94 mercruiser 350 low idle after thermostat change

[alldodge]

If your seeing sparks when the wires are moved, remove the wires and find out why

Have it tested if you wish, I'm trying to find out if the motor can be started with the ALT disconnected. If it will start and not blow the fuse, then its the ALT that has an issue

 

[Blizzmet06]

Had the battery tested just to be sure and that checked out fine. I think the problem is with the starter solenoid. Trying to find out how to ohm test it.

 

[Blizzmet06]

Found the main battery cable to starter had bad insulation and was shorting to the starter itself. Found that the IAC slots were stripped and replaced that. Boat idles better but still not 100%. Before I couldn’t keep it running now it will fluctuate between 590-650. Also think there’s some electrical issues as the cannon plugin moved slightly would kill the radio. Put a clamp on it to hopefully get better connections. Took it on the lake for a test run and noticed the automatic blower would intermittently turn off. Not sure if that’s supposed to happen or if it’s further proof of electrical issue. Boat ran fine between 1000 rpm and 3200. Would not go over 3200 even with throttle pushed all the forward. Stalled when I went to reverse in gear when loading back on trailer. I think IAc is still an issue. Mechanic said was only getting 2 of 4 signals and from what I’ve read the IAc needs both phases to work 100%. Not sure where to go from here. Mechanic said he can’t get his scanner to work on the mefi1 even though it says 93 and newer.

 

[Blizzmet06]

Also forgot to include that the oil and fuel gauges are no longer working. Also replaced the TPS.

 

[alldodge]

You still have corrosion and bad connections. Moving the cannon plug, loosing blower motor power, all are things that also will effect the ECM. A bad connection doesn't give the ECM clean power and can effect all sensors

If the mech scanner can read Merc, it can read a MEFI 1, probably and issue with connections again. I connected my scanner to a MEFI 3 last week and this motor was clean, but it wouldn't connect. It turned out to be corrosion on one pin

 

[Blizzmet06]

I’m getting a really high voltage reading from battery at rest. It’s reading over 15 volts with the multimeter. I read on another post that high voltage can cause issues with ECM and limit the RPMs to 3000. What could cause high voltage read at battery and starter terminal?

 

[alldodge]

Reading a 12V bat at rest (motor not running, no charger connected) will never read more then 12.7V, unless it was just disconnected from the charger/alternator. You might need another meter

If your alternator when running is producing more then 14.5V then either the ALT is bad, or the sense lead is not connected to the ALT. There are 3 wires connect to the ALT

Orange - main output to battery shoul be battery voltage full time even with motor OFF
Red/Purple - sense lead should be battery voltage full time even with motor OFF
Purple - Excite lead will have 12V when key is turned ON and when motor is running, and no voltage when key is OFF

 

[fishngolf]

Ok so I found the issue of the variable voltage. It turns out to be the 25 year old Malibu Computer that controls the dash. I unplugged it and then the voltage held consistent. Turns out the Multi meter I have is not accurate. I verified that I can run without the computer as I have the traditional gauges. I took it out again tonight for a test and it runs well up to 3200rpm. It will not exceed it. Can it be stuck in limp mode? If so how would I reset?

 

[Blizzmet06]

I did notice the water flow of the left exhaust is not the same as the right side. Please see video link: https://youtu.be/CyGNNTBjslk

 

[alldodge]

I don't see an issue on the hose, because a hose cannot give the pump ass the water it can pump, so what does make it thru follows the path of least resistance. The vid shows the starboard side with less water, even the port side has low to higher flows. Look at the hose routing on the motor to see if there is a difference, and could also be some corrosion in the exhaust

Where at the place where a scanner needs to be on the motor so the issues can be seen what the different sensors are telling the ECM. Sensors have been replaced but don't know what there telling the ECM.

I read back thru the thread and didn't see where the fuel pressure was read

 

[Blizzmet06]

Can’t find that fuel pressure port anywhere. Previous owner said he replaced the ignition control module with one from his truck when he was working on getting the thing started. Does the Ignition control module control timing at higher RPM’s? Could that be why I’m only seeing 3200 under load or would I not be able to get it at idle either? I have the original he removed wondering if it’s worth putting it back in. I’ll see if I can order the fuel test port from a shop.

 

[alldodge]

Can’t find that fuel pressure port anywhere.

Post 2

Its not a port, you remove the fuel line going into the throttle body, then use the fitting (Tee adapter) and connect one end to the TB and the other to the fuel line. After install a gauge can be installed

 

[Blizzmet06]

Could the Ignition control module be causing the 3200 max rpm under load?

 

[alldodge]

Not likely, the coil either works or it does not. If the coil was weak then there would be a missfire as the rpms increased if not even at lower rpms

From the beginning we have been chasing a low rpm issue. We are assuming that the motor is in good shape and the prop has not been changed. So low WOT rpm can also be a weak motor (low compression) or prop with to much pitch

 

[Blizzmet06]

Was able to borrow a scanner and received error code 42. Says electronic spark timing malfunction. Book says to look at the ICM. Here’s a video of the engine stats not sure if anything is out of the norm. https://www.youtube.com/watch?v=ct0Rr0FJEEg&feature=youtu.be
Can the wrong icm that the previous owner pulled from his truck be causing my low WOT?

 

[alldodge]

My MEFI code shows IC (Ignition Circuit) or bypass circuit.

IC grounded and/or bypass open or ground

Can the wrong icm that the previous owner pulled from his truck be causing my low WOT?

I doubt it but are you sure this came from a truck?

 

[Blizzmet06]

I put the original one in and now I can get rpm up to about 3800. Idle seems a little less smooth but too end has certainly increased. Not sure what IC open or grounded could be.

 

[Blizzmet06]

Here’s the scanner data with the original icm back installed. Still get error 42 but the rpm at wot are higher now. I’m thinking timing may be off. Can you see via the following it’s jumping around quite a bit range wise at idle. https://www.youtube.com/watch?v=nqMt3mdPPbA&feature=youtu.be

 

[alldodge]

Your timing is jumping around, pull plugs one at a time to see if idle changes

 

[Blizzmet06]

What can we learn by pulling plugs?