GT-40 issue - Mechanic gave up

[MEtoFL]

Hello all,

First time poster, here we go:

Issue:
My 1999 Ski Nautique with GT-40 pro boss won’t start. It’s been sitting with my mechanic (who has no diagnostic <(code reader> tools), and he’s run out of options. I’ve called every Marina in the region (Sebago Lakes Region, Maine) and none have the diagnostic tools to pinpoint the issue. I’m stuck and my next step (I think) is to purchase a code reader and try to figure out the issue. My mechanic thinks it may be an ECM issue, but I don’t want to drop $800 on a hunch. Any help would be appreciated to either suggest somewhere to take my boat in Maine, or if someone can point me to the right direction which code reader I should purchase to start working my own diagnosis.

Background:
I purchased my ’99 SN about 4 years ago. It’s run flawlessly for the first 3 years that I’ve owned it (prior owner was a friend who took meticulous care). Toward the end of last season the RPMS appeared to struggle (pulse) at around 3000 RPM. When I dropped it off to winterize, my mechanic took a look and suggested a tune-up in the spring. In April he did a full tune up, changed the sparks and the rotor hub (which showed some deterioration) and he suggested that would be the fix. My mechanic ran it several times, and it ran like a champ. I picked it, filled it up with fresh gas (threw some star-tron in – which is my routine procedure) and headed to the lake. I dropped it in, it started right up, ran it for a couple hours and the pulsing RPM was gone – ran great. The next day, I ran it again for about an hour, brought i back to the dock, put it in neutral, and the boat died. It wouldn’t restart until the 4^thor 5^th attempt. It restarted, I got it to the mooring and turned it off for the night. About 2 days later, I started it after 3-4 turns and giving the throttle about 1/2 . Got to the dock, put it in idol, and it died. I tried for about 3 days after to restart it and it never restarted.

Diagnosis to date:

• Fuel pressure good: I have a fuel pressure gage and I tested pressure at the filter and on the rail (both had about 40 PSI at start).
• I replaced the MAP sensor (based on some other research)
• Brand new sparks – spark is good and wires are good
• Brand new rotor
• Compression is good
• Fuses are good

Mechanic think it’s the ECM.

I’m hoping to get the boat back on the water before July 4^th…. Any suggesions/help, please?

[Peter6000]

Sorry about your troubles, I have a Innova 3140 OBD1 +2 tester with the ProBoss (Ford) adapter would sell it for $50+ shipping if you interested.
It will report a bad sensor and you can do a test with engine running.
The Gt40 has only a handful of sensors that can be tested easily with a multi-meter if you don't have the ProBoss manual its in this forum under Manuals.

https://www.planetnautique.com/Corre...e%20Manual.pdf

Check the sensors one by one.
Check ignition timing and make sure all spark plugs are firing a cheap inline spark tester is a handy tool. A ignition oscilloscope is the best way to go.
The TFI module is a common problem if spark power is low.
Mark sure all injectors are opening you can just carefully touch them with the engine running you feel the click, a mechanics stethoscope works as well.
If not sure you can test the injectors by disconnecting them all, build up fuel pressure and use a external 12V power source to open the injector for 0.5 sec or so and watch the fuel pressure drop. Compare all of them should be the same. This is a good way to find a stocked injector. If your fuel pressure drops quickly like in 30 sec or so with all injectors closed you have a leaky injector. My pressure stays above 30psi for about 30 minutes.
If all fails and you think its the ECU itself you can send it to me (VA) I have a bench test setup for these old controllers.

[core-rider]

Have the injectors been tested to make sure they are firing? A quick check with a test noid like this would answer that question... https://www.harborfreight.com/11-pie...set-97959.html

You said the spark plugs are new, but have you checked for spark at the plugs? Remove one and hold the ground strap to a good grounding spot on the engine... have someone turn the engine over and see if you can hear/see spark.

Only thing left is compression which for no we will assume is there. These should be the only things you need to at least make the engine kick over and produce some kind of combustion. Now if you see that spark or injector pulse is missing then I'd follow that correct path to further diagnose the issue. It could possibly end up at the ECM, but these inexpensive tests will give you a better indication of paths to follow. Your mechanic should have already done this instead of just being a parts replacer, but more and more there's no such thing as proper mechanics anymore unfortunately.

[SilentSeven]

Time to find new mechanic or just do some simple diagnostics yourself. Here's what I would do to narrow down a no start. First, determine which of the 3 systems below are not working. A no start is either you have no spark, you have spark at the wrong time, or you have no fuel. You have to figure out which one is not correct. Don't worry about compression right now; even an engine with bad compression should still start.

If your mechanic is any good, they should be able to tell you now the status of each of these systems. If they can't, get a new mechanic.

- check for spark firing, simple plug test can determine if you have spark.
- check for injector electrical pulse - get ford style noid light
- check for fuel pressure at the rail - there are lots of posts how to check the FP system in these boats. I would start with a basic pressure test.

If you have no spark, you'll need to work backwards through the system to ID possible issues. Items of particular interest - distributor hall sensor can get flaky causing run issues. Fix is a rebult cardone distributor (no need to buy the PCM version). Rebuilt distributor is about $100.

Some links to help with the distributor.
https://www.planetnautique.com/vb5/f...one-seen-this=

https://www.planetnautique.com/vb5/f...r+part+numbers

If you have no injector pulse, you'll need to review the triggering sequence but this may also be related to a distributor problem. Check (as I don't remember) if this engine has a CPS (crank position sensor) as it may be responsible for the injector pulse.

Fuel pressure at the rail can be checked with a fuel pressure tool. Lots of auto parts stores will loan tools now (Autozone). Check what fitting is needed and verify you have fuel pressure. You should build initial pressure when you turn on the ignition to the run position but the FP won't run again until you start to crank the engine; this is a safety feature.

There are solutions for replacing the ECU - see this thread - I built one for about $150 with an Ebay donor ECU and the help of a member who burned the Moates chip. https://www.planetnautique.com/vb5/f...r-gt40-efi-ecu

Good luck! My guess...distributor or fuel pressure problem. Investing a $100 in a new distributor will rule out lots of problems quickly and equates to an hour of shop time. Cheap gamble if you ask me.

[shag]

I can't remember 100% but if the GT40 has the individual power packs for each cylinder mounted all together on the back of the motor, your symptoms sound very familiar. I believe this is a classic problem that occurs with those.

[MEtoFL]

Thanks to all of the responses.

Peter, I'll certainly take you up on that offer - I send you a PM.

Most of what has been recommended has been completed thus far (leading us to believe it's an ECM:

1. I have confirmed I have a spark at the plug
2. I have checked the fuel pressure at the rail (good w/40 PSI)
3. Mechanic checked the compression all good

I'll ask if he checked the injectors and consider possibly replacing the distributor before I got the ECM route. Hopefully I'll get that reader and it will shed some light...

[SilentSeven]

If you have good spark and FP, then it's either no injector pulse or spark timing. I'd put a noid light on the FI harness and see if you have pulses. It would be odd for timing to be off but it's a simple check.