1jz jerky deceleration

**1jzDan** · 20-09-2012, 04:12 PM

Hi folks,

I have a small issue with my 1j cressida. Its running a gt35r and sard 650cc injectors through a Haltech 2000. There is an issue of severe jerking on deceleration, acceleration seems to be OK.

Is there a common issue which may cause this or is it likely to be a tuning issue? The engine is a bit worn but seems to have reasonable compression.

Cheers.

**doommachine** · 20-09-2012, 07:05 PM

Haltech is likely the issue. Not that theyre bad ecu's but if it was tuned for "power runs" only and not driveability...

**1jzDan** · 20-09-2012, 07:07 PM

I would hope it was tuned to perfection considering the cost lol. I'm assuming there isnt anything I can adjust on it to make it better? Probablly better to get the tuner to fix it really.

**stealth** · 20-09-2012, 08:29 PM

Originally Posted by 1jzDan

I would hope it was tuned to perfection considering the cost lol. I'm assuming there isnt anything I can adjust on it to make it better? Probablly better to get the tuner to fix it really.

It'll be the decel. load settings. If the injectors turn off completely on decel. it'll feel jerky as all hell. In most tunes the fuel values will taper off with lower loads, my bet is it's tapering off too quickly, so the injectors are turning off too soon when you come off the pedal.

Can you download the software to tune Haltechs or do you need a license?

**1jzDan** · 20-09-2012, 08:38 PM

Oh ok, I have the current software, I used it to see what volts my battery had as I didn't have a multimeter handy. Can i adjust the decel or am I risking buggering the tune?

**midnight_purple_GA70** · 20-09-2012, 09:27 PM

should be able to adjust decell settings without too much of a drama... might be worth calling dale at castle hill exhaust and see if he would be able to somehow provide you with rough decell settings for your setup... he certainly knows his haltechs but not sure if he would be willing to tell you much over the phone... worth a shot

**stealth** · 20-09-2012, 09:49 PM

Providing you can talk to the ECU with a laptop, easy to change, not much risk involved, you're playing with low load, low rpm areas. Dunno about the software, but you might not even need to touch the tuning maps!

Make a save of the complete map before you change anything, good failsafe.

You need to add fuel in the low load areas, around -15 and -25 mmhg of load, from say 0-4000 rpm. Just go by feel, shouldn't need more than 10% adjustment.

OR.

Check if there's a deceleration fuel cut feature. This is the injector turning off thingy I was talking about.
There'll be a load setting (in vacuum - mmHg/psi), what ever this is set at is too high I'm guessing.

Don't have much Haltech specific knowledge sorry lol

**stealth** · 20-09-2012, 09:53 PM

i.e. a bit of a head scratch and play with a laptop, will save you $220/hour on a dyno

**1jzDan** · 20-09-2012, 10:07 PM

Thats awesome. I'll send the tune over to the Haltech forums, as a paying customer they seem to be happy to look over their customers maps. Rather than me totally fucking it up lol, but I might have a play in the mean time, after I save the original then I can reinstall if it doesnt work hehe.

Cheers for taking the time to reply!