Ted G

iTrader: (1)

Okay, so I broke down and bought the Diacom software. I was scanning 04 525 EFIs that are having a stalling problem when warm. New IAC motors are already installed (not by me). So I go to the test section of the software and try the IAC test. Engine idling in neutral I start to run the percent up and down in the IAC test and the rpms don't seem to change?? Am I doing something wrong or is there no response from the IACs? All 3 motors seem to do the same thing when trying to test but only two stall when warm. No codes stored. It seems to me like the idle rpms should go up and down in conjunction with the percent up or down you dial in with the Diacom.

Ted G

iTrader: (1)

Ttt

Dave_N

Ted,
I use Diacom just about every day, and I can't remember ever doing an IAC test on a 525, but the IAC test should allow you to change the idle RPM as you open/close the IAC.

Is it a modified or stock 525? The two wire Pulse Width Modulated IAC's only work with engine vacuum, so I'm guessing that a big cam could affect the way they operate.

You might try powering the IAC directly as described below to see what happens.

Dave

Ted G

iTrader: (1)

Thanks Dave, that's what I thought, I'll try the pin test and see what happens. When I saw the IAC test I figured it would be a snap, guess not.

Oh, BTW the engines are still factory sealed bone stock.

Dave_N

What are the IAC's doing? If they are already mostly open at idle you won't have much "dashpot" effect under rapid deceleration. In a few cases, I have had to adjust the throttle plate stop screw to achieve a lower IAC count at idle, more "room to move " for the IAC, and therefore more resistance to deceleration stalling. However, I have never done this on a ECM/PCM555 system.

Can you post a screen shot of the IAC activity (from the graphs screen on Diacom). Graph the IAC position, engine speed, and throttle position.

Dave

Ted G

iTrader: (1)

Thanks for the input Dave, I will try and get some more Diacom info up. But it is gonna be tough, the engines will usually only stall after running hard for a while. Yesterday we also got a check engine light while they were running, but the owner turned the batteries off and I couldn't get a code out of it after that. We did find fuel pressure on one at 60+ psi so that needs to be fixed first, but the IAC thing has me stumped.

Ted G

iTrader: (1)

tt

Ted G

iTrader: (1)

Okay, follow up, just for kicks.

There were a few issues causing the problem. The tech that worked on them before was told by Merc to adjust 30-35% IAC at idle in gear-can't be done. They need about 50 or so in gear and 35 out, but even at those settings there was an issue. Turns out that this boat had the Neutral switches disconnected because they were acting up and putting it in protection mode. We hooked one of the switches back up and watched the IAC numbers. Turns out that the ECU will drop or raise the IAC percent approx 10% instantly when the Neutral switches show a shift out or into gear. If the switches are not hooked up the IAC percent will eventually get where it needs to be, but in that time frame the engine can stall. Gotta love some new technology and an old school tech