600HP Power Adder - Accel and Fast Accel adjustments.
Hello everyone. I have done a lot of reading on this site and it is very informative.
I have a customer's 1981 Pontiac Trans Am with the 4.9L Turbocharged Pontiac V8. I deal specifically with this engine as a side business and offer the FiTech 30004 as a fuel injection conversion kit for these cars.
Engine Specs: 1981 4.9 (301) Turbo V8. As far as I know, the engine is stock except for 1.65 roller rocker arms and a free flowing exhaust with no cat. This is a draw through turbo with no intercooler. The throttle body has the plug in the base for a draw through boosted system and the MAP signal is from a hose off the intake manifold. Cam setting is at 1. Engine pulls 18" of vacuum at idle. IAC is 3-5. I know I should probably bring that up a little. Idle speed is 700.
Ignition: MSD Pro Billet locked out and using the FiTech Timing control along with an MSD Blaster 3 coil. Base timing is set at 12°. Idle timing is at 16° and adjusted from there based on MAP and RPM.
Fuel system: Spectra EFI direct fit fuel tank with Aeromotive e85 340LPH in tank pump (planning on trying e85). WIX 33737 Corvette fuel filter with 60 psi regulator. Pump is at 100% above 1500 RPM. Stock 3/8" steel fuel line with -6AN hoses to the throttle body. Fuel pressure shows 60 psi at idle.
The car runs great. It is a little shaky in the morning when cold (44° temps in the morning here in Wisconsin right now). There is supposed to be a coolant hose going to the carb plenum to help with cold driveability, but this was removed, so I can understand why it has some flaws when cold and the customer doesn't want it installed because it is a summer time cruiser so I'm sure during the hot summer, this will not be an issue.
My main problem is with the Accel 170 and Fast Accel 170. I still have the lean tip in problem. I have the Accel 170 pretty much maxed out at 95 and even started adding to the decay to get it to last a little longer, but it still tries to go lean and over compensate. Even fully warmed up it does it. Mainly when cruising, coasting and then getting back into the throttle. AFR goes 15-16 and then here comes the 10.4 after. Why can't I get this thing to go rich at tip in after 0 TPS? I would like to see an instant 12 AFR when I crack the throttle off idle or after coasting, but it seems like I can't get it to go there?
Some other info that may be needed. I actually lowered the cubic inch setting in the controller to 285 cubic inch from 301. My logs looked like the Trim % was always pulling on average 10-15% fuel. The 301 has some very inefficient cylinder heads and this seemed to help. But I wonder if this is effecting my Accel and Fast Accel?
Very interesting build.
Your cubic inch selection should not have an effect. Have you confirmed fuel pressure at the throttle body? Pressure drop during throttle change?
Can you send a Datalog?
Quote from Austin DeHaas on April 25, 2019, 10:25 amVery interesting build.
Your cubic inch selection should not have an effect. Have you confirmed fuel pressure at the throttle body? Pressure drop during throttle change?
Can you send a Datalog?
I just emailed a datalog to you Austin.
I still need to confirm the fuel pressure during throttle opening.
Just wanted to update what I found on this and that I think I have it solved.
The problem was with lean tip in and a hanging rich condition after.
The engine always felt like it idled rough. Almost to the point of a misfire. I checked compression and all cylinders were over 125 psi. All cylinders were firing when doing a cylinder drop test by pulling off spark plug wires.
No matter what I changed on the settings at idle, timing, AFR, the roughness never went away. I have a 1980 301 Turbo Trans Am with a factory Quadrajet carb that ran and idled better than this car.
I was at my wits end trying to figure this out and finally decided to swap the throttle body with a brand new one I had available.
Just bolting it on with no throttle cable hooked up, the engine seemed to run the same. Rough idle. I then tried to increase the throttle under the hood when I noticed it was stuck and would not move. Closer inspection showed that the rear throttle shaft stop linkage on the passenger side was rubbing the plenum that the throttle body mounts on. Closer inspection of the original throttle body showed it was also rubbing. Usually I cut or bend this part of the linkage when I sell my kits, but this car was converted by another person prior to my kit.
Bending the linkage out of the way and bolting the unit back on seems to have cured my rough idle. Aparently it was causing the throttle body to lift off the gasket in that corner and create a small vacuum leak that the computer couldn't consistantly compensate for.
Now the idle is smoother and the transitions from idle to acceleration are a lot smoother. Just need better weather to start putting some learning miles on it. The logs are not showing the hanging rich AFR. Acceleration settings still need to be played with, but it is running and sounding better already.
Thanks to Austin for all his help and feedback on this special case.