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Hey everyone, been a minute since I've been on here. Got tasked to tune a holley efi on a big block 454 with hillborn individual throttles that is running extremely poor. Right off the bat it would barely run and it was discovered that the distributor was timed incorrectly, which was resolved. I am new to the holley efi platform so it has been a bit of a learning curve for me. The main issue I was having was a huge discrepancy in AFR from bank to bank. The engine refused to run smoothly above a 13.6 afr on the passenger side bank, while the drivers bank was operating at a pig rich 9:1 AFR(running on pump 93 gas). This was with the same injector pulsewidth across all cylinders. The dominator ecu to the best of my knowledge can not do 02 control on seperate banks. It only gives me the option to run left, right, richest, leanest or average. If I attempted to run the engine below 13.6 at idle and cruise it started to backfire out of two trumpets on the passenger side. I swapped the injectors from bank to bank with no change in the issue. At this point I decided to do a dynamic compression test to see the health of the engine and came up with some alarming numbers.
1 -130psi drivers bank
2-150psi passenger bank
3-150psi drivers bank
4-155psi passenger bank
5-135psi drivers bank
6-185psi passenger bank
7-155psi drivers bank
8-179psi passenger bank
The two highest compression cylinders (6 and 8) ended up being the two that were backfiring. It was decided the engine would be removed and dissembled. Upon inspection the lowest cylinders had broken rings and the cylinder walls appear warn on most of the cylinders. Further the valves on cylinders 6 and 8 were white, which I interpretted as running lean.
My conclusion on this was that the variation in afr was due to lower VE in the cylinders that were running rich and higher VE in the cylinders that ran lean with the collector AFR reflecting an average of this. I am curious to see what you guys think of this situation and if the conclusion I came to is correct. Thanks in advance for comments and suggestions!
Do you have experience tuning individual throttlebodies? They're a bit of a different animal, because you don't have a normal manifold pressure signal.
This is my first time tuning individual throttles. This set up uses a vacuum manifold in the center of the V with lines from each intake runner to it and then a line to the map sensor from the manifold. Vacuum is definetly lower then I am used to seeing but does read consistent map signals. How would the effect bank to bank variation though?
Are you running sequential injection, semi sequential, or batch fire? It's unusual to run MAP based control on ITB's. It's usually Alpha-N (throttle based). Also, which Holley are you running? Most of those are meant for bolt on throttlebody injection/downdraft style manifolds. ITB's are not so straightforward. How is your acceleration enrichment set up? Where is the throttle position sensor? So you have separate widebands located in the exhaust? So where is the closed loop fuel controlling to?
Did you speak to a Holley rep at any point on which EFI product to buy and how they recommend to set this up?
Assuming your ECU can be configured to work well with an individual throttle EFI setup, it's still very important that all eight of the throttle stops are mechanically sync'd so each cylinder gets an equal amount of airflow at idle. A sync tool like this one should be helpful: https://www.efihardware.com/products/325/Synchrometer-Flow-Meter
It's also important that the mechanical linkages open each throttle blade similar amounts at low throttle angles, or you can end up with drivability problems and bad behavior from some cylinders too rich and others too lean when you're trying to drive the car. If the airflow sync tool measures high enough to be used when you're pressing the gas pedal a little, I would check that also.
It's extra work, but doing a compression check and using a timing light to verify spark for each cylinder is happening at the correct angle is a good plan and can save headache later down the road. You may need to add marks to the pulley to check some of the cylinders, paint pen or a sharpie marker usually works well for this. This is especially true if working with an unfamiliar ECU. I've received logs from tuners who did multiple full-throttle dyno pulls and didn't realize the engine was down on power because only 7 of the 8 cylinders were firing, it can be difficult to hear on high-strung V8 engines.