Tonyrodz's Tahoe Build Thread

Snowbound

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I'll give it a shot. Afaik there's only 1 coolant temp sensor which is located on the ds head. How can you tell if it's open or closed loop? Will it say it?

Yes, the Tech2 will list loop status. And also look at the coolant temp and see what it says and if it’s close to where the gauge says temp is.
 

Tonyrodz

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Is there 2? One for gauge and one for ECM? See if it’s showing a reading with the scanner. The STFTs should be constantly adjusting based off pre-cat O2 sensors. Scan the O2 readings and coolant temp. Also see what the status says if it’s in closed loop or open.
This is idling around 2000 rpms, closed loop. Warmed up.
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Tonyrodz

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O2 sensors--
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Whatever this is--Inactive.
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Tonyrodz

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Just numbers instead of the graph. Like "Cyl 1 = 35" "Cyl 2 = 13" etc. There seems to be an issue with higher misfires on cyl 1.

Rare that the instantaneous STFTs would be steady at 0; are your upstream O2 sensors working? Do you see a change in the STFTs?

If they continue at 0 then the LTFTs should eventually come down closer to that. LTFTs are an average of the STFT over a longer period of time. Seeing your LTFTs over +10% means that the ECM has been adding fuel for a while to compensate for a lean condition. Generally you want the sum of the ST and LT fuel trims to add up to something lower than 10%.

So if your STFT Bank 1 is 2%, and the LTFT for the same bank is 6%, 6+2= 8% which is generally acceptable.
Same issue if the sum of the same bank trims is negative. Goal is between -10% and +10%, but closer to 0 is best.

Seeing the trims at the higher rpm could help determine if there is a vacuum leak or something else.

EDIT: bump your idle up to 600 rpm or so for the low reading. That's a really low idle you have there.
This is the history--
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Coolant temp sensor seems to read in the range--gauge and tech2.
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Tonyrodz

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At around 600 rpms.
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I'm sorry I'm all over the place, I'm still trying to figure this tech 2 out and I'm posting the info as I find it.
 

Tonyrodz

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Now it's not doing anything! WTF!
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That was around 600 rpms.
This one is at idle, under 500 rpms. It just keeps going--misfiring.
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Let's just ignore the history misfires. You likely had a problem at one point but it sure doesn't show up in the current misfires, at least at 618 rpm, for this ignition cycle.

Do you know why your idle is so low?
 

Tonyrodz

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Let's just ignore the history misfires. You likely had a problem at one point but it sure doesn't show up in the current misfires, at least at 618 rpm, for this ignition cycle.

Do you know why your idle is so low?
I sure don't. It started about 2 1/2 yrs ago. I've had a random misfire since I bought it 4 yrs ago. I can't afford to take it to anyone so I'm hoping I could get some good advice. My check engine light has been on steady. Weird that it's not misfiring at 600 rpms. This vzn is a POS!
 

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I sure don't. It started about 2 1/2 yrs ago. I've had a random misfire since I bought it 4 yrs ago. I can't afford to take it to anyone so I'm hoping I could get some good advice. My check engine light has been on steady. Weird that it's not misfiring at 600 rpms. This vzn is a POS!

Next time you have the Tech 2 on it see if the desired RPM is close to the actual RPM.
 

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