Merc 600 SCI IAC 1 Amp Fuse Install
 

I want to install the in-line 1 amp fuse to prevent IAC failure damage to the computer. Threads talk about it but no real specifics. Can Someone take a minute and post info on what wire to install this on and any photos would be appreciated, Thank you!!

There are two wires connected to the IAC and I don't recall the colors but you can figure out which one to put the fuse on fairly easily. The PCM controls the ground to the IAC and the other wire will have 12 volts with the ignition turned on. The 12 volt wire is connected to a 20 amp fuse that powers the boost controller and the IAC, which you can find in a fuse holder mounted on the plate near the PCM. Use a voltmeter/test light to figure out which one has 12 volts and that is the one you want to have the fuse installed on. I recommend unplugging the two connectors to the PCM whenever you are testing circuits, just in case.

Worst case, you can just put a fuse on both wires and it will be fine.

GF?

Red with blue & white with blue , I would like to do this also I went through the ECM burn last year .

Thank you both for posting will dig into this and post back.

Is it Fountain problem? I've seen a bunch go out of them, sometimes taking the ECM with it.

Not specific to Fountain, all 600/700sci's are prone.

Had an IAC failure second season after getting boat, knew from reading to kill ignition power immediately to save ECM. Been replacing IAC's every other year now, cheap insurance to eliminate failures.

Kelly, did you do the 1 amp fuse on the power to the IAC?

Did not do the fuse, figured I would just replace IAC's every other season and not have any failures. If I remember correctly, Smartcraft gave a low voltage warning for the idle control circuit which I believe was caused by the old IAC drawing high amps from being carboned/gummed up.

Have not seen that warning since replacing valve regularly. I viewed the fuse as protection for neglecting to replace IAC's, a known and well documented service concern. Thought it better to do preventative maintenance than reactive, in order to protect wiring harnesses and ECM.

The fuse is a great way to protect the ECM during an IAC failure, I've just decided to follow a replacement schedule which eliminates failures.

That would be one more think to try to remember not good for me .

Hi Kelly O, where exactly is this IAC, how much are they worth and do you know if this is still a problem with latest 700's ? I am also very big on preventitive maintenance but have not really heard of this failure .
Thanks, Mark

Is this only on the SC motors or will this stop ecm failures on the 555 ecm's on other mercruiser motors?

I recommend installing the fuse even if you are replacing the IAC every season. I do not believe it has anything to do with being gummed up since I have had perfectly clean ones fail and the pintles were never stuck. Plus, the IAC is a stepper motor and the current draw is independent of load so it wouldn't matter anyway.

GF?

Ive repaired 2 ecm drivers on 2 different 700 boats, so after the 2nd one i learned a lot about this problem after talking to a couple of, what i think are a good source, marine mechanics and one said fuse both wires the other said for sure the negative and wouldn't hurt to do the positive so i did both. I looked up a wire schematic for my motor based off serial # just to see how that circuit is wired and you can figure out which wire is the negative if you choose to do only the negative

Do you think a 10 or 15 amp fuse would be better ?

From what I have gathered from this site, low voltage will destroy the PCM, 10 or 15 amp lets too much thru, 1 amp will save the PCM. Am I correct people in the know?

Correct, you need a 1 amp fuse to properly protect the PCM. I installed the inline fuses on my 700SCi's eight years ago and they have protected my computers many times.

Ttt

Hey, GF?, I've been looking at the wiring diagram tonight. The PCM controls the ground for the IAC (as well as other controls). The 12v source is shared with the boost controller. This 12v source is supplied through the fuse from the Main Power Relay. I don't see how a 1A fuse on the 12v source is going to to protect the PCM, as they are not connected. A high amperage situation on the negative side of the IAC could result in damage to the PCM.

Would you further explain your logic. I appreciate it!

Terry

There are two wires on the IAC. For all practical purposes, power into the IAC will equal power out. It does not matter which wire the fuse is installed on, current flow will be the same in both.

Although I have never had an IAC failure on our 496, I did replace it last year just because. I do like the idea of the 1 amp fuse however and will put this in.

For whoever asked, the IAC is located on the rear of the intake manifold.

[ATTACH=CONFIG]565655[/ATTACH]

[ATTACH=CONFIG]565656[/ATTACH]

Talked to Eddie Young a couple weeks ago and he says the red w blue tracer is already fused along with some other components so I will put it on the white w blue tracer according to his diagram .

Right - which is the "negative" (PCM) side of the IAC circuit. (white w/ blue tracer)

Actually, you can't have high amperage on the negative side of the IAC without the 12 volt power source. The damage to the PCM occurs when the IAC coils melt and create a direct short between the 12v power source, which is on a 20AMP fuse and the PCM which is ground when it is trying to move the IAC. I've tested many failed IACs and they don't short to their housings, only across the two leads. It technically doesn't matter which IAC lead that you put the 1 amp fuse on but it's best practice to fuse the positive side of a circuit.

GF?

Correct.

I think you will need to keep the 20 amp fuse because that circuit supplies power to the boost controller as well. Plus, even a 10 amp fuse won't protect the PCM from an IAC failure.

GF?

Just some of jist --- The red / blue wire is the IAC connection / feed to the IAC by pass valve. That also is spliced up to the area of 4 fuses 20 to 25 amp.

The IAC -- white / blue wire goes to the PCM connector B. -- That's the middle connector on the PCM

Had a PM asking, so I wanted to just post a followup, this is what I made for mine. I should have made the harness shorter, but it was a little easier to assemble at this length.

1 Amp fuse.

[ATTACH=CONFIG]567621[/ATTACH]

ALL_IN!, nice setup, would you mind sharing the part number / source of the connectors you used? I've searched in the past and never could find the male/receptacle side.

Thank you,
GF?

It took me a while to find them too. ...quite a while, in fact. I work in the auto industry, so I had to reach out to some of my resources for some part numbers.

The connector bodies are ....
AMP SSC-2 Black Female
AMP SSC-2 Black Male

Usually, you have to buy like 5 million of them to get the 4 I needed. But I found a website....
www.CycleTerminal.com
...that sells smaller quantities, and even has kits with the terminals, locks, and seals. I already had the proper crimper for the metri-pack / superseal type terminals.

About $20 or so in the two that I made. The 1 amp fuses are also hard to locate, locally. So Amazon was the source.

I could not find 1 amps also so I went with 2 amp .

Try Amazon. I believe you would be safer with 1 amp vs 2 amp. But I don't know if anyone knows for sure. The 1 amps have evidently been holding up to the IAC amperage draw under normal conditions.

Ebay them up "1 amp blade fuse"

http://www.ebay.com/itm/25-Pack-1-AM...YAAOSwImRYK1b8

http://www.ebay.com/itm/FUSE-ATC1-CO...sAAOSwNphWa2qH


Or get a kit of all sizes so you have them for future projects.

http://www.ebay.com/itm/180-Pack-ATC...UAAOSw7GRZEntt

So if you burn a 1 amp fuse replace IAC , 2 amp fuse ? be nice to know the specs on these IACs what amps they draw .

All In pm sent I see you have answered my question

Here we go

You guys know this right --- under certain engine serial runs for the 600 sci thre was a Merc racing SB 2008 -05 circuit protection / starter / sense circuit Alternator / wiring harness that needed to be done ? It was on the recall list as well.

You better check to see if it was done. I ran a few of you guys serial numbers whom bought service manuals off of me and 2 out of 5 600 sci owners were not done that fell into the SB engine serial range. Just passing on the info.

Thanks for the info The ones I just posted will be going on 700sci

Is this 1 amp fuse mod only necessary on the 600 SCI or would a Merc 525 efi or 496 Mag share the same risk with the IAC?

I think that was me, what do I need to do?

i havent heard of 525 and 496 having issues

I have definitely seen it on the 496 but not on a 525.
Eddie