Dies under hard braking
I'm down to one last issue on my FITECH install. Car is a 1980 trans am with a bored 455. RAIV cam, with Rhodes lifters, performer intake, ported cast iron manifolds, 2.5 inch exhaust with crossover. MSD ignition allowing timing control with the FITECH. Tranny is a Tremec 5 speed with 3.08 rear gears.
As it is tuned now, I get 12-16 combined mpg. I have gotten 22.7 on the highway running AC and 75-80. Vacuum at idle is 16 inches. Car is smooth and pulls to 5200 rpms easily. Starts hot or cold. Only starting issue is after it has sat for more than 3 days I have to let it spin a few more times, even if I let the pump pressurize the system first.
This summer I when I was running AC and would brake it at 60% or greater, the car would die. I thought it was due to the AC compressor causing drag.
Today I came up on my driveway too fast and got on the brakes a 70% or so and the car died during the turn into the driveway. Not so much fun as I lost power brakes and steering.
None of the times it happened, would I say it was full on panic braking. The car can brake in a hurry as I have tested it and it can do 60-0 in 98-104 feet. Car was in 4th or 5th gear at the time. I'm guessing something is off in the idle control settings but not sure where to look.
Any help is appreciated. The motor needs to stay running during hard braking.
Raise your loop up value on your idle control. Also disable your DFCO feature by raising the enable temp to its max limit.
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You may solve the problem with DFCO disable only. Start with that.
These steps are also usually necessary for stick shift applications. Most have difficulty shifting and bogging after shift with default settings.
I appreciate the help. I maxed out the DFCO enable temp to 300 and will try to drive it some this week. I usually try to make only one change at a time to eliminate variables.
Anytime it has died, the clutch has been engaged if that wasn't clear or makes a difference. I like the motor to be engaged during braking if I need to correct the car with throttle. I only push the clutch in if the car slows to such a speed that the rpms would drop below idle. I don't hit both pedals immediately under braking.
I'm pleased with how the motor responds during shifting but would always be interested in pointers. I did play with IAC values to try and smooth out rpm drops between shifts. I'm pretty consistent with around the town driving shifting at 2000-2200 and seem to have it where the rpms slowly drop to the needed rpms for the next gear. Don't know if that's what the IAC controls are for but it did seem to work well.
I'm still learning on these systems, but couldn't ever imagine going back to a carb.
Thanks again.
Let me clear up my comments. Your issue happens with some combinations. Nothing to do with the standard trans. Some guys with standards have trouble in between gears. Both issues have similar fixes.
Glad you are ultimately happy with your Fitech. I know I have a bunch of carbs collecting dust in my shop. We will get yours dialed in. Just be patient.
I turned off the DFCO and got to drive it yesterday and today. I watched the MAP and was surprised at how often it would dip below 28. I was really amazed at how long it would stay below 28 on long coasts to stop lights. Seeing that I started watching the AFR trim and it had to add a lot less after shifts than before. Shifts at RPM's 2500-4000 where much improved over before.
I didn't get to test anything more than 65-20 stops over the last two days, but it never died.
When it did it in the summer months with the AC on it was 75-20 stops. The one that did it recently was well above that. I'd say it was a long time for the fuel to be shut off.
Any downsides to running with the DFCO shut off?
So far so good.
You may find a small decrease in fuel mileage.
Update: I got an email back from Bryce explaining the Max Drop Rate setting on the DFCO menu. You can activate the DFCO and tune its sensitivity to fast RPM drops. Try raising the number to something like -100. Tuning this may be more suitable to your needs.
I'll try tuning the sensitivity. I got to do an 80-20 deceleration today and a 70-10 and the rpms held nice and smooth at 1000 rpms. On the 80-20 I noticed some faint popping in the exhaust.
Turning it back on and adjusting the sensitivity seems to have worked fine. I did lower the DFCO cut to 22 and the return to 24. I was seeing some MAP readings consistently below 28 and as low as 16. The faint popping is no longer heard. Thanks for the help.