Knot 4 Me

IAC does nothing off idle once you get the throttle blade opened up..

Sydwayz

iTrader: (1)

I wouldn't think so, but it's actually "Intake Air Controller", not idle air controller (per Mercury). When you have a sour IAC, it affects the engine at multiple RPMs. That's what has me wondering. I swapped them anyhow, and I have a new spare.

BUP

iTrader: (9)

Some of the terms for PCM / 496

IAC = Idle air control and it is described as working PWM = Pulse width modulation not IAC counts for the PCM apps.

IAC PWM% = Idle air control valve duty cycle percent

IAT = Intake air temperature

IC = Ignition Control

Idle map str = Idle rpm MAP strategy and this is the same as MAP idle check.

T-RAV

iTrader: (1)

I had a similar problem, but it had backfire in there also on both motors one this year and one last year. Last year it was a crank sensor, this year it was plugs.

MER Performance

Brian,
Did you happen to read the TPS closed to WOT? I believe; the IAC is held open to a certain percentage over idle. If it's responding properly to changing loads, start-up and ramp down, I wouldn't expect it to be bad. Your fuel pressure should increase under lower MAP. If you didn't already do it, just check to see the difference in fuel pressure between the 2 engines.

Sydwayz

iTrader: (1)

Was the crank sensor throwing a code/signal/beep? I have a spare one as well.
Thanks!

Sydwayz

iTrader: (1)

40PSI on both engines at the fuel rail, as soon as I charge it. It drops slightly/briefly when I bring it up to 3000 rpm on the trailer in neutral, but catches back up.

TPS with the engine off at:
Idle: 1.5%
WOT: 87%.

It was at 77% at WOT, but I did some adjusting on the cables as thought I might have a little cable stretch/adjustment issue. With the engines off, I used the Rinda to calibrate both engines to the 1.5% and 87% numbers.

Sensor voltage at 5VDC appears to be fine, and the TPS follows suit when adjusted with engine off and 1000-3000 RPMs in neutral. I'll check again running it today.

Thanks for your time Mark!

T-RAV

iTrader: (1)

Nope threw nothing. I was reading threads on backfire and did plugs that was no change and someone had said crank sensor so I gave it a try and it cleared right up. I will say when I did plugs on mine this year it was like you described, not a huge difference in them, one looked a little lean. Changed them anyways and it cleared everything up. Are you getting backfire when under load?? Like coming on plane?? It's probably something simple...

Sydwayz

iTrader: (1)

No backfire.
For future reference; backfire under load is indicative of fuel boost pump failure as well. I have a spare, but have not installed. On all of my checks so far, I don't have any fuel pressure issues. I will re-check this afternoon.

T-RAV

iTrader: (1)

Sorry yes the fuel pressure was always the first thing I would check. Good luck! Keep us posted on what you find.