Mercruiser 5.0 mpi No Start

[18Booth]

Hello everyone, I am working on a 2003 Mercruiser 5.0 MPI OM625338 that is having start-up issues. When I turn the key on I can hear the beep and can hear the fuel pump kick on. Try to start it, and it just cranks and will not fire. However, if I spray some starting fluid in the throttle body it will fire and run great. Any ideas? I have to use spray every time to start but again while it’s running it runs excellent. Just completely stumped.
Heres what I have done so far:

Fuel filter changed
Scanned the engine and no codes popped up
New cap and rotor
41 psi at the fuel rail on top of the engine
Pulled the little filter out of the throttle body and that still didn’t help.

 

[Scott Danforth]

welcome aboard

what RPM are you getting when cranking? if your battery is weak, it wont spin the motor fast enough for the ECM to fire the injectors. you should be spinning above 220 RPM, a good battery will spin the motor closer to 300 RPM

41 psi is a bit low

 

[alldodge]

The injectors are not being turned ON and as Scott mentioned the motor needs to turn fast enough. What is the tach showing?

 

[18Booth]

I will try starting it today and see what the tach is showing. The boat is plugged in at the dock and the battery charger is on while I’m trying to start it so you’d think that would be enough boost to start fine? But I will check to see what year the batteries are and load test them too. Thanks guys and will keep you posted

 

[tpenfield]

Just looking through a Mercruiser MPI manual (not the exact one for your engine, but probably similar) Just wondering if the the engine 'thinks' it is in "fuel cutoff mode" because the distributor IC module is not sending pulses at low RPM.

FUEL CUTOFF MODE
No fuel is delivered by the injectors when the ignition is OFF, to prevent dieseling. Also, fuel pulses are not delivered if the ECM receives no distributor reference pulses, which means the engine is not running. The fuel cutoff mode is also enabled at high engine rpm, as an overspeed protection for the engine. When cutoff is in effect due to high rpm, injection pulses will resume after engine rpm drops slightly.



The distributor is supposed to switch to switch from 'IC module' control to 'ECM' control at/above 300 RPM. Just wondering if the ECM is not receiving the reference pulses as it should when the RPM is below 300 and therefore not firing the injectors.

:noidea:

 

[Searay205]

Interesting thread. On my old boat 1988 3.0 liter I tested numerous starters and they all cranked the engine about 200 rpm. I guess starter technology has improved to get 300 rpm. my issue was the starter would take forever to fire the boat and I found it was only cranking 100 rpm, had been submerged once. New ones were 200 rpm really helped starting the engine LOL!

 

[tpenfield]

Well, I'm not sure that many starters can/do get the engine up to 300 RPM. I think there is some confusion about the required cranking speed of the engines . . . Based on my research the "300 RPM" is when the (EST) ignition timing transfers control from the distributor (IC Module) over to the ECM. Not that the starter has to get the engine up to that speed, as I don't believe that many starters quite get there, but it is merely when the transfer of control happens.

Below 300 RPM, the ECM does not 'think' the engine is running yet, and it is letting the distributor handle the ignition timing . . . essentially what is called 'base timing' at that point. The ECM will have an injector pulse for 'starting mode' (below 300 RPM) and also for 'running mode' - that is calculated based on all of the sensor input.

As to the OP's issue, it appears that the injectors are not firing until the engine gets over 300 RPM, and the use of starting fluid is probably what is allowing the engine to get to that speed, whereas the starter motor alone cannot. It seems like below 300 RPM the distributor is not sending the ignition pulses to the ECM. I believe the ignition pulses should be coming from the IC module in the distributor.

That's my take of the situation . . .

 

[muc]

fuel pressure is 43psi +or- 2psi. It should drop 4-6psi with high vacuum at idle.
this engine has a crank position sensor that supplies engine speed information to the ECM. the distributor is just a spark switch.

I would check the contents of the fuel filter for anything other then good fuel, and check for battery voltage to the injectors.

 

[18Booth]

If the crank position sensor was bad, the engine wouldn’t run at all correct?

 

[muc]

If the crank position sensor was bad, the engine wouldn’t run at all correct?

Yes,usually.
But they can rarely be 1/2 bad.
Suggest you check voltage at injectors, both at key on and cranking. This is a good opportunity to use the min/max feature of your DVOM.

 

[18Booth]

Cranked the boat over today and it definitely is cranking over fast enough. The tach climbs as your cranking it over. Load tested both batteries and there are at 12.5 and under load at 11v. As the engine is cranking over, there is a spuratic beeping noise that I know wasn’t there before. It happens every time your rolling it over. Anything to do with the startup?

 

[alldodge]

Need to see if there are codes, could be the beeping is voltage is falling off

 

[18Booth]

There were no codes besides the ones that will always pop up like 130, 75, 119 etc. I did notice the voltage gauge basically bottoming out past 8 volts while the engine is cranking over but it definitely had enough voltage because it cranks over very well

 

[alldodge]

I'm going with the distributor module as Ted mentioned. If the boat voltmeter is showing what the ECM/Dizzy is actually seeing then it would be an issue, but in most cases it would not be showing actual

 

[muc]

Maybe I'm missing something?

I'm going with the distributor module as Ted mentioned. If the boat voltmeter is showing what the ECM/Dizzy is actually seeing then it would be an issue, but in most cases it would not be showing actual

Next post from O.P. “Replaced sensor in distributor, but there are no wires connected to it. Is it WiFi or Bluetooth?”

 

[alldodge]

Maybe I'm missing something?


Next post from O.P. “Replaced sensor in distributor, but there are no wires connected to it. Is it WiFi or Bluetooth?”

I took Ted's post as it had EST ignition, did not look using his SN until now. So I messed up again for not looking at everything. Have never had a problem saying I messed up or missed something

Your the smart one here, help us out what is the problem

 

[muc]

Your the smart one here, help us out what is the problem

I’m not sure about the “smart one”. I look at it as I’ve had MANY more opportunities to make mistakes and learn from them. 30 years of factory schools helps to.

One of my sales pitches when looking for a new job was that I’ve made or seen just about every possible screw up once.

I thought i was helping by pointing out that this isn’t a EST system so the distributor probably doesn’t have anything to do with the issue. And the next logical step is to check fuel quality and battery voltage to the injectors key on and cranking.

I’m a big fan of testing instead of guessing.

 

[alldodge]

next logical step is to check fuel quality and battery voltage to the injectors key on and cranking.

If you would have ended with something like this, then I would say I messed up, but there was nothing of how to proceed,

Maybe a what needs to be done next for the OP, that is my point

 

[muc]

2 days ago I posted this.

fuel pressure is 43psi +or- 2psi. It should drop 4-6psi with high vacuum at idle.
this engine has a crank position sensor that supplies engine speed information to the ECM. the distributor is just a spark switch.

I would check the contents of the fuel filter for anything other then good fuel, and check for battery voltage to the injectors.

 

[muc]

Yesterday I posted this.

Yes,usually.
But they can rarely be 1/2 bad.
Suggest you check voltage at injectors, both at key on and cranking. This is a good opportunity to use the min/max feature of your DVOM.

I thought I was making troubleshooting recommendations. If the O.P. Wants to listen to others, not much I can do. If the O.P. doesn’t know how to these steps, they could ask.

Just thought they were being led down the wrong road with the focus on fuel pressure and distributor module.

You can lead a horse to water..............