P0307 missfire 1996 chevy


May 21, 2020
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I have a 1996 tahoe i keep getting a flashing then goes to a solid cel. Spark and fuel/delivery has been eliminated as problems. Ive noticied it happens more while driving on highway as yesterday driving to work about 30 mins into the drive it started to do it. Last friday i belived i fixed it, it ran fine all weekend and monday.

All the things ove done to it
Noid light all connectors
Fuel pressure test/ leak down
Checked for spark with a tester
Pulled cap off to inspect
Checked for vacume leaks

While driving the code came up and checkes freeze frame it said system a and b has not satisfied conditions to go to a closed loop im thinking that has something to do with it


Supporting Member
Dec 16, 2010
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Loo E Z an uh
You have a code for a cylinder 7 misfire. It's intermittent, and does not set an active CEL until you've driven for a distance, which is to say that the engine is loaded and at full operating temperature.

You obviously have access to some kind of scan tool, so my next few questions will be based on that assumption.

1. Is the misfire only present while driving, with some load on the engine? Or does it keep misfiring on cylinder 7 once it has begun?

2. You have a scan tool. Can you see live data? If so, you should be able to see the PID indicating that the engine is in open or closed loop, though that should have no bearing on a single cylinder misfire.

3. If you have a scan tool, can you see misfire counters? If so, how quickly is the misfire count increasing on 7? Are other cylinders also misfiring, but not enough to set a code?

4. How do the fuel trims, short and long term, look while you are driving and the truck isn't misfiring? You may need a helper to watch while you drive, or vice versa. Looking for a rich or lean condition, especially on bank 1.

Simply doing a fuel system leakoff, noid testing, and cap inspection won't tell you if you have a failing injector, plug wire shorting or opening due to vibration, dielectric breakdown in the cap causing a misfire/crossfire, bad insulator on a spark plug, etc. My 97 would start misfiring under load, seemingly at random, when I switched to NGK TR55 instead of the standard ACDelco 41-993 plugs. Switched back (to an old, used set mind you) and had no further misfires. Bottom line is you haven't truly eliminated fuel and spark yet.


Supporting Member
Supporting Member
Feb 19, 2018
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Play swaptronics and try to get the misfire to change cylinders. exchange the #7 Coil, plug, wire (one at a time) with an easy to get to cylinder and if the misfire moves, you've found the problem.


I'm Awesome
Aug 7, 2019
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Dallas, TX
So you are saying it doesn't go into closed loop? Are the O2 sensor there? Is this your truck or a customer's?

If it stays in closed loop, that needs to be fixed first. Otherwise you can't even look at fuel trims to try to diagnose the issue.

Otherwise, do an injector balance test and report back. Not uncommon to have intermittent injector malfunction, which is really difficult to diagnose.

Report back.