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1993 Mercruiser 4.3LX starting isue

carbed, injected? engine serial number? If not injected, power during cranking is supplied by the starter solenoid
 
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At the starter solenoid NOT THE SLAVE , the outermost small lug supplies power during cranking only. It is opposite the small lug with the
yellow/red wire. If you dont have this stud, you have an automotive starter installed.
 
Look at the oil pressure switch It is above and near the oil filter,

there should be two purple wires going to it (the switch is a normally open switch) and when oil pressure is present the switch closes and power is conducted thru the switch to the pump. There should also be a purple/yellow wire attached to one side. If it is attached to the wrong side then the "cranking" power which is supposed to come from the starter solenoid to power the fuel pimp during cranking will not supply the power until the switch is closed.

see schematic below
 
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Thanks Jack. I will take a another look at the wiring. On a different note...My Tachometer is erratic. It does not always register above zero, sometimes it will drift up and down. Never excessively high but seldom stable or believable. Similar dysfunctions at high and low speed. Any ideas?

Greg
 
on the back of the gage under dash...

there is a selector switch...

see what it is set on and change it and then change it back and see if that helps........with power off.
 
Push IN on the tach switch and wiggle it back and forth to clean the connection.

On the 'no fuel pump without oil pressure' business, it's a USCG requirement. You can install a by pass switch to run the fuel pump before trying to fire the motor. I did this on my boat to avoid all that destructive cranking. Run a wire from the connection on the oil pressure (idiot light) switch to a momentary switch at the hellm, then to ground.

Jeff
 
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Thanks for the tach advice, I will give that a try next. As for the wires connected to the oil pressure switch--changing them resulted in fuel pumping into the carb in less than 3 seconds--big improvement. I am anxious for further "cold" starts!
 
I have a 4.3 mercuiser and fully charged 1000 batt. Hooked up. I am getting power to my gauges blower bilge etc but when I turn the key I don' t even here a click or a crank to the engine. Could it be my ignition switch?
Any suggestions?
Thanks craig
 
wjcmphoto said:
I have a 4.3 mercuiser and fully charged 1000 batt. Hooked up. I am getting power to my gauges blower bilge etc but when I turn the key I don' t even here a click or a crank to the engine. Could it be my ignition switch?
Any suggestions?
Thanks craig
Click to expand...

Ayuh,.... Welcome Aboard Craig,.... You oughta start a thread of yer own, 'bout yer problem, as this one is Greg's,......

You'll get better answers that way,....
 
Regarding the fuel pump and starting issue...Perhaps residual fuel (from a start the day before) was the reason for fuel prescence and engine firing after only 3 seconds of cranking (after switching the two wires connected at the fuel pressure switch) A subsequent start a couple days later resulted in (again) no engine firing until oil pressure registered, about 25 seconds of starter cranking. Carb has been disassembled and cleaned. Floats have integrity--no leaks. Shouldn't fuel remain in the carb float bowls for days, effecting a relatively quick start?
 
Yes.........it should..........it does evaporate some though..........

It is impossible to need that much cranking..........

It may be that the fuel pump is bad and allowing fuel to leak back thru......


When cold and after sitting for a few days...........make a jumper, disconnect the two purple with yellow wires from the pressure switch and jump them together. This will bypass the pressure switch. It also wont matter if the Purple wire is connected or not so don't worry about it this is used as a "bypass for power when cranking but with the pressure switch bypassed the pump should get immediate power.


Now turn the key to the ON position. You should hear the pump running immediately. If not the pump is bad. If so try to start the motor.

If it does then the pump is ok....If it still needs a lot of cranking then you need to figure out why............either bad pump allowing fuel to leak back into gas tank or a carb issue.........

If it does and you have time let it sit for a few more days and retry to start from a cold starting point.

If it does start with the oil pressure switch by passed then the problem is with the Purple wire that feeds the pump from the pressure switch when cranking........Maybe a voltage drop due to a bad connection or weak connection within the starter solenoid..........

Cant be much else.........
 
My tachometer has an adjustment on the back. Three areas are [4], [6], and [8]. May have to do with number of cylinders? Anyway, I rotated the adjustment both directions and returned to the setting I found it at. Then I cleaned the terminal connections on the ignition coil. Sunday the tachometer display was steady and believable. Thanks for the tip. I continue to search for the cause of pathetic acceleration and no more than 3000 rpm at full throttle and 28 mph. Boat used to do 40 mph. Mechanic inspected carb that he cleaned and disassembled. He said the main jets were "crudded up" but cleaned up well. He has suggested the cap, rotor, and coil be replaced. Think that makes sense? Pumping the throttle at max speed had no effect on rpm or speed. WOT should be 4400-4800 rpm.
 
""""""""""""Mechanic inspected carb that he cleaned and disassembled. He said the main jets were "crudded up" but cleaned up well.""""""""""""


I am thinking he missed something...........
 
Greg of Racine said:
........................... He has suggested the cap, rotor, and coil be replaced. Think that makes sense? Pumping the throttle at max speed had no effect on rpm or speed. WOT should be 4400-4800 rpm.
Click to expand...

I always thought when troubleshooting engine performance you verify the ignition system first. When was your last plug change? Wires? Cap? Rotor?
 
Plugs were last changed probably 2000. I cleaned, gapped and inspected plugs last week. I cleaned cap and rotor. Wires, cap, rotor and coil, I can not say when/if they have ever been changed. When is it time to check cylinder compression?
 
Greg of Racine said:
Plugs were last changed probably 2000. I cleaned, gapped and inspected plugs last week. I cleaned cap and rotor. Wires, cap, rotor and coil, I can not say when/if they have ever been changed. When is it time to check cylinder compression?
Click to expand...

2000 on the plugs??!!!
R U Serious???
Nothing is "forever".
 
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..."Shouldn't fuel remain in the carb float bowls for days, effecting a relatively quick start? "

Not on my old boat! Those carbs were bone dry after a week of sitting.

Jeff
 
Changed cap, rotor and coil. Had to pull distributor to remove rotor. Reinstalled and set timing 4 degrees at idle. Test run: excellent acceleration and WOT 3800 RPM (Spec: 4400-4800) 35 MPH. Will look into prop pitch change next. Is there a provision for "base timing" with the Thunderbolt IV? And, I may, just for kicks and comparison, change those 15 year old spark plugs.
 
Thunderbolt 4 you set base timing as with any old style timing proceedure. Set to spec by turning distributor. Thats it.
No grounding of timing module
A v6 should be approx 6-8 degrees before top dead center.
 
So...not enough progress regarding resolution of my problems. Mechanic feels electric fuel pump is not supplying adequate fuel to carb. Supported by long crank-to-start time observation that fuel does not reach carb until after 25 seconds of cranking--coinciding with oil pressure build-up. Since timing was reset, no acceleration in forward gear beyond 1200 RPM. Carb has ben disassembled, inspected, cleaned and adjusted. Replaced rotor, distributor cap, coil, plugs and oil pressure switch. Mechanic feels something limiting fuel available to electric fuel pump. Perhaps a faulty check valve. Ever heard of blockage at fuel pick-up within fuel tank?
 
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