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Old 05-27-2016, 06:07 PM   #1
not this alero
AleroB888's Avatar
AKA: Greg
Join Date: Nov 2005
Location: Fort Knox area, KY
Age: 68
Posts: 1,300
Vehicle: 1999 Alero V6
AleroB888 Gettin' there
New Engine, Misfires at Low RPM

Part I

This is a fresh rebuilt engine with porting of intake and heads, beefed up bottom end but a not too radical cam.

There are pretty severe misfires at lower RPMs, and vibration, but gets considerably smoother higher up in the RPMs. Top end torque is good, much better than stock. The misfires appear real, given the rough running of the engine, but the plugs look perfectly clean when checked. Exhaust vapor is clean. There is only about 200 miles on the engine so far.

In particular, this is a 3400 built-up block, 3500 heads, 3500 LIM, 3400 UIM. '99 timing chain, CR appox. 9.1, Cam is a step up from stock.

I had a local shop install the engine. When it was first fired up, they said it ran about 10 seconds then blew oil out the oil filter gasket. They put another filter on and it happened again. So I told them to replace the oil pump, which I still have. This time it stayed running, but only if the gas pedal was held slightly open. I drove it 3 miles home, but it ran very rough, a lot of vibration.

Originally, there was synthetic oil put in, but I drained it out after about 20 minutes of run time, 3 miles of driving, then changed to Autozone brand regular oil. The first oil was darker, but no visible particles. Second oil change at 50 miles, looked perfectly clean.

After some idling and low speed driving, the misfires remained. The power/ torque seems to be excellent, it does better cruising when above 2000 RPM.
I want to believe that there is some kind of ignition or electrical issue, but I need to hear all possible theories on it. It idles like an old Harley ....
1999 GLS MP90 supercharged / 2003 GL MP62 supercharged / 2004 GLS stock
Magnuson MP90 / TOG's / 3 in. Magnaflow exhaust / MSD ignition / LS1 MAF / Racetronix pump / HP Tuners / TCE 68mm TB / 36 lb Inj
= Best track time: 12.951 @ 104.48, 1.839 60 ft. (Beech Bend Raceway Park, 11-23-13), 50 Deg. F
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