modded 402 idle/brake stall problem
02-27-2009, 12:01 PM
#1
Staging Lane
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modded 402 idle/brake stall problem This is my buddy’s car. It’s a 98 auto vette with a 402. Don’t know
the exact mods, but it has aftermarket heads, a cam with duration
in the 240’s, a ported fast 92mm, and a throttle body to match.
The fast intake and throttle body were recently installed and caused
the car to idle at 2000rpm. Normally it’s at ~1000rpm. It was tuned
before the fast installation by someone else, but still had some drivability
issues. The car was tuned to operate in open loop with the maf.
To start, I took out some idle airflow and got the idle down to ~1300rpm,
but if I take out anymore the car won’t crank. Any other tables I need to
play with to get this idle down some more?
This is the main problem. When you’re at a dead stop, if you try to stall
the car up timing goes to 0* and the car dies. But if you’re rolling and get
the car stalled up before coming to a complete stop, everything is fine.
In the attached scan in frames 278-463, you can see when trying to stall
the car up from a stop, timing drops and the map reading rises. At frame
1479, the car was stalled before coming to a stop and everything seems
to work fine.
Attached are the tune files. The “bastune” is the tune from the other
tuner. The other is the change I’ve made which is only in the idle airflow
table.
Thanks in advance.
the exact mods, but it has aftermarket heads, a cam with duration
in the 240’s, a ported fast 92mm, and a throttle body to match.
The fast intake and throttle body were recently installed and caused
the car to idle at 2000rpm. Normally it’s at ~1000rpm. It was tuned
before the fast installation by someone else, but still had some drivability
issues. The car was tuned to operate in open loop with the maf.
To start, I took out some idle airflow and got the idle down to ~1300rpm,
but if I take out anymore the car won’t crank. Any other tables I need to
play with to get this idle down some more?
This is the main problem. When you’re at a dead stop, if you try to stall
the car up timing goes to 0* and the car dies. But if you’re rolling and get
the car stalled up before coming to a complete stop, everything is fine.
In the attached scan in frames 278-463, you can see when trying to stall
the car up from a stop, timing drops and the map reading rises. At frame
1479, the car was stalled before coming to a stop and everything seems
to work fine.
Attached are the tune files. The “bastune” is the tune from the other
tuner. The other is the change I’ve made which is only in the idle airflow
table.
Thanks in advance.
02-27-2009, 03:29 PM
#2
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I don't have HPT, so I can't see the tune. There are a handful of tables that are idle-related. It almost sounds like a vacuum leak or perhaps a sticking TB blade (some brands out there seem to have that issue). I assume the Desired Idle Speed values. are set to a normal rpm like 900-1000 rpms. Just to make sure, I would check for a vacuum leak or a stocking TB blade first.
Did this problem start after you lowered the Desired Airflow value?
This is the main problem. When you’re at a dead stop, if you try to stall
the car up timing goes to 0* and the car dies. But if you’re rolling and get
the car stalled up before coming to a complete stop, everything is fine.
the car up timing goes to 0* and the car dies. But if you’re rolling and get
the car stalled up before coming to a complete stop, everything is fine.
02-28-2009, 12:24 AM
#3
Staging Lane
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I also thought it was a vacuum leak at first, because 1000rpm is a pretty
big jump. We sprayed carb cleaner all around the intake and couldn't find
anything. Desired idle is set to be at 1000rpm.
When he cranks the car the throttle blade is pulled shut. I don't think we
checked what it was doing while in gear.
He had the brake stalling problem before I lowered the idle airflow also.
big jump. We sprayed carb cleaner all around the intake and couldn't find
anything. Desired idle is set to be at 1000rpm.
When he cranks the car the throttle blade is pulled shut. I don't think we
checked what it was doing while in gear.
He had the brake stalling problem before I lowered the idle airflow also.
