BUP

iTrader: (9)

I hear U and believe me I know also. As always you have to try the easy and least expensive things first to rule everything out before you get to the last possible PCM issue. I really was leaning that way as well about your PCM. I have seen 1st hand.

I have more to say about the IAC / ECM / PCM issue but really don't have the time to write the story book about it up here. Will later though. I know MPI is the way to go but in real terms on marine apps we see a lot sensor / computer issues in which always seems to start showing up around the 6 to 10 year mark. Even worst on saltwater apps and if the boat sits for long periods of time. I have to get some things done myself now. Good luck

Rich Lurz

swapped PCM to the working engine and it fired right up and ran fine. moved the pcm back to the no start engine and it goes right back into alarm. all connectors are clean and I have continuity thru the wiring to the IAC.I understand the crank and cam sensors but what has me baffled is that I can not get the IAC code to stay cleared. I clear the code and wait two minutes and I go back into alarm. I did not put the PCM from the working engine because I did not want to risk causing problems to it assuming I have an electrical problem. By putting the suspected bad PCM on the working motor and it starting right up, I think I can rule out the PCM.If I could get the IAC code to clear, I could chase the no start problem with a clear head.

BUP

iTrader: (9)

OK this will be a puzzle to fix but I want to understand what exactly you did. The no start engine you took that PCM off and put it on the good starting motor and the good motor started fine as always plus ran fine, is this correct or do I have it backwards ?

or did you take off the good PCM from the good starting running engine and put that on the no start bad engine and then that engine finally started right up and ran very well ?

BUP

iTrader: (9)

Forget it I re read your post and understand it fully. Sorry about that one. IMO you most likely have a short(s) and or a bad ground(s) in the no start engine wiring harness and or connections that is tied in to the IAC or a main power relay / connection problem..

This is a Ford IAC mounted to mercury adapter on the rear of the intake manifold. It really controls idle speed by controlling the amount of air bypassing the throttle plates. That air enters the IAC valve from the rubber hose connection to the throttle body. The air exits the valve then flows into the cast passages in the intake manifold. GM auto / Truck side used it for the EGR valve.

The IAC is really a valve actuator that is controlled by PWM = pulse width modulation thru outputs from the PCM. The IAC is normally closed and gets it voltage from the MPR = main power relay. Also IAC opens when its ground is completed thru the driver in the PCM. Next as the IAC valve opens at different stages , the PCM modulates the ground. Example if the outputs from the PCM to ground the circuit by 50 % the IAC valve would be open half way just as the same if it was to be fully open the circuit would be grounded 100%. Pulse width modulation is looked at as a % of time on versus the % of time off and is infinitely variable.

A failure in the IAC and or its circuit will show a fault so again IMO somewhere in the wiring / connection / harness / is a connection problem or a short or corrosion or moisture. Check B7 at your connector that plugs into the PCM or any grounds that could be bad. along with splice 105 (red lead goes to splice 105) . .

Also check your main power relay (MPRLY) and any of its connections. I would swap that out (MPRLY) from the good engine to see if that changes the no start engine. TRY THIS FIRST AND SEE WHAT HAPPENS.

.

Rich Lurz

Bup, thanks again for your input. I will be deep into it this weekend. I have been battling the nightly thunderstorms all week so I've been only getting an hour or so after dinner to chase this problem. I was some what relieved that the PCM was not the problem.Seams to me you've been down this road before.

sutphen 30

try switching the crank sensor.then the cam

Sydwayz

iTrader: (1)

FWIW, the crank & cam position sensors are available at RockAuto.com for about 1/4 the price of Mercury.
Yes, you read that right. 25% of Mercury's price.

[ATTACH=CONFIG]525950[/ATTACH]

Rich Lurz

Bup, going thru wiring diagrams this morning and found that there is a fuse holder between the relays. Opened it up and found the fuse blown on terminals E -F. It protects the 105 splice. Swapped it out and the engine roars like a tiger. I assume it went when the IAC shorted. I must admit I am somewhat embarrassed but then again I'll be on the lake this afternoon, so life is good. Thank you all for your help. Happy Boating

Sydwayz

iTrader: (1)

That's great news! Can you take a picture of this fuse/holder/location?

Rich Lurz

Mounted right behind the PCM and the relays.