H/C/I 98 Z won't idle/ surges
08-18-2010, 02:52 PM
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H/C/I 98 Z won't idle/ surges Whats up guys-
I'm going to buy a 1998 Z/28 tonight, and I have a question about the car not wanting to idle and stalling out when you start it.
Mods:
Stock bottom end
ported stock heads
.581 comp cam (guess it would be the 224/224)
Long tube headers
LS6 intake
TCI 4l60e
Not sure about injectors or throttle body but looked stock. It has been in the garage for last 4 years since he stopped buying a tag and trailering to the track and he was scared to drive on street. Cranked monthly if not driven.
So the car starts up good but then gets real rough with the idle and stalls out. Its fine if you give it some gas to keep the revs up. Car soudns real clean if its revved up and runs REAL strong.
It just doesnt idle well when cold, and will still stall out when warm but I haven't seen it really up to operating temps yet.
He said that is was tuned several years ago at a local dyno shop and put down 360/380HP.
So what happened to the car? Has the battery went dead and it forgot idle tune up? Does this seem like a car that hasn't been tuned?
First thing I'm going to the local dyno tomorrow and have hit correct the idle maps with HPtuners for drivability.
Just wondering if its safe to drive home, and if it learn more on its own until I get it tuned. Also, when the computer switches over to the 02's the A/F should be safe with the mods right?? Until I get a full tune done on the dyno?
I owned a motorcycle dyno for a while so I'm trying to now learn ls1 ECM etc.
JP
I'm going to buy a 1998 Z/28 tonight, and I have a question about the car not wanting to idle and stalling out when you start it.
Mods:
Stock bottom end
ported stock heads
.581 comp cam (guess it would be the 224/224)
Long tube headers
LS6 intake
TCI 4l60e
Not sure about injectors or throttle body but looked stock. It has been in the garage for last 4 years since he stopped buying a tag and trailering to the track and he was scared to drive on street. Cranked monthly if not driven.
So the car starts up good but then gets real rough with the idle and stalls out. Its fine if you give it some gas to keep the revs up. Car soudns real clean if its revved up and runs REAL strong.
It just doesnt idle well when cold, and will still stall out when warm but I haven't seen it really up to operating temps yet.
He said that is was tuned several years ago at a local dyno shop and put down 360/380HP.
So what happened to the car? Has the battery went dead and it forgot idle tune up? Does this seem like a car that hasn't been tuned?
First thing I'm going to the local dyno tomorrow and have hit correct the idle maps with HPtuners for drivability.
Just wondering if its safe to drive home, and if it learn more on its own until I get it tuned. Also, when the computer switches over to the 02's the A/F should be safe with the mods right?? Until I get a full tune done on the dyno?
I owned a motorcycle dyno for a while so I'm trying to now learn ls1 ECM etc.
JP
08-18-2010, 02:55 PM
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Oh yeah-
The car was REAL rich at idle and almost ran us out of the garage.
I'm hoping to drive it 45 miles home so I just hope that the tune-up is not real lean until I get it tuned.
The car was REAL rich at idle and almost ran us out of the garage.
I'm hoping to drive it 45 miles home so I just hope that the tune-up is not real lean until I get it tuned.
08-18-2010, 03:07 PM
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Without looking at the tune you can't be sure if it will go into closed loop (run with feedback from the 02s to keep it at stoich) or if it has been tuned to run just open loop. If it is open loop then you have no idea what you're dealing with unless you have a way to scan while driving, preferably with a wideband. Running really rich at idle and stalling are indicative of trying to run a cam on a stock tune, but it could also be a case where it lost the long term trims and is struggling to relearn due to a dead battery if the tune wasn't done right the first time. With no information I'd be cautious about driving it.
08-18-2010, 03:15 PM
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Without looking at the tune you can't be sure if it will go into closed loop (run with feedback from the 02s to keep it at stoich) or if it has been tuned to run just open loop. If it is open loop then you have no idea what you're dealing with unless you have a way to scan while driving, preferably with a wideband. Running really rich at idle and stalling are indicative of trying to run a cam on a stock tune, but it could also be a case where it lost the long term trims and is struggling to relearn due to a dead battery if the tune wasn't done right the first time. With no information I'd be cautious about driving it.
We did drive it around for 5-10 minutes, and it pulled real hard and temps looked good. But it never really got up to operating temp,so being real rich may also have something to do with that.
I'm going to buy EFIlive now that I'm getting the car. Only scanner I have now is a handheld code reader and Im not sure if it will read when the car is on and what feedback it has for me.
08-18-2010, 03:24 PM
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EFI Life will get you straight, just spend some time learning the scanner, making logs, and then making small changes - you'll find it's the best 'mod' you'll ever do. Richness at idle is a common problem with a cam, and you must cut back the VE and RAF tables to compensate for it. It seems that some shops do a "dyno tune" by making some WOT runs to set the air/fuel and timing and just ignore everything else that effects drivability and idle. It may be worthwhile to pull the lid/intake hose and maybe clean out the throttle body and IAC motor to make sure it isn't sticking after sitting that long as well.
08-18-2010, 03:36 PM
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EFI Life will get you straight, just spend some time learning the scanner, making logs, and then making small changes - you'll find it's the best 'mod' you'll ever do. Richness at idle is a common problem with a cam, and you must cut back the VE and RAF tables to compensate for it. It seems that some shops do a "dyno tune" by making some WOT runs to set the air/fuel and timing and just ignore everything else that effects drivability and idle. It may be worthwhile to pull the lid/intake hose and maybe clean out the throttle body and IAC motor to make sure it isn't sticking after sitting that long as well.
I know what you mean.. Inertia only dynos are good for WOT A/F and some drivability tuning. I want my car tuned on a good dyno with load control. Thanks for the tip on cleaning out the TB
