Question about LTFT

[Dirktdolman]

I have been chasing a P0300 random misfire. So the other day I used the PID list from the Calc.VET. After capturing the log I ran it and noticed the Bank 1 and Bank 2 LTFT were different. It was my understanding Bank 1 was one side of the motor and Bank 2 was the other side. If that is the case I would think they both should be close if not the same. Bank 1 was 14. something and Bank 2 was 11.4 about. This would lead me to believe I have a lean condition going on which might be causing my misfire. Any Ideas?

I have a 03 Silverado LQ4 4L80 4 X 4.

20255

[joecar]

B1 is different than B2 only by a few percent, this is ok and is not necessarily...

the problem is that they are both significantly away from zero, they are adding more than 10% fuel...

since they are not pegging, they are able to maintain trim,so this is not the reason for the misfire...

but two questions remain:
- why are they not within 5% (or less) of zero...?
- what is causing the misfire...?

[joecar]

From your log, I noticed that when you open throttle (to say 75%), MAP increases, but MAF barely climbs (does not go above 130 g/s), and RPM stays almost the same...

this leads me to think your air filter is clogged.

[Dirktdolman]

I will check it but it it is not does that mean there might be a problem with the MAF? I had an oil pressure sender go bad (direct short the signal voltage) this summer and it all but shut the truck down. They thought there might be something wrong with the MAF at that time.

[joecar]

Yes, it could be the MAF itself.

Also check the MAF plumbing (loose or collapsed).

[Dirktdolman]

Plumbing is good.

Is there a good way to test the MAF itself?

[Dirktdolman]

I forgot to mention the P0300 only happens on deceleration. Normally I would think this means a vacuum leak. I have had a evap leak test completed but I do not know if they checked the manifold for leaks.

[joecar]

Plumbing is good.

Is there a good way to test the MAF itself?At WOT, as engine spins past 5000 rpm, MAF should be reading 275 g/s or mor.

[joecar]

I forgot to mention the P0300 only happens on deceleration. Normally I would think this means a vacuum leak. I have had a evap leak test completed but I do not know if they checked the manifold for leaks.
Do a CASE Relearn, and see if the misfire DTC still occurs.

[Dirktdolman]

I will give both a check and see, Thank You.

[LastCall]

You can log MAF airflow and see what it is doing.

You can also check the wing by measuring voltage at the MAF connector. Should have 5 volts on the yellow signal wire, ground to battery and positive to signal wire.

[Dirktdolman]

I ran a quick log to check the airflow. I never got to 275. I guess I need a new MAF. Any recommendation or just go with OEM? This truck is used as to tow an enclosed trailer with Motorcycles.

20275

[statesman]

This might seem like an odd question... but have you made any attempt to tune that thing at all? Also, have you done anything silly like de-screen the MAF?

[Dirktdolman]

As far as I am concerned, more information is better so keep the question coming. The only adjustments I have made were to the Transmission and Speedometer. The MAF as far as I know is OEM (with the screen). I cleaned it at the time I replaced the motor. The truck has about 225,000 on it. I replaced the motor at about 200,00 with a GM motor. I replaced the crank and cam sensors with new from GM at the time of the engine replacement. I installed a new Delphi fuel pump and Napa FPR at about 150-175,000. A new Fram Air Filter and Autolite spark plugs were replaced about 5,000 miles ago. The Oil Pressure switch was just replaced by GM about 1500 miles ago (who knew if this goes bad it will take the complete engine down).

[Dirktdolman]

Sorry I meant to post this before.

20277

[joecar]

I ran a quick log to check the airflow. I never got to 275. I guess I need a new MAF. Any recommendation or just go with OEM? This truck is used as to tow an enclosed trailer with Motorcycles.

20275At 5800 rpm at WOT your MAF under-reports (205-225 g/s)...

you can see in attached pic that MAF g/s barely rises as rpm sweeps up:

20278


this causes reduced fueling (since fueling is proportional to airmass)...

meanwhile trims generally go positive to to maintain stoich in CL.

[Dirktdolman]

Thanks Joe I will pick up a OEM MAF tomorrow morning and run a couple more logs.

I tried to do a CASE learn but kept getting an error. It would never get to 4000 before doing the hiccup.

20282

[joecar]

...

I tried to do a CASE learn but kept getting an error. It would never get to 4000 before doing the hiccup.

20282Are you opening the throttle to bring rpm up (to get over 4000)...?

[Dirktdolman]

Yes, not sure how do get the RPMs up without opening the throttle.

First warm up engine to operating temp...

then with vehicle parked and engine running at idle:
- connect scantool (click green connect button),
- goto DVT tab,
- select controller,
- click Activate,
- goto Learning subtab,
- click CASE Relearn (see next line),
- open throttle to increase RPM above 4000, you must do this within 10 seconds (see next line),
- when you get the stumble/misfire (it will be quite notcieable) immediately release throttle,
- let engine spindown to idle,
- after reaching idle, turn off engine and wait 20 seconds,
- while waiting 20 seconds, you can click Deactivate.

You may possibly have to have brake applied and/or parking brake applied during this.

Only one CASE relearn can be done per ignition cycle

[joecar]

...

I tried to do a CASE learn but kept getting an error. It would never get to 4000 before doing the hiccup.


Are you saying that the stumble/hiccup would occur before 4000 rpm...?

Does the scantool display an error...?

Can you post the scantool log (do select all copy/paste from the text shown on the Console tab).

[joecar]

Hi Dirk,

statesman and me have discussed your MAF reading low, he pointed out that your altitude is 2000 ft which reduces BARO to 88 kPa, and this will cause lower MAF readings.


Question: do you have previous logs on this tune, we want to see LTFT's and MAF readings...?

Thanks.

[joecar]

Also, there's an experiment we want you to try: raise the MAF table B5001 by 12% throughout.



( your engine/parts have many miles on them... we're still hoping you get a new MAF anyway )

[Dirktdolman]

I installed a new GM OEM MAF. This is a quick log after the install. I have not changed the B5001 at this point.

20284


This is a log from when I did the CASE learn. It looks like I was wrong earlier when I said it did not hit 4000 RPM.

20285


Joe I did not understand what you meant when you said to

"Can you post the scantool log (do select all copy/paste from the text shown on the Console tab)"

[Dirktdolman]

I pulled this tune on 15 Sept



20286

[joecar]

...

Joe I did not understand what you meant when you said to

"Can you post the scantool log (do select all copy/paste from the text shown on the Console tab)"Post the text from the Console tab.

[joecar]

I installed a new GM OEM MAF. This is a quick log after the install. I have not changed the B5001 at this point.

20284

...
Ok, this log with the new MAF shows 247 g/s at 5800 rpm... this is an improvement.


Increase your MAF table by 12% and take another log.

[joecar]

...

This is a log from when I did the CASE learn. It looks like I was wrong earlier when I said it did not hit 4000 RPM.

20285

...Ok, that shows the fuel cutoff stumble...

now, do it again, and at the instant the engine stumbles, immediately release the throttle (all the way off) and let the engine spin down to idle, let idle stabilize itself, switch off ignition key and wait at least 15 seconds.

[joecar]

I pulled this tune on 15 Sept



20286Set B3618 to EQR 1.175 to be safe.

[Dirktdolman]

Here is a run with the changes

20287

20288

[joecar]

Ok, now add 3.5% back to the MAF table.

[joecar]

Here is a run with the changes

20287

20288You set PE to Lambda 1.175 (i.e EQR 0.85)... this is why your log shows EQR 1.0 during WOT (PCM will not go leaner than EQR 1.0)... this is dangerously lean.

when you look at B3618 or B3605, pay attention to the units (see upper right panel).


Do this:
- open tunetool,
- go Edit->Properties and set Commanded Fuel Units to EQR, and click Ok.
- exit tunetool,
- restart tunetool,
- goto B3618 and set it to EQR 1.175.
- save file and flash to PCM.

[Dirktdolman]

Original Value in the 1500 hz cell was 0.209783. I added 12% to that, making it 0.23495696. So do I add another 3.5% (making it 0.2420056688) or remove 3% from the 0.23495696 (making it 0.227614555)?

[Dirktdolman]

Is this what you are talking about?

20289

20290

[joecar]

Original Value in the 1500 hz cell was 0.209783. I added 12% to that, making it 0.23495696. So do I add another 3.5% (making it 0.2420056688) or remove 3% from the 0.23495696 (making it 0.227614555)?
Sorry, I meant take 3.5% back out.

[joecar]

Yes. Click the +.00 button to increase precision

[joecar]

Sorry, I meant take 3.5% back out.
After adding 12%, take 3.5% back out.

[Dirktdolman]

Here are a couple runs I made today with the new settings.

20297
20298
20299

20300

[joecar]

Ok, trims look to be closer to zero...

there are a few things I still don't like:
- I like to see the HO2Sx1 voltages get to 920 mV, but your log does not show any WOT.
- I like to see no KR.

[Dirktdolman]

Not sure about the HO2Sx1 but I did see the KR. What do I need to do?

[joecar]

What fuel are you running...?

[Dirktdolman]

89 oct 10 % Ethanol

We are about 2400 ft elevation

[joecar]

LQ4 has CR 9.5 so you should be ok.

Do you see any oil on the inside of your intake manifold...?

[Dirktdolman]

LQ4 has CR 9.5 so you should be ok.

This is good news


Do you see any oil on the inside of your intake manifold...?

I have not noticed any, WHY?

[joecar]

Ingesting oil allows knock to occur... your log shows knock events.

[Dirktdolman]

Hopefully that is not the problem. The motor only has about 25,000 on it.

Can injectors cause this problem?