Im gonna RE-ITERATE on my false lean comment, at DEAD IDLE ive seen false lean even on 3" exhaust in a hot rod , its a well known thing in tuning world hence the delay auto learn until a few hundred rpms above idle and 2 or 3 % TPS , you should be manually tuning idle anyways, otherwise your idle afr will usually end up richer then it shows on afr gauge and it will be wandering all over, once your off idle you got nothing to worry about, let it do its job, just LIMIT how much it can tune/compensate, Holley sets the range way too high in factory settings.

Smitty,

The builder has it in open loop below 1000RPM and has been working on the idle tune manually. He also assures me the IAC wiring is correct, and that the volatile idle is due to the VE table not being dialed in.

I just checked, and the IAC is a 2-wire unit. I'm told that's the typical Ford PWM IAC, which is what Merc used for the 496, as opposed to the GM or Chrysler 4-wire stepper. I'm assuming this tosses the wire swap idea out...?

Thanks. Brad.

Guys,

So there have been a few…. Developments….

I don’t want to get into a bashing session on the builder, as I’m confident in the engine he built, mechanically, but he was struggling to get anywhere and admitted to not having a strong grasp of the Holley stuff. I have a new guy doing the tuning on the engine. A mutual friend turned me onto the guy that does his drag engines, and this guy REALLY knows the Holley stuff. After making a few changes to the basic tune parameters, like enabling “idle spark”, we have it starting at zero throttle and purring like a kitten…


On his suggestions, we also made some hardware changes…


The old Ford IAC adapter plate


Machining a block-off plate


Old IAC location deleted


New GM stepper IAC installed on the throttle body

No more hose from the IAC at the rear to the throttle body.

We also adjusted the throttle stop a bit. There is a ~5-16” hole in the throttle blade; OEM Merc. IAC now runs ~5-10%.

The TPS also seemed to be getting flaky and losing signal, so he gave me a new one. The new wiring is laced into the harness and everything is all buttoned up. Prop is on the drive and the drain plug is in. Looking at either tomorrow or Tuesday to head to the ramp for (hopefully) final tuning. I’m going to download the software on my wife’s laptop and he is going to to show me how to further adjust the tune through the learn table transfer. I’m hoping to not have to do that, but we all know how this goes.

Thanks. Brad.

Sounds good Brad. Since your wallet is open I'm thinking hydraulic steering, 280 K-Planes and a nose cone

glad you got it sorted out.can't wait for the water report

SecondWiind,

What on earth makes you think the wallet is “open”…? I wish…..

Baby steps, man. Baby steps.

Thanks. Brad.

Guys,





We had a very productive day on the water. We spent about three hours running the boat through its paces, live tuning using the closed loop learn function, from idle to WOT, including many planings of varying intensities. By the end of it, the “learn” was making 0% corrections from the base tune. Tuning is essentially done.

Overall, the engine runs very well. I’m a little underwhelmed with top speed, but I think much of that is the fact that the prop needs some work after finding the bottom early last year on this very lake (all four blade tips have reduced cup/pitch).

Thanks. Brad.

Brad what kind of mph did you see on the top end today? And what was your previous best mph?

had to feel great to get it back on the water!

Brad, is that the CFO doing a spot check on the finccial investment? Or Doing a DOGE investigation?

Glad you got the boat in the water and running up.

No shame on the builder. EFI is largely governed by known knowns, or cylinder bore washout can become a reality.

Don't be shy on the MPH...even if it's a bit less than you had before. The primary exercise was to repair and refresh the problem engine.

Tartilla,

I don’t begrudge the builder. I believe he built a stout engine. Part of me wishes he’d been more honest about his grasp of the Holley stuff, but then, if he had, I’d probably still have the 555, so…

No. That was the tuner’s CFO. They had to drop a vehicle off in the area, and she was his ride, so she tagged along. My CFO had to work. She was miffed about not being there, but glad we got it on the water. It worked out, as that gave us a chance to tune the engine at expectable weight loads.

We maxed out at 70-71GPS, which, if memory serves, was about all we’d get with the less-than-perfect prop, 600lbs of human and 3/4” tank of fuel. The tuner indicated that IAT was probably our primary limiter, at ~110-115° (ambient was ~85°). He wasn’t worried about it, just not getting the air we’d want for more power. We did see almost 5lbs of boost, though. The smaller blower wheel gave on the boost, but took on the IAT.

I am very happy. I think with a fresh prop, just the CFO and I and 1/4 tank, we’ll be back to previous performance levels (76-77MPH), or maybe a bit more. At the end of the day, I have a functional boat. With a few leaks (water and coolant) that I need to track down.

Thanks. Brad.