Lil Truck
I spend to much time here....
- Joined
- Sep 26, 2002
The past 2 days I have been attempting to fix a stumble that occurs under full boost at 4500 and above.
See attachment.
Stock 109 41k miles
New cam and timing chain - 100 lb springs
55 lb injectors, with modified ECU
Power Logger
AFX Wide Band O2
Stock 41k MAF w/KN
Stock Coil pack & Module
Heated O2 sensor
New set of Autolite 23 @ .030
New set of GM 8mm plug wires
All sensors set to spec
HP fuel pump and hot wire set to 43lb no vac.
BB 2 step
VDO tach w Caspers mod
Caspers knock gauge
Alky kit single nozzle
Dyno run, 110 and alky.
History, this is an 87 GN modified for TSA class. For the last year it has been the additional modifications for street driving and has been running flawless on the street. At the track in 2nd gear I have been feeling a mild miss or stumble (no knock) it is 8th mile so it just gets into 3rd at the end of the run.
I thought it was just plugs and changed them. Idle was smoother and street driving crisp.
The attachment shows what it is doing from 4500 up to 5400 redline. It does not matter if it is at 20 lbs boost all the way to 30 lbs.
The Tachometer connection from the Dyno was attached individually to all 6 plug wires. Only 2 of the wire were consistently steady with spark even at idle. After the first day I changed out the spark plugs, spark plug wires, MAF, and the coil pack & module. All New GM Parts from NOS for GM and Kirban.
The first pull was much better than the previous day but still not gone. As the motor and parts got warmer the problem gets more noticeable. All 4 pulls on the second day were slightly better but the problem is still there? I disconnected the VDO tach, no change. Made I run low boost alky turned off, no change.
The only thing that shows on the Power Logger files is a loss of RPM when the stumble occurs, every sensor reads perfect.
I have 3 Coil pack and modules. The coils all test good cold or hot.
Can the Modules be tested?
Could the modified ECU be causing this?
I appreciate you input,
Thanks Steve
See attachment.
Stock 109 41k miles
New cam and timing chain - 100 lb springs
55 lb injectors, with modified ECU
Power Logger
AFX Wide Band O2
Stock 41k MAF w/KN
Stock Coil pack & Module
Heated O2 sensor
New set of Autolite 23 @ .030
New set of GM 8mm plug wires
All sensors set to spec
HP fuel pump and hot wire set to 43lb no vac.
BB 2 step
VDO tach w Caspers mod
Caspers knock gauge
Alky kit single nozzle
Dyno run, 110 and alky.
History, this is an 87 GN modified for TSA class. For the last year it has been the additional modifications for street driving and has been running flawless on the street. At the track in 2nd gear I have been feeling a mild miss or stumble (no knock) it is 8th mile so it just gets into 3rd at the end of the run.
I thought it was just plugs and changed them. Idle was smoother and street driving crisp.
The attachment shows what it is doing from 4500 up to 5400 redline. It does not matter if it is at 20 lbs boost all the way to 30 lbs.
The Tachometer connection from the Dyno was attached individually to all 6 plug wires. Only 2 of the wire were consistently steady with spark even at idle. After the first day I changed out the spark plugs, spark plug wires, MAF, and the coil pack & module. All New GM Parts from NOS for GM and Kirban.
The first pull was much better than the previous day but still not gone. As the motor and parts got warmer the problem gets more noticeable. All 4 pulls on the second day were slightly better but the problem is still there? I disconnected the VDO tach, no change. Made I run low boost alky turned off, no change.
The only thing that shows on the Power Logger files is a loss of RPM when the stumble occurs, every sensor reads perfect.
I have 3 Coil pack and modules. The coils all test good cold or hot.
Can the Modules be tested?
Could the modified ECU be causing this?
I appreciate you input,
Thanks Steve