I think were at, it does fine when cold but once warmed up the issues start, or for the most part. Have tried so many different fuel pressure things that just don't see it being pressure anymore. It has to be something telling the ecm to change control parameters. The real puzzler for me, is the ecm were swapped and it stayed with the motor, or did it? Sorry if its a repeat question

Are you sure higher IAC values mean it's closing down the air passage?
On my car, higher IAC values= opening up air passage. If that's the case, then It's trying not to stall.

The injector cleaning would be a good idea anyway when buying a used boat. Any idea when the prev owner had them serviced?

1. Yes

2. I agree now after adding fuel pressure with the adjustable regulator. The fact that the issue clears when the vac line is removed from the regulator and the pressure goes to 34-36 seems to simply be masking the real issue.

3. I agree and that's where my thoughts when I initially started the thread and began with sensors and modules.

4. Yes I swapped ECM's side to side and the issue stayed with the motor. The second motor ran as usual with the ECM swap.

Keith

Did some quick research and found you are correct 0 steps is fully open, blocking the air coming in anything higher is allowing air to enter. I'm still confused as to why the engine goes to needing more air to operate when hot at the same desired idle speed.

The previous owner did have both engine's injectors gone through; however, that would be prior to my purchase in 2015. At this point, I'd no longer consider the cleaning applicable. It's next on my list after re-checking the timing.

A buddy and I messed with the motor again tonight. It ran on idle from the time we started it and 30 minutes thereafter without stalling. That was until we blipped the throttle and it died instead of returning to idle.

We did notice when unplugging the MAP sensor the IAC stopped chasing from 20's to 40's, settled in the single digits and the engine ran smoother. The part I don't understand is why the MAP output wire had a value which was moving when unplugged on the harness side.

Shouldn't the output wire from the MAP to the ECU be dead when removed?

Keith

Unless the MAP is pulling more current, which drops the 5V reference, or the ground side of the MAP which is inside the ECM maybe be floating somewhat

The map was 2.0-2.2v when idling, the manual specs 1-1.5v.

Is what you are describing a harness issue?

The IAC controls idle speed only, not mixture. If the IAC number is rising, the ECM thinks the idle speed is too low for the current conditions. Injs (and carbs) don't like to sit for long periods. They can get gummed up. That's why your daily driver can go a long time between inj service but a boat that can sit for months at a time will need inj service much more often.

If you're seeing voltage on the sensor when it's unplugged, it's most likely a cap discharging or a bad ground on your voltmeter. Try the other eng but turn the key on for a few secs to charge up the circuits then back off before testing (make test same as bad side)

I went back over the last few posts and it's starting to look like a vac leak to me.
1. Idle quality improves when fuel press is increased.
2. Dies after throttle blip. Intake vac decreases then increased dramatically. This would make an vac leak worse as it drops back down to idle speed.
3. Your intake vac measurements right at lower limit.
4. Runs better when cold. ECM enriches the mixture at low eng temps which would help cover up a vac leak. When eng warms, mixture goes leaner making vac leak more of a factor.

You could use your scanner to compare MAP readings between both engs. Swap MAP sensors and repeat measurements to make sure MAP sensors agree. Make sure to take all MAP readings at exactly the same eng speed. Or just look for vac leaks the ol'fashion way with a can of carb cleaner and a fire extinguisher handy.

Thanks I will record the MAP readings of both (hopefully today) and report back. I'm also going to search for a vac leak with carb cleaner at the same time.

Thanks for hanging with me on this guys!

Keith

Ok tested both MAP sensors on the bad engine and both read the same.

Had the injectors cleaned, (unknown to me) repaired two stripped intake plenum bolts on the far port side, new ignition module, tested pick up coil, tested ignition coil, inspected cap, had ZERO water in fuel. Fired up and had the same issue stalling at idle when the engine warms up. IAC counts climb as the engine heats, as high as 72, max spec is 40.

After that I double checked timing and found it to be higher than 8* BTDC; somewhere north of 12* BTDC as the crankshaft pulley marks weren't even in the frame of the timing light. Was starting off somewhere left of 12* BTDC and I clocked the distributor from approximately an 11:30 position to 1:00 using a reference mark on the cap to get to spec base timing. At the point the engine was idling hot without stalling and vacuum was 15 which is manual spec for a hot engine. The IAC was still high and steps dancing around but not stalling.

When we're done dodging hurricanes and tropical storms I'll get it on the water to test and report back.

Keith