Boost lag in first and second gear caused by?

[Sean73]

I think it might be timing and gearing.

 

When you adjust the AFM for bigger injectors, you fool the ECU into thinking the engine is at a lower load point then reality to avoid overfueling. Unfortunately, the load (and RPM) is also used to set the timing according to the timing map.

 

So, essentially you're shifting the timing advance curve to higher loads. I bet in first and second gear, you are getting very little timing advance, because the ECU thinks there is no load. Without timing advance, spool-up is sluggish. It seems to be a flaw in the AFM tooth adjustment strategy.

 

The situation would be worsened by 3.9 gears, which won't load up the engine in 1-2 gears.

 

A way to test this would be to lower the boost level to the lowest setting of your MBC, then add a degree or two of timing at idle, and take a test drive. See if the extra timing makes a difference.

 

Also, you might have overshot the AFM adjustment a bit, since you are running lean off boost. Back off on the adjustment, and see if you can find a compromise between off-boost driveability and full boost safety. The happy medium in fueling might also find you a happy medium in the timing curve.

 

On my home-programmed Z31 ECU, adding timing to the vacuum section of the timing map makes a huge difference in spooling. Even so, I don't always reach maximum boost in 1-2 gears before having to shift with my 3.7 diff and 720 truck tranny (not good ratios for turbo car). I hope to fix this with a 3.54, and as much timing as possible in the vacuum portion of the maps.

 

Hope this helps.

[VinhZXT]

Thumper,

Sean73 is correct. Your problem is the AFM. I have stock T3 and stock EFI and for awhile I was having this same problem. The problem occurred when I was playing with my AFM awhile back trying to save some gas. I adjusted the AFM spring too stiff. I had to back it off a couple of teeth at a time and test driving it. Now I can get 4 or 5 lbs of boost on 1st gear and full boost on 2nd. There is a quick way to check this without boosting it also. Let your car cruise on 2nd gear at little bit above 3K RPM and watch your boost gauge. If it doesn't have enough fuel it will make sudden jumps. This is when it bogs and will not boost. Do that for all gears and you will see what I am talking about. Good luck

[Thumper]

I forgot about the ecu adjusting the timing from the afm. I now know it is not cause by fuel. I have gone from 10:1 to 16:1 a/f ratio and it changes nothing. I am in the process of putting a 3" exhaust on and a 3.545 rear-end. So this will help. Also installing an npr intercooler so I can turn my timing back up had it retarded 2 degrees for long pulls in 4th. So this all should help i'll let you know tom how it goes.

[Guest bastaad525]

Bigger exhaust and the 3.5's will DEFINATLEY make a difference, though i still doubt you'll see full boost in first gear.

[yo2001]

left foot braking and ebrake.

[VinhZXT]

I have a correction to make. After the adjustment of the AFM I get full boost in 1st gear and now I have no problem getting to the 5K RPM. Before that I had a hard time getting beyond 3K in 1st gear.. FYI.. Try to loosen a couple of teeth of the AFM and test drive it. I doubt the other stuffs you are changing will make a difference. Good luck