idle RPM and IAC counts are not responding

[mmigacz]

The winter is finally starting to lift in Wisconsin. I pumped water into the block of my boat and started messing around with the idle today. Below is brief summary of my setup:

-351W ford engine
-ski centurion, straight inboard boat
-mild cam
-gt40p heads
-1227747 ECM
-fuel pressure 18psi
-5.7L injectors (truck)
-no EGR
-no VSS
-no O2 feedback (running in open loop for now)
-No Knock sensor (esc)
-Manual transmission set-up
-I do have a wideband hooked up
-I do have an emulator

I got the engine to idle pretty good at 1050 RPM. The crazy thing is, the closed loop idle is set at 850 RPM. The other crazy thing is, no matter how much I open the throttle blades (idle adjustment screw), the IAC counts will not come down. They seem to hover around 79 counts. I attached my bin and and a log file. I let the engine idle from the beginning of the log to about 48 seconds.

Any idea's why the idle won't come down or why I can't get the IAC counts to lower?

6822

6821

[steveo]

-no VSS
-no O2 feedback (running in open loop for now)

...

I got the engine to idle pretty good at 1050 RPM. The crazy thing is, the closed loop idle is set at 850 RPM.

...


not that i know anything about that ecm, but think about that for a second ...

[mmigacz]

Sorry, the part I need advise on is:

It won't idle less than 1050RPM, even though I have it set at 850.

When I say closed loop idle, I mean the IAC is in closed loop, trying to maintain a consistant idle RPM (850 target).

I could be wrong, but I didn't think the target idle RPM needs o2 feedback to be maintained, right?

[jim_in_dorris]

Too much airflow past the throttle blades, screw the stop in and watch the idle.

[EagleMark]

How many IAC counts when this is happening?

Yes, Desired Idle in $42 is CL and fully warmed up. Most boats run a low thermastat and never reach what a stock bin thinks is warmed up.

EDIT: Data log shows 160*f, it's not warmed up. IAC counts are in 80's and keeping idle high because it's cold. I'll look at your bin in the AM and see if I can make the changes needed to be warmed up at 160*f and lower your IAC count for cold...

[mmigacz]

Any idea's?

[EagleMark]

Yeah lot's of ideas and then I saw your cam specs and this is in a boat, no O2 so how do you tune it? Fuel VE1 table has some major issues...

Even if you got the idle down to 850, in a boat that is not going to be low enough RPM to get into gear... BANG! Even if you have a blip switch. Then take off and be to fast for no wake or docking.

Anyway here's your bin back with a couple changes to get IAC counts lower, but I'm not sure with a 160*f thermastat and no O2 sensor OL does not respond to desired CL idle as well as CL.

[steveo]

many marine boxes of the single lever variety also advance throttle slightly when in gear all on their own, or the linkage can be adjusted to do so.

he's also a shaft drive probably with a pretty soft transmission engagement, so engagement at low idle might not even be a problem.

with a boat i might just ditch the IAC anyway and just use the blades. it's not like you need any of the fancer IAC stuff like throttle-speed follower, and you spend very little time at idle in a boat, so a bit higher of an idle wont hurt anything. people are generally used to cold-starting a boat with advanced throttle anyway, which im sure would work fine.

obviously this thing is dry exhaust above water? fresh water use only?

no real reason you cant use an o2 sensor, but shouldn't really be necessary. boats are pretty easy to tune, you dont have a lot of load variation, it's only going to use a very small portion of the VE and timing tables. there's pretty much a 'getting on plane' and an 'already on plane' zone in those maps, and you'll almost never be outside of them except in weird situations like dropping the throttle hard from plane, or trying to climb a giant wave with a boat full o' people.

[EagleMark]

Boat tunes spark advance and VE tables sure don't resemble car tunes!

[steveo]

welcome to my world.. boats are what i do.. always throws me for a loop. at least inboards are car-like.

you want to see weird FI, look at some of the outboard crap i deal with...

"65kpa at idle and 60 kpa at wide open throttle, but 20kpa while cranking!? what the hell..."

"20 degrees of idle spark...... ATDC!? on a four stroke!? that cant be right.. well i'll be damned."

"one exhaust cam is advanced 10 degrees, the other one is retarded 8 degrees, but the sensor says they're both retarded 15 degrees? if i fix it, it doesnt start?? must be by design..."

[Fast355]

welcome to my world.. boats are what i do.. always throws me for a loop. at least inboards are car-like.

you want to see weird FI, look at some of the outboard crap i deal with...

"65kpa at idle and 60 kpa at wide open throttle, but 20kpa while cranking!? what the hell..."

"20 degrees of idle spark...... ATDC!? on a four stroke!? that cant be right.. well i'll be damned."

"one exhaust cam is advanced 10 degrees, the other one is retarded 8 degrees, but the sensor says they're both retarded 15 degrees? if i fix it, it doesnt start?? must be by design..."

Yea its hard to teach an old dog new tricks.....talking about the 350.

What threw me for a loop with my 350 powered boat was the lack of vacuum advance, still don't understand that logic.....Seems under certain part-throttle conditions the engine would want more timing. Unloaded at 3,500 rpm I run ~30 mph on plane on the primaries of the Q-Jet and pulling nearly 12 in/hg of vacuum. With a full load and a skier or two I am same RPM and only 6 in/hg. Flat out it runs 4,600-5,000 rpm @ 47-50 mph depending on the water/load/etc and roughly 1 in/hg vacuum. My boat spends alot of time at idle or just off-idle at only a mph or two, sometimes for over an hour or more.

[Fast355]

Boat tunes spark advance and VE tables sure don't resemble car tunes!

Which I find weird in itself. I remember one of the GMEFI list guys doing a TBI conversion on a 4.3 in a boat. Claimed he used the stock 4.3 Astro van fuel/spark maps on the boat. Only tweaked the idle and away it went. Yet myself and others have had to completely re-engineer the tables.

[EagleMark]

The stock boat timing tables I've looked at are very flat and advance is always there, they don't pull a load like a car when accelerating, prop just spins faster till boat speed catches up, it's more like same load just increasing RPM. Defiantly a different world!

[lionelhutz]

Did you put a 10k resistor on the ALDL port/link? That's a pretty quick way to make it idle at 1000rpm.

[steveo]

The stock boat timing tables I've looked at are very flat and advance is always there, they don't pull a load like a car when accelerating, prop just spins faster till boat speed catches up, it's more like same load just increasing RPM. Defiantly a different world!

maybe on a ski boat, but most larger boats actually pull one hell of a load when they're getting onto plane, especially where i come from, where they're all big deep hulls. not so much with skiboats and lake fishing boats, they're pretty efficient and shallow.

two common acceleration vectors, one getting onto plane, one once its on a plane, and that's pretty much it..

the load depends entirely on the propeller design, gear ratio, and hull configuration, but obviously it doesn't matter much in the end, since all marine engines will run the same calibration no matter what hull the engine ends up being attached to.

but there's still a bit of variation sometimes, gotta be careful.

we had an outboard engine we played with a few years ago from a very big mfr, there were thousands of them all over the world that ran fine, but when we deployed them at this particular region, they'd lean out and explode almost instantly. hundreds of them.

it ended up being that the mfr didnt map it for the specific condition of 'flooring it to get up a giant wave, then back off really fast down the other side so you dont flip over', which turned out being due to a certain shape of wave that's uncommon in most places, but is pretty much year round in this particular fishing area.

the transitional air fuel ratio at the top of the wave actually leaned it out so bad it melted holes in pistons.

they were backing off the throttle, but it was still under quite a bit of load for that moment. this engine had no map sensor, it was fixed fueling based on TPS only. a new calibration from the mfr solved it, and they'd go for thousands of hours like that.

apparrently you dont really hear the loud popping of being very lean for a moment when your exhaust is underwater....

[mmigacz]

Eaglemark:

This isn't a stern drive (I/O) transmission. Its a velvet drive, which is a small automatic transmission that only shifts from nuetral, forward and reverse. Its a 1:1 gear ratio. I ran this engine set-up last year with a Holley 600. Idling at 850 isn't an issue when you shift into gear. I do have an exhaust riser that will except an oxygen sensor. Currently, I am tuning everything with a wideband. I understand that my VE table needs alot of work, but working on the idle was my first step.

I appreciate the feedback. When I'm done looking through your suggestions, I'll most likely have some follow-up questions.

Steveo:

This is a wet exhaust, but the O2 is in a location that does not get wet. The O2 bung passes through the water jacket, into dry exhaust chamber. The mixing of water and exhaust happens abount 12" after of the O2 bung. I'm probably going to add a narrow band for closed feedback in the future. For now, I want to get it dialed in with the wideband.

Wouldn't the IAC be beneficial when shifting from nuetral to drive and vise versa?

[steveo]

Wouldn't the IAC be beneficial when shifting from nuetral to drive and vise versa?

only if the ecm has advanced knowledge that you're about to go into gear, otherwise nah. most marine engines only have one idle speed setting in gear or out. like i said earlier, a lot of control boxes will advance throttle a bit when you go into gear anyway.

[mmigacz]

Eaglemark:

I tryed your suggestions, and did get the IAC to lower to 20 steps, at the desired 850 idle RPM.

Thanks!

[EagleMark]

:happy:

[mmigacz]

Eaglemark:

I have couple questions with regards to some changes you recommended. I had the below tables set up like:

6908
You suggested to change them to:

6909
Can help me understand what these changes are doing?

[EagleMark]

Well the TPS% is to keep it out of PE unless it's really needed... 80% TPS.

The other is to keep it closed loop idle. Which may have been an error on my part?