P0101 + P0300 = ?

[cam3439]

No problem.

I added in checking fuel pressure above. You can rent tools from autozone or O’Reilly’s to check it.

If you can, post your fuel trim numbers (short trim and long trim from both banks) so we can review them. It may help point us to the right direction. Take readings when the engine is cold and after it has reached operating temp.

 

[tlynch]

No problem.

I added in checking fuel pressure above. You can rent tools from autozone or O’Reilly’s to check it.

If you can, post your fuel trim numbers (short trim and long trim from both banks) so we can review them. It may help point us to the right direction. Take readings when the engine is cold and after it has reached operating temp.

Thanks! I'll try to do that today.

 

[Rocket Man]

Have you tried the simple things like the plug wires and plugs, maybe one or two wires aren’t making good contact, check the plugs to see if one is cracked, and if nothing obvious swap wires and coils to see if the misfires follow the swapped over parts.

 

[tlynch]

Have you tried the simple things like the plug wires and plugs, maybe one or two wires aren’t making good contact, check the plugs to see if one is cracked, and if nothing obvious swap wires and coils to see if the misfires follow the swapped over parts.

That's a really good idea. I'll add that to my to-do list.

 

[tlynch]

If you can, post your fuel trim numbers (short trim and long trim from both banks) so we can review them. It may help point us to the right direction. Take readings when the engine is cold and after it has reached operating temp.

I did a little data collecting when I made the mail run tonight. Here's what got for LTFT when cold:
Bank 1 7.81%
Bank 2 5.47%

STFT was 0.00% on both banks when cold.

After 15ish minutes of running, LTFT was this:
Bank 1 -0.78%
bank 2 -3.12%

STFT when warm varied between 0 and 5%

I now have my phone set up to graph STFT, so I should be able to show the movement a bit better next time.

 

[cam3439]

Based on the data, I don’t feel you have a vacuum leak.

Do the fuel trims start ******* close to or at max value (could be - or + %) when driving or varying RPMs?

Were you able to rule out fuel pressure?

You may also want to rule out the plugs, wires and coils like recommended above by rocket man.

 

[Fless]

I did a little data collecting when I made the mail run tonight. Here's what got for LTFT when cold:
Bank 1 7.81%
Bank 2 5.47%

STFT was 0.00% on both banks when cold.

After 15ish minutes of running, LTFT was this:
Bank 1 -0.78%
bank 2 -3.12%

STFT when warm varied between 0 and 5%

I now have my phone set up to graph STFT, so I should be able to show the movement a bit better next time.

STFTs will show 0% in open loop, with no "trim." Once it goes into closed loop (after warming up a bit) they'll start to show and should vary somewhat, always adjusting. Combine your STFT and LTFT for each bank (so you have a sum for each bank) and close to 0% is best; I think just about any total under 10% will be good.

 

[tlynch]

Based on the data, I don’t feel you have a vacuum leak.

Do the fuel trims start ******* close to or at max value (could be - or + %) when driving or varying RPMs?

Were you able to rule out fuel pressure?

You may also want to rule out the plugs, wires and coils like recommended above by rocket man.

Thanks.

I just took the cold observation on the driveway, let it warm up, then made a run to the mailbox. I haven't had a chance to collect FT data on the road, yet.

I have not looked into fuel pressure yet.

I have not ruled out plugs, wires or coils. We'll see what I get done over the weekend.

Thanks for your help!

 

[tlynch]

STFTs will show 0% in open loop, with no "trim." Once it goes into closed loop (after warming up a bit) they'll start to show and should vary somewhat, always adjusting. Combine your STFT and LTFT for each bank (so you have a sum for each bank) and close to 0% is best; I think just about any total under 10% will be good.

Thanks. I'll try to collect better data. Tonight I mostly was just getting the display set up for the app. The little bit of info I got doesn't sound alarming. Nothing over 10%, and combined LT/ST under 5%.

 

[2008yukonxlslt]

Thanks.

I just took the cold observation on the driveway, let it warm up, then made a run to the mailbox. I haven't had a chance to collect FT data on the road, yet.

I have not looked into fuel pressure yet.

I have not ruled out plugs, wires or coils. We'll see what I get done over the weekend.

Thanks for your help!

I second the fuel pressure remark.
My 08 Yukon was misfiring and acting up but no hard codes. Would come and go, usually when wife was driving. Mine seemed much worse at around 1/4 of a tank for some reason. Never when it was above half, no idea why that was. Truck was pretty new so I did not suspect electrical especially cuz up here we get a lot of rain and all my previous vehicles that had plug and wire issues always showed up more in the rain. This was showing up on beautiful sunny days with less than half a tank and no codes. In “ugly” mode would mis hard, particularly under accel greater than half throttle. Once, on a whim, I filled it up right away when it happened and problem gone. That really convinced me that it had to be fuel related.
Long story short, put in a new fuel pump and problem gone.
Wish I would have diagnosed more but I was not sure how to do that, I kinda figured that if it were something obvious then the ECM would have figured that out and set a code; doesn’t it monitor fuel pressure?
Anyway, I googled and saw that fuel pump issues were not rare so I rolled the dice and got lucky.
I would definitely include a potential fuel pressure problem for your issue, it would be great to hear from anyone who has diagnosed this type of issue and what is best technique.
Good luck with yours.