Interesting Issue: MAF failure = Idle tables ignored. Cant tune VE because of it

[Dragframe]

So im working on my 2007 Silverado with a 4.8 and ran into something interesting.

I put a 224/230 .553/.546 111+2 Cam, bolt ons, stall, various stuff in the last week.


What i found is when i cause the maf to fail by reversing the values in c0301 and c0302 (So i could dial in the V VE tables), the ecm completely ignored what seems like all the idle tables. It attempted to idle at 500 rpm with 28 degrees on timing. I did everything... changing the idle airflow, max idle area, and idle set points all over with no change in the way the engine tried to idle.

After a lot of searching i found a obscure post about a similar issue stating on some e38's... the ecm ignores the idle tables when a map/maf failure is detected. So.....

I put the maf settings back so it would not fail... and boom... it instantly idled and appears to respond to my changes in the idle tables.

So if i cant fail the MAF.... how am I supposed to log and tune in SD to get my VE dialed in?

I appreciate any help. TIA

[joecar]

When the ECM ignores idle tables on MAF fail, which tables is it using...?

[gmh308]

it is worth pushing your VVE table up and down. For example try 15% up and see if it gets better. SD MAF on scan should match Real MAF. Roughly that is. If your setup has moved the airflow away from stock too far, yes idling may be a challenge.

[Dragframe]

When the ECM ignores idle tables on MAF fail, which tables is it using...?

It uses the high octane spark table rather than the idle spark. B1829, B1821, b1651, b1652, all what seems like all the idle tables are not referenced Whatsoever. You can change the values to whatever you want and log it.... it will act exactly the same. Tries to idle at 500 rpm using the high octane spark table. Its like the ecm loses its mind without the maf. Really frustrating.

[Dragframe]

it is worth pushing your VVE table up and down. For example try 15% up and see if it gets better. SD MAF on scan should match Real MAF. Roughly that is. If your setup has moved the airflow away from stock too far, yes idling may be a challenge.

Have tried this with no luck unfortunately. Im nearly positive it is not referencing the idle tables.

[statesman]

Can you post your tune file?

[Dragframe]

Yes sir I can albeit a bit reluctant due to embarrassment lol

I had a turbo car i built when i was 19 back in 07-08... Put a SD operating system on it and tuned the car easily. Car is still driving around 10+ years later with my tune. But this e38 has me really screwed up.

Its currently set up totally open loop with DFCO turned off. I basically turned all that off... started with idle stuff till it idled well enough to drive (intending yo return to it and do it right). Then was going to put it into SD and tune the VE table. That is where i can into this issue. So i hacked up the maf table and a number of other htings till the truck ran ok and left it there lol. The Truck idles fair and driving it is surprisingly bearable with this hacked up tune. But id like to do it right!

Be easy on me lol.


22905

[statesman]

Try this tune file, it's set for SD.... let me know if you still have the idle issue.

[Dragframe]

Try this tune file, it's set for SD.... let me know if you still have the idle issue.

Thank you. I'm Nashville till Saturday so ill load er up on the truck when i get back! Illl report back then. Though your changes look pretty similar to that which i already tried.

Would you like me to post a log of me trying it when i get back ?

[statesman]

Would you like me to post a log of me trying it when i get back ?

Log not needed... but if still has the idle issue, then give me a list of all the codes it's throwing (DTC's).

[Dragframe]

Log not needed... but if still has the idle issue, then give me a list of all the codes it's throwing (DTC's).

So its a no go. Truck wont idle. Throws a p0103 code like one would expect. Same symptoms I describe above. Just doesn't even attempt to hold the set idle speeds. If i'm not holding the throttle open, it drops to 300-400 rpm.

Loaded the other tune back in it, and idles great. Its like the ecm just freakin loses it without the maf.

I've tried failing the maf in the tune... or removing the wire from the maf... tried removing the wire and making it fail quickly in the tune. All with the same result. Ecm doesnt even attempt to hold the idle speed.


Now i have not in all this time attempted to drive it in Sd. i suppose even if a person couldn't make it idle in sd... he could still try to drive it around to tune the VE table? Im starting to believe i got a stange e38. Would straight maf only be a viable alternative?

[statesman]

Would straight maf only be a viable alternative?

Definitely.... that's how I run my own vehicle. Most people don't give the MAF sensor the love it deserves, but it really does work well when tuned correctly.

I had hoped that if you still had the idle issue that your PCM would give us some codes to point us to the problem... it certainly is a weird problem that I've never seen before. I've got no idea why your PCM doesn't like going into SD, but if you're happy to run MAF only then it's something I would recommend.

[Dragframe]

Definitely.... that's how I run my own vehicle. Most people don't give the MAF sensor the love it deserves, but it really does work well when tuned correctly.

I had hoped that if you still had the idle issue that your PCM would give us some codes to point us to the problem... it certainly is a weird problem that I've never seen before. I've got no idea why your PCM doesn't like going into SD, but if you're happy to run MAF only then it's something I would recommend.

I enabled the maf from 500rpm up and the wideband seems to hold a more stable afr. Idle is a bit strange running maf only. Hard to describe. But it seems to drive well overall. Also seems to go into PE quicker for some reason. Might be something i play with going forward.

[Dragframe]

So what would cause low vacuum when on MAF only? Finding that with running maf only (no other changes), im dealing with vacuum/brake issues that i hadn't run into before. I have read a lot of guys have issues with "big" cams and maf only.

[statesman]

List everything you've changed/modified on your vehicle.

[Dragframe]

List everything you've changed/modified on your vehicle.

its a 2007 4.8 with the Cam listed in OP... ls6 valve springs. 1 7/8 long tubes.. 3" Y pipe.. full 3" exhaust with open style muffler... 3200 stall converter... 4.56 gears.. and nitrous.

I put on a cheap cold air intake on yesterday and it didn't seem to affect the tune (pretty much why i never bothered with a CAI lol)


Also! Ever since i put the gears in the dash lights up like a christmas tree after 10 min of driving. Pretty annoying but have searched and haven't found a fix

[1FastBrick]

its a 2007 4.8 with the Cam listed in OP... ls6 valve springs. 1 7/8 long tubes.. 3" Y pipe.. full 3" exhaust with open style muffler... 3200 stall converter... 4.56 gears.. and nitrous.

I put on a cheap cold air intake on yesterday and it didn't seem to affect the tune (pretty much why i never bothered with a CAI lol)


Also! Ever since i put the gears in the dash lights up like a christmas tree after 10 min of driving. Pretty annoying but have searched and haven't found a fix

You need to change the gear ratio. I believe its called the final drive ratio on the ECM/TCM combo's

[joecar]

+1 on gear ratio. And also tire size.

[Dragframe]

+1 on gear ratio. And also tire size.

I did hange the gear ratio in both the ecm/tcm. I didnt change the wheels/tires on the truck so i didnt mess with that. Though it does have some really freaking strange numbers in there for the tire size. But the speedo is dead on and it shifts fine and thats what it was when i got the truck and its was completely factory

[Dragframe]

Posting a response so the next guy with the same issue figures it out.

b1703 is what table needed to be adjusted to allow it to idle without the maf. It had a really low number like 60 in the field. I just entered the values from b1701 into it and it idled I was able to get my VE table fairly close'ish. One thing to note though... the transmission must default to full line pressure without the maf because after setting everything up to tune the VE... the tranny was banging shifts and blew a cooler line. i didnt log any transmission parameters, i only took two drives to get my lower VE tables close ish, then turned the maf back on. Having a loaded dyno and being able to lock it in a gear would have been awesome to get all the VE dialed in. Maybe ill revisit the VE later

I still have a crazy issue with turning on STFT. They jump all over the place with no rhyme or reason. Even at idle. I have them turned off for now. Maybe forever lol

[statesman]

b1703 is what table needed to be adjusted to allow it to idle without the maf.

Somehow I missed that when I went through your tune file. Glad you found it.


I still have a crazy issue with turning on STFT. They jump all over the place with no rhyme or reason. Even at idle. I have them turned off for now. Maybe forever lol

STFT can bounce around a lot if it's not set up properly. Can you post a log?... I'd like to see how 'crazy' they are.

[joecar]

...

b1703 is what table needed to be adjusted to allow it to idle without the maf. It had a really low number like 60 in the field. I just entered the values from b1701 into it and it idled I was able to get my VE table fairly close'ish.

...



Somehow I missed that when I went through your tune file. Glad you found it.
...

I believe what was said, I'm just not sure the reason why that table would prevent running MAF at idle.

[joecar]

One thing to note though... the transmission must default to full line pressure without the maf because after setting everything up to tune the VE... the tranny was banging shifts and blew a cooler line...

The trans tune would have MAF DTC entries in the max line pressure, you can disable those.