replaced alternator now VE table wrong XFI

#1
Have XFI 2.0 from Hartline running a caspers adapter harness. Been on the car for 3 years now, had the idle and part throttle tune set for 3 years now haven't needed to make any changes. Replaced alternator (wasn't having any problems, stud came loose while working on wiring, opened up to tighten found capacitor bad so installed new alt I had in box on shelf), also month earlier replaced battery because of age (was cranking slow). Now car is idling at 10:5 with big clouds of smoke out tail pipes. Had to reduce VE by more than 10 at idle to get back to a 12.5-13 AFR. Drove car tonight part throttle, cruse conditions 40-55mph o2 correction is -10%. So it appears to be whole map not just idle. Compared to saved file from march same VE table. Fuel pressure 45 psi hose off like it always been. Looked through all settings everything seems to be correct. air temp and coolant temp look to be correct. Injector pulse width at idle went from 0.8% in past to 0.4% today to get same AFR.

Found this thread:
https://www.turbobuick.com/threads/xfi-voltage.327840/

Checked old log files battery voltage today on XFI at idle 14.0-14.1V, in the past 13.0V at idle. Always had 14.4 at alternator and battery then and now.

Injector opening offset vs battery voltage I believe is unchanged from when I received the xfi. 13.0V .85 14.0V .72

So what caused this change? Did the voltage reading on XFI going from 13.0V to 14.0V cause it? Is the permanent solution to wire XFI using a relay directly to battery bypass the stock harness? I would prefer to retune the car one time, so I want to fix this before I start working on the tuning.
 

Boost231

What's An Intercooler
Staff member
#2
Yes and yes.

Higher voltage to the xfi is causing it. Also its recommend to bypass the factory wire and get a solid feed to the xfi

Sent from my SM-G950U using Tapatalk
 
#3
Okay. I wish I would have known that 3 years ago would have just done it day one. Tuning the car is still fun, like everyone else with these cars I put a lot of work into the part throttle tune and would prefer to doing WOT tuning, not redoing this.

Thank you.
 

NY Twin Turbo

All the good stuff.....Times 2.
#4
The same thing happened to me when I provided hot wires to all my major components. Injectors, XFI, Ignition, etc....

First, I would provide a dedicated voltage whip to feed both the XFI and to the injector harness, being sure that they are both getting the same voltage. Then, I'd like to be sure to start with the known certain proper Offset Map for my specific injectors.

Then you can tweek your VE from there. In a perfect world, it would probably be good after that no matter what the voltage is. And then again, maybe not.

But if you get the VE correct at common voltage numbers, and later you still discover it's off again when there is lower voltage, I would leave the VE map alone and instead tweek the Offset Map. Just a little pull-up or pull-down on the line will get you just right.

You may want to try to tweek the Offset Map under different voltage conditions, when cold on a cold day with the hood open and with no accessories on, and when hot as hell with everything on. Fans, radio, lights.....everything.

But first be sure to start with a good VE and Offset map after you provide typical voltage to both the XFI and injectors.

It worked for me.
 

NY Twin Turbo

All the good stuff.....Times 2.
#6
That was going to be my followup questions, do I need to hotwire the injector harness, and should I be adjusting the voltage offset table.
thank you
You don't "need to". But if your using the proper voltage off-sets for your particular injectors, and you hope that this will be the end of your tuning, it would be best to give the injectors the same voltage the XFI sees.

But again, some small adjustments may still need to be made from there.

Before I begin filling a VE map, I like to provide the XFI with as much "true" information as possible to start.

The one exception, I lie to the XFI about the higher load VE numbers because it doesn't know the alky injection exists. But in this case........we all do.
 
#8
Also as a temporary solution. How successful would I be to take my old map good map and just adjust the injector voltage offset till it is closer to correct. I am looking for a solution that will let me drive this car without redoing the entire be table while I rebuild trans in my pickup
 
#9
I am also considering just subtract 15% from entire ve table that way it will get me back into a range where o2 sensor can control .
Or I could turn self tuning back on. But I wasn’t very successful with that originally so I turned it off and tuned myself.
 

NY Twin Turbo

All the good stuff.....Times 2.
#10
So what are the standard voltage offset numbers for the narrow body Siemens 60 lb injectors.
https://documents.holley.com/techlibrary_injectorflowdatarev2.pdf.

Double check your map against this chart, I guess. I think there is a file in the XFI for most of the common injectors.
Also as a temporary solution. How successful would I be to take my old map good map and just adjust the injector voltage offset till it is closer to correct. I am looking for a solution that will let me drive this car without redoing the entire be table while I rebuild trans in my pickup
All things being equal, should work just fine. Good enough to leave alone after that. But I happen to be a big fan of giving the injectors and the XFI the juice.
I am also considering just subtract 15% from entire ve table that way it will get me back into a range where o2 sensor can control .
Or I could turn self tuning back on. But I wasn’t very successful with that originally so I turned it off and tuned myself.
No. Don't do that!

The amount of off-set error is not the same everywhere. It will be worse at smaller pulse widths. A miss-calculated injector opening/closing time is a far greater percentage of the total at shorter pulse widths (lower load points).
 
#11
Thanks for the link.

Long term Plan will be to hotwire computer and injectors. Just looking for a short term fix. O2 is pegged negative during cruse can't control. I am going to subtract 10% off the map 100kpa and below, up to 3,000 RPM, leave the rest of it alone. That will get me into range where O2 can control. Then I will just make some logs while driving to work and home, and can make some corrections from that. That way I can get started on the trans rebuild, and order some parts for the hotwire. Will do the hot wire after I have the truck back on the road.
 

NY Twin Turbo

All the good stuff.....Times 2.
#12
Thanks for the link.

Long term Plan will be to hotwire computer and injectors. Just looking for a short term fix. O2 is pegged negative during cruse can't control. I am going to subtract 10% off the map 100kpa and below, up to 3,000 RPM, leave the rest of it alone. That will get me into range where O2 can control. Then I will just make some logs while driving to work and home, and can make some corrections from that. That way I can get started on the trans rebuild, and order some parts for the hotwire. Will do the hot wire after I have the truck back on the road.
Try to stick to the off-set corrections if you can. That's easy to adjust back after your hot-wires.