why are my trims so high in the positives?

[mvvette97]

2003 stock silverado 5.3 engine. Nothing done to it at all. Runs good but ran a long and was shocked to see how high the trims are. Any idea what I should do to change this? Here is a log and the stock tune

[joecar]

Check for airleaks... for example, is PCV system leaking...?

[mvvette97]

I checked and didn't find any air leaks at all. this factory tune is kinda strange compared to all the others I have seen. I noticed that the injector flow rate table has all the same numbers from start to finish. Never seen that before. honestly I don't understand how that would work because of the different map and loads of the engine at different RPMs. How does a tune like this change with loads are RPMs and such?

[joecar]

I checked and didn't find any air leaks at all. this factory tune is kinda strange compared to all the others I have seen. I noticed that the injector flow rate table has all the same numbers from start to finish. Never seen that before. honestly I don't understand how that would work because of the different map and loads of the engine at different RPMs. How does a tune like this change with loads are RPMs and such?
Is your FPR manifold referenced...?

What year/model/veehicle is this...?

[mvvette97]

what is FPR? it's an 03 silverado 5.3

[Dirktdolman]

FPR = Fuel Pressure Regulator

[joecar]

Truck typically has FPR located at the fuel rail(s), and has an air/vacuum hose going to the intake manifold (not to be confused with the pulse damper),

[joecar]

If FPR is manifold referenced then IFR is flat (same value in all cells).

If FPR is unreferenced (or baro referenced) then IFR is slopef (as sqaureroot of pressure across injector).

[joecar]

The reference hose adds MAP to rail pressure (i.e. at the top of an injector), this cancels out MAP at the bottom of the injector, thereby keeping the pressure difference across an injector always constant, this keeps the IFR constant.

[mvvette97]

ok I looked and it does have the pressure regulator on the rail and has vacuum full time to it. i just don't know why it runs so high in the positive trims. Just for fun I made a tune from an 05 I believe and it has the sloped injector flow table. So I just done a copy and paste with all the fuel tables, maf, airflow and everything. Gave it a flash wondering if it would run really at all and was surprised to here it fire right up and run smooth. Went for a drive and trims were in the -1 to +3 range. Trucks seems to run fine and trims are way better. Is that strange or what? That was just changing all the airflow like VE, maf and all fuel related tables. I just installed a wideband to see what full throttle is doing. Haven't tested it yet. So what do you think of this? I mean if the trims are good and PE mixture is good will it hurt to run it with this tune? As I said before my stock tune was just crazy lean on the trims. Truck ran fine but as much fuel as the O2s were adding I can't imagine that would be an ideal tune. What would you do?

[joecar]

That is strange... run this tune (LTFT -1 to -3 % range) and capture a few logs... if it runs good then keep it, if wideband shows PE fuelingis not rich enough, then increase PE table B3618 a little.


( I've seen strange stuff, not to worry )

[joecar]

( log in post #1 shows MAF under-reporting )

Post new log/tune files.

[mvvette97]

What do you mean under reporting? i have been working with the tune I made and have it -3 to 0 while cruising and the wide open running at 12.9 on the wideband. I have had a little idle problems "-7 trims" but think I got that dialed in pretty well now. Truck runs fine. I drove 40 miles and was getting about 18mpg on the highway so that's not too bad.

[joecar]

MAF is not reading a sufficiently high value for the TP and RPM... I'll post a pic shortly...

[mvvette97]

do ya think the maf could be bad making it run lean? The guy I bought the truck from said last year it threw a maf code so he cleaned the maf and after that the code never came back. Makes me wonder if there is something wrong with it possibly

[mvvette97]

well just for kicks I ran down to the local salvage yard and grabbed another maf and put on it and flashed it back to all the stock fuel and air tables. It was much better but still running a little lean. was in the +5 trims. So I just bumped the maf table 5% across the board and now the trims at cruise look great. now I have a kinda rich idle though. Here is a log I just ran at cruise and idle at the end of the log.

[mvvette97]

An update on my truck. I have been playing with the tune ever since I started this thread. I have changed pretty much everything in the tune and had it running good. Just installed a set of headers so I have been playing with it again. Just seems like I would have it dialed in then it would change a little. Well today it tripped a light with a MAF code like it did a year ago. Guessing the maf is not quite right since it threw the code a year ago. I kinda wonder if this is what has been causing alot of my problems. Tuning around a bad maf. So I threw on the spare maf I bought and went for a run. She was running super rich and wide open was like 11.1 afr. So adjusted trims and got the wide open set back to 12.9 now. So I wonder if that MAF was causing alot of my problems? I'm still running the sloped IFR table even though it had the flat table but my trims are pretty good. Cruising it is -1.4 to about -3.9 so seems pretty good overall.

[statesman]

What MAF code did you get?

[mvvette97]

It was a P0101 code. The guy I bought the truck from said he got that code so he cleaned the maf and it never came back. That is till today. I cleaned it again but then decided to just put the new used maf on and try it.

[statesman]

P0101 can mean problems with the MAF sensor, but it doesn't necessarily have to be a problem with the MAF sensor. You get P0101 when the MAF's reported airflow is not in good agreement with the VE table's calculated airflow... so if you've been messing with the MAF curve then it can throw a P0101 if the MAF no longer agrees with the VE table.

GM had a few different MAF sensors for different vehicles... they had different part numbers and they all read the airflow differently. I'm guessing that your replacement MAF sensor has a different part number to the original, which is why your fueling suddenly went super rich.

If your getting good fueling with a sloped IFR table, then there's possibly something wrong with the manifold referencing function of your pressure regulator.