with RPM. drivability is very good. wont quite pass smog of less than 1 percent CO have replaced plugs, wires, ICM, coil. have tested fuel pressure, MAP, EGR idle air control. TPS,
Apr 18, 2026 at 4:56 PM
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STRAILER
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So there are a few things that can cause this issue.

1. Leaking or dirty injectors
2. Fuel pressure regulator
3. Engine coolant temperature sensor
4. O2 sensor lazy or biased rich
5. Exhaust leak ahead of O2
6. Compression issue on one cylinder
7. Base engine timing / distributor issue

Here is a guide to help fix the problem

https://www.2carpros.com/articles/why-an-automotive-engine-will-run-rich

Have you run the codes? This guide will show you how

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Also, please go over this video to help check the compression. If we have a problem here nothing above will fix it.

https://www.youtube.com/watch?v=KOxIm1F8AW0

Please go over these guides and get back to us.
Apr 19, 2026 at 8:48 AM
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WJBARNICKOL
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I get decent looking fire pluses from coil when cranking it into a spark plug,( no engine firing). When running the fire pulses are wildly erratic, vary by 10 to 1 voltage. And they are the same on all plugs.
Apr 22, 2026 at 7:48 PM
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STRAILER
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Did you run the codes to see if any are stored? Also I would check for vacuum leaks and I would replace the MAP sensor. What are the compression readings? Here is a video to help with the vacuum leak test.

https://www.youtube.com/watch?v=LRKWV4Are5c

Please go over this guide and get back to us.



Apr 23, 2026 at 7:49 AM
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WJBARNICKOL
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I ran codes until I could do it properly and ended up Clear. I ran vacuum leaks by carb cleaner spray and by water flooding outside of engine, no change. Tested MAP with vacuum pump and oscilloscope, works to spec. Just finished compression: 1@ 150 2 @ 170 rest 160's. I assume I would get a code if temp sensors were bad? (I actually now remember one set a code cause I ran the scan with the engine cold) I'm going back now to do more checks on spark jitter and fuel injector pulses. Will reply after that
May 12, 2026 at 9:42 PM
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STRAILER
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I have seen the EGR leak internally which can cause a symptom like an intake leak, if you can remove it here is a video on how to test it.

https://www.youtube.com/watch?v=DqUCbbKdWf4

Please let me know what you find.
May 14, 2026 at 3:04 PM
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WJBARNICKOL
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At this compression, would a leak down test be really necessary? (I don't have the proper tester but could throw one together if needed
May 15, 2026 at 11:02 PM
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WJBARNICKOL
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...before I put the spark plugs back in.
May 15, 2026 at 11:03 PM
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STRAILER
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No, you don't need a leak down test, did you check the EGR valve for internal leaks?
May 17, 2026 at 3:27 PM