Fastbird

Helping a buddy out here, recently had his car at a very reputable tuner after a fresh motor build.

440 LSX
Ported RHS LS7 heads
Ported MSD Intake
251/269 .675/.675 114* cam
NW 102 TB
Fast 85lb Injectors
LS7 Map and LS3/7 MAF
Stock fuel system with BAP

Issue is at 3500 the car just dies for a second, then recovers and pulls.



Tuner is saying change injectors and throttle body. I have a NW 102 on my car so I doubt that's it, but 85 lb/hr injectors I think are too much for 600-650 RWHP N/A (I was at a acceptable duty cycle on my TT car at 760 RWHP on a TT setup). I think the injectors might be the culprit as the fueling is going into PE but I'm no expert. Thought I'd query some minds here. I can't see it being anything mechanical as it would most likely present issues before/after 3500 RPM also.

I have a HP Tuners datalog but don't have HPT myself if anyone wants to see it.

Fastbird

I just downloaded the trial version of HPT and was looking at the log. Lean spike to 14.17 AFR at the dip, RIGHT SIDE ONLY. Thoughts?

CTD

I'm curious post up the log & lets have look

tblu92

It is rare to have a lean spike only on one bank--I assume you are using a wideband to get your AFR data during PE----
I would look for the simple things 1st---These engines are very ground sensitive--I have seen similar results as yours where a ground not installed would make bank 2 injectors not to pulse correctly
2nd I would look at the fuel bypass system or the fuel pressure regulator if equipped --often a mismatch is fuel is caused by an improperly plumbed fuel system
3rd an exhaust leak on one side even if small can create during PE the side without the leak to run lean---
Check your fuel pressure at WOT by fashioning a gauge and taping it onto the windshield to confirm fuel pressure in the gear that is 1:1 see if the fuel pressure drops at all--The most fuel is used at peak TQ RPM --on an auto trans 1:1 is 3rd gear

Fastbird

Sorry, been at work all day. 12's as normal, so I only have a couple of evening hours before I do it all again.

A wide band was hooked up but the lean spike was noticed by the car's reaction in person, but looking at the log, the Bank 2 front O2 sensor voltage TANKS down to 43mV at it's worst, seemingly out of nowhere. Bear in mind I'm new to HP Tuners so I'm probably missing a critical graph or chart somewhere. 10:33:55:9xx is when the event happens in the log. You can see the passenger side go really lean and hang low for a few ticks in the log before recovering, coinciding with the dip in the dyno graph.

I'm uploading the log to google drive, will post a link momentarily.

Try this: https://drive.google.com/open?id=0Bz...Vk2SGxNMzFSblE

CTD

Looks like the newest version of HPT, I've not updated. I cannot look, can you post a screen of the problem?

Fastbird

I'll post up a couple of screen caps when I get home this evening.

schpenxel

If you looked at the log in more detail you'd see that narrowband O2 readings for BOTH banks dip along with the WB sensor.. though one bank does dip more than the other. One only gets down to ~700mV, but it still dips enough to be significant IMO.

enoniam

I can't open the HPTuners file here at work, but look at the airflow values in it and see if they dip as well at 3500. If so you have an issue with the airflow calibration, if not look at things like injector pulse widths and also look at the PE table in the tune to make sure it doesn't have a dip in it.

schpenxel

PE table is flat lined

MAF table doesn't have a dip right there

Inj PW in the log is flat until towards the end of the dip then starts increasing again

enoniam

But what does the scanner say about what the MAF is reading? Is it dipping or flatlining there and then going up?

schpenxel

https://www.corvetteforum.com/forums...yno-graph.html

enoniam

Thanks schpenxel for the link.

The thing jumping out at me looking at the HPTuners screen shots in that link is how the injector PW is flat until after the lean spot. RPMs and airflow are both going up before that, which should indicate a growing need for fuel in each cycle, but with the flat injector PW it is staying constant until after the lean spot?

I see that Dynamic Airflow was also logged - it would be interesting to see if that was also flat where the Injector PW was flat. If so I would suspect the fix is in the VE table or something related to how other than the MAF input the Dynamic Airflow is calculated.

schpenxel

I don't have time right now to set the charts back up like I had them in the previous shots, but here is a quick one with O2 sensor and dyn airflow readings

Looks like a dip (or at least a slower increase) to me

enoniam

It isn't flatlined though like the injector PW.

I'd look at the injector calibration tables and make sure things look copacetic there.

schpenxel

It is using FAST injectors if I remember right.. so your guess is as good as anyone's on whether the data is right or even close to right. I'm going with "not a chance in hell"

I believe the IFR table is flat lined (on a non vacuum referenced system if memory serves), so that is an obvious concern in addition to the other injector data tables that are probably wrong

enoniam

Yes, from what I'm seeing it looks like injector data needs some work.

Fastbird

my buddy with the car should be seeing these threads at this point and you guys are blowing my mind with this. Really great insight from everyone and it's very much appreciated.

enoniam

Should probably take a look to see what Cylinder Airmass is doing before being too sure it is in the tune's Injector data. If it is flatlined where the injector PW is flatlined then it is NOT a problem with the injector data. But if it is going up and the PWs are not then I'd say for sure an injector calibration data issue.

schpenxel

Cyl air added