496 ho electrical issue?
 

https://youtu.be/qdwlNfZM2Xw

I had the boat out the other day and fried the IAC. Replaced it and pig tail the other day and was able to clear the code with my diacom software. When I went to fire it up it does what was shown in the video. The key was on and it was randomly cycling. It will always crank however I cannot read the pcm with the scan tool as it acts like it is not getting power when it is doing this.

The boat did fire up and run for about 10seconds as normal but then lost power again.

Has anyone came across this before? I was thinking maybe bad ignition switch? I thought maybe main power relay but it will always crank and I didn't know if that relay controlled power to that starter.

Any help would be appreciated!

Start with your grounds on battery and also verify the grounds on the back of the block.

Then, if it does the same thing check the power lead connection that has the 50A breaker on the engine and your ignition switch.

Could be a bad key switch but I doubt it. Check the stuff Keith mentioned. MPR provides power to the engines system, not the slave starter relay. You can swap the MPR with one of the others which are next to each other, they are the same.

I'm not at the boat right now so it might be a dumb question. But which one is the MPR?

Isnt the 496 IAC issue like the 600SCI and 700SCIs? On the 600 and 700s if the IAC goes it it usually takes the computer with it.

Don't know your serial number but you will either have 2 to 4 small square relays. If only two relays then one is the MPR the other is for the fuel pump, just swap one for the other. If you have three relays then the third is the slave start relay, and all three can be swapped with one another. If 4 are there then you have digital shift controls

If when you turn the key you should hear the fuel pump run for a few seconds. If nothing happens it could be the computer like VoodoRob mentioned. Don't know right now, just need to find out what is going on.

http://www.mercruiserparts.com/bam/s...31819/12826/30

Not that I know of and I have lost a dozen IAC's over the years.

It kills the IAC driver in the 555 pcm when the iac is bad and the owner continues to operate the engine. It can also melt the iac wiring plug/harness and start a fire.

If it kills the Iac driver does the pcm need replaced or can it be saved?

My experience also , Send the 555 to Jeff at Whipple and have him fix it.

Yup, Whipple....

https://whipplesuperchargers.com/ind...&product_id=73

So would the Iac driver cause the power to cycle to entire system like in the video?

Also is their any specific procedure when swapping PCM's? I don't want to screw up 2 of them.

ohm out the iac wiring back to the pcm,,make sure its not shorted to ground anywhere.

wow,,It only took me 30mins to fix my friends pcm on his 1075's.gonna have to bill him some extra mula.:D

How did you repair it??

So, if you fry the ECM it does what he has in the video?

OP - Did you figure it out?

I worked on it today and no I haven't figured it out. It was happening at random today.

Here's what I know.

The Iac is new and the wires are not grounding out anywhere.

Swapped relays one at a time. Relays are good.

I tried to get a reading on ignition switch but couldn't get to it while it was acting up.

I did have a MAP input hi code in the history I'm not sure if this has to do with it

Here is another video from today. Notice the erratic alarm and relays. It does this with just the key on.

https://youtu.be/l322_TPba8c

opened the pcm up,,saw the fried transistor and replaced it w/ one from a spare pcm I had laying around.put it back together and its been fine ever since.

sounds like you have a VOLTAGE Problem to me --- you can even hear the fuel pump(s) turn on and off on their own. Loose battery cable at the starter is my guess or back side grounds for the easy fast checking areas .

Info --- The IAC that fails can knock out ECM 555 / PCM 555 no matter of the engine - 4.3 / 5.0 / 5.7 / 6.2 = ECM 555 --- then / 8.1 PCM 555. An IAC that fails can knock out IAC driver internally in the ECM / PCM - this can lead to many problems for the engine including not even starting. IMPORTANT Have you checked the fuse for the IAC circuit ??? is it good and connected properly ? Do you have power there ??? I would check there ASAP.

Open your throttle half way does the engine start ??? Open your throttle fully --- but be ready to pull back very quick if the engine starts.

What is fuel pressure here - even while cranking ? Put a fuel pressure gauge on this engine and monitor the fuel pressure while its cranking and trying to run

IMPORTANT watch your volt gauge or use a volt meter or the scan tool to watch your engine voltage. Key on what is it ? steady 12.7 volts ??? or is voltage dropping / or coming and going, if so the fuel pumps will never keep fuel flowing period because they require steady correct voltage to operate, just as every thing else that requires correct steady and stable voltage. Important areas to check, So voltage is number one area to check first.

You have to rule out what it is not the problems and problem areas - so testing is what you need to do first before the parts changing takes effect here. That's a waste of money for any boater and a dart thrower way to fix a boat. .

Your location is ??? In person this would not be hard to diagnose at all.. Just to start with the testing is 1, simple stuff first - do you correct voltage and all the time steady correct voltage even for cranking the engine ? - next is do you have fuel moving when the fuel pumps come on and while cranking - does it maintain correct fuel pressure of no ? Next is do you have CONSTANT steady spark even while cranking - sealed inline spark checkers best cheap tool to have. These are always the easy first checks to perform when an engine does not start -

You can watch voltage drop or rise using the scan tool - or even with a cheap volt meter. Check the starter for any power problems ie : battery cables, 90 amp fuse at the starter - then back side grounds - then the 50 AMP fuse engine side if applicable since you did not post an engine serial number here - Next the main power relay do you have power there ??? and so on. You need correct steady power all the time at every 12 V system on the engine INCLUDING back side of the ALTERNATOR --- did you check connections there as well and voltage ????.

NEXT IMPORTANT do you really know how to read the scan tool - not having fault codes means nothing - you said you had a map sensor fault ? You also could be having a problem with the 5 volt sensors harnesses especially on the back side of the engine. There is also a smart transom circuit / harness as well that is a 5 V. .

Instead of 100 % automatically thinking the IAC driver in the PCM is bad, why not test the IAC ??? Back to scan tool, what is the IAC reading with key on and when the engine starts ? This can tell you what is going on before jumping to huge conclusions. Like I said you have to test all these things and rule out whats not the problems and problem areas, moving forward to be able finding the problem area(s).

It also looked as you had a tach signal at the gauge in the video, IS THIS CORRECT ??? If not at all then Crank sensor si bad ? But 99 % of the time a truly bad crank sensor the engine will not start at all and you will not have a tach signal.

I gave out a lot of good info here and if you are close to Texas - I have to say this would not be hard for me to figure out all the problems in person using the proper tools and the proper way to test systems that would pin point the engine issues and a no start running engine. .

What ECM MEFI 1 ?

You just do not open up ECM's like with what with a jack knife ?? If he did fix a PCM 555 controller he got darn lucky as hell period.

Also I have been getting into more and more of the ECM and PCM testing if there is a problem with them plus have fixed some as well. With that said - not all ECM's are fixable either. I would have to say about 50 % of what I have seen is and 50 % not fixable.

First of all Thank You for taking the time on your reply!

I agree with you that is is a voltage issue.

Yes I do have a tach signal.

So the motor will always crank when key is turned over. However when it is acting up there is no power to the fuel pump, pcm etc... so my question is what could be affecting the power to all those circuits ( I currently don't have a schematic). Also if it runs fine sometimes as in the video is it safe to assume the issue is not PCM related?

I have checked all battery cables and ground connections. I still can't help but think it has something to do with originally frying the IAC. I had to put a new pig tail on it as it did melt it. The issue is only with the starboard motor.

Engine serial number is 0W378033

Swap PCM's from star-port motors to rule that out.

Next time it does what was in the vid, put your finger tips on top the relays. The MPR will click ON and stay ON, the FPR will turn off after a few seconds.

The PCM applies a ground to pin B-4 which activates the relay. If your not getting a click, I would remove the relay and use a meter to see if the pin is going to ground when key is turned ON

[ATTACH=CONFIG]565378[/ATTACH]

Check your cannon plug on the back of the engine. Mine was doing something kind of similar....found a broken ground pin in the cannon plug, causing an intermittent loss of power to the helm (key switch)....mine wasn't as bad as yours, but it would randomly shut off while going down the lake, and them come back alive. I could also sometimes turn the key while on the trailer in the garage, and had to bump the cannon plug to get it to make a connection.

Here's a vid I took of what I'm talking about. The pin should NOT turn freely in the molded connector.

https://www.youtube.com/watch?v=FEu7YVVgDuk

When it is being erratic the relays are all clicking on and off. However at times no relays or anything will click no power to pcm either. So what sends power to PCM AND MPR?

How many years did that take you to find? Holy crap!

That is a very good possibility! I could have pushed on it or something when replacing the IAC.

I'm not gonna lie....I swapped ECUs between engines, swapped a bunch of relays, checked a bunch of wiring, replaced a few other parts, and cussed a LOT while chasing this down.

Happened to find it while spreading out the pins on the connector in an attempt to rule out a bad connection there.

Well I got a chance today to put it on the hose and came to the conclusion that the ECU is the problem.

The starboard motor (the one that cooked the IAC) would fire up then die within 10seconds. Swapped with port motor and it would run fine. What was weird was when I would put bad ECU on the other motor and it would stay running. It would throw knock sensor codes and sound the alarm every minute or so but it wouldn't die.

I figured I would send the ECU to whipple.

word of the warning for the unknown Taking the good PCM and putting it on the bad engine can be one way to knock out that good PCM = it very wise to start with the bad PCM and put it on the good running engine and see how its runs.

Then see if it is matching all the engine running parameters in the scan compared when it running with the known good PCM. You have to scan both times before the PCM swap and after with the unknown possible bad PCM. .

Thank whomever I have never knocked out any PCM's because I would not risk the testing of the known good PCM that way but always took the unknown PCM and put it on a known 100 good running engine. I say this because I know boat owners and even so called good techs doing this and ended up knocking out a good ECM / PCM.

The 600 SCI with a bad coil(s) is a prime example of this -Swap and plug a good known PCM in and power up - crank over engine - bad PCM that was good 2 mins ago.

Most likely I could test this PCM as well. My experience has grown a lot in the past 2 years for ECM / PCM testing and some even repaired.

So what fault codes and any spec parameters out of spec ranges on the scan with swapping the good PCM over to bad engine, now runs good ? also you are testing unloaded and below 2500 rpms as well that might not give you the total picture --- but it could as well. Just saying.

Thank you for the advice. When good pcm is on "bad" motor their are no fault codes and motor operates properly. When bad pcm is on "bad" motor it won't stay powered up and running long enough to check codes.

When bad pcm is on "good" motor it stays running but has 2 KNK Sensor codes. And 2 beep alarm every minute. I didn't notice any parameters out of line however I don't do this every day so I could have missed something.

I would say that when I melted the IAC it must have screwed something up in the pcm...?

Yes the IAC driver but you could test for that on the scan and with the scan tool. . I hear you also so good luck with it. Just posting to pass along for people to watch out testing systems on marine apps.

Since sutphen 30 mentioned Merc 1075 HP , it seems he may have opened up Mercruiser's? newer designed (PCM) 03 microprocessor (Propulsion Control Module (PCM) 03 microprocessor: Ignition System: PCM 03 Distributorless) which resembles the looks of item number 3? in the following link, http://www.mercruiserparts.com/bam/s.../31278/14371/5

Here's some detailed info on the 1075 HP engine model if interested, http://brucebullockmarine.com/mercur..._1075_sci.html

If so on opening up the PCM 03 model, and knowing Whipple opens up the 555 and 1075SCI almost daily sure makes one wondering the best way to open and close a 555 in order to have a look around? Are you that adventurous Bup?:coolcowboy:
https://whipplesuperchargers.com/ind...&product_id=73

Of course PCM 03 is basically Merc words for a special PCM -- these all came out for the Merc racing engines in 2003 - it still is Motorola 555 -- aka triple nickle -- aka PCM 555 --- no matter how you slice and dice it. And even in some brochures is listed PCM 555 for the Merc racing engines

also in 2007 it was change to PCM 07 as the new calibration for Merc racing engines and so forth but guess what it still was Motorolla 555./ pcm 555 .

http://www.baymarine.com.au/mercury-...i-sterndrives/

PCM 07 can be verify in the link reading above . More of marketing words as the racing division has always separated itself from the black production side.

Just adding --- for my comment on the mefi 1 and jack knife, I was being a smart azz but again its still a 555 (1075 SCi) and I knew that already. Not a hocus pocus - its opened and now sealed shut tight . .

If you like to put a bad pcm /or ecm in my hands to test and possible fix it, but I will state, 1,again not all are fixable and 2, is, I am still working at it so that I become better addressing the possible fixes. . I will not do it for free especially when another services will be billing as well. I will be happy to at least test it if you like ? Saying this in a good way.

I also own a personal 496 so I am very on top of the PCM 555 issues plus whats going on anything that a scan reports . Thanks, if that post was an offer

Thanks Bup for the additional info covering the later designed ECM/PCM's numbers. I also recall them having an ECM-09.

Unfortunately I don't have any 555 ECM's laying around and I stopped working on boats professionally at the end of 08 so I'm outdated as far as Merc goes and I don't have access to things/ECM's like that any longer. The post above was just peaking an interest of what it would take to repair one was all....Just thinking out loud of course but maybe someday a member here on OSO would be willing to send you an old/bad one for you to play around with and if so maybe do some sort of technical write up of what you found or possibly repaired mainly since you mentioned you're starting to put some more interest into their failure rate. Fixing forum members ECM's might be a good/easy/fun retirement project someday... $$$.;):)

Thanks as well - PCM 09 is CATALYST side Mercruiser PCM / it also is on a newer version as well .

to complete the post above as I cut it short ---- PCM 09 which is a Visteon component PCM

PCM / ECM 555 Motorola are no longer being used for years. -

PCM 09 Visteon started in mid to late 2009 for model year 2010. It change again with calibration and name changed to PCM 013 still Visteon component.

At one time Visteon was a Ford owned company. I do not know who currently owns Visteon.

soonenough, Any word from Whipple regarding your PCM yet?

Was following another 496 PCM issue on another forum around the same time as yours and the repair from Whipple turned out to be a failed 4Mhz clock chip inside the PCM, http://www.riverdavesplace.com/forum...=1#post2642245
Below is the main quotes from the other thread,

Nothing yet. They received it on the 23rd so I hope they get to it soon.

the failed clock chip = the ECM is dead. When you scan the ECM / PCM as far as I have seen is nothing = no communication period from the scan trying to read the ECM / PCM

IMO the chip might have changed from the manufacturers as being part of the problem - prob cheaper quality possible here. Also IMO heat related issue might be the possible cause for the clock chip failure.

If I could ever get of enough ECM failures to look at -- IMO possible I could track down the problem.

Also the OP here I believe can scan his engine ???? plus the engine starts and runs ???? is all of this correct ?? if a scan can be done IMO possible not a clock chip failure.