99 chevy silverado 2500 4x4 Has a 6.0 L with bad misfire under a load and is not setting a code. San tool is showing up to 175 misfires per cycle. sometimes it would show number 1 misfire in the data part of the scan tool, still not setting a code even after more than 2 different cold to warm trips. I swapped the #1 coil, plug and wire with the #3 coil, plug and wire. It still showed #1 as misfiring sometimes but mostly would show the total misfires. I cleaned the mas air flow sensor, and no change. I did a injector balance test and all injectors tested the same. I checked for a vacuum leak with smoke checker machine, no leaks. I don't understand why it won't set a misfire code. Help thanks, Brad
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Re: Has a 6.0 L with bad misfire under a load and is
Hi Brad, I ran into the same problem your going thru, swapped cylinder plug and wire ,and the scan kep telling me it was still seeing the problem on the same cylinder, smoked it too,nothing made sense! Until i took the whole fuel rail off carefully not to let the fuel run out all over the engine,Had a white rag folded up and handy,tilted the rail assembly and left the fuel run on the cloth,OMG! the rust that came out of there, I pulled every injector out of the rail,cleaned the inside of the rail with air pressure and carb cleaner. Its when I was checking the injectors that I found the culprit,the rust pieces had made it thru the injector but were trapped in the screen of the injector! I hope this cures your.
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This sounds more like a misfire under load than a transmission issue. This is one of the most misdiagnosed problems we see on a regular basis. The fact that it is only noticeable while going up an incline leads me to believe you likely have worn out spark plugs, and/or a weak ignition coil.
While you do not have a check engine light on, this can happen when you have only a minor or very intermittent misfire. Once the misfire becomes worse or happens more often, the computer will turn on the light- or cause the light to flash indicating a serious misfire which could cause catalytic converter damage.
Try having your garage monitor their scan tool data for real time misfires while driving it under a load such as the incline you mentioned, or even while brake-torquing the engine (pushing the throttle slightly while the transmission is in gear and the wheels are chocked and brakes applies) This can help duplicate the conditions where you noticed the issue. Monitoring the misfire data can help them pinpoint which cylinder(s) is misfiring and swapping spark plugs or ignition coils between cylinders can determine which component is causing the issue.
The SES light flashing means the engine management software has detected a misfire condition resulting in exceeding 3 times the federal limit of emissions. Under heavy load such as acceleration one or more cylinders are misfiring and once cruising speed is reached the engine is under a lighter load (10 to 20 percent ) that is why it stops flashing several causes of misfires are worn spark plugs ,spark plug wires, faulty ignition coil or coils fuel injector or fuel pressure problems a quick check of the computer to retrieve trouble codes should identify the problem cylinder or cylinders and will direct you in the right direction to find the faulty component but will not tell you exactly what is wrong certain test must be performed to isolate the cause.