Starting Problem Mercruiser 5.7

I have changed the cap, rotor, ICU, and the sensor in the distributor. The engine turns over, tries to start, then just turns over.

 

Is there a computer connector somewhere on the boat? Can you have the trouble codes read?

Check the idle air control motor on the throttle body (I'm assuming since you have an engine computer that it's fuel-injected?). Usually on cars they stick open, not shut, but it's worth checking.

Could be a vacuum leak. Do you have a MAF sensor on your intake? If so, if the intake is loose after the sensor it may be running too lean to start.

Check a plug after you try to start it to see if it's wet - make sure you're getting fuel.

 

Stonebreaker,
The engine is not fuel injected. The computer module has connetors but not the type that module can be plugged into for testing or reading the error codes.
The last time I checked the plugs, most of them have carbon on them and I think that means a rich fuel mixture.
The only items I haven't replaced are the spark advance module that sits in front of the ICM (Ignition Control Module) and the wires. The wires are less than 4 years old.
I noticed that the choke was not operating (butterfly stuck open) but I don't think that would cause it to not start?
I also noticed two wires on the choke. What do they do? One is ground, the other one??? goes into the wire harness.
Really stumped on this one.
Appreciate your suggestions.

 

I'm not as familiar with carbed engines as I am with fuel injected ones (mentioning the ICU threw me - sorry). I would assume the wire on the choke runs to a temp sensor somewhere, probably connected to a coolant temp sensor (this is an electric choke, right?). Try applying voltage across the choke's contacts to see if it operates. You might try spraying a little starting fluid into the carb to see if the choke is actually the problem (be careful or you won't have any eyebrows left at the end of the day!)

 

Stonebreaker,
The choke is electric but that is where the fun begins. The electricity heats a metal coil connected to a detent connected to the butterfly. When the coil gets warm it starts to unwind pusheing the detent from left to right forcing the butterfly open. That is it.
The butterfly was stuck open. Now only part of it is stuck open. The part that is on the choke end, not the linkage end. The shaft the butterfly or choke plate, now operates but now I have to replace the shaft connecting the choke coil to the butterfly and the other end that connects to the linkage. At the linkage end, when the choke opens, the linkage pushes a cam in front of the throttle mechanism forcing a higher RPM to start. Once warmed up, the throttle operates again, the cam falls out of the way and then there is normal idling.
I still have my eyebrows but I'm loosing everything else.

 

So were you able to get the engine started?

 

No! Once the shaft broke, the mosquitoes eating me and it getting dark, I closed up the boat and will give it another shot after work later today. I really didn't do anything so I don't anticipate the beast to start now anyway.

 

Hay Kid will your MCM 5.7 start 1st time every time once its warm? If so your on the right path ' the Choke If not Your Ignition Base timing could be at fault IF you have a Thunderbolt 5 type you can lock the engine into base timing mode by using stiff wire inserted into the correct connection under the bottom of the Ignition module and then earthing that wire this lock the timing into a set position not effected by the EMC. The correct Timing can be set using a timing light. Removal of the wire returns the engine timing to Service Mode.
also check that distributor is not 180 degrees out.
One other thing, If you what to keep your eyebrows and your Boat is To make sure you have the Flame Arrestor on the Engine each time you attempt to start It. Ive seen 3ft. high Flames come out of motors without a Flame Arrestor on Start Up, even ones that run and start well.

 

Alex, what pin position does the wire go in the ECM to change the timing mode? The engine is not an MCM but it does have a Thunderbolt ignition. The correct connection is a big deal as the ECM goes for alot of money. A wire strapped or grounded in the wrong place can be an expensive mistake.
When I was able to start the engine, I didn't have problems starting it when it was warm. Even cold, with a defective choke, a change in the fuel and air mixture should enable the motor to start. But it don't.

 

I can look it up for you and your correct timing spec if you email me your model and engine numbers My email adress is alexfletchermarine@iinet.net.au
regards Alex

 

Alex,
Thanks, I'll do that.
Last status, after breaking the choke shaft holding the choke cover plate, I decided to check for voltages to make sure once the shaft was either repaired or replaced, it would work. No voltage at the purple/yel wire to the choke. Then I realized the same color wire feeds the electric fuel pump. Now I know that the fuel pump was working because I used to hear it operate and I checked to make sure it was pumping a good stream. Now it does not. I pulled the connector apart and ran 12 volts to the positive side of the connector to the pump and it pumped gas like a champion.
Could this be caused by the Knock control module? That is the only thing I have yet to replace.

 

Does the wire come from the knock control module? Usually, the knock control module would work to pull timing, not fuel, so without knowing your particulars, I'd say no, probably not. If you're not getting voltage when you should be, first thing I would do in your shoes is check the fuses. If the fuses are OK, then trace the wiring and find the section where the voltage disappears. Could be as simple as a bad connection, or possibly a bad fuel pump relay. On my car, I have both a fuel pump relay control circuit fuse and the fuel pump fuse itself.

 

Stonebreaker,
Thanks for the info on the fuel relay. I saw mention of that in documentation I read. I don't know where the relay is but I'll start to look as soon as I can get to it. Didn't think that I could have blown a fuse. At least I know where they are and I'll check those as well.

Thanks

 

I was following your problem and after reading the part about the choke operation, I joined to tell you something. If I understand what you said about the choke setup, it has a fast idle cam on it. If it does, the carb is off an automobile engine and it probably also has vacum ports. If this is so, the carb can be made to work by plugging the ports AND REMOVE THE FAST IDLE CAM! If you pull it into gear at a high idle, it will either bust the dog clutch or tear the cleats off the boat if you are docked. I would not have butted in, but if what you described is a fast idle cam, its extremely dangerous.

 

Uh, Bill, the cam has no control over the idle set screw on the carb - so I don't see how the cam would have any way to control idle speed.