1999 40hp fires over and instantly shuts off

[mjl66o]

I recently picked up a 1999 Evinrude 40hp 4stroke which I have found is a rebadged df40 Suzuki, the motor has been sitting for years. I rigged the motor and have been trying to get it running it cranks and fires then shuts down instantly but will not stay running. If I try to start after it shuts down it will backfire, then crank without firing over if it sits for around 5 minutes it will crank and fire again still shutting down instantly. I have switched in a different ECM with no change in symptoms. I found a faulty cam sensor and replaced it currently the crank and cam sensor are testing within specs according to service manual. I purchased new 8.5 suzuki software there are no current stored faults and when observing fault logs the system does not detect failures in the system when cranking. Any recommendations on what to test next would be appreciate.

[redlowrey]

It sounds like it is either not getting enough starting fuel, or to much fuel, do this simple test, crank the engine over for about fifteen seconds, turn it off and remove the plugs and see if they are all wet, all dry, or only a couple are wet. If they are all wet, crank it over and see if a lot of fuel is being blown out the spark plug holes, you may have injectors that are stuck open, if it doesn't, install the plugs and lift the warm up leaver all the way and crank it back over, it should start.
If you haven't equipment to check fuel pressure and do an injector balance test, this will give me an idea of what is happening, just note the plugs condition when you pull them out.

[mjl66o]

I just tested it after 15 seconds of running the plugs smell like fuel, but none are wet. I lifted the warmup lever and same symptoms are present. I hooked up the scan tool I do not see an option for injector balance test but in the data logger there is injector failure count, and it does not log any failures for what that is worth when testing. I can read fuel pump duty and fuel injected amount I ran a log for about 55 seconds and was able to get it to fire twice during that time. Both times as soon as it fired over fuel pump duty dropped from 80-100% down to zero and the fuel injected amount stays at 16mcc except after the second fuel pump shut down it drops out for about 2 seconds before picking back up once the fuel pump is commanded back on. It looks to me like something is causing the computer to shut down fuel and possible spark as soon as it senses the engine is running and I am not sure what it is.

[mjl66o]

Here is the log when performing this test, you can hear the engine fire over just before the fuel pump demand goes to zero the first time it sounded like a few cylinders fired and shows better in the RPM the second time it was a very short sound I am guessing only one cylinder firing before it shutdown.

[redlowrey]

After seeing what you have done gives me some direction, the computer is shutting injection off, it is not seeing the correct voltages on pin C8 12 pin connector white plug, and D11 12 pin connector black plug. Your system if it has five separate plugs going to the computer has got the early type neutral switch set up that uses two inputs for information where the later uses one input.
So with the key on in neutral C8 should have zero volts on it, and five volts when in gear, D11 zero in neutral, and cranking voltage between 6 and 12 volts when cranking.

With the key on in neutral the computer will send a five volt bias voltage out of C8 to ground via the starter relay coil, in neutral this will be pulled to ground, when in gear neutral switch open no ground five volts.
Do some voltage drop tests on those pins and at the neutral switch either side, use battery negative for your meter ground. I have a gut feeling there is high resistance in your neutral switch, leaving some bias voltage on C8 when it should be zero key on in neutral.

[mjl66o]

Thank you for you help I just went out to perform voltage tests and both pin C8 and D11 are factory capped and not in use on this model. I have attached a picture of the connector schematic my repair manual has given me in case it is not accurate.

[redlowrey]

Does your computer have five individual plugs going to it, the picture you sent is the same as my early 2000 df suzuki manuals. Evinrude wiring might be different, any way get your multimeter and connect black to battery neg and probe the neutral switch and the associated wiring, suzuki use brown from ignition key to neutral switch, then yellow and green from neutral switch to starter relay coil ground.

With the key on in neutral there should be zero volts in that circuit, when you put it into gear you should see five volts, what I think is happening the when you turn the key to the start position the engine starts and when you let go of the key the computer is seeing five volts in the circuit and shuts off injection. leave the key in the start position longer and see if it runs longer.
Before you bypass the neutral switch check if there is any voltage in the circuit in neutral.

[mjl66o]

The ECM has 5 connections I am unable to find good schematics for the Evinrude I was using the Suzuki but now that I see D11 is capped but Suzuki is calling for that to be used I will have to chase wires to verify application on anything. As far as the neutral switch the engine shuts off before the key is released. I can chase wires and do voltage tests but based on your description keeping the key in the start positions will verify this is not the cause correct?

[redlowrey]

Ok can you just check the voltage at the neutral switch with the key on both sides to see if it zero, if it is then I go to the next step.

[mjl66o]

Ok I will check it tomorrow I did watch the neutral switch with the computer on the data logger and change during a test in which I had two failures.

[redlowrey]

It should tell you neutral switch on, or off. Or it might not, never thought of asking if it come up on your sds.

[mjl66o]

It says on during the whole test I performed.

[redlowrey]

If there is no voltage on the neutral switch either side with the key on, move your probe or test light to the injector supply voltage grey wire and note what the voltage is with the key on, and then how much voltage drop there is when you are cranking.

If it’s dropping more than three volts the main control relay may be dropping out, but I think you should see that on the sds.

About two years ago a guy on the forum had exactly the same engine, same symptoms engine would crank, start and stop, same five pin computer plug but c8 and d11 we’re in the computer,his problem was high resistance in the neutral switch.

There was too much resistance for the bias voltage to drop to zero, but when the voltage was higher coming from the ignition switch there was enough to go through the switch to the relay coil to ground and energising the starter, he kept saying there’s nothing wrong with the neutral switch.

In the end I told him to connect a test light to ground and probe the neutral switch, then crank the engine, guess what the engine started and kept running, the test light was pulling the bias voltage to ground, he then had a big spat because he had spent a lot of time on it and it was the switch.

[mjl66o]

I follow you and I am having the same symptoms you describe I was getting back voltage on the neutral switch circuit. So, after replacing the neutral switch with a spare I started to think it was the ignition switch which I dont have the key for the spare. I then reviewed the schematic found on attached link and when the key is in the start position the white (B+) grey (ignition) and brown (start circiut) are supposed to be connected so I bypassed the whole remote system and connected these three wires at the engine and have the same issue.

[redlowrey]

Ok, now we are getting some where, how high was the back feed voltage, if it was higher than five volts then it would not be the bias voltage sent out by the computer.

You need to find which pins the computer is using for the neutral circuit, just look at the colour of the wires, then look at the computer for the same colour.

Just remember even if you bypass the ignition switch, neutral switch, and jumped the starter, it still won’t start if there is any bias voltage on the pin the computer is using on the safety circuit.