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Please HELP me get my EFI running

Chris,

Not yet, it was on backorder, should be here this week.

I did get a Rinda Techmate Pro, but it says the engine has to be running to check it!

I am beginning to wonder......the tach and volt gauge both drop to ZERO after a few seconds of cranking. Any chance my rectifier box is bad, causing not enough voltage at the ECU?

Docksidemarineservices said:
Did you get the new ECU yet?
Click to expand...
 
Chris,

I think I found some more interesting information out while testing.

Below is a picture of my service manual and, in pencil, the ohm measurements I was getting.
Photo on 4-19-20 at 6.14 PM.jpg

Today, I found some instruction on a simpler way to test a 3 phase rectifier/regulator. Using my multimeter Diode test setting and checking flow from..........

positive lead (on positive rectifer/reg red wire) to each of the 3 yellow AC leads (from alternator to rectifier/reg)
negative lead (on positive rectifer/reg red wire) to each of the 3 yellow AC leads (from alternator to rectifier/reg)
&
positive lead (on negative rectifer/reg black wire) to each of the 3 yellow AC leads (from alternator to rectifier/reg)
negative lead (on negative rectifer/reg black wire) to each of the 3 yellow AC leads (from alternator to rectifier/reg)

I show voltage/flow BOTH directions between the negative rectifier/regulator lead and all 3 AC yellow leads.

Also.......I removed the ECU and looked at the back. I can see the tops of 5 capacitors. 4 of them look bulged up, which is consistent with a failed cap from my experience. However, it is hard to tell is they are popped/bulged or maybe the potting compound was thicker on these 5.

Is it possible that the engine would not run because the regulator/rectifier is blown? That the tach and voltage gauge drop off when cranking because power is not being supplied from the regulator/rectifier?

Is it possible that the blown regulator/rectifier killed the ECU?



Docksidemarineservices said:
Did you get the new ECU yet?
Click to expand...
 
UPDATE

I figured out the problem.

The rectifier regulator went bad. The AC (supply from alternator) to the ground wire reads flow both ways with a diode checking meter. No bueno.

It blew out the ECU.

These Mercury ECUs are poorly built with very little protection. They can blow from a bad fuel pump (different side of the board) OR in my case, a bad rectifier/regulator.

I was able to find a used ECU to test. It turned out to have the fuel circuit blown. I was able to run the engine by using my ECU to charge the fuel system/pressure. Then swap ECUs and run the engine until fuel pressure dropped.

A new ECU and it runs. Lot of headache and $ later of course.
 
boardhauler said:
UPDATE

I figured out the problem.

The rectifier regulator went bad. The AC (supply from alternator) to the ground wire reads flow both ways with a diode checking meter. No bueno.

It blew out the ECU.

These Mercury ECUs are poorly built with very little protection. They can blow from a bad fuel pump (different side of the board) OR in my case, a bad rectifier/regulator.

I was able to find a used ECU to test. It turned out to have the fuel circuit blown. I was able to run the engine by using my ECU to charge the fuel system/pressure. Then swap ECUs and run the engine until fuel pressure dropped.

A new ECU and it runs. Lot of headache and $ later of course.
Click to expand...

Good job... Sorry you didn't get much help from me or this page on this issue.... When these Pull start FI engines came out I was wondering what kind of out of the ordinary issues they were going to have... Well here is one... There should be a way to modify the charge circuit and power circuit for the ECU and pumps when you add an electric starter to the engine to isolate the ECU.
 
Last edited:
Figured out the issue. I hope this helps many others.

The computer/ECM is fragile, expensive and unrepairable. a huge number of otherwise serviceable engines with many years left, are sitting in parts yards due to the expense and difficulty troubleshooting this issue.

If you have a fuel delivery issue. It may be the hp fuel pump is an aftermarket model that draws slightly more amps than the factory pump spec. This is the high pressure pump. The factory replacement is extremely expensive and many knock offs exist. They can also damage the fuel
circuit in the ECM. But no worries, a relay to turn on the hp pump with the ignition switch fixed it, perfect.

Or, if the ECM is still sending 12v to actuate the Hp pump, but it is an aftermarket and draws too many amps, use the ecm circuit to actuate the relay. Which can now deliver adequate amps to the hp pump.
 
boardhauler said:
UPDATE

I figured out the problem.

The rectifier regulator went bad. The AC (supply from alternator) to the ground wire reads flow both ways with a diode checking meter. No bueno.

It blew out the ECU.

These Mercury ECUs are poorly built with very little protection. They can blow from a bad fuel pump (different side of the board) OR in my case, a bad rectifier/regulator.

I was able to find a used ECU to test. It turned out to have the fuel circuit blown. I was able to run the engine by using my ECU to charge the fuel system/pressure. Then swap ECUs and run the engine until fuel pressure dropped.

A new ECU and it runs. Lot of headache and $ later of course.
Click to expand...


What’s the chance you still have that test ECU?

My motor has the EXACT same symptoms that yours did. I found this thread when searching the ecu part number. Mine has had the high pressure pump replaced with a knock off. Still have fuel pressure, but no spark. Wondering if the ECU burnt up because of the pump. Really not wanting to drop $800 on a new ECU as a guess.... Same symptoms as yours. Coils will spark once when cranking, then nothing. Tach will jump up to 500 rpms when cranking, then drop to nothing. Still trying to test a few things, but my gut says the ecu is part or all of the problem.
 
Kraken,

Sorry, I sent the other ECU back to the used parts shop that I purchased it from. Check eBay, facebook marketplace, craigslist. Don't forget to cross reference all the Tohatsu ECU part numbers that will fit also.

These Mercurys are bad news. A big part of the problem is that Tohatsu makes everything and Mercury just marks the price waaaay up, then provides little to no support with repair or troubleshooting.

I had some good help from the Tohatsu techs. They were much more knowledgable and helpful. They were the ones that turned me onto the specs for the HP fuel pump that they purchase to put in these monsters.

I do suspect that the aftermarket fuel pump that was put in my engine could have caused all the problems. They draw way too many amps. This must strain the ECU , starve it for power and blow out either the ignition circuit or the fuel circuit.

The used parts shops have a lot of these engines sitting around that are perfectly good. No one wants to put a pricey ECU in.

For me, I'm looking for one of the newest 2 stroke Yamahas. They burn pretty clean and run great. The best engines around in my opinion. Travel around the world, they are everywhere, running and running and running. Suzuki has been working hard to establish themselves also. Very good feedback from owners and sales/service.
 
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