Thought I would share my challenge...

[mrogersmike]

I picked up an 06 GT recently with 73k and lots of mods (see sig) that appear to be fairly old. Came with a crappy tune that had the PCM locked up with no way to find the tuner. Bought a reman PCM and sent the paper weight out to reprogram in hopes for a spare (it was only 150 bucks so why not). Decided to do the tuning myself as I've tuned before, might have been 10yrs ago. Mostly to spare myself the issues that come with canned tunes, unavailable tuners so I can't change whatever whenever etc....

The car runs and drives pretty good and everything seems to work, with one exception. I think it has a vacuum leak that I have yet to find.

I started with the stock file on the reman PCM and compared it with a half dozen others and found it reasonable to believe it's good. On startup as soon as the cold start fueling was done it would stumble and stall before the fuel trims had a chance to try to correct anything. I could tell it was real lean. So I dropped the stoich to around 13 something and it ran, sort of. The fuel trims were still positive but at least it ran. "The maf transfer curve hasn't been calibrated". I thought that's it! So I messed with it till I got 5% total fuel trim correction with stoich back to 14.64 all the way till WOT. We're burnin' tires now fellas'! Just can't get that trans to shift right. Well I found that we're using them maf numbers to calculate load which everything else is using too. So I look at my maf curve numbers again and compare to the stock file and WOW, they're about 30% more! So I go to the injectors to look over the flow rates and they seem ok to me. I did lower the flow rate numbers by 30% and returned my maf transfer curve back to stock and yep, it ran great. But as always, when you try to band-aid a problem with tuning the wound just gets deeper. "We're in the weeds now boys".

I replaced the bank 2 upstream O2 because it seemed lazy and was late responding and it seems to match the bank 1 close enough now. (clue?)

Ok, It may not of happened "exactly" that way but it's an entertaining way to show a few truths.

- I proved you can't band-aid a mechanical issue with a tune
- The car is running 30% excess fuel (minus the correct maf transfer curve) and likes it
- The issue can't be an exhaust leak because that would dump excess fuel in and stall. This thing wants excess fuel
- We must have unmetered air entering the manifold somewhere
- It needs to have the correct maf curve transfer numbers in before I go any further
- I can't find the leak

So with all that mumbo jumbo, is it really a vacuum leak? Could it be that not tuning the VCT adv/ret for the cams yet cause this? I wouldn't think by 30%(minus the correct maf transfer curve). I can't believe it's actually using that much air. Am I missing something?

I just need to find that D$%N leak, that's my theory. Share yours if you'd like, or giggle and move on for more entertainment. Have a great day!


[ATTACH]114165[/ATTACH ]10721.hpl

[JuiceNA]

I maybe oversimplifying here, but, what air intake are you using? Put in the maf transfer for that MAF and leave it alone.

It almost sounds like you have a low fuel pressure or injectors data is wrong.
As for a potential vacuum leak, if nothing is obvious, brake booster?

[Thatwhite5.0]

You should be adding 30% fuel to the stock maf transfer for the 95mm maf housing. Multiply the entire stock maf curve by 1.3.

[mrogersmike]

I maybe oversimplifying here, but, what air intake are you using? Put in the maf transfer for that MAF and leave it alone.

It almost sounds like you have a low fuel pressure or injectors data is wrong.
As for a potential vacuum leak, if nothing is obvious, brake booster?

I've attached the tune and log to the original post to help show fuel pressure and inj data which I believe is correct. Stock inj and a C & L 95mm CAI. When I put in the correct maf transfer the fuel trims are adding in the up to 45-60% total. I don't think I can just run it like that if that's what you meant. I pinched off the line at the intake that goes to the brake booster, no change.

[mrogersmike]

You should be adding 30% fuel to the stock maf transfer for the 95mm maf housing. Multiply the entire stock maf curve by 1.3.

Thanks for participating. So just to be certain I'm not out in left field here, when I say maf transfer I'm thinking the maf airflow vs voltage table under airflow. is that correct? I'm thinking it gives an airflow per volts range that directly corresponds with the inside diameter of the housing the maf sensor sits in. The strategy uses this to fuel and calculate load for a given airflow. So it has to be correct or load/torque values for the transmission and I don't know what all else will be skewed. Or am I all wet here? Oh, I edited the original post to add the tune and log files if that would help.

Oh, I have the correct maf transfer info (I think) for the CAI. I got them from the How to tune your Mustang article written by Eric I believe that I found here in the forum. It just happens the car in the article has the same one. I'ts a bunch less than 30% and it's way too lean to run with those numbers in there.

[B E N]

Use the maf data in this tune to get you going.4 29 95mm maf.hpt

[mrogersmike]

Use the maf data in this tune to get you going.4 29 95mm maf.hpt

Thanks for your suggestion. I'll give it a try. I think I get what it's trying to accomplish. I'm looking at a snow storm starting tonight so an update with log may be a few days out.

[Thatwhite5.0]

After multiplying stock or using the correct maf transfer (maf vs volts), that should have your fuel trims with in 10% rich/lean and you can dial it in from there. You shouldn't have to do anything with the injector data. I'd verify your injectors are correct for 2006 if you're using stock injector data. There's a possibility you have a clogged or faulty injector causing lean conditions.

[iceman321]

spray some starting fluid around your intake and hoses to find the vacuum leak . injector o rings are another common location. You will notice the difference in rpm when you find the leak.

[metroplex]

You'll need to fine tune that MAF transfer function. When I bought the Saleen intake for my 07 GT from Saleen, Saleen wouldn't send me a transfer function so I had to build it myself. I used both methods: an actual external Wideband O2 as input and the onboard narrowband O2 sensors. The results were the same as long as you know what you're looking for and doing. Once it was dialed in, it worked like factory stock.

[mrogersmike]

Thanks to all who have given your thoughts and opinions, it is very much appreciated!

Yep, still waiting to be right some day. Smoke tested today, no significant leak. The bank 1 VVT solenoid gasket where it comes through the valve cover leaked at 4psi. The throttle position sensor mating surface leaked a little but nothing else. So on to trying the tuning suggestions made.