4.8 Hot Start and Fuel Trims / VVE

Losing my marbles a tiny bit. I've been chasing my tail for quite a while now, and I think I must be missing something basic.

I have a 4.8 with the "low buck truck" cam: Lift .552/.552, Dur @.050 212/22X, LSA 107 Deg. I have a TBSS intake with the flex fuel injectors.

I have reverted to my starting point, and have attached it with a basic idle log and a hot start log.

I have been trying to follow Cringer's method, but my LTFT and my charts don't seem to jive.

I am logging lambda from the AC input with this math: ((([7101.10]/0.5)+10)/14.7)

I could use a leg up.. feeling pretty defeated at the moment.

I'd get the part number off of the injectors and make sure you have the correct data in the tune for the injectors you have. Have you done any VVE tuning yet?

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Originally Posted by LS ROB

I'd get the part number off of the injectors and make sure you have the correct data in the tune for the injectors you have. Have you done any VVE tuning yet?

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Just checked my Injector data - it got changed somewhere along the line. Updating...

Haven't tried VVE tuning. Call me chicken. Ha.

Updated tune with corrected injector data, and a quick around the block log. It is definitely better.

I'm reluctant to fiddle with the VVE table until I'm a little more confident my data isn't garbage.

Whats your injector part number?

Add cylinder airmass to your channels.

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Originally Posted by RDF1

Whats your injector part number?

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They are 12594512, which are listed as 38# for a 5.3 w/ flex fuel.

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Originally Posted by LS ROB

Add cylinder airmass to your channels.

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Will do.

Fresh copies of the tune and log.

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Originally Posted by DanN

They are 12594512, which are listed as 38# for a 5.3 w/ flex fuel.



Will do.

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Here is LMG injector data.

MANY thanks RDF1.

Here is the latest tune and log. I have updated to the LMG injector data and made a small tweak to the MAF tune.

Still working on this with limited.. success?

At one point I thought I had it, but it seems I don't. My hot start is over 5 seconds (no throttle input).

I tried some suggestions from Cringer's Youtube for the Cranking VE vs Map vs RPM and Idle Startup airflow vs Run time (off time) vs ECT. It seemed to work the one time I forgot to log, but not so much since.

I also did a little dabbling in the VVE.

Seems it needs more fuel on cranking?

Give this a go to see if it helps at all. If it starts, let it idle for a good while.

Attachment 162242

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Originally Posted by LS ROB

Give this a go to see if it helps at all. If it starts, let it idle for a good while.

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It did start; I let it idle for a full 10 minutes. Then I stopped it and restarted, and logged another 3 minutes. The restart was quite good I'd say.

So..all you did was set Final Idle Airflow Min vs RPM vs Gear back to stock. I didn't think that would really matter given it's a manual with no gear feedback...

That's right; with a small adjustment added.

When you have a manual trans, which row does the tune use?

Attachment 162294

I believe it to use the whole table. I could be wrong on that though.

Set P/N rows to 0 and see what happens.
Or select gear in the channels and see what it defaults too.

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Originally Posted by LS ROB

I believe it to use the whole table. I could be wrong on that though.

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Quote:

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Originally Posted by RDF1

Set P/N rows to 0 and see what happens.
Or select gear in the channels and see what it defaults too.

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I will test that tomorrow, row by row.

Here is a "cold start" log from today.. but it's like 85 degrees out. :cool:

Still longer cranking than we'd like I think.

Take it for a drive and see how it does. Were you fiddling with the throttle on that cold start?

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Originally Posted by LS ROB

Take it for a drive and see how it does. Were you fiddling with the throttle on that cold start?

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No, I did not touch the throttle until it had been running for nearly a minute; had to move it to a different parking spot.

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Originally Posted by DanN

I will test that tomorrow, row by row.

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"Tomorrow" was a few days ago now, but it appears that when you have the tune set to "Manual", only the neutral row is used. I haven't gone for a long drive with it, but this works "around the block".

If you have a fancier transmission that had a TCM, it may well use all the rows - but for my "dumb" AR5, it only seems to use the neutral row.

My current Minimum Final Idle Airflow Minimum table:

Attachment 162630

Did you happen to get a log? I'd be curious to see if the throttle blade is still active with the new airflow numbers. I would have thought that the whole airflow table is "supposed" to be used unless the ECM defaulted to the P/N row if something isn't jiving. Do you have a clutch position sensor?

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Originally Posted by LS ROB

Did you happen to get a log? I'd be curious to see if the throttle blade is still active with the new airflow numbers. I would have thought that the whole airflow table is "supposed" to be used unless the ECM defaulted to the P/N row if something isn't jiving. Do you have a clutch position sensor?

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I did. I'm curious what you find.

I did wire in the clutch circuit that the P12 used to the E38, but I'm not sure it's actually doing anything, or how to tell in the tune. Electrically they appeared to be the same, so I expect it does "work", for whatever that means.

Attachment 162659
Attachment 162660

I would start back over on this. The Airflow table cant be helping you at all and it looks like to me that you have misfires when going WOT. Check all of the plugs, plug wires and coils to see if they're all snugged up. I wouldn't do any WOT stuff until you get the VVE and MAF heading in the right direction. Maybe someone with more experience can verify the misfires.

Quote:

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Originally Posted by LS ROB

I would start back over on this. The Airflow table cant be helping you at all and it looks like to me that you have misfires when going WOT. Check all of the plugs, plug wires and coils to see if they're all snugged up. I wouldn't do any WOT stuff until you get the VVE and MAF heading in the right direction. Maybe someone with more experience can verify the misfires.

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I thought my MAF was pretty good, but perhaps my charts are bad. I've looked at the VVE a little bit, but haven't made any big changes.

The misfire is new. I'll dig into that for sure.

If someone with known good graph setups could show me my log in their tables, I could confirm if mine are any good. I could be dealing with garbage-in garbage-out here.

OK - I did some testing.

Idling in the driveway I was getting random misfires, and it would go OL -Fault.
I reverted the FIAM table to the old one. I still got misfires.
I reverted the whole tune back to one I had from July 15, and the misfires disappeared.
I changed the FIAM table back to the one I was using with only the Neutral row populated, and got no misfires.

So it appeared to me it was something in the tune that was causing the misfires, but I'm not sure by what exactly. Maybe my VVE meddling?

I decided to wildly change the VVE table - I exchanged the truck table for a Corvette one, and took 25% of it out right off the top.

I took it for a gentle cruise around the block - didn't get into WOT at all.
No misfires.
Hot started like a champ.
appears to be really, really rich.
Overall, felt pretty good.

Now I'm not 100% sure how to properly tune the VVE, but I think the MAF is ok - If someone would take a look and give thoughts / suggestions I'd happily drink a beer on their behalf!