Hey guys,

I have been trying to do some tuning on my Haltech recently and one of the things that I have been having trouble with is the transition from cruising to decel. When I let off the throttle the car will pop, sometimes loudly for a second or two and the wideband with go all over the place before finally going full lean. I was able to fix it by raising the stock injection time threshold to around 1.5 ms, but then my cruise control wouldn't work. The threshold has to be set all the way down to about .85 ms for the cruise control to work. Does the stock ecu ever call for less than .85 ms on decel???

I also noticed that if I watch the fuel injection time while driving it never does to 0, even when during no-throttle decel. Does this mean that the decel fuel cut is not even activating?

It never used to do this with the UTEC, because the stock computer was in control on decel.

 

If u want to see if decel cut is working monitor the 'Decel Cut Raw'. From my experience for cruise to work it is around 0.800 to 0.900ms.

If your injector dead times are not correct you may get a pop on decel also so insure your dead times are correct otherwise you will be chasing your tail.

 

You can also tune your max vacuum column to read lean... For me it's at -11 psi. I tune it to an AFR of 16 or higher. If you tune that column the AFR will not wildly fluctuate during the transition to a full fuel cut. I kind of like the split second burble though.

 

Wouldn't the max vacuum column also be the "no load revving" column? Wouldn't tuning that column lean cause you to have a lean condition when revving to take off in 1st? Or holding higher rpm for a drag launch?

 

Thanks, I will try monitoring the decel cut raw.

I didn't change my dead times from what Hal set them to. The latency numbers that came on the spec sheet from Deatschwerks are much much higher than what I have in the Haltech. It would suck to change them now because I would have to re-tune most of my fuel map! Plus, if I went with higher latency numbers, wouldn't that just result in even more fuel and thus more backfires?

 

I would check with Hal why he has not used the dead times off the spec sheet. He probably has a valid reason for this. Otherwise if you do change your dead times then yes a retune will be partially required

 

Injectors should goto 0ms on decel. Usually less than 2.0% TPS is a good place to start decel fuel cut. I believe default on the Haltech is 1.5%. You also want to make certain you are seeing sub 2% TPS while under decel or you going to struggle getting a clean decel cut.

 

Thanks guys!

I double checked my TPS and APS calibration and they are both correct. And I have my decel cut set to 2% TPS, .5 second delay.

I am hoping to log the decel cut raw along with IPW and TPS tonight to get a better idea of what is going on.

 

No, you never reach that high vacuum on take off. At least I don't. Only on decel. My Haltech display is up on my 7" touchscreen constantly so I have hundreds of hours watching that little cursor move around load sites.

 

How is that touch screen? Is it pretty easy to use for tuning? How much would it cost for something like that? I always thought it would be cool, but I wasn't sure how functional it would be.

 

What about cruising down a hill at very light throttle? I guess it wouldn't matter if it were lean in that situation though.

 

Yes it will go to high vacuum downhill. Like you said, the engine seems perfectly happy in the 16-18 range when there's no load.

The touchscreen is fantastic for gauge displays. It is very, very cool. The Haltech GUI is so flexible that the small display isn't that big a deal. Very easy to hit spacebar, P, and a number while driving to fine tune that fuel (probably better to have someone else drive!).



This was customized from a DigitalWheelz kit, but they don't make these anymore I don't think (you could check mp3car.com).

 

Popping could be a lean condition. I'd be curious what your A/F actually does when it's 'all over the place'. Maybe there is too short of a pulse width to the injectors during decel and the injectors are going on/off.

 

I double checked and the injectors never turn completely "off" during decel. I logged the decel cut and it is definitely activating (goes from 0 to 1) but the lowest the "injection time" ever goes is about ~1.4 ms. Is the injection time supposed to go to 0.00 when decel cut goes to 1?

I also installed my external MAP sensor and holy crap what a difference! I would highly recommend to anyone running a Haltech off the internal MAP sensor to install an external one with the shortest vacuum line possible. I logged both sensors simultaneously and it's amazing how much quicker and more crisp the external one responds! The car drives a LOT better too! Shifting has improved 10x. It also seemed to reduce the decel pops, but they are definitely still there.

dj- when the A/F "goes all over the place" it basically goes full lean, then shoots back to ~14:1 for a split second, then goes back to full lean and stays there. It is during this A/F swing that the exhaust pops.

Oh and just for fun, I tried setting the injection time threshold to 1.5 ms again. Sure enough the pops are completely eliminated, but the cruise won't work.

 

I don't know if it makes a difference or not, but I noticed in my logs that the transient throttle enrichment seems to never go below ~10%

???

 

I've actually had customers ask me to MAKE their car pop and gurgle on decel, because they like the sound. LOL

 

How exactly do you accomplish that? Because I will just do the opposite

It doesn't bother me that much I guess. It got a little better after I switched the the external MAP. The worst is when i am on the highway and I cancel the cruise...or when I rev match on a downshift.

 

I just fatten up the fuel in the low vac columns and take away some timing

 

I am going to try leaning out the high vacuum column.

I also noticed that in the Haltech Base Map for the 350z that they have the injection time threshold set to 2.5 ms! Why would they do this in the base map if it kills the cruise!?

 

oh the haltech woas. Mine is giving me a hard time. I don't think it's the haltech though, i think my car is possessed. I can't get it to drive smooth anymore. I'm leaning towards my injectors now. maybe it will be a simple fix like that.