Mercruiser 5.7 not getting spark

KaeG · Feb 12, 2013

Hey forum users. We have a problem here. Can't get my boat running! I'm not entirely sure what year this motor is, but it is definitely a 2001 or newer, with the DEI ignition system. Just like the one found in my truck. Or your blazer. It is not getting spark. I have tested 12v present @ coil, 12v present @ coil module (that little black thing next to coil), and 12v from that module to the coil when cranking. If this was a truck motor i would have it running already, but there are quite a few components installed here that make it quite different to diagnose. Fuel pressure is good, injectors are activating, new plugs. Could somebody please telle what my next step would be? I thank you in advance.

Bondo · Feb 12, 2013

Re: Mercruiser 5.7 not getting spark

KaeG said:
Hey forum users. We have a problem here. Can't get my boat running! I'm not entirely sure what year this motor is, but it is definitely a 2001 or newer, with the DEI ignition system. Just like the one found in my truck. Or your blazer. It is not getting spark. I have tested 12v present @ coil, 12v present @ coil module (that little black thing next to coil), and 12v from that module to the coil when cranking. If this was a truck motor i would have it running already, but there are quite a few components installed here that make it quite different to diagnose. Fuel pressure is good, injectors are activating, new plugs. Could somebody please telle what my next step would be? I thank you in advance.

Ayuh,.... Welcome Aboard,... 1st thing to do is find the Serial Numbers on yer motor....

We've gotta know what yer workin' on, Exactly....

blouderback · Feb 12, 2013

Re: Mercruiser 5.7 not getting spark

Do you have the safety lanyard connected at the helm?

Don S · Feb 12, 2013

Re: Mercruiser 5.7 not getting spark

blouderback said:
Do you have the safety lanyard connected at the helm?

The kill switch kills power to the coil, and he has 12V to the coil.

Problem is, it must be EFI because a carbed engine only used a Thunderbolt V. Without a SN, it's impossible to say where the problem is.

KaeG · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

Don S said:
The kill switch kills power to the coil, and he has 12V to the coil.

Problem is, it must be EFI because a carbed engine only used a Thunderbolt V. Without a SN, it's impossible to say where the problem is.

Thanks for the responses guys. I will get you a serial number, as soon as I figure out where it is! Lol. And to my understanding the guy we bought this boat from removed all the safety/kill devices. From what I can see there is only the neutral safety switch and shift interrupter that remain. I see no lanyard switch.

Don S · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

The serial number is usually on a tag on the flame arrestor cover. There is another metal tag just above the starter on the motor where the flywheel cover attaches.

KaeG · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

Alright guys, the only tag I found was on the rear starboard side. #0W626302 Mercury Marine. Anything that may have been stamped on the block has corroded away.

KaeG · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

And Don is correct this is EFI w/ DEI ignition system. Merc ECU right on top of the motor. I tested .997 volts coming from ECU to ignition module by coil. Seems to me that ECU should be supply a 12V signal to ignition, not .997V. So something is inhibiting my ignition.

Don S · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

Might want to recheck that serial number if you actually have a 5.7L. That 0W number is your Merc serial number and it shows you have a 5.0 engine, not 5.7

Mercruiser 5.0 MPI Alpha I Gen II outdrive.
Serial No: 0W626302 Model No: 4M410GLTT\

That OW number is also way too new.
Is this a throttle body efi system?

Don S · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

Just in case you have a newer engine with the older fuel system, and we understand what a DEI distributor is. Which distributor do you have from the picture below.

The other thing we need to know is which ECM you have.

KaeG · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

Hey Don, thanks for your input. If it shows a 5.0L than it must be. Just looked too similar to my 5.7L. In case you can't tell I'm not much of a boat guy. But hoping to be! And I have the distributor shown in the second picture. Module is a Motorola from Mercury #ECM0501

Don S · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

Module is a Motorola from Mercury #ECM0501

So I take your ECM in the picture is the lower right (correct)? I don't memorize every part number that may be found on a module.

Was that the actual serial number? If it was, it all makes sense, but it's not a 5.7.

PS you can't tell by looking if an engine is a 5.0 or a 5.7. They look the same on the outside.

Fun Times · Feb 13, 2013

Re: Mercruiser 5.7 not getting spark

KaeG said:
I tested .997 volts coming from ECU to ignition module by coil. Seems to me that ECU should be supply a 12V signal to ignition, not .997V. So something is inhibiting my ignition.

I'd look at this as something else is not telling the PCM to activate the ignition coil driver module. You have already tested for and found 12v going to the coil & ignition coil driver module, you're good there. The coil & ignition coil driver get their 12v from the same fuse wire, PNK/WHT.

I would first suspect something's amiss within the crankshaft or camshaft position sensors, wiring, tachometer, etc, due to more common failures.

As an example only, see this thread,
http://forums.iboats.com/mercruiser...-but-will-not-spark-no-rpm-diacom-590452.html

While cranking the engine over, does the RPM gauge move at all?

KaeG · Feb 14, 2013

Re: Mercruiser 5.7 not getting spark

Don S said:
So I take your ECM in the picture is the lower right (correct)? I don't memorize every part number that may be found on a module.

Was that the actual serial number? If it was, it all makes sense, but it's not a 5.7.

PS you can't tell by looking if an engine is a 5.0 or a 5.7. They look the same on the outside.

Don, it is the module pictured in the lower right. Thank you. I'm not sure if that was the serial number or part number. It was the only legible number on the module labels.

KaeG · Feb 14, 2013

Re: Mercruiser 5.7 not getting spark

Fun Times said:
I'd look at this as something else is not telling the PCM to activate the ignition coil driver module. You have already tested for and found 12v going to the coil & ignition coil driver module, you're good there. The coil & ignition coil driver get their 12v from the same fuse wire, PNK/WHT.

I would first suspect something's amiss within the crankshaft or camshaft position sensors, wiring, tachometer, etc, due to more common failures.

As an example only, see this thread,
http://forums.iboats.com/mercruiser...-but-will-not-spark-no-rpm-diacom-590452.html

While cranking the engine over, does the RPM gauge move at all?

This is kind of the direction I was going. We have batt + supply to coil and coil driver. We have 12v (drops to 8-9v when cranking) from driver to coil. No signal from ECM to coil driver. Ground on driver is good. I'm not near the boat today but I will check those things you suggested when I get back to it. How can I check camshaft sensor or crank sensor signals/correlation without a scan tool?

Don S · Feb 14, 2013

Re: Mercruiser 5.7 not getting spark

Well, since we are now sure of what you have, here is the manuals for your 555 ECM.

Service Manual #36 Rev 1 SBC - Download - 4shared - Don S

There are a lot of tests that can be done without a scanner, things like checking the fuses, seeing if the main power relay is working etc.

You will have to spend some time reading the manual before you understand all it's saying, and putting all the right wiring diagrams together.

KaeG · Feb 20, 2013

Re: Mercruiser 5.7 not getting spark

Thanks for the manual Don. Finally got back to the back to the boat. Here's what I have so far:

No rpm on tach. However I found the tach lead from ECM and connected my DMM set on Hz seems I have tach signal (do t know if I did that right)
Ran through MPR test. Relay clicks on and powers up ECM. ECM sending power back to relay.
I have all necessary B+ at coil and coil driver. I have good continuity from coil to coil driver, and good continuity from ECM to coil driver. Not sure what the signal is supposed to be from ECM to coil driver.
Here's what has me stumped:
I only have 3.5v on the CPS sensor connector. Ground side showing 5v. Going through the flow chart it seems to assume I have no cam sensor. I tested the same 3v at distributor, and 5v on the ground circuit. I'm assuming the two components share the circuits. Cam sensor inside distributor? I also cannot find any of the splice packs (specifically 100 and 101).
Going to walk away from it now before I short circuit my brain.

Fun Times · Feb 20, 2013

Re: Mercruiser 5.7 not getting spark

Now do yourself a favor and google How to test both crankshaft and cam position sensor. There's lots of reading to do and videos to watch online to help you through the process of elimination.

Also unhook the gray wire off the back of the tach as a test.

Good luck.

Don S · Feb 20, 2013

Re: Mercruiser 5.7 not getting spark

If your tach is shorted to ground internally, that will kill your spark. Removing the gray wire off the tach itself will stop that short and you could get your spark back. You can't do it on the engine, you have to take it off the tach.

Mercruiser 5.7 not getting spark

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