Mercruiser 5.0 MPI Delayed Ignition Alarm

[Xerxes3rd]

I have a 2002 Stingray 240 CS with a Mercruiser 5.0 MPI I/O (Mercruiser S/N: 0M347458). When I started the boat this season, it fired up and ran for a few minutes, then died. Now, when I turn the key in the ignition to the "Run" position (without trying to actually start the engine), the ignition alarm doesn't do its test beep like normal, and I don't hear the fuel pump run (normally it runs for a few seconds, I assume to prime). After about 20 seconds, the ignition alarm sounds steady on, and the fuel pump runs continuously. If I cut off the safety/lanyard switch, the fuel pump stops, but the alarm continues. The engine will turn over if I try and start it, but it won't actually start. On the gauges, I get battery voltage, but the oil pressure gauge remains at 0 (although I do see the needle move a tiny bit when I first turn the key). I checked the main cannon plug, and it passes a quick visual inspection (although it was really difficult to remove).

Any thoughts? Thanks!

 

[alldodge]

Check the fuses and the main power relay (MPR). The MPR is next to the fuel pump relay and both are the same type

At one of the other sensors check for 5V on the pink wire. The easest may be the water pressure switch on the PS cooler, or IAC

As for the way the alarm is work, it is working correctly. Your not getting the initial 2 beeps because something is not right when power is applied. The ECM is seeing something that is not correct so no 2 beeps. Leaving the key ON then the timer times out and a solid alarm sounds.

 

[Xerxes3rd]

Both relays seem to be fine; I checked them with a meter and a 12V supply (I forgot that I had replaced them recently). I’m reading 0.2V across the terminals on the IAC wire.

 

[alldodge]

I’m reading 0.2V across the terminals on the IAC wire.

If the 0.2 is across the pink and ground, then you have a shorted sensor. Place meter on pink and ground, then one by one remove sensors until 5V shows back up

 

[Xerxes3rd]

I’ll check them tomorrow, thanks!

 

[Fun Times]

Try wiggling the main cannon plug all around while the key is on to see if that help any...Also carefully wiggle all the wires on the engine and at the ECM.

Tap on the relays lightly along with the ECM to see if something changes with key on....Hopefully you didn't lose a circuit driver component within the ECM possibly on the 5 volt side for example...,https://whipplesuperchargers.com/index.php?dispatch=products.view&product_id=73

 

[QBhoy]

Try messing with the lanyard toggle. This would do exactly as you described.

 

[Xerxes3rd]

Try wiggling the main cannon plug all around while the key is on to see if that help any...Also carefully wiggle all the wires on the engine and at the ECM.

Tap on the relays lightly along with the ECM to see if something changes with key on....Hopefully you didn't lose a circuit driver component within the ECM possibly on the 5 volt side for example...,https://whipplesuperchargers.com/index.php?dispatch=products.view&product_id=73

I tried tapping the relays and no change. Is there a general bench-test procedure for the ECM if I pull it out? I should be able to apply +12v to simulate the "key on" signal and measure the pin that drives the pink wire output. I'm capable of replacing board-level components.

 

[Fun Times]

Is there a general bench-test procedure for the ECM if I pull it out? I should be able to apply +12v to simulate the "key on" signal and measure the pin that drives the pink wire output. I'm capable of replacing board-level components.

Not that "I'm" aware of experience wise for bench testing but I have recently read where a highly respected Mercuiser master tech that hangs out on an offshore boating forum has started to test the 555 ECM's and then open them up for repairs and at one point he made it sound sort of easy to where they just pull apart but don't quote me on that.

So with knowing that if you have some board-level component experience, you get mercuiser's service manual # 36 that shows the pinout locations/numbers/wiring colors going into the ECM to help give you an idea of wire pins travel, "possibly" some tools, wire harnesses/connectors from a place I believe has something to do with part manufacturing of these units by studying the following links below and probably the added general guided help of iboats residence member of computer motherboard design/repair, etc. DouglasW .... I bet you probably could take the time to figure out if the ECM is a problem and repair as needed....If you do test & open it up 'Be sure to create a you-tube type video documentary.

https://www.offshoreonly.com/forums...uiser-ecm555-pcm555-flashing-calibrating.html
https://neweagle.net/support/wiki/index.php?title=Controllers#ECM-555-48_.28ECM48.29
https://neweagle.net/support/wiki/index.php?title=MotoHawk-Platform
https://www.offshoreonly.com/forums...355702-anyone-have-bad-ecm-s-need-tested.html

 

[Xerxes3rd]

Sorry for the delay in updates. I ran some more checks, and have determined that the lanyard switch is working. With the ignition key switched to "on," I get 11.8v on the purple wire (called "wake" in the schematic- Service Manual 31 page 4D-7). I measured this at the diagnostics connector.

Once the ignition key is on for 20 seconds, the main power relay and the fuel pump relay both close. This tells me that the ECM is capable of driving both relays (presumably using low-side relay drivers), and that both relays are operational.

At this point I assume the ECM might be spitting out a fault code over the CAN/diagnostic lines? It looks like the cheapest way to read the code(s) is the Bluetooth VesselView Mobile kit (8M0115080) for about $250.

After looking at the ECM itself, it doesn't appear to be easy to open to get at the board, so I'd prefer to eliminate other options before cracking it open.

Any additional thoughts would be appreciated, and thanks for all the help so far!

 

[alldodge]

Once the ignition key is on for 20 seconds, the main power relay and the fuel pump relay both close

Don't think its the ECM right now, but maybe. Taking 20 seconds to energize the relays is way to long, MPR happens when turning the key and the FPR should happen right after that.

I would focus on the 5V which should be on the sensors post 4

 

[QBhoy]

I know it seems obvious but try another battery.
I had a similar thing few seasons ago where the engine would turn over but not start...but on release of the key it would sometimes take a cough and splutter. Plain thinking would suggest it wasn’t the battery of it can turn it over right...I was wrong.
Turns out these things are that power dependant that they will it fire unless it thinks it has a certain level of juice to it.
When I was turning it over it simply didn’t have enough beans to fire it...until the load from the starter was removed by releasing the key. For that brief moment, it detected it now had enough and would give an attempt at firing, but obviously not start because the engine was only just turning over after key release.

 

[Bdaviskar]

Is it consistently 20 sec? Or does the time vary when the wake alarm finally sounds and the FPR is turned on.

 

[Bdaviskar]

If it varies you could have a loose connection or corroded wire anywhere in the 12v circuit. Did you check the wires and connections behind the dash to the 20 amp fuse or ignition switch?

 

[Xerxes3rd]

Don't think its the ECM right now, but maybe. Taking 20 seconds to energize the relays is way to long, MPR happens when turning the key and the FPR should happen right after that.

I would focus on the 5V which should be on the sensors post 4

Will do; I'll find a good point to measure the 5V line. I agree about the 20 seconds- under normal operation, the MPR closes immediately, the alarm sounds for a second, and the FPR should close for 3-5 seconds.
​​

I know it seems obvious but try another battery.
I had a similar thing few seasons ago where the engine would turn over but not start...but on release of the key it would sometimes take a cough and splutter. Plain thinking would suggest it wasn’t the battery of it can turn it over right...I was wrong.
Turns out these things are that power dependant that they will it fire unless it thinks it has a certain level of juice to it.
When I was turning it over it simply didn’t have enough beans to fire it...until the load from the starter was removed by releasing the key. For that brief moment, it detected it now had enough and would give an attempt at firing, but obviously not start because the engine was only just turning over after key release.

Good point. Would connecting a jump pack do the trick if a battery was bad/poor? Alternatively, I suppose I could swap my start & run batteries to see if that makes a difference.

Is it consistently 20 sec? Or does the time vary when the wake alarm finally sounds and the FPR is turned on.

It's consistently 20 seconds, and after 20 seconds, the alarm is continuous and the FPR is on continuously as well. I assume the ECM is waiting for some other condition to occur before it closes the MPR (since the low side of the coil goes to the ECM, I assume it's in direct control of both relays).

If it varies you could have a loose connection or corroded wire anywhere in the 12v circuit. Did you check the wires and connections behind the dash to the 20 amp fuse or ignition switch?

I checked voltages on both legs of the 20 amp fuses. I assume the 12v wires there are OK, since the ECM is capable of closing both the MPR and FPR, as well as running the fuel pump?

 

[alldodge]

Measure 5V at water pressure sensor on the power steering cooler