Absolutely frustrated with this Mercruiser engine

Hoplite808 said:
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Well, good news, I guess. The shop got back to me today about the injector tests. 3 of the injectors have a short when cold and another 4 of the 8 have a short when they are hot. So I gotta go find 8 new injectors. Anyone know where I can find a set that won’t break the bank?
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Hate to tell you, but break the bank. Start fresh and enjoy your boat (hopefully). :)
 
Update on the fun time I’m having. Replaced the injectors and it wouldn’t start. Took the injectors out and got them tested and found a couple of defects. Replaced and tested replacements and all 8 tested ok by a professional shop. $1000 later the engine now won’t run at all. I still can’t find a professional mechanic willing to look at it either. Does anyone have any idea what the heck could be wrong with this thing?
 
Hoplite808 said:
Update on the fun time I’m having. Replaced the injectors and it wouldn’t start. Took the injectors out and got them tested and found a couple of defects. Replaced and tested replacements and all 8 tested ok by a professional shop. $1000 later the engine now won’t run at all. I still can’t find a professional mechanic willing to look at it either. Does anyone have any idea what the heck could be wrong with this thing?
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Well, it sounds like you need to start over with the troubleshooting to at least try to narrow down whether it's fuel or spark. IIRC, the basic engine is sound (compression, cam timing), so it has to be fuel/spark. Without reading back through all of the previous entries, try a bit of fuel or ether into the throttle body to see if it tries to start. That would tell you that you have spark. If it does, check for twelve volts at the injectors. If that's good, see if the injector signal pulses while cranking. No light would be no power to the injectors (should be on anytime the key is in the "Run" position), and no pulsing light would be ECM and/or sensor related.
However, if it doesn't try to start with fuel down the throttle body, check for spark. Keep in mind that using a spark plug against the block won't tell you everything you need to know, as the relative narrow gap doesn't load the system like what the engine applies. It needs to be able to jump around a 1/4" gap. If it won't you may have a weak coil.
My apologies if I'm repeating what's already been posted earlier by others.
 
Hoplite808 said:
Update on the fun time I’m having. Replaced the injectors and it wouldn’t start. Took the injectors out and got them tested and found a couple of defects. Replaced and tested replacements and all 8 tested ok by a professional shop. $1000 later the engine now won’t run at all. I still can’t find a professional mechanic willing to look at it either. Does anyone have any idea what the heck could be wrong with this thing?
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I'm a bit confused. The second sentence says it won't start and sentence 5 says it now "won't run". Does it start and run poorly now? It makes a difference because the only thing I believe you changed were the injectors.

You went from a running engine that would not go above a certain rpm to one that refused to start and now runs poorly by "just" changing the injectors. That screams a fuel delivery problem. Am I missing something?

I realize you have addressed the pumps, pressure valve and injectors but if it is indeed worse now.....something is off with the rail pressure regardless what your gauge reads.
 
Hoplite808 said:
Update on the fun time I’m having. Replaced the injectors and it wouldn’t start. Took the injectors out and got them tested and found a couple of defects. Replaced and tested replacements and all 8 tested ok by a professional shop. $1000 later the engine now won’t run at all. I still can’t find a professional mechanic willing to look at it either. Does anyone have any idea what the heck could be wrong with this thing?
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To add to Nathan and John's post(s) The only thing you changed was the injectors? I would check that the injectors are firing. You can get an electronic injector tester that has a light in it. The injector wire just plugs into it and you can see if it is firing. A cheap 12v test light will also suffice.
 
This might be a good thing. Things got worse after working on the injectors which may mean you're working in the right area. Focus on anything you touched... connectors, wires, etc. Are you 100% sure the injectors are good, now? Got anyone nearby that you can borrow injectors from?
 
Hoplite808 said:
Update on the fun time I’m having. Replaced the injectors and it wouldn’t start. Took the injectors out and got them tested and found a couple of defects. Replaced and tested replacements and all 8 tested ok by a professional shop. $1000 later the engine now won’t run at all. I still can’t find a professional mechanic willing to look at it either. Does anyone have any idea what the heck could be wrong with this thing?
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What do you mean 'you can't find a professional mechanic to look at it'? Do you mean they don't travel? Someone on that island must be able to handle your problem, maybe the boat has to be taken to them.

You've got a year and much money in this, the boat has never ran correct since you've had it. Respectfully...I think all your efforts should be in finding/getting your boat to someone that can fix it.
 
Where did you get the new injectors, please post a link, I hope they are the right ones and oem quality. The cheap knockoffs may cause issues just like this
Hoplite808 said:
Update on the fun time I’m having. Replaced the injectors and it wouldn’t start. Took the injectors out and got them tested and found a couple of defects. Replaced and tested replacements and all 8 tested ok by a professional shop. $1000 later the engine now won’t run at all. I still can’t find a professional mechanic willing to look at it either. Does anyone have any idea what the heck could be wrong with this thing?
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Problem solved! You’re welcome. Hi tech bullshat. Old man walks away muttering….
458C931A-1A9F-4415-944D-E2A462103ABF.jpeg
 
You really need to know now with noid lights if the injectors are firing. Personally I would take it to a Marina on the island or call around. There has to a merc certified tech somewhere. Will follow till you figure this out it is strange
 
Pirate Lady said:
Problem solved! You’re welcome. Hi tech bullshat. Old man walks away muttering….
View attachment 140919
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Definitely a choice.....but it doesn't come cheap. Fuel pump....new distributor and of course any systems that rely on the ECM. It is tempting if you can't figure out the real problem. I think the OP is working on the right area but it is frustrating when you can't see what the engine is actually doing and whether or not it actually has enough fuel pressure.

I would switch to a carb if the ECM is fried .......that pays for the conversion.
 
PlayDate said:
Definitely a choice.....but it doesn't come cheap. Fuel pump....new distributor and of course any systems that rely on the ECM. It is tempting if you can't figure out the real problem. I think the OP is working on the right area but it is frustrating when you can't see what the engine is actually doing and whether or not it actually has enough fuel pressure.

I would switch to a carb if the ECM is fried .......that pays for the conversion.
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That must mean it's the $2500 ECM. Ouch. Yeah, $1500 from Jegs is a bit easier. for sure.
 
SKybolt said:
That must mean it's the $2500 ECM. Ouch. Yeah, $1500 from Jegs is a bit easier. for sure.
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Marine carb, distributor, coil, fuel pump, intake and timing tape for the harmonic balancer will get you a heartbeat.:)
 
PlayDate said:
Marine carb, distributor, coil, fuel pump, intake and timing tape for the harmonic balancer will get you a heartbeat.:)
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Complete ignition conversion kit (electronic ignition - no points), $550
Intake manifold - $450
Carb - $269 for @Pirate Lady's Quadrajet (I like Quadrajets!)
Yeah, it's drastic, but it'd get you going. But, they can be made to run just fine with the stock setup.
Any progress made on the tests pointed out earlier?
 
We have carburetors on our twin 7.4s. One would not go over 2000RPM under load. With no load it would go to 4,500+ RPM with no effort. You have high pressure fuel system mine was low pressure. Perhaps your fuel pump is going but has not failed and does not pump at the rate it did when new but still puts out good pressure. A fuel pump for me was 200 for you it is probably a lot more.
 
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