1997 GT40 quiting sporadically

have been on this forum multiple times over the past 3 years and haven't heard of anyone reporting this particular problem, but I'll bet others have suffered from it. I have a 1997 Ski Nautique with a GT40. Beginning about 3-4 years ago, the engine would, on rare occasions, shudder, partially quit, run again, sometimes quit altogether. I attributed it to possible water in the fuel and started adding a fuel additive to absorb the water. At first, it was only a couple times a season, but it became more and more frequent. On a couple occasions, I had to get towed in. By the time I got home to trouble shoot it, it ran fine. After searching the forums, talking to experts, I did all the things I've read about in the forums: changed the low pressure fuel pump, ECA and fuel pump relays, checked the fuel pressure at the injector rails, checked for blocked pickup tube or venting in the fuel tank, cleaned the connections to the inline 50 amp fuse, checked the kill switch, checked the electrical grounds, swapped out the ECA with one from another same model year boat, new distributor cap, plug wires, etc. As it became more frequent and definitive, it seemed to act like someone intermittently was pulling the kill switch. Finally, over the fourth of July, the engine quit for good and it would not run. It turned over fine, but no go. I had copied the PCM maintenance manual years ago and was able to follow some of the diagnostic routines, and had purchased an OBD1 code reader but no abnormal codes ever came up. What I really needed was the breakout box to completely diagnose the system. I found one on e-bay for $100 and began to go through the diagnostic routine in the manual. To make a long story shorter, I was getting power to the ECA relay, but no power to the ECA itself. This would indicate that the ECA relay was bad. I had already switched this out, and had four relays on hand. I kept getting the same fault. Certainly four relays couldn't all be bad! I tested all four relays by putting 12v across the appropriate contacts, and all worked fine. So even though I could measure a voltage to the relay, for some reason it wasn't tripping the relay. The power to trip the relay comes from the ignition switch, and I noticed that it was about 1.5 volts less than the battery voltage. Could there be some corrosion or bad connection between the ignition switch and the ECA relay? I traced the purple ignition wire from the ignition switch through all the connectors back to the engine, testing for resistance at each segment. The wire then goes to the accessory starter solenoid where another wire (brown) connects to the same terminal. This wire then goes directly to the ECA relay. There was a huge resistance across this segment. As I opened up the wire bundle, there is a diode (1N4001) between the solenoid terminal and the ECA relay, the purpose of which is to protect the ECA from someone inadvertently hooking up a battery backwards. I placed a jumper across the diode and Voila'. the engine started and ran perfectly. There are actually two diodes in parallel coming from different terminals on the solenoid. I just had to jump the one directly attached to the purple ignition wire. I asked my brother, an electrical engineer if diodes fail, and he said they do, but it's not all that common. Depends on the circuit. These diodes can be had for about 10 cents apiece. I splurged and bought five for 32 cents apiece, hoping they must be better quality. I now have 100 years worth of diodes. I ran the boat for a couple hours yesterday, and it runs perfectly. In retrospect, it all makes sense now. The diode was dying and intermittently wouldn't allow enough current to open the ECA relay, hence the surging, quitting, etc. Pulling the kill switch has exactly the same effect as it is wired directly into the ignition circuit. I hope this post helps others who have the same problem. Four years of headaches, hundreds of dollars in replacement parts, and many man-hours of work, all due to a ten cent diode!

gun-driver wrote: Nice work and a very good write up Thanks

What he said

I'll TRY to download some pictures that MAY be helpful. These were taken after the FIX.
First, the location of the accessorY starter solenoid is just below and behind the ECA and fuel pump relaYs. Two brown wires are coming off this into a wire bundle.

A closeup of the solenoid with the two brown wires that have the diodes:

The wire bundle that You have to take apart to identify the wires and the diodes that power the ECA relaY and ultimatelY the ECA:


I hope this helps.   Not sure whY the spelling is incomplete for some words.
It looked fine when I tYped it.

boneflier wrote: I'll TRY to download some pictures that MAY be helpful. These were taken after the FIX. First, the location of the accessorY starter solenoid is just below and behind the ECA and fuel pump relaYs. Two brown wires are coming off this into a wire bundle. A closeup of the solenoid with the two brown wires that have the diodes: The wire bundle that You have to take apart to identify the wires and the diodes that power the ECA relaY and ultimatelY the ECA: I hope this helps.   Not sure whY the spelling is incomplete for some words. It looked fine when I tYped it.

That's awesome. Thanks for posting that.
My problem seemed to have turned out to be some crap in a little screen in the anti-siphon valve.