Tonyrodz's Tahoe Build Thread

[Tonyrodz]

We need to see the STFTs once they start counting; the O2 sensors need to warm up and get workin'.

Can you show both fuel trims (short and long) at idle, then at 2000 rpm?

It was warned up--drove for almost 1 hr. This was at my low idle, around 450 rpms. I can def get that tomorrow or Friday. So you'll need st/Lt at 2000 rpms? What does that misfire graph look like? The one you're talking about. Thx for your help too @Fless This van has been driving me crazy for years. It actually stalled on me driving through an intersection today, and it wouldn't restart. I heard the TC bang a few times today while driving. No trans codes tho.

 

[Fless]

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.

 

[Tonyrodz]

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.

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

I've never changed the O2's. Bought it with 110k and it now has 151k. I do think both cats are partially clogged, one more then the other. I was actually going to hollow 1 out. Would that cause my issues?

 

[Fless]

Are you having driveability issues? If you think the cats are clogged it's a relatively simple procedure for a shop to check the in and out pressure to confirm.

Do you suspect one side more than the other? Which one?

 

[Snowbound]

Clogged cats wouldn’t cause this issue. You’d see low efficiency convertor code.

Could be a bad coolant temp sensor. If it’s staying in open loop there wouldn’t be any STFT data.

 

[Snowbound]

I hate that I can’t use Tapatalk anymore. Thought I got kicked off the forum early this morning.

 

[Tonyrodz]

Clogged cats wouldn’t cause this issue. You’d see low efficiency convertor code.

Could be a bad coolant temp sensor. If it’s staying in open loop there wouldn’t be any STFT data.

I actually changed that, thinking that might've been the issue.

 

[Tonyrodz]

I hate that I can’t use Tapatalk anymore. Thought I got kicked off the forum early this morning.

No more tapa crap.

 

[Snowbound]

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.

 

[Tonyrodz]

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.

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?