Secondary Adjustment
So here is an interesting one. A month or two ago I took my unit to Fitech to have the ECM replaced under warranty. It would die whenever it got hot. Anyway, unrelated to that issue, after they replaced the ECM I reinstalled the unit, but now it wouldn’t idle. After emailing back and forth a few times with them, they had me replace the IAC with no change to the issue, and finally bring it back down to them. They put it on a test engine stand and it worked fine. Note: their test engine is a 350 SBC. I was kind of baffled at this, but I begrudgingly took it back home because they said there was nothing wrong with it.
Put it on my motor, still wouldn’t idle. Note: my motor is a 468 BBC. I noticed after trying to watch it try to idle that the AFR was dipping to 11.1 even with the IAC at full open. So I kept turning up the butterfly adjustment screw until it would idle, and finally adjusted it so that the IAC steps were in range.
I was surprised to find that I was at 3.5-4 turns. Way more than Fitech said it needed to be, but this ultimately solved my problem, and it was back up and running fine. Fast forward a month. I was making some adjustments to my throttle cable, and I noticed that while fully opening the throttle, the secondaries were not opening all the way. I debated if I wanted to play with this, but untimely I did. I adjusted the threaded rod so that the secondaries hit the end stop at the same time as the primaries.
I think here is where all my mysteries are explained. Because the secondaries were not opening all the way, they also were not as open as the primaries were in the closed position, resulting in less air going through the butterflies at idle. This explains the 3.5 turns to get it to idle. Now I’m back to 2 turns.
Now, how did it get this way? I am assuming that when Fitech took the unit apart to replace the ECM, they took the linkage apart and didn’t adjust it properly when they reassembled. I assume it was adjusted properly before because it’s unlikely they touched the adjustment screw and it idled fine before at around 2 turns.
As to why I mentioned the engine sizes, it takes far less air to idle a 350 than a 468. This explains why it idled fine on their test stand.
Just thought this would be good information for everyone in case someone else runs into something like this.
I am certain that the primaries and secondaries should be adjusted to be in sync. It didn’t make any sense that the secondaries were not opening all the way.
Penny for anyone’s thoughts.
I had to adjust the secondaries as well. In my case, it was that when in idle, the secondaries were open slightly more than the primaries so there was not enough resistance from the linkage to keep the secondaries fully close. This caused the secondaries to stay open sometimes leading to a "hanging" idle situation. I adjusted the secondaries so when in idle the linkage is in "contact" with the primaries. This solved the issue.
Elsewhere in this forum I explained this issue and criticized the fact that FiTech makes no mention of the secondaries adjusting screw. I guess their premise is that it shouldn't be adjusted, but in some situations it needs to. I didn't even realize it existed until after two years of ownership and headaches with hanging idle.
My answer from Fitech when I could not get my IAC above 0-1 - it worked. In my instance it appeared the rear blades were held open too far even though the front blades are used for adjusting the IAC. Different problem to above, but indicates that adjustment of rear blades may be necessary.
On setting the IAC I would kind of start over. You want to look at both idle set screws which on this unit is on the throttle linkage side of the throttle body. Make sure that the rear throttle screw is making contact with the adjustment arm of the rear blades. If it is not, screw the set screw in until it makes contact with the arm and go ¼ turn in making sure you see the blades move. Most common issue is people setting the IAC with the front blades only, this will cause all types of idle and running issues. Let the engine get up to operating temperature 165-170 or higher then you will adjust the front and rear throttle blades until we get the IAC number under 10 but not stuck on 0. If it is stuck on zero you will unscrew the throttle blades front and rear until we get a reading under 10 but not staying on zero. If it is above 10 you will screw in both front and rear screws until the number is again under 10 but not sitting on zero. You want to do this adjustment with the car in park or neutral and no AC on. Once this is done you will wan to shut off the engine and let the ECU power down (about 30 seconds) and this will reset the TPS back to zero and you are now good to go. You should see the idle catch itself when you go from park to drive or any accessories turn on like the Fan or AC. Hope this helps.
Thanks, this is nice info.
I am fighting a perpetual lean tip-in issue (3 years since I've owned the system, seems kind of ok sometimes, but never really fixed despite 50+ Accel and maxing out 3D Accel). In addition, over time I have had a number of weird issues:
Rpm's always drop very fast despite adjusting the IAC/RPM Decay
Erratic fuel learn changes under steady state throttle/RPM
Once in a great while, my idle and IAC values sit high (45 IAC, 1500 RPM), then go back to target RPM with 5-10 IAC.
Today, I noticed playing with the throttle body that I am seeing the same as DJ, in that my secondaries are noticeably less open than the primaries on WOT and at idle. There is a bit of play manually moving the secondary before the threaded rod hits the primary (at WOT and idle). I am definitely going to adjust the slack and redo the idle adjustments.
My question to start off with, is what is the point of the rear idle screw, and why wouldn't you just back it off? That way the front/rear are in sync, and then you just adjust the primary screw to get your IAC's at 3-10. Feel free to roast me if I'm missing something obvious.
Thanks again for this info, and I will update ASAP what I find, crossing my fingers this makes some sort of difference.
Justin
I would like to know that myself why cant it be set up just like a mechanical carb you press the pedal they all 4 open at same time and rate ,,, remember the old 660 center squitter holly's
I don't know if this is the correct way, but what worked for me was to adjust the secondary so there is no play in idle. You have to go back and forth between IAC and secondary adjustments until all is good. At full throttle my secondaries are slightly behind (maybe 90%), but in real life I doubt it will make any difference.
the other issue I have is I have the dual power adder and the throttle pressure is like 50 pounds lol I am thinking of trying to un hook the slave throttle body throttle spring
Quote from taylorteamracing on December 16, 2019, 7:38 pmthe other issue I have is I have the dual power adder and the throttle pressure is like 50 pounds lol I am thinking of trying to un hook the slave throttle body throttle spring
You may be able to unwind one turn, or less, off the spring to see if it works.
Quote from taylorteamracing on December 15, 2019, 1:36 amI would like to know that myself why cant it be set up just like a mechanical carb you press the pedal they all 4 open at same time and rate ,,, remember the old 660 center squitter holly's
I personally think there could be improvements in the linkage setup, and how FiTech checks it (or doesn't) for play.
I am going to to look at it long and hard and see what I think will work this week ill report back