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Misfiring

Tiny
RJGILBERT90
  • MEMBER
  • 1990 GMC SIERRA
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 7,000 MILES
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.
Wednesday, January 31st, 2018 AT 4:02 PM

11 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
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
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Wednesday, January 31st, 2018 AT 11:40 PM
Tiny
RJGILBERT90
  • MEMBER
  • 6 POSTS
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.
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Thursday, February 1st, 2018 AT 5:13 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
It does sound like it is a set of plugs. Have you removed them to see how they are burning?

Roy
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Thursday, February 1st, 2018 AT 7:21 AM
Tiny
RJGILBERT90
  • MEMBER
  • 6 POSTS
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.
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Thursday, February 1st, 2018 AT 8:03 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
What jets are you running in the carburetor?
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Thursday, February 1st, 2018 AT 8:41 AM
Tiny
RJGILBERT90
  • MEMBER
  • 6 POSTS
Throttle body has standard SMP-TJ7 injectors bought from Summit.
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Thursday, February 1st, 2018 AT 9:27 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, so this is fuel injected.
Is this obd 2 or obd 1?

Roy
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Thursday, February 1st, 2018 AT 11:48 AM
Tiny
RJGILBERT90
  • MEMBER
  • 6 POSTS
Obd1.
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Thursday, February 1st, 2018 AT 12:14 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Can you read the block learn and integrator on the scan tool? That will tell me if it is running rich or lean.

Roy
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Thursday, February 1st, 2018 AT 12:44 PM
Tiny
RJGILBERT90
  • MEMBER
  • 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
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Tuesday, February 6th, 2018 AT 8:01 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good find. Who would have guessed a bad new part.

Roy
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Tuesday, February 6th, 2018 AT 8:10 AM

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