Engine knocking and smoking?

Tiny
ROBBURGESS525
  • MEMBER
  • 2003 GMC C3500
  • 95,000 MILES
Duramax diesel, knocking and smoking. Plugged it into a scan tool, and shut off #8 injector. Ran without knock or smoke, just with a miss. Replaced the injector twice with no positive results. Chased wires for short, haven't found anything. Where do I go from here?
Sunday, November 13th, 2011 AT 10:36 PM

11 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
First of all, you need to check something before the injector. Check for power on the supply side. The pcm grounds the injector and commands it to fire by the quad driver in the pcm. If the pcm continually grounds the other side, the injector will be on all the time. Verify this before replacing any more injectors.

Is the check engine light on and what code?

Roy
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Monday, November 14th, 2011 AT 2:31 PM
Tiny
ROBBURGESS525
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  • 6 POSTS
I have power everywhere I should, can't find any shorts, no chafed wires. I tore it back apart last night to switch #8 with #2. I am putting it back together now. If it #8 again, I know it isn't injector. Should I look towards the FICM?
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Monday, November 14th, 2011 AT 3:46 PM
Tiny
ASEMASTER6371
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Once again, you need to look at thr return wire to ficm to see if it is constantly grounds leaving the injector on. If you use a test light, look for the light to flash, if it does not, then it may be the ficm. Do not guess, confirm it first before replacing anything else.

Roy
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Monday, November 14th, 2011 AT 4:07 PM
Tiny
ROBBURGESS525
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  • 6 POSTS
What color is the ground wire in that harness? I do not have an fsm for the truck.
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Monday, November 14th, 2011 AT 5:21 PM
Tiny
ASEMASTER6371
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You dont need one. Pull off the connector and find which one has 12 volt power. That is the supply. The other is the ground wire.

Roy
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Monday, November 14th, 2011 AT 6:12 PM
Tiny
ROBBURGESS525
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I have good ground there, and power to the injector. No etc's, and all fuel pressure and injector balances are where they should be.
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Monday, November 14th, 2011 AT 7:07 PM
Tiny
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Does the ground pulsate when you crank the motor?

Roy
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Monday, November 14th, 2011 AT 8:36 PM
Tiny
ROBBURGESS525
  • MEMBER
  • 6 POSTS
To answer your question, no. Replaced ficm, still no positive results. Checked entire harness for short, found nothing. Is the ficm pulling a positive power in the 2 leads coming up through the harness or pulling grounds from somewhere that could be causing the problem?
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Wednesday, November 16th, 2011 AT 2:45 AM
Tiny
ASEMASTER6371
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The ficm provides the ground for the injector.

You still never answered if the ground side pulsates when cranking.

Roy
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Wednesday, November 16th, 2011 AT 2:55 AM
Tiny
ROBBURGESS525
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It did not pulsate with the test light on it. Do you know if on an otc genisys 2 scan tool if when shutting off injector 8 or if it shuts off the 8th injector in the firing order?
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Wednesday, November 16th, 2011 AT 6:11 AM
Tiny
ASEMASTER6371
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It turns off the cylinder number injector.

Does your scan tool do a buzz test for the injectors?

Roy
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Saturday, September 26th, 2020 AT 2:11 PM

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