misfiring

1990 GMC SIERRA
7,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
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RJGILBERT90
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  • 6 POSTS
installed a 350 5.7 engine. Everything new. when driving at any speed in overdrive and just touching accelerator to maintain speed, will miss. if you give it more gas it does not miss. some times does it when just starting from stop .
Jan 31, 2018 at 8:02 AM
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ASEMASTER6371
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good morning.

Do you have a scan tool that can read cylinder miss fires to determine which cylinder is causing the miss? It could be an injector, vacuum leak among many other things.

is the check engine light on? I am also concerned about the transmission. a faulty torque converter can cause a shutter which feels like a misfire.

Roy
Jan 31, 2018 at 3:40 PM
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RJGILBERT90
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I do not have a scan tool. The check engine light is not on. The injectors are new. The intake is new and installed with new gaskets. The torque is a 2000 rpm stall B&M converter. The miss is not a hard miss.
Jan 31, 2018 at 9:13 PM
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ASEMASTER6371
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It does sound like it is a set of plugs. have you removed them to see how they are burning?

Roy
Jan 31, 2018 at 11:21 PM
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RJGILBERT90
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Plugs look to be burning a little rich. Plugs, wires, cap, and distributor are all new. Throttle position sensor is new. EGR valve, and solenoid are new. Map sensor is new.
Feb 1, 2018 at 12:03 AM
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ASEMASTER6371
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what jets are you running in the carburetor?
Feb 1, 2018 at 12:41 AM
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RJGILBERT90
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Throttle body has standard SMP-TJ7 injectors bought from Summit.
Feb 1, 2018 at 1:27 AM
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ASEMASTER6371
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Okay, so this is fuel injected.
is this obd 2 or obd 1?

Roy
Feb 1, 2018 at 3:48 AM
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RJGILBERT90
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obd1.
Feb 1, 2018 at 4:14 AM
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ASEMASTER6371
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Can you read the block learn and integrator on the scan tool? that will tell me if it is running rich or lean.

Roy
Feb 1, 2018 at 4:44 AM
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RJGILBERT90
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  • 6 POSTS
Found the problem. The distributor cap that came on the distributor was an after market brand. Cranked engine at dark one evening, could see fire going from cap to coil on the outside of cap intermittingly. Replaced cap with Delco -Remy cap, problem solved
Feb 6, 2018 at 12:01 AM
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ASEMASTER6371
  • ✓Experienced Mechanic
  • 52,796 POSTS
Good find. who would have guessed a bad new part.

Roy
Feb 6, 2018 at 12:10 AM
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