need help
Thread Starter
Racer
Joined: Jan 2004
Posts: 300
Likes: 1
From: Wollongong NSW
need help
a couple months ago rebuilt my l98 to a 383, got a "uni chip" installed to tune a/f ratios (this is a piggy back type of chip). Anyway my tuner got 12.5 :1 air/fuel right across the rpm range and dynoed it giving 375rwhp, decent power but when the rpm is under 2200 you cannot jump on the gas as the car will stumble and cough but from 2200 and above it runs hard. Also if rpm drops to 2000 and below the car is subject to intermittent stumbling/ coughing even when holding rpm steady, and you have to be real easy getting on the gas. because of this i can't use 6th gear on freeway or just roll through a corner as upon accellerating out the car dies, almost as if there is no fuel.
If anyone can help it would be great as this is p*^%$ng me off, my tuner is telling it is not in the tune
he thinks a sensor or the ecm is faulty or i may need an after market computer system. if this was the case why is it strong above 2200rpm.
My mods are in my sig. fuel pressure is 46psi
If anyone can help it would be great as this is p*^%$ng me off, my tuner is telling it is not in the tune
he thinks a sensor or the ecm is faulty or i may need an after market computer system. if this was the case why is it strong above 2200rpm.My mods are in my sig. fuel pressure is 46psi
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
It's too lean at low engine speeds and low manifold pressures (higher vacuum). On the dyno you're running WOT, which is at a higher manifold pressure range. Do the same thing at part throttle and you'll be in a different area of the fuel map. Go back and put it on the dyno, but instead of measuring HP at WOT, run it in the 1500 to 2200 rpm range with a small to moderate load (i.e something that requires a small amount of throttle) and check the a/f ratio there.
Dan
Dan
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
No problem. I should add that I've experienced the exact same driveability issues you're experiencing. I'm running an Accel DFI Gen VII+ and tuning it myself. Had it running great at the track and on the dyno for HP pulls but the driveability was very poor. I started focusing on those areas in the graph and richening those cells and it made a tremendous difference.
Good luck,
Dan
Good luck,
Dan
Thread Starter
Racer
Joined: Jan 2004
Posts: 300
Likes: 1
From: Wollongong NSW
dan
don't know much about tuning so sorry for the dumb questions,
are you running aftermarket computer system, if so did you need to add this in or will the stock ecm handle this with the help of the chip,
thanks again for your help, much appreciated.
don't know much about tuning so sorry for the dumb questions,
are you running aftermarket computer system, if so did you need to add this in or will the stock ecm handle this with the help of the chip,
thanks again for your help, much appreciated.
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
Hey, no problem on the questions - I wish I could provide more help. I'm running an aftermarket computer system, which completely replaced the factory ECU and wire harness. The factory ECU will work with what you've got though with the right calibration in the chip, but that's something I don't know how to do. And it seems like you should be able to achieve a good tune with the uni-chip.
Dan
Dan
