1997 GT40 suddenly quits intermittently

[boneflier]

I 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!

[JGordon210T]

Had the same thing on my 95 Sport. It blew my mind how small they were and their placement into such a large wire. Gratifying feeling when its fixed.

[Kev]

I have been wrestling with a similar problem in our 98 SN. The engine starts and idles normal, however when it warms up 5-7 minutes it developed a slight hesitation from 1000rpm through to 4000 rpm. The revs seem to drop back by about 25 rpm. It is not noticeable from idle to WOT, only when trying to hold a steady state.
I have changed all of the consumables, plugs, wires, distributor cap, rotor, coil, both fuel pumps and filters etc tested some of the sensors MAP, Coolant, Air, throttle position. Inspected all the connections and reworked all the grounds. Checked compression and fuel pressure. All OK.
I have now purchased the diode and hope that it may be the issue as you have found. It does seem unusual that a diode may act in this way, normally working or not.
Is it hard to find in the loom did you take a picture. Hesitation issues in GT 40s seems to be very common, although in saying that we have not had an ounce of trouble over the past 19 years until now.

[boneflier]

I will try to explain where the diodes are located with these pictures taken after the fix.
This is the location of the accessory starter solenoid, just below and behind the ECA and fuel pump relays. The two brown wires each have one diode. They join together in the wiring bundle which you have to take apart.



A close-up of the solenoid with the two brown wires pointed out.

The wire bundle that contains the diodes in the wires that power the ECA relay.

I hope that helps.

[Kev]

Thank you so much for that. I will go to the river on Sunday and get them swapped out. Will post the outcome. Heres hoping after 10 months.

[Kev]

Hesitation issue continues after replacing the two diodes. Any further help or advice from anyone would be gratefully received.
To summarise, the GT40 EFI starts a hesitation of about 100 rpm after it warms up. Some times the engine needs to be switched off for the heat soak. The hesitation is consistent at all RPM above idle. The engine will start and idle every time and responds to WOT as expected with no hesitation observed. There is also nothing observed when run on the trailer.

I have done the following:
Replaced correct heat range plugs
Replaced Wires
Replaced Distributor Cap and Rotor
Replaced E-Coil
Replaced High Pressure Pump
Replaced Low Pressure Pump
Replaced Fuel Pump Relay
Replaced ECU Relay
Replaced the two diodes to the ECU relay
Replaced the Fuel Cell Filter and high pressure pump hose
Replaced Raw Water Pump
Replaced Battery

Conducted Compression test 140 psi all within 10%
Confirmed the Spark timing at 5Deg with SPOUT removed.
Cleaned the anti syphon breaker valve
Cleaned Spark Arrestor
Cleaned all electrical connectors
Cleaned all earthing points
Changed the ECU power source from the battery box to the Assist solenoid.
Checked the function of MAP sensor
Engine Coolant Sensor
Engine Air Temperature Sensor
Throttle Position Sensor
Fuel Injectors have been removed, cleaned, flow tested.
Fuel pressure is 39psi engine running.
Alternator output is 13.5 volts
Power at fuel pumps is 12 volts
A code reader has NO fault codes come up for KOEO or KOER.
The ECU has no obvious defects evident on the board however no ability to test here in Australia to my knowledge.
I have spoken to SkiDim in the past also.
Anyone with further suggestions please advise as I am just about at the end with the exception of the ECU which I would have to source from the USA at a fair expense and that may not be the issue. I am also unable to locate a breakout box out here which makes things difficult.
Ideas please.

[gary s]

The only thing I see that you have not changed is the PIP sensor- Ford or Motorcraft part number FOSZ12A112-A https://www.rockauto.com/en/moreinfo...122107&jsn=628 It seems that there has been problems with them posted on the Correct Craft Fan site- everyone who has had trouble has just changed the complete distributor rather than just the sensor assembly. The gear has to be removed and the shaft removed to get to it.

[Peter6000]

The only thing I see that you have not changed is the PIP sensor- Ford or Motorcraft part number FOSZ12A112-A https://www.rockauto.com/en/moreinfo...122107&jsn=628 It seems that there has been problems with them posted on the Correct Craft Fan site- everyone who has had trouble has just changed the complete distributor rather than just the sensor assembly. The gear has to be removed and the shaft removed to get to it.

I would also replace the TFI you can use the automotive version from a ford bronko.
I have the part no somewhere if you need it.


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[Peter6000]

And check the MAP sensor puts out frequency, instructions are on the manual.

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[Peter6000]

And check the MAP sensor puts out frequency, instructions are on the manual.

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Never mind I just noticed you tested the map.

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[Kev]

Success at last. After some 30 odd hours spent between on water testing and workshop testing the issue has been resolved. Initially found the signal from the ignition module to the ignition coil dropping out intermittently, found there was no heat transfer paste on the ignition module, possibly causing the module to overheat. Replaced the paste and retested with Oscilliscope, massive improvement but not fully resolved. During on water test the hesitation occurred 6 times in one hour. Fault identified as distributor output to ignition module intermittently dropping out. Distributor removed and stripped, found some corrosion and the pickup loose and the Hall effect sensor rubbing on the pickup. New distributor has resolved the issue.

[DW SD]

Thanks for the update! Sounds like a challenge to hunt down


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[GJpearce]

This is a common problem in these older boats (mine is a 2002 GT40) and most all of us are now DIY mechanics,,,,,everyone tries to re-invent the wheel. Putting in a replacement relay is a simple $20 fix. If that does not work check the low pressure pump under the fuel filter cannister. You can run a long set of jumper wires from the battery to the pump. Then try starting the engine....fixed???? I had a hard time finding a switchable power wire, so I ran a lead from the always hot red wire near the relays threw in a toggle switch and now a simple 2 part engine start procedure- toggle switch, then start button and then have to remember that toggle switch always needs be off when done for the day. I think it is likely a good anti-theft fix as I have hidden toggle switch. FUNNY THING IS BOAT OFTEN STILL RUNS WITHOUT FLIPPING TOGGLE- so it is an intermittent power supply issue to the fuel pump. Easy to throw thousands of dollars in parts and mechanic bills for these intermittent electrical issues.
YOUR FORUM IS A LIFESAVER!!!!

[Old Spico]

Do you have a part number or link for the diodes?

[SilentSeven]

Beginning about 3-4 years ago, the engine would, on rare occasions, shudder, partially quit, run again, sometimes quit altogether.

boneflier

When you had the problem, could you also describe this as a rapid ignition cutout - almost like someone turned the ignition off then back on in quick order? I had this issue (very occasional) on my last boat and could never figure it out. My boat never quit running...just flashed off and on. Very curious if you have found the source.