50+ STFT at idle?

[geo53PSI]

I've got a 2005 4.8 swap into a truck, it has a cone intake and headers, other than that its pretty much stock.

The vehicle is very hard to start hot or cold, have to give it a bit of throttle before it actually even tries to idle. It will take about a good minute before the idle evens out and that's only when the PCM is adding 50+ of fuel on the trims.

I have not messed with anything on it and want to see what you guys think.

Injectors were ordered from ebay part number 25317628 . I'm thinking they may be questionable as far as the flow rate and stock data not matching to them, the truck seems to want more fuel at idle. alot more fuel!

The tune and scan are attached.

Thanks in advanced for all the help.




HardStart50+Trims.hplAttachment 59465

[GHuggins]

So it's got different injectors then? Or injectors that are supposed to be the same, but don't appear to be? Sounds like the injectors are wrong, wrong in the tune or the MAF and intake tubing have been changed greatly reducing the amount of air being seen going into the motor?

[geo53PSI]

The same number 25317628 injector was on the vehicle preciously but some injectors were no good so a new set of injectors were ordered from ebay.

They have the same part number stamped 25317628 but acoording to the scan and just from what Ive see they seem to be flowing like much smaller injectors than the 25.2lbers that they are supposed to be.

I have not yet touched the injector data on it.

The intake just has a cone filter but i dont beleive that would be enough for it to add +50 on the trims.

[schpenxel]

Pretty much all the airflow/fueling tables look stock except for PE EQ ratio. Attached is what is supposed to be a stock 2005 Sierra 4.8 tune file if you want to take a look at it

I'm honestly surprised it starts at all like that... those are some pretty massive fueling corrections.

What MAF are you using?

You can either just start tuning it from here and get fuel trims down by changing airflow tables, or you can do some more research and try to be totally sure those are the same/stock injectors that the tune is currently setup for. It's kind of a catch 22 until you know the fuel injector data is accurate

Assuming it IS accurate data, then go through the normal tuning steps... disable MAF if it has one, tune VE/SD. Disable VE/SD, tune MAF. Or just one or the other if you want to leave it SD or MAF only. Personally I'd probably disable the MAF first and see what happens.. then adjust the VE table from there.

I'd look into the fuel inj data a little more, then start changing airflow tables if you can't find anything saying what you have is any different from stock..

From what I remember there is a 4.8, 5.3 and 6.0L of that truck, so I'm wondering if there are other fuel injector options.. though if you had gotten ones that were too big I'd expect fuel trims to be negative, not insanely positive..

Attachment 59497

[68Camaro]

you should check fuel pressure at the rail. sounds like pump may be bad

[schpenxel]

Def. worth checking.

[geo53PSI]

I thought the pump was going bad as well because it was first hooked hooked up wrong to the filter but it is showing 59 at the rail.

[geo53PSI]

Yea it was very hard to start, you have to give it a bit of throttle to get it started then when it warms up it starts on its own but stumbles very badly.

The MAF is the stock MAF that came with the 4.8

The injectors have the following numbers on them 25317628 with two pintle holes at the tip short style injector.

Im wondering if these are actually 22.1lb injectors as opposed to 25.2lb injectors.

From the data log i got Ive always suspected that the motor is not getting enough fuel because the trims are 50+

I may need to track down correct data for some 22.1lb injectors

I beleive that the current data on the tune are for the stock 25.2lb injectors

[schpenxel]

Intake may be doing weird things to the MAF vs. the stock one.

I'd do some basic rough adjustments on the MAF and VE tables to get the fuel trims back to sanity for now

[geo53PSI]

I tried downloading the attached stock tune you posted but its not working?

[schpenxel]

Not working for me either... try this one. This is supposed to be a 2005 Sierra 4.8 stock tune.

1412642551.hpt

[geo53PSI]

So I've compared several stock 4.8 files; the file that schpenxel posted is the same in the injector data from my file for 25.2lb injectors(Delphi 25317628 with two pintle holes) ...

After searching I found that the 99 Silverado 5.3 stock file has the data for the 21.8 lb injectors, which I believe are the actual injectors on the truck as opposed to the 25.2lbers they were supposed to have sent...

The only problem is the current data on the truck for the 25.2lb injectors is set up for a returnless fuel system, the data for the 21.8 injectors that i need from the 99 silverado 5.3 are from a return style fuel system... ??Attachment 59639

question is how would I make that data from the 99 silverado work on the 2005 4.8

[schpenxel]

Honestly I'd just leave the inj. data alone unless you're sure you find something that is more accurate. I'd start working on airflow tables to get fuel trims in line.

[GHuggins]

Or, it wouldn't be correct - BUT you would at least have the correct "kinda" slope - you can just multiply your current flow rate by what ever percent your fueling is roughly off, then verify your 400kpa settings between the two are very close...... Return style is set to 58 or 60psi - adjustable still has that setting in "it's" tune...

[geo53PSI]

Mostly worked on Gen 3 and SD with wideband...This one does not have a wideband so I'm thinking start off by multiplying the VE table by 1.20 since the LTFT are maxed out at 25 ...fail the MAF...flash.... Clear the trims and log the LTFT..if they fall withing +/- 5 ..disable LTFT and move on with STFT...??

[geo53PSI]

Or, it wouldn't be correct - BUT you would at least have the correct "kinda" slope - you can just multiply your current flow rate by what ever percent your fueling is roughly off, then verify your 400kpa settings between the two are very close...... Return style is set to 58 or 60psi - adjustable still has that setting in "it's" tune...

I follow you on multiplying the flow rate with the injectors...not sure what you mean by verifying the 400kpa?

[schpenxel]

Mostly worked on Gen 3 and SD with wideband...This one does not have a wideband so I'm thinking start off by multiplying the VE table by 1.20 since the LTFT are maxed out at 25 ...fail the MAF...flash.... Clear the trims and log the LTFT..if they fall withing +/- 5 ..disable LTFT and move on with STFT...??

I'd just disable the MAF and see what fuel trims are at then. Then make rough adjustment to VE table based on that

[GHuggins]

I follow you on multiplying the flow rate with the injectors...not sure what you mean by verifying the 400kpa?

It's the 40 setting when referencing the manifold vacuum flow rate settings...

Then you can adjust via MAF and VE as Schpenxel has described...

[geo53PSI]

So after some VE table tuning yesterday it seems like something is very wrong or I am missing something!

First thing I tried was the injectors data...the trims went down a bit to 39 but still hard to start. So I reverted back to the original inj data on the tune an proceeded to fail the MAF and tune the VE

Disabled the LTFT (set min ETC to 285)
Set P101-P103 to MIL on First Error and unchecked the SES boxes
Set the MAF Frequency Fail to 1

Started seeing what the trims were before messing with the VE

STFT trims were still at +50 , pretty much worked the entire VE and multiplied by 1.20 , trims got better to +18 so I multiplied by another 1.15 and got them to +5 on one bank and 0 on the other.

Truck turned on great and idled way better.

At times though when I would stab the gas pedel it would seem to go to high idle and I would have a dead pedal..it would not go up on RPMS.. I then would turn it off then back on and everything was back to normal..turned on great and idled good.

The VE table did look ridiculous though...I mean it was very high! over 100 right on start cells.

I enabled the MAF back on and it reverted back to the same old hard to start and +50 trims :/

I began to check the intake and found a dime size hole on the intake tube a few inches behind the MAF..So we switched intake tubes...checked for leaks on the tube and it all seemed good.

Turned the truck on again and same thing....stumbling start and +50 on the trims...

I did not tune the MAF as of yet , the MAF is the stock one part #25168491 Delphi

At this point I'm not sure if the MAF is bad or what? The VE table is way too high in my opinion...

Fuel pressure stayed at 60 all the time so pump is good and injectors are getting pressure..I've attached the tunes with both the MAF on and failed as well as a scan for each MAF on and off.

Attachment 59687
Attachment 59688
scan fixed leak MAF On.hpl
Scan MAF Failed Trims edited.hpl




Any input?

[schpenxel]

Just leave the MAF off and dial in the VE table. Obviously injector data is wrong, but at some point you have to pick what you're going to use for inj data and leave it alone. You can't dial in the air flow table(s) while changing fuel injector data or you'll be going in circles. My opinion--don't make it more difficult than it has to be.

If you haven't tuned the MAF table(s) then it's no surprise fuel trims are all over the place with it enabled. You're running an intake that is nothing like the factory one, so of course the factory MAF curve is wrong for your setup.

I've also moved this thread to the gen 3 section. Might get more help there regarding the idle speed.