94 mercruiser 350 low idle after thermostat change

[fishngolf]

Got the ECM back installed and fired up engine. Won’t stay running. Mechanic verified IAC not functioning and is not getting signal from ECM.

Does the TPS control the ecm’s signal to IAC? Not sure what to do as ECM checked out ok but IAC not getting signal.

 

[alldodge]

Does the TPS control the ecm’s signal to IAC?

No, the ECM controls IAC and the ECM gets info from the TPS as to where the throttle plate. All must have good connections. Connections from ECM to IAC along with grounds and 12V power

 

[alldodge]

I would do some real cleaning and checking of all connections. Sitting for that long can cause all kinds of corrosion, and also cause issues with sensors

 

[Blizzmet06]

Checked the grounds all seem clean and tight. Replaced the TPS and still having issues. Computer is still throwing a ton of codes. Took a video for reference.

https://youtu.be/8d2GRBvKcZk

 

[alldodge]

A ton???

13 - not applicable but showing because something is loose
21 - TPS open or shorted to ground (means it does not know but there is an issue)
42 - IC circuit is either open or shorted to ground, something has corrision

Again a lot of dirt in the connectors, so my guess would be at this point is you need another harness because there is one or more bad connections and it has yet to be found

 

[Blizzmet06]

Not sure what those numbers mean. Mechanic said he couldn't get his scanner to work would that make sense if the harness is the problem?

 

[alldodge]

If the scanner wasn't working, what was beeing shown in the vid?
Yes, if the harness has issues, then this can cause many problems

 

[Blizzmet06]

That’s the dash display. It has a Malibu computron

 

[Blizzmet06]

One thing I didn’t check was the cannon plug connections. Could that be related?

 

[alldodge]

Its possible, the motor gets power and some grounds from this connection

 

[Blizzmet06]

Took a loot at the cannon plug last night. There was so much dielectric grease in there it got forced up and looked like caulk at the seem connection. Is that normal? I’m thinking removing and cleaning with electrical contact cleaner would be better.

 

[alldodge]

If it is dielectric grease then there should not be an issue so long has the pins fit tight and grease can help keep moisture out.

 

[Blizzmet06]

Having a hard time finding the TBI fuel pressure fitting. Thinking about taking another look into the VST tank which seemed to be my problem last year.

 

[Blizzmet06]

Checked VST no problem there. Cleaned all the grounds and now having a problem with the 90 amp fuse on the starter. I blew it when I went to start the engine. Got a replacement and same thing. As soon as I turn the engine over no more power to gauges and the second fuse blew. Seems like the starter is shifting out the system. Any ideas?

 

[alldodge]

Disconnect the orange wire going to the alternator along with the 2 other small wires

 

[fishngolf]

Orange wire is connected to the fuse with the red lead to harness. Do I leave the red connected? I only have one other small wire on a separate terminal. Attached image is the same setup I have. How do I determine if its the alternator or the starter?

 

[alldodge]

Orange wire is connected to the fuse with the red lead to harness. Do I leave the red connected?

Yes, but might be easier to disconnect the wire along with the others at the alternator. With the 90 amp fuse being blown (square thing) then the ALT may be shorted. You could connect the Red/purple direct to the battery cable because the motor is protected by the 50 amp breaker on the motor

 

[Blizzmet06]

Can I do a multimeter test to determine if starter or alternator so I don’t do any further damage?

 

[alldodge]

The fuse does not pass power to the starter, so it blowing was not the starter. Can disconnect the battery then measure resistance from the orange wire to ground. The orange should go straight to the ALT

 

[Blizzmet06]

Moved the wires a bit and saw some sparking at the starter solenoid. As the fuse is connected to the battery lead if there’s a big short at the solenoid wouldn’t the fuse pop? Thinking about replacing the starter. Should I disconnect and have the alternator tested?