Absolutely frustrated with this Mercruiser engine

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?

While we may disagree on Quadrajets.....it does have to be a Marine version which I'm guessing may be a bit more than $269.;)
 
I like both carbs and EFI systems. There is no doubt that a properly maintained EFI system will outperform a carb over a wide range of rpms. The challenge is there is a lot more that can go wrong with the system from the high pressure pumps to the fuel injectors and ECM.

How much will an EFI system outperform a carb? Plenty of Youtube videos on the subject using dynos to measure the results. On a stock carb big block of 310 horsepower it is usually worth 30 horsepower at different rpm points. But that is only part of the story. If you run continuously at 3,000 rpm and tune the carb for that there really isn't much of a difference between the two.

There is no question that real time fuel management will beat a carb but for reliability in an apocalyptic world and green "New Deals".......it is hard to beat them for their simplicity.
 
@Hoplite808
I'm sure it is frustrating, plus a five hour time zone difference doesn't help with remote diagnostics.

I am not trying to be disrespectful or argumentative but...
If you truly can not find a good mobile mechanic, that has the right tools for an older EFI, and if you can't take it to a shop, you are going to have to commit to really learning this engine and invest in some tools. You can't keep throwing parts at it, that will break you for sure.

I am a retired ASE Master HD Mechanic, with extensive marine experience as well. You have to set aside the frustration and get very methodical about each thing you do. Write it down, make lists. Every test/step needs to prove or disprove something specific.
I would agree with others you really need a https://www.rinda.com and/or at very least some noid lights, a DVM, test light. Do you have a manual and parts break down?

Parts
https://www.marineengine.com/parts/...n-v-gm-454-v8-19941996/0f115700-thru-0f802349

Manual
https://www.scribd.com/doc/232174880/7-4L-454-Mercruiser-Manual#

Remember every time you touch it you may fix the issue or you could also introduce a new issue at the same time.
Work slowly and cautiously, your engine is 27 years old (mine is 29) harnesses and connectors get brittle, pins get loose, weak and corroded. You have had the top end completely apart for the heads, and several times now for the injectors and other fuel and electrical components. You had to disturb a lot of components.

So step by step.
The engine does not run at all now Y / N?

1. Your harness has three fuses in covered holders. ECM battery, ECM Injectors, Fuel Pump. check these again.
2. Injectors on your model fire in two banks of four injectors. So if one injector was "shorted" you lose all 4 injectors. This is where NOID lights help simplify checks.
3. Check the harness carefully, is there any points where insulation is cracking or peeling?
4. Any chafing at any of the securing loops, grommets, corners?
 
... There is no question that real time fuel management will beat a carb but for reliability in an apocalyptic world and green "New Deals".......it is hard to beat them for their simplicity.

This! Exactly. Marine Quadrajet or Edelbrock basically the same as long as no Holly and it doesn't get any simpler. Add a Malory with electronic conv. and your set. As Nathan pointed out a few post's back.
 
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.

There is exactly one Mercruiser certified mechanic in the whole state as far as I can tell. He is overwhelmed with work and just doesn't have to time available for a trouble call for me. I've called near about every legitimate marine mechanic on the island and they all either say they are too busy or they only will work on diesel. If I had a trailer perhaps I could leave it at a shop somewhere until they had time but I don't, and I also don't have $15,000 to buy one. The only haul out yard here will charge about $500 to haul out and then $83 dollars per day on the hard. They also require the mechanic scheduled prior to the haul out so it's on the hard as short a time as possible as they lack room to store boats.
 
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.

The new injectors installed and no leaks with the test gauge plugged in and reading 37psi the engine cranks over and if I spray a bit of starting fluid down the throat it sputters a bit but won't run. I've checked for spark at all eight cylinders and spark is good and strong. Timing has been checked, rechecked, and rechecked again and is dead on before I changed the injectors. Electric pump in the vapor separator tank is brand new and the mechanical lift pump on top of the sea water pump is also brand new. When it was running, the fuel pressure held at 37psi under load even when it was struggling to exceed 2000 rpm's. This is why I thought to pull the injectors and have them tested as they are the only thing left in the fuel system that could have a fault. I connect my continuity tester to the test plug and bridge the A and B connectors to put it into test mode. I count the beeps then to see if it throws any codes. It is not throwing any. I'm at a complete loss as to what is wrong with it. Perhaps the company that tested the injectors for me failed me as I found in the SELOC manual that the injectors should show 12 ohms of resistance +/-0.4. I checked that and they all read 12 ohms exactly on my meter. The only other thing I cant explain is there is a 12 gauge grey wire that comes out of the main harness that ends near the ECU that I can't figure out what its purpose is. If I connect it to a ground the engine alarms sound on the console nonstop but still no codes and the engine will still start and run with the old injectors with no difference in performance, or rather the lack thereof. So for now it's just loose. This wire does not seem to exist on the wiring schematics that I have. On the schematic the only grey wire should be 14 gauge and I found that and it is connected to what it's supposed to (Fuel relay to high pressure pump).
 
There is exactly one Mercruiser certified mechanic in the whole state as far as I can tell. He is overwhelmed with work and just doesn't have to time available for a trouble call for me. I've called near about every legitimate marine mechanic on the island and they all either say they are too busy or they only will work on diesel. If I had a trailer perhaps I could leave it at a shop somewhere until they had time but I don't, and I also don't have $15,000 to buy one. The only haul out yard here will charge about $500 to haul out and then $83 dollars per day on the hard. They also require the mechanic scheduled prior to the haul out so it's on the hard as short a time as possible as they lack room to store boats.
I wish we could do more to help you. As @hughespat57 made mention of, be very methodical in all that you do, and you'll find the problem. Maybe he'd like to take a little vacation to come visit you...
 
...if I spray a bit of starting fluid down the throat it sputters a bit but won't run.
I would think that then points to a fuel delivery issue. I know you've been all over the injectors and fuel delivery, but have you been able to determine that the injectors are actually being fired by the ECM? Maybe look into this kit. I know that shipping to the Islands sucks, but what else can you do? - https://www.ebay.com/itm/1156776659...rdMipAEAdf9CvEmxKEQCvnJpA=|tkp:Bk9SR46246XXYQ
The only other thing I cant explain is there is a 12 gauge grey wire that comes out of the main harness that ends near the ECU that I can't figure out what its purpose is. If I connect it to a ground the engine alarms sound on the console nonstop but still no codes...
This intrigues me; what possessed you to try shorting it to ground? Anytime I have an unknown wire go to ground, it ends in smoke!
If I connect it to a ground the engine alarms sound...and the engine will still start and run with the old injectors with no difference in performance, or rather the lack thereof. So for now it's just loose.
I'm confused by that last statement. Are you saying the engine will run with that wire shorted to ground?
 
Was the timing chain disturbed during any of this work?
 
The new injectors installed and no leaks with the test gauge plugged in and reading 37psi the engine cranks over and if I spray a bit of starting fluid down the throat it sputters a bit but won't run. I've checked for spark at all eight cylinders and spark is good and strong. Timing has been checked, rechecked, and rechecked again and is dead on before I changed the injectors. Electric pump in the vapor separator tank is brand new and the mechanical lift pump on top of the sea water pump is also brand new. When it was running, the fuel pressure held at 37psi under load even when it was struggling to exceed 2000 rpm's. This is why I thought to pull the injectors and have them tested as they are the only thing left in the fuel system that could have a fault. I connect my continuity tester to the test plug and bridge the A and B connectors to put it into test mode. I count the beeps then to see if it throws any codes. It is not throwing any. I'm at a complete loss as to what is wrong with it. Perhaps the company that tested the injectors for me failed me as I found in the SELOC manual that the injectors should show 12 ohms of resistance +/-0.4. I checked that and they all read 12 ohms exactly on my meter. The only other thing I cant explain is there is a 12 gauge grey wire that comes out of the main harness that ends near the ECU that I can't figure out what its purpose is. If I connect it to a ground the engine alarms sound on the console nonstop but still no codes and the engine will still start and run with the old injectors with no difference in performance, or rather the lack thereof. So for now it's just loose. This wire does not seem to exist on the wiring schematics that I have. On the schematic the only grey wire should be 14 gauge and I found that and it is connected to what it's supposed to (Fuel relay to high pressure pump).
When you say Injectors did you replace with the correct Mercury P/N? There are Saturated (high impedance) and there are Peak and Hold (low impedance) injectors - they are not interchangeable.
I don't see if you have tested for +12V power to the injector wire harness when the ignition is turned on. There is always +12 volts on one side of the injector connector - the ECM switches the bat negative side.
 
Chinese knock off injectors are impossible to tell from the real deal visually. Flow testing is the only way to know for sure. Also pricing is a dead giveaway to what your buying.
 
The only other thing I cant explain is there is a 12 gauge grey wire that comes out of the main harness that ends near the ECU that I can't figure out what its purpose is.

Now you have my curiosity going. Let me do some digging on this.
 
Okay.....I show three GRY wires coming out of your ECM:

Wire #1 Goes to the Manifold Absolute Pressure (MAP) sensor
Wire #2 Goes to the Throttle Position Sensor (TPS)
Wire #3 Goes to Fuel Pump Relay

Is that what you see?
 
grey has been a tachometer color for years
I agree but his EFI wiring diagram shows three Grey wires coming out of the ECM. Ironically the resolution on the Mercruiser site wiring diagram is terrible but you can make out GRY and that wire probably needs to be connected for the engine to run.
 
Just for clarity the Engine Harness wiring diagram which is separate from the EFI Wiring Harness... does show a separate grey wire at the engine harness connector which is not used. A picture would help confirm it.
 
Okay.....I show three GRY wires coming out of your ECM:

Wire #1 Goes to the Manifold Absolute Pressure (MAP) sensor
Wire #2 Goes to the Throttle Position Sensor (TPS)
Wire #3 Goes to Fuel Pump Relay

Is that what you see?

The fuel pump wire is the grey wire I found connected correctly and also the correct gauge. What the 12 gauge wire goes to I have no idea as the only 12 gauge wires should be red.
 
Whose injectors did you replace with? Did you put a noid light on the injector plugs to check for a signal?
 

Forum statistics

Threads
112,945
Messages
1,422,738
Members
60,928
Latest member
rkaleda
Back
Top