496HO: would IAC cause this? 1 engine lagging intermittently lagging 100-400 RPM
#11
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IAC does nothing off idle once you get the throttle blade opened up..
#12
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.
#13
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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.
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.
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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.
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.
#17
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.
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.
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!
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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...
#19
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...
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.