496 HO lost voltage to IAC

[RCAF_FB_FHDOG]

I have 2007 496 HO with manual controls. It started beeping codes at the end of last season. I replaced the MAP sensor and the IAC with filter due to their age.
I'm still getting codes, so I took it to the local Bass Pro for ECM scan. It had many hits for the IAC valve. We also tried to control the IAC stepping via the laptop.
We got no response. I'm checking for voltage on the IAC wires and get none with IGN on but no cranking. I do not see any wiring damage on harness at either end.
Has anyone ever experienced something like this before.

 

[alldodge]

What codes are you getting?
Does the motor die at idle but you can keep in running in throttle only mode?

 

[Bt Doctur]

See if this helps. from Man 36

 

[Fun Times]

Unfortunately losing the IAC driver inside the 496/8.1l engine PCM is a common problem. Typically the IAC gets stuck and may even eventually melt and in some cases the IAC connector will catch fire if not noticed in time.

The IAC driver inside the PCM shorts out If the wire harness connector gets damaged, the IAC seizes up or becomes hard working sometime caused by a dirty IAC muffler. Clean the throttle body and IAC passageway and replace the IAC muffler before installing a replaced or repaired PCM.

Also be sure to ohms check the wiring between the PCM and the IAC.

There is an option to repair vs buying a new PCM. Dennis @ Whipple Industries (AKA) Whipple Superchargers out of Fresno, CA is able to repair the PCM for less money than buying a new PCM. Information below,

Whipple Superchargers, the performance technology people, can now repair many of the 2001 to 2009 model year 555 ECM and PCM’s used on the Mercury Marine and Mercury Racing engines. Common issues such as the IAC failures and coil driver failures can all be repaired saving you thousands of dollars. No need to spend $2000+ on a new computer, just let the experts at Whipple fix if for you.

This is as simple as removing the ECM/PCM from your engine (3-bolts and 3-connectors), shipping to Whipple Superchargers and within a couple of days, you can have your ECM/PCM back ready to bolt on and go boating. No tuning, no reworking components, no head aches, just bolt on and go.

ECM/PCM repairs for some of the following: 200, 225, 250, 275, 300 XS engines. 135, 150, 175, 200, 225, 250, 275, 300, 350 Verado engines. 4.3L MPI, 5.0L MPI, 350 Magnum MPI (and Horizon), 350 Scorpion, 6.2 MX MPI, 377 Magnum, 377 Scorpion, 496 Magnum Base, 496 Magnum HO, 525HP EFI, 600SCI, 662SCI, 700SCI, 748SCI, 850SCI, 1025SCI, 1075SCI, 1200SCI.

Prices start at $500.
http://whipplesuperchargers.com/inde...&product_id=73

Since you live in Texas, iboats members are willing to help you out at no charge.

http://clubsearay.com/showthread.php...276#post398276

 

[RCAF_FB_FHDOG]

Additional info:
[FONT=arial, helvetica, sans-serif]Engine ser# OW652687. Engine runs and will idle. It will code after running a few minutes, or above 3000 rpm. When IAC was replaced, I noticed the far end from the solenoid had come apart. We scanned it with a factory authorized Panasonic laptop. Codes cleared, but then came right back. Tech was unable to step IAC up or down with his laptop. The connector shows no sign of overheating/melting. I appreciate the electrical schematic. I will ohms test wiring and check fuses. It smells like the IAC driver is fried, but these additional tests will be helpful. Thanks for the help.[/FONT]

 

[alldodge]

Additional info:
[FONT=arial, helvetica, sans-serif]Engine ser# OW652687. Engine runs and will idle. It will code after running a few minutes, or above 3000 rpm. When IAC was replaced, I noticed the far end from the solenoid had come apart. We scanned it with a factory authorized Panasonic laptop. Codes cleared, but then came right back. Tech was unable to step IAC up or down with his laptop. The connector shows no sign of overheating/melting. I appreciate the electrical schematic. I will ohms test wiring and check fuses. It smells like the IAC driver is fried, but these additional tests will be helpful. Thanks for the help.[/FONT]

With it idling my first thought is there is not an issue with the IAC, getting codes above 3K RPM suggest other issues. Would like to read what codes your getting

 

[RCAF_FB_FHDOG]

The only code showing was for the IAC. After replacing a burned fuse, voltage restored on pink wire to IAC (12v). No movement still on IAC plunger after this. I will check continuity on grn/blk wire to ECM next. If good, then problem shouild be in ECM. I will check next when lighting permits.

 

[alldodge]

While your at it check the shift switch on the shift plate. If the ECM thinks it's in neutral there will be a 2/beep when rpm's reach 3500 and will reduce power

 

[rossi45]

I had to do a functional test on my IAC last week to make sure it was getting power. I found this video very helpful. It shows how to test for voltage and resistance. Defintiely a good starting point before replacing parts.

 

[RCAF_FB_FHDOG]

I had to do a functional test on my IAC last week to make sure it was getting power. I found this video very helpful. It shows how to test for voltage and resistance. Defintiely a good starting point before replacing parts.

I didn't see the video link.

 

[1996Starcraft]

I had to do a functional test on my IAC last week to make sure it was getting power. I found this video very helpful. It shows how to test for voltage and resistance. Defintiely a good starting point before replacing parts.

I don't see the link either.

 

[achris]

I don't see the link either.

Because it a 4 year old thread.... Please read the forum rules.

Closed...