Hi All,

I am a bit tired, so I havn't properly analysed this issue yet.

Symptoms:
When cruising, occasionally there feels like a slight "tugging" backwards.. It's very faint, almost like your being hit by a head-wind...

Anyway's today I logged it (sorry in advance for the big pic):



ps - my Wideband only reads upto 16.0 (which is why it flatlines there)

Mods:
2.5L MAP shortblock
Kelford 214b's
AMS 750R (3.5" intake)
Cobb 3" catback
TurboXS HFC
98RON (92.5oct)
TephraXMOD V2

 

so I am assuming that the lean condition is what is causing my "tugging" issue.. I may be wrong..

so while I am looking at it this pic, I can see that the load/ipw drops of right when we start going lean.

makes sense..

But why?

the bottom trace shows the MAF_Calcs AND MAP_Calcs and Load.

The first two of which are NOT really changing..... maybe its a temp correction... let me have a quick look

edit - The ECT/MAFIAT and MAT are all flatlining, ie they arn't going up or down.. so its not a temp correction..

 

ok - so it looks like a Load calculation issue...

my boost is dropping off - which is causing the Load to read lower...

Here is a bit of a better pic - things scaled properly

 

what kinda looks like is happening:

at point #103, the ECU decides that the MAP signal has become unreliable (maybe because of that sudden increase)

so the ECU starts to interpolate to the MAF signal (hence the smooth downward turn from #103 -> #123

 

Rather than worrying to much about the internals of whats going on - I think I am going to increase my MAFScaling to the full 1.8x instead of my conservative 1.6x.

That will bring the MAFCalcs a bit closer to MAPCalcs.. And should reduce the lean problem if the ECU decides to "choose your own adventure" with the Load variable..

 

So I used a 1.7x multi for MAF Scaling - instead of 1.6x and it seems heaps better:



I would like to work out what's going on with the load humps (ie @ 6031)

 

Tephra,

I am having this issue also. I thought it was maybe the transmission (GSR) and/or transfer case. I was going to take my car over to Sheps this winter to have them do the "upgrades". I only feel this "tugging" or like you said driving in a head wind while i am cruising down the interstate at 70-80 mph. My mods are FP Red and pretty much all supporting mods except for cams. My internals are stock.

 

what intake do you have?

I bet if you log AFR and then when you feel it occurring hit WOT (just for a TPS reference marker in the log) you will see it going lean..

 

I have the Akuma 3" Intake. I got the intake scaling off of John (@ Akuma) when Michael (Golden) and i started tuning the car.

How would the MAF scaling be affecting this, since we are feeling this "tugging" during cruise? I thought at cruise the car is in closed loop and does not use the MAF scaling?

 

in very simplified speaking:

if the MAFScaling diverts too far from the MAPScaling then when the ECU goes to calculate Load it can get it slightly wrong.

you issue may be completely different, but log like I said, if it's lean then you can work on it

 

I wish i could take it out for a drive and log it but it is put away for the winter I think my scaling could be off because when i did some WOT pulls my AFR would not be consistent from pull to pull but my fuel trims are within 1 so i think they are pretty good. I am new to tuning but have learned alot from the forums and Golden. I dont know if it could be my fuel pump (DW300) but i am going to rewire it this winter and put in a new Fuel pressure regulator with fuel pressure gauge.

 

Hey Tephra, does it mainly happen when cruising in 4th or 5th? I also have the taller final drive in my car. I've noticed under certain conditions my car almost has a tugging, very light shuddering feeling. Initial thoughts were surge related, so recirculated the diverter 100% and that helped. Yet it still did it, even with a bone stock diverter I could replicate it. What I may be describing could be different but the symptoms sounds about that same.... I just dont have the logs. Since it felt surge related I have upped my hotside on my CBRD 33rb turbo from a .63 to a .82 housing. Hoping that helps. Looks like Bryan may be tuning my car soon in person which I'm happy about. Crossing my fingers.

 

I have a ralliart and using one of Bryans basemaps, 2.7.016. I have the exact same feeling in my car, not as much at highways speeds, but i'd say in 3-4th gear at around 40-70km/h. I was discussing this with Rich and used the exact description of feeling like a wind is hitting the car. When I am able I will try to log same parameters as you and see if I have a similar pattern. Just glad to see i'm not the only one feeling something like this and not me being crazy.

 

sub'd for info.

 

Dave - i have been spending HOURS on this same issue aswell. except i have kinda the opposite .... AFRs at cruise sit in 14s and then suddenly go to 9s and 10s for no apparent reason (using cruise control on the freeway!) , and every now and then go up around 16.

I too thought it was from when MAF and MAP Loads drift too far apart. Glad we're on the same page. Have been doing lots of tweaking to bring them in line with each other at all rpm/load points and things are much better - now they are generally 10-15 apart (rather than 20-30) my fuelling is more stable.
I was getting Load calc switching aswell, almost seemingly at random.

I have to say, this setup has been a b!tch to tune, getting it all perfect at part throttle and cruise.