3800 gm use labscope to check if timing chain has jumped
- craig.phillips
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4 years 11 months ago #28962
by craig.phillips
How can I use my labscope to check timing chain on a 01 buick lesarbe with a 3800 motor. I think I need to check the 3x and cam sensor at the same time just not sure what to look for.
thanks
thanks
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4 years 11 months ago #28964
by Tyler
Replied by Tyler on topic 3800 gm use labscope to check if timing chain has jumped
For that engine, you'd want to check the relationship between the 3X CKP and the CMP. You can tap into both at the Ignition Control Module connector. Pin J brown/white for the CMP, and pin H (light blue/white) or pin G (yellow) for the CKP. I don't recall which CKP pin is which, 3X or 18X. :silly:
You'll also need a known good to compare to. I don't have one on hand, but I remember that the CMP pulse centers over every other 'medium' pulse of the 3X sensor.
If you haven't seen it already, this video will help with CKP identification:
You'll also need a known good to compare to. I don't have one on hand, but I remember that the CMP pulse centers over every other 'medium' pulse of the 3X sensor.
If you haven't seen it already, this video will help with CKP identification:
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4 years 11 months ago #28966
by Chad
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."
I have learned more by being wrong, than I have by being right.
Replied by Chad on topic 3800 gm use labscope to check if timing chain has jumped
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."
I have learned more by being wrong, than I have by being right.
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4 years 11 months ago #28967
by craig.phillips
Replied by craig.phillips on topic 3800 gm use labscope to check if timing chain has jumped
My cam sensor is right in between the medium 3x signal. so i have backed out of thinking it is out of time. I also put my scope in the number 1 injector and the cam signal wire and the injector on/off square wave is stacked on top of my cam sensor square wave. So now I have started looking at other reasons for a no start condition. I have noticed I never get a cam sync at my scanner. but i have the cam square wave at pcm. I am leaning towards a pcm issue at this moment..
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4 years 11 months ago #28984
by Tyler
Replied by Tyler on topic 3800 gm use labscope to check if timing chain has jumped
So you do have injector pulse, then? That's good news for the ECM.
Are you missing anything else? Spark, fuel? Will it run with an external fuel source?
Are you missing anything else? Spark, fuel? Will it run with an external fuel source?
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4 years 10 months ago #29720
by GypsyR
Replied by GypsyR on topic 3800 gm use labscope to check if timing chain has jumped
I wouldn't even do any of that stuff. For a quick rough idea I would do like a relative compression test. Disable fuel. Ignition signal #1. Amp clamp on the battery cable. Crank and observe how close #1 fires to your compression peak. You want to see something like 10 degrees BTDC so just to the left of the peak. This isn't precision setup, so don't seat the actual degrees. If it looks like it's firing way early, right at TDC , or way after, there you go.
First time doing this you probably want to try the setup on another car or two (whatever kind of car is handy) that are in good shape so you know what it's supposed to look like.
There are more precision ways to do this where you can be sure it has jumped and even figure out by how much. THis is just a quickie "Is it broken?" check.
First time doing this you probably want to try the setup on another car or two (whatever kind of car is handy) that are in good shape so you know what it's supposed to look like.
There are more precision ways to do this where you can be sure it has jumped and even figure out by how much. THis is just a quickie "Is it broken?" check.
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