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4.3 MPI Crank No Start / No Spark

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DazzaP

New member
Hi All
I'm at a total loss. I'm pretty good with engines, etc., but this has me beat, and I bet it's something simple. Back story below...
We were out boating last summer, testing rpm on a new prop, so the top speed run was all good for 5 minutes, then the engine cut out. Checked the engine had oil leak, so I guess the oil pressure switch did its job; I suspect it split the hose. Wouldn't restart, so got towed back.
Ive replaced the oil pressure switch, pressure sensor, complete ignition coil and module, dizzy cap.
Ive spent a few hours now trying to diagnose the issue but drawing a blank; everything checks out, but what seems strange is, as per the drawing attached Im loosing voltage to the top plug pink wire when its plugged in, but according to the diagram, tI shouldn't be as its spliced at junction 108.
You can hear fuel pump kick in and prime..
Any other ideas please.
 

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DazzaP said:
Hi All
I'm at a total loss. I'm pretty good with engines, etc., but this has me beat, and I bet it's something simple. Back story below...
We were out boating last summer, testing rpm on a new prop, so the top speed run was all good for 5 minutes, then the engine cut out. Checked the engine had oil leak, so I guess the oil pressure switch did its job; I suspect it split the hose. Wouldn't restart, so got towed back.
Ive replaced the oil pressure switch, pressure sensor, complete ignition coil and module, dizzy cap.
Ive spent a few hours now trying to diagnose the issue but drawing a blank; everything checks out, but what seems strange is, as per the drawing attached Im loosing voltage to the top plug pink wire when its plugged in, but according to the diagram, tI shouldn't be as its spliced at junction 108.
You can hear fuel pump kick in and prime..
Any other ideas please.
Click to expand...
Don't just replace parts if you haven't found that they're bad, through testing.

Press in on the lanyard clip on the kill switch- if the lanyard has been left in place for a long time, they tend to stop pressing on the switch enough to allow the engine to start. You can connect a multimeter to the purple wire on the coil to find out if that's causing the problem- if it IS the cause, you won't see 12V.

The pump will prime whether the kill switch is working, or not.

Because you haven't owned this boat since it was new, you don't really have much of a baseline for its condition- it might not be a bad idea to take it to a good Mercruiser dealer so it can be connected to the diagnostic computer- that will show data that can be used as a reference in the future, if something else goes bad.

One thing that will prevent it starting when everything else is OK- if the TPS shows 100% throttle, it won't start. 100% throttle while cranking is the method for clearing a flooded engine.

Ignition modules fail, same with the pickup coil. Also, the diagnostic tool will show data for all sensors and the IC module will throw a code if it's bad.

What year is the engine?
 
The pump will prime whether the kill switch is working, or not.
Click to expand...
Incorrect, key sends power to purple wire
Purple wire goes thru kill switch then to MPR. If MPR does not get power then no power to ECM and nothing works
 
AllDodge said:
Incorrect, key sends power to purple wire
Purple wire goes thru kill switch then to MPR. If MPR does not get power then no power to ECM and nothing works
Click to expand...
If the safety switch doesn't close, nothing gets 12V. ECM has power from battery, with ignition input when required- the key isn't the main source for the ECM and when the ECM receives the input from the ignition switch, it primes but if it doesn't see RPM, it won't run, am I totally wrong about that? This is the way Indmar set up their engines, although Mercruiser definitely does some things differently.
 
jimn said:
If the safety switch doesn't close, nothing gets 12V. ECM has power from battery, with ignition input when required- the key isn't the main source for the ECM and when the ECM receives the input from the ignition switch, it primes but if it doesn't see RPM, it won't run, am I totally wrong about that? This is the way Indmar set up their engines, although Mercruiser definitely does some things differently.
Click to expand...
Merc doesn't work that way
Purple from key goes thru engine connector to the engine harness. Engine harness connector transfers 12V to ECM harness and changes to pink wire which turns ECM on. ECM applies a ground to MPR which applies power thru fuses to other circuits including FP. ECM applies ground to FP relay for few seconds
 

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AllDodge said:
Merc doesn't work that way
Purple from key goes thru engine connector to the engine harness. Engine harness connector transfers 12V to ECM harness and changes to pink wire which turns ECM on. ECM applies a ground to MPR which applies power thru fuses to other circuits including FP. ECM applies ground to FP relay for few seconds
Click to expand...
Do we know what model year of this engine?

The cool fuel pump gives the OP additional things to check.
 
I think it's 2001.

It's 4am in the morning here I don't like to be beat. What I can't understand as per picture attached, when both plugs are unplugged pink wire has 12v on both, when plug in black plug you loose 12v to the orange plug, but according to wiring diagram you shouldn't. Should I add a 12v feed just to test?
 
You should not loose 12V but I would not apply an additional 12V to make it happen. Might draw to much current and blow something expensive

Something has a bad connection. A bad connection is like a resistor. With no current being drawn there is 12V on both sides, as soon as current is being drawn the 12V drops
 
OK, I just had a quick 10 minutes to have another play. I probed the pink wire 12v that goes into the ICM while it was plugged in. I had 12v, but as soon as I turned on the ignition, I lost the 12v. I have no Idea why??
 
Again it's most likely a bad connection
Things get turned on by the key and things start drawing more current

Check the 12V engine harness connector to ECM harness connector. Should be at the rear of the motor near the engine to helm main connetor
 
AllDodge said:
.Again it's most likely a bad connection.....
Click to expand...
agreed, and that could also be the splices inside the wiring harness or damaged wires. Bad electrical parts can also induce large current draws which can make the voltage drop.

you can check all the connector pins that share a a given circuit....if you find a 'low' voltage at one connector, it could be the part that its plugged into or the connection points (or wires) between that spot and the 'good' portion of the circuit.
 
OK, sorry, I have not had an update in a while; boats have been to two shops now; the first one was a waste of time and money.
Anyway, here is an update: it's currently in a shop where they had it running, then they went in the next day to test run, and the same issue wouldn't start.
I spoke to them today, and it's running again, but the new coil and ICM are overheating / smoking, so they shut it off; this is the 2nd new coil and 3rd ICM that has been fitted.
So, I guess this is where the issue lies; they recommend I take it to an auto electrician. Any idea what is causing the coil to overheat please?
 
FWIW, swapping parts is NOT the same thing as diagnosing the problem....based on the suggest from the second shop, I'd say they are in over their head (or dont want to deal with it)...the good news is that they recognize it and are being somewhat honest with you.

Overheating coils usually experience an over-current condition....this needs to be verified by making the proper measurements. It could be caused by any of the potential problems identified in the previous posts...
 
DazzaP said:
OK, sorry, I have not had an update in a while; boats have been to two shops now; the first one was a waste of time and money.
Anyway, here is an update: it's currently in a shop where they had it running, then they went in the next day to test run, and the same issue wouldn't start.
I spoke to them today, and it's running again, but the new coil and ICM are overheating / smoking, so they shut it off; this is the 2nd new coil and 3rd ICM that has been fitted.
So, I guess this is where the issue lies; they recommend I take it to an auto electrician. Any idea what is causing the coil to overheat please?
Click to expand...

If any aftermarket electronics have been installed, I would disconnect them ASAP.

Has the battery been load tested? If the voltage drops, bad things can happen.

Do the shops that tried to troubleshoot this have service manuals?

What is the serial number of the engine? Specific info is hard to find without that.
 
jimn said:
If any aftermarket electronics have been installed, I would disconnect them ASAP.
Click to expand...
No.
jimn said:
Has the battery been load tested? If the voltage drops, bad things can happen.
Click to expand...
Brand new 1000CCA just fitted.
jimn said:
Do the shops that tried to troubleshoot this have service manuals?

What is the serial number of the engine? Specific info is hard to find without that.
Click to expand...
First shop mercruiser dealer even though though I felt like ai knew more than them after speaking to them. Second shop build boats and use mercruiser engines.

Serial is 0M635389
 
Serial number helps
555 ECM and HSV Distributor

What ICM (Ignition control module) is being replaced? HSV has a cam sensor but Merc doesn't use it. The ECM is about $2K each
 
DazzaP said:
No.

Brand new 1000CCA just fitted.

First shop mercruiser dealer even though though I felt like ai knew more than them after speaking to them. Second shop build boats and use mercruiser engines.

Serial is 0M635389
Click to expand...

One of the first steps I would do is check the voltage between the battery's posts without any cables connected, then from the battery - post to the solenoid's + post- if you measure a difference in voltage, it means the cable is resistive. Repeat, but use the battery's + post and connect the other lead to the ground point on the engine block- again, if you see a difference, the cable is resistive. If that ground point has several wires, remove the bolt or nut, clean any bare metal, put some grease on it, clean the ring terminals & replace any that have been damaged and try it again.

I would also recommend measuring the resistance from the distributor base inside of the cover and use the grounding point as the reference. You shouldn't see resistance and if you do, about .1 Ohms is OK. More is a problem because even a small resistance causes enough voltage drop that things start to do strange things.

Attach the meter's probes to the battery posts and have someone crank the engine. If the voltage drops below 10VDC, you have some kind of problem. If the ends of the battery cables are very stiff and not as stiff as you bend them farther from the ends, it may be time to replace the cables.

Building boats is great, but unless someone has seen goofy problems in boats, they won't be able to do much. Veteran techs who have worked at good dealerships tend to stay and trust me- they have seen some weird problems. Builders shouldn't see many problems because they're working with new engines, harnesses, outdrives and controls/dash- most problems don't show up until the boats have been in the wild for awhile unless the gauges and other electronics have a problem unique to them, or a trending problem.

Does your tach have a bare wire, or a sealed plug? In either case, disconnect the plug or the gray wire- if that wire shorts to ground, the engine will stop running or it won't start.
 
FWIW, that ignition is High Voltage Switch (HVS)...and concur with AllDodge's question on the "ICM Replacement"...

Has anybody tried to "adjust the timing" on that engine...especially at the 'first shop' your boat visited?
 
jimn said:
One of the first steps I would do is check the voltage between the battery's posts without any cables connected, then from the battery - post to the solenoid's + post- if you measure a difference in voltage, it means the cable is resistive. Repeat, but use the battery's + post and connect the other lead to the ground point on the engine block- again, if you see a difference, the cable is resistive. If that ground point has several wires, remove the bolt or nut, clean any bare metal, put some grease on it, clean the ring terminals & replace any that have been damaged and try it again.

I would also recommend measuring the resistance from the distributor base inside of the cover and use the grounding point as the reference. You shouldn't see resistance and if you do, about .1 Ohms is OK. More is a problem because even a small resistance causes enough voltage drop that things start to do strange things.

Attach the meter's probes to the battery posts and have someone crank the engine. If the voltage drops below 10VDC, you have some kind of problem. If the ends of the battery cables are very stiff and not as stiff as you bend them farther from the ends, it may be time to replace the cables.

Building boats is great, but unless someone has seen goofy problems in boats, they won't be able to do much. Veteran techs who have worked at good dealerships tend to stay and trust me- they have seen some weird problems. Builders shouldn't see many problems because they're working with new engines, harnesses, outdrives and controls/dash- most problems don't show up until the boats have been in the wild for awhile unless the gauges and other electronics have a problem unique to them, or a trending problem.

Does your tach have a bare wire, or a sealed plug? In either case, disconnect the plug or the gray wire- if that wire shorts to ground, the engine will stop running or it won't start.
Click to expand...
Thankyou for time with this response it's really appreciated. The boats still at the shop, I'm going there today to go over some of "hopefully" resolutions everyone has replied with. Funny you mentioned the tach wire I spoke to them yesterday about that, they are going to check that out. If that is the issue, does that mean the tacho is bad or just the cable or connection.
 
makomark said:
FWIW, that ignition is High Voltage Switch (HVS)...and concur with AllDodge's question on the "ICM Replacement"...

Has anybody tried to "adjust the timing" on that engine...especially at the 'first shop' your boat visited?
Click to expand...
Not as far as I am aware on timing the timing by controlled by the ECM.
 
That's the coil driver, and if it's burning up (smoking) then check the 20 amp fuse, it should have blown. Maybe it's been replaced with a wire and no fuse. The coil and coil driver, along with the injectors are powered from the MPR thru splice 108. So if it's actually getting hot and smoking, something is really wrong
 
DazzaP said:
Not as far as I am aware on timing the timing by controlled by the ECM.
Click to expand...
Exactly...and you don't want anybody moving that distributor ....

The relay's contact could also be marginal...suggest it get checked to make sure there is no voltage drop across it when powered ON.
 
AllDodge said:
That's the coil driver, and if it's burning up (smoking) then check the 20 amp fuse, it should have blown. Maybe it's been replaced with a wire and no fuse. The coil and coil driver, along with the injectors are powered from the MPR thru splice 108. So if it's actually getting hot and smoking, something is really wrong
Click to expand...
Cheers, fuses are all good. It was one of the very first things that I and the boat place checked, just to be sure its on the bank of three mounted on the engine. You would think it would blow the fuse first, though.
 
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