08 350 Mag MPI: No Spark & Negative Turning Tach While Cranking. Banging My Head Against The Wall

[shyrwall]

08 350 Mag MPI: No Spark & Negative Turning Tach While Cranking. Banging My Head Against The Wall

Hi

I really hope there is someone wise here you knows exactly what my problem is I already had 1 "generic" boat mechanic look at the problem and 2 mechanics from a Mercury service center. Neither could understand what the problem is.

First off. Boat was working perfectly for 3 hours. Moored it. Came back a week later and no spark. When cranking there is no spark at the ignition coil. This of course rules out the distributor so I haven't even looked there. I have the newer type of engine where the ignition coil driver is screwed onto the coil.
My system has both a camshaft position sensor and a crankshaft position sensor.

I have changed the Ignition Coil, the ignition coil driver, the camshaft position sensor, the crankshaft position sensor. The ECM has also been changed.
I have verified continuiety of all the wires from the various sensors. See picture. I have also verified the neutral switch and gear switches and those wires to the ecm.

If I measure with a multimeter the wire coming from the ECM B23 to the IC Driver B (WHT/DK GRN in picture) there is a constant 5V when the ignition is on and when cranking. I dont know if this voltage should vary any when the ECM is sending the signal to the IC Driver to fire. If that is even what the ECM does..

Also what is weird, but maybe this is normal, is that I am getting +12V on the high voltage connector in the coil when the ignition is on and no change when cranking. Yes I connected the multimeter to the high voltage since I've given up and wanted to see if there was any reading..

I also replaced the grounding to the engine frame just to be sure there wasn't high resistence or something there.

Any clue? Please help

 

[shyrwall]

Forgot to mention that my tach jumps and goes negative while cranking. And when connecting a computer to the ecm it shows no errors (and gives no beep errors).

Does anyone know where the tach is connected to in all of this? It's not connected to the coil which i first thought.

 

[Fun Times]

Hi, welcome to iboats!

What year is the engine?
Engine serial number handy?
Bravo or alpha stern drive?
Your topic title appear mixed up as you have 350 5.0L Mag MPI.... a 350 Mag would be 5.7L where 5.0 is 305L.. We can easily correct the title once you can provide the engine details better.

The tachometer gets it's starting signal from the Crankshaft sensor/Circuit.
May want to try disconnecting the gray wire from the rear of the tach to see if the engine will start/get spark back as an internally shorted tach will keep an engine from starting.

I believe someone else recently had about the same symptoms you have with the negative tach reading and no spark that ended up having an odd issue...Don't recall what it was right away but if it comes to me and I can find it, I'll let you know...Could also try google searching Merc or possibly Volvo penta negative tachometer while cranking to see if anything comes up.

 

[JustJason]

Forgot to mention that my tach jumps and goes negative while cranking. And when connecting a computer to the ecm it shows no errors (and gives no beep errors).

Does anyone know where the tach is connected to in all of this? It's not connected to the coil which i first thought.

​There are always going to be codes on Mercruiser engines. Whenever somebody says that they hooked up a computer and it shows no codes/errors I don't believe them. Which scan tool was being used, and which codes came up when the scan tool was hooked up? I know that there will be at least 4 codes that pop up.

 

[shyrwall]

Hi, welcome to iboats!

What year is the engine?
Engine serial number handy?
Bravo or alpha stern drive?
Your topic title appear mixed up as you have 350 5.0L Mag MPI.... a 350 Mag would be 5.7L where 5.0 is 305L.. We can easily correct the title once you can provide the engine details better.

The tachometer gets it's starting signal from the Crankshaft sensor/Circuit.
May want to try disconnecting the gray wire from the rear of the tach to see if the engine will start/get spark back as an internally shorted tach will keep an engine from starting.

I believe someone else recently had about the same symptoms you have with the negative tach reading and no spark that ended up having an odd issue...Don't recall what it was right away but if it comes to me and I can find it, I'll let you know...Could also try google searching Merc or possibly Volvo penta negative tachometer while cranking to see if anything comes up.

Hi and thanks for the response.

Not sure what the year is. The boat is a 2008 Crownline 240LS. 2 serialnumbers are listed on the engine cover. One on the official sticker and then another one written on by past owner. Official = 1A418545, Written = 1A311531.

It's def a 350 Mag so yeah 5.7L.

I forgot to mention but I already tried (tried so much stuff.. ) disconnecting the tach wire with no difference. I will try googling to see if i can find something more about the negative tach thing.

Next thing I will try is to look a bit more at the crankshaft sensor. As I've understood it that sensor will also tell the ECM to fire the fuel injectors. So measuring if the fuel injectors are firering might point to to the crankshaft sensor. Even if I already changed it..cabling..who knows. Have to try something

 

[shyrwall]

​There are always going to be codes on Mercruiser engines. Whenever somebody says that they hooked up a computer and it shows no codes/errors I don't believe them. Which scan tool was being used, and which codes came up when the scan tool was hooked up? I know that there will be at least 4 codes that pop up.

Hi

The scan tool was used by the mercury service team. It was an old Mercury CDS MM-46944. I only saw a printscreen of the errors in the "fault history" section . There was one about Trim Sensor short which is an old problem I have ignored since the sensor needs to be replaced. The second error was of the camshaft position sensor but that was because the connector was unplugged while doing some testing. Resetting the history then showed only the Trim sensor.

 

[Fun Times]

Boat is a 2008 Crownline 240LS. 2 serial numbers are listed on the engine cover. One on the official sticker and then another one written on by past owner. Official = 1A418545, Written = 1A311531.

1A311531 comes up as an MERCRUISER SEA 350 MAG Bravo MPI / 1.7 Exhaust Riser Height / Model Number 444C0HMUU.
Is the engine a Sea-Core from merc?

1A418545 is coming up as a MERC bravo transom assembly W/EXH tube, Model Number 6811001N1.

 

[alldodge]

Are you getting 12V at the coil Pink/Wht pin C-A ?

 

[shyrwall]

Hi again

I solved it. So relieved

So I started looking at the crankshaft sensor today. Like I said wire continuety of all 3 wires (E in the picture posted by alldodge). However when I measured the grey 5V wire at the connector I only got 1V. That was strange... Opened up the plastic harness and about 15cm in from the connector the grey wire was almost completely cut. Obviously not 100% since my multimeter said it passed the continuety test but I guess if I instead had switched to checking the wire resistance the ohms would have been much higher than it should be. Anyway I fixed the wire and the engine started up immedietly.


So some theory.

I assume since the ECM never got the signal from the CPS it didn't send any fire signal to the IC Driver.

Regarding the tach going backwards/negative. When checking the ECM 555 Diag Module it appears that in this model the tach signal is actually coming from the ECM A10 and not from any sensor/coil or whatever. Since the ECM is a computer (doh) what if the algoritm to calculate the rpm fails if the pulses from the crankshaft sensor is 0/non existant. And results in a negative number. Which then reads on the tach as negative. Just a thought

Just happy it is working now

 

[Fun Times]

Good to hear/know you located the problem and was able to repair it.:thumb:

Sort of like mentioned, if the ECM doesn't see anything from the Crank Shaft Sensor (even due to bad wiring ), then the engine (ECM) is not going to get any reference signals to start properly activating the engines cranking, starting, running modes which includes the firing up the Tachometer, fuel injector pulses, coil spark & coil module in this case.

Since the wire was cut and being a bravo drive, have you recently installed a new sew water pump or any other service down in that general area? I ask due to in some certain circumstances, during servicing the sea water pump brackets tend to end up in the general area of the crank shaft sensor which could end up compromising the sensor and/or wiring.

 

[shyrwall]

Good to hear/know you located the problem and was able to repair it.:thumb:

Sort of like mentioned, if the ECM doesn't see anything from the Crank Shaft Sensor (even due to bad wiring ), then the engine (ECM) is not going to get any reference signals to start properly activating the engines cranking, starting, running modes which includes the firing up the Tachometer, fuel injector pulses, coil spark & coil module in this case.

Since the wire was cut and being a bravo drive, have you recently installed a new sew water pump or any other service down in that general area? I ask due to in some certain circumstances, during servicing the sea water pump brackets tend to end up in the general area of the crank shaft sensor which could end up compromising the sensor and/or wiring.

The impeller was changed in the pump about 1.5 years ago. It could have happened then. If i wiggled the cable a bit it did start to work. So maybe the problem existed for a while and corrosion or just some movement of the cable now made it stop work.

I also changed the IC a few months ago due to "no spark" also. And after changing the IC it immedietly started working. But now I think that maybe while working around the engine I came in contact with that wire and it started working again. I kept the old IC so I will try changing back to verify. Then I would atleast have a spare

 

[JustJason]

Hi again

I solved it. So relieved

So I started looking at the crankshaft sensor today. Like I said wire continuety of all 3 wires (E in the picture posted by alldodge). However when I measured the grey 5V wire at the connector I only got 1V. That was strange... Opened up the plastic harness and about 15cm in from the connector the grey wire was almost completely cut. Obviously not 100% since my multimeter said it passed the continuety test but I guess if I instead had switched to checking the wire resistance the ohms would have been much higher than it should be. Anyway I fixed the wire and the engine started up immedietly.


So some theory.

I assume since the ECM never got the signal from the CPS it didn't send any fire signal to the IC Driver.

Regarding the tach going backwards/negative. When checking the ECM 555 Diag Module it appears that in this model the tach signal is actually coming from the ECM A10 and not from any sensor/coil or whatever. Since the ECM is a computer (doh) what if the algoritm to calculate the rpm fails if the pulses from the crankshaft sensor is 0/non existant. And results in a negative number. Which then reads on the tach as negative. Just a thought

Just happy it is working now

​Glad that you found it, and thanks for the follow up. You should have (or the mechanic with the scan tool should have) been getting a code for the CKP. If the reference voltage is good at the ECM, but low at any various sensor, then that sensor is not going to be sending the correct signal back to the ECM, and will cause it to trip a code. If you just unplugged the CKP and cranked the engine over it would flag a code for the CKP. You kept on saying this entire time there were not codes.... when there should have been. The person using the scan tool might want to go back to school to learn how to use it. Food for thought.

 

[alldodge]

You bring up a good point Jason, he may also have an old scanner without any software updates

 

[JustJason]

You bring up a good point Jason, he may also have an old scanner without any software updates

​He said he was using CDS, which is the latest and greatest. I just pulled the book for giggles. He should have had a code 132 and it would have said something along the lines of 132 VR SNSR STR. I use Diacom and not CDS, but even my Diacom would have flagged a code for the CKP.

 

[shyrwall]

VR SNSR STR is also suppose to produce a bell warning. Even with a pulled cps connector and cranking there is no bell warning. A pulled connector would not produce a bell since the ECM has no idea of knowing that its pulled. It's not a dedicated +5V or 5V ground going to it so there would be no way of detecting if the CPS is there or not. So I think the VR SNSR STR error would only trigger if there is noise or something on the signal wire. Bad that no error triggers if there is a lack of signal.

 

[shyrwall]

It might also be that VR SNSR STR is only if the sensor fails while the engine is running. Might make sense since STR is "strategy". Not if the sensor has failed and you are cranking.

 

[achris]

Easiest test for CPS is to watch the software and monitor the RPM during cranking. If the CPS is working, you should see about 250 to 400 RPM. If nothing shows, then something not right with CPS or circuit.... (I also have Diacom, and it's very easy to see on their 'front page')

Chris...........

 

[alldodge]

Welcome cgm12mgc
This thread is over a year old. Need to start a new thread and link this one in it. We will be there to help