Old jetboat restomod
Discussion
Bought a 98 seadoo challenger twin engined jet boat, it has been sat as a non runner for a few years.
A couple of boat mechanics apparently had a look and couldnt get it sparking, so I took a punt and bought it cheap, suspecting a blown ecu, and the ecus are no longer available anywhere at any price at the moment.
after some initial checks of power and ground feeds and checking the DESS post and buzzer I have come to the conclusion the dess/accessory portion of the mpem ecu is toast, the mpem is 4 ecus potted in epoxy together as 1 unit and incorporates all the fuses and relays for all the 12v accessories.
the 97 is much easier to fix in this situation, on the 98 the mpem controls absolutely everything electrical, and is a sealed non servicable unit.
There is an easily repaired diode that pops the 5a mpem fuse, but on my boat the 5a fuse has been replaced with a 10a fuse, so my theory is the 5a fuse was blowing and some f
knugget put a 10a in its place causing a more catastrophic failure.
repair option 1 is depot the mpem and trace and repair any faults i can find. There are no board schematics so I will need to reverse engineer and make best guess attempts at diagnosis using a meter, scope and component curve tracer.
Depotting without damaging the board will be the challenge. Does anyone have any tips for this?
option 2, 3 and 4 will require me to build a bespoke electrical box to bypass the mpem for all the 12v accessories and ancillaries, pretty much rewiring from scratch, Because I will be wet mooring at loch lomond from march to october I will add a transponder immobiliser and a gsm alarm which will also monitor battery level and bilge pump operation and a bilge water alarm. To keep the bilge going as these have a rep for weepy carbon seals I will fit a solar panel and charge controller. Bluetooth tunes, and upgraded speakers and a small sub go without saying, need some 90s hardcore/techno on a 90s boat.
option 2 convert the stators and wiring to take 2 96 spx 787 jetski mpems then add some relays and circuitry to trick them to behave like the boat ecu (rev limit in neutral/reverse, fuel reserve switch etc)
option 3 same as option 2 but use 2x MSD 4255 aftermarket performance tuneable jetski ecus and piss about with the wiring to suit as these normally work in conjunction with the original mpem but there is a standalone workaround. These have went up in price recently and would attract import duty coming from the states so unless I can find used ones I dont really want to spend that much.
option 4 megasquirt/megajolt, fully tuneable and can go efi to try to improve on the 1mpg that these boats are known for, but every time I have went down the megasquirt route you never feel like you are done tuning, its impossible to resist the temptation to tinker. Plus I dont want to overdo it and melt pistons, 2 strokes are unforgiving like that.
Option 5 break it and sell the spares, but there arent may of these left running, because of the mpem issues, the market is limited. Plus I want to drive the fker.
The thing was a state but a few hours with the rotary polisher and wool pads are working wonders
A couple of boat mechanics apparently had a look and couldnt get it sparking, so I took a punt and bought it cheap, suspecting a blown ecu, and the ecus are no longer available anywhere at any price at the moment.
after some initial checks of power and ground feeds and checking the DESS post and buzzer I have come to the conclusion the dess/accessory portion of the mpem ecu is toast, the mpem is 4 ecus potted in epoxy together as 1 unit and incorporates all the fuses and relays for all the 12v accessories.
the 97 is much easier to fix in this situation, on the 98 the mpem controls absolutely everything electrical, and is a sealed non servicable unit.
There is an easily repaired diode that pops the 5a mpem fuse, but on my boat the 5a fuse has been replaced with a 10a fuse, so my theory is the 5a fuse was blowing and some f
knugget put a 10a in its place causing a more catastrophic failure. repair option 1 is depot the mpem and trace and repair any faults i can find. There are no board schematics so I will need to reverse engineer and make best guess attempts at diagnosis using a meter, scope and component curve tracer.
Depotting without damaging the board will be the challenge. Does anyone have any tips for this?
option 2, 3 and 4 will require me to build a bespoke electrical box to bypass the mpem for all the 12v accessories and ancillaries, pretty much rewiring from scratch, Because I will be wet mooring at loch lomond from march to october I will add a transponder immobiliser and a gsm alarm which will also monitor battery level and bilge pump operation and a bilge water alarm. To keep the bilge going as these have a rep for weepy carbon seals I will fit a solar panel and charge controller. Bluetooth tunes, and upgraded speakers and a small sub go without saying, need some 90s hardcore/techno on a 90s boat.
option 2 convert the stators and wiring to take 2 96 spx 787 jetski mpems then add some relays and circuitry to trick them to behave like the boat ecu (rev limit in neutral/reverse, fuel reserve switch etc)
option 3 same as option 2 but use 2x MSD 4255 aftermarket performance tuneable jetski ecus and piss about with the wiring to suit as these normally work in conjunction with the original mpem but there is a standalone workaround. These have went up in price recently and would attract import duty coming from the states so unless I can find used ones I dont really want to spend that much.
option 4 megasquirt/megajolt, fully tuneable and can go efi to try to improve on the 1mpg that these boats are known for, but every time I have went down the megasquirt route you never feel like you are done tuning, its impossible to resist the temptation to tinker. Plus I dont want to overdo it and melt pistons, 2 strokes are unforgiving like that.
Option 5 break it and sell the spares, but there arent may of these left running, because of the mpem issues, the market is limited. Plus I want to drive the f
ker. The thing was a state but a few hours with the rotary polisher and wool pads are working wonders
Found out with a modification to the stator pickup trigger I can fit a pair of zeeltronic programmable racing cdi units and gain a bit of horsepower. These are around £200 each, so I want to check both engines are mechanically sound before I spend that, so I might buy one and use it to test both engines one at a time before buying another.
Another potential way to test the engine is to try one of these https://www.ebay.co.uk/itm/383715650562
as pickup coil impedence looks similar, just for testing purposes only just in case I am flogging a dead horse with engines needing rebuilt, the advance curve will be wrong and I wouldnt trust my safety on the water to some £7 chinese electronics but it would be motivating just to hear the thing fire up.
Another potential way to test the engine is to try one of these https://www.ebay.co.uk/itm/383715650562
as pickup coil impedence looks similar, just for testing purposes only just in case I am flogging a dead horse with engines needing rebuilt, the advance curve will be wrong and I wouldnt trust my safety on the water to some £7 chinese electronics but it would be motivating just to hear the thing fire up.
XJSJohn said:
What is the actual engine component of the jet drive's? Aren't they usually an off the shelf motor of some variety that gets used in many other applications. May be a cheaper "proper" ecu that will at least start the engines and let you test before splashing 400 quid?
787 rotax, but not quite the same as the jetski units. it can be done, but the precise jetski unit i need is out of production, so i would need to find 2 identical good used units and 2 matching immo keys and also i would need to wire an additional immo reader. used parts are getting rarer so I would be around £800 by the time i source everything, and the jetski units are missing a couple of key features.I am going to test if both engines run using the ecu from a hyoseung gy6, then if they are ok I will order a pair of ignitech dccdip1 race ecus, then map them to suit, as they have universal programmable inputs to add all the nicities like switchable maps, 3d mapping with a tps and map sensor, torque limit in reverse and neutral, retarded timing and low rev limit on overheating etc.
Edited by OldGermanHeaps on Monday 14th September 20:04
upholstery is properf
ked, all the fuel hoses are rotten, coolant lines are cracked, carbs are full of rusty water, accelerator pump diaphragms and fuel pump diaphragms are split, a lot of the ancilleries are falling apart because of uv exposureBUT
with a rudimentary homemade loom and thy hyeoushungloveyoulongtime gy6 150 scooter ecu wired in and a good sniff of brake cleaner both engines were able to fire up and sound healthy, so to work it is.
Going to buy a jetarmor retrim kit, change the colour scheme, strip it back to the bare hull, polish it up, ceramic coat the bottom, vinyl wrap the top, new electrics and fittings and fixtures and with the fresh upholstery it should look a bit better. then I will either depot and attempt to repair the ecu, or fit the ignitech units and rewire all the ancillaries if that is a dead end. I dont want to chance the gy6 ecus for any more than a test run as i dont think a 787cc 2 stroke twin will last long running on a map setup for a chinese 150cc 4 stroke single.
Checked everywhere I can possibly think of even used google translate to contact foreign companies its impossible to find a working correct ecu for this boat.
Edited by OldGermanHeaps on Wednesday 16th September 19:27
I managed to get enough of the potting off to repair the ecu.
It runs on brake cleaner, carb and fuel pumps are gubbed but al least its worth fixing.
https://youtu.be/qyRQ1EUa4nY
Ordered full new jetarmor upholstery in red white and blue for all seats and sundeck. ripping up the old flooring and fitting grey eva imatation teak flooring.
got carb and fuel pump rebuild kits, new steering wheel, new graphics, some vinyl wrap and some new fixings and trim, going to touch up engine paint and give everything a damn good clean, fit a garmin gps/sonar, fit thrust vectors, new stereo, extra speakers, additional bilge pump and going to do a bit of rewiring. Mrs says I cant take it to the house until the campervan is finished though.
It runs on brake cleaner, carb and fuel pumps are gubbed but al least its worth fixing.
https://youtu.be/qyRQ1EUa4nY
Ordered full new jetarmor upholstery in red white and blue for all seats and sundeck. ripping up the old flooring and fitting grey eva imatation teak flooring.
got carb and fuel pump rebuild kits, new steering wheel, new graphics, some vinyl wrap and some new fixings and trim, going to touch up engine paint and give everything a damn good clean, fit a garmin gps/sonar, fit thrust vectors, new stereo, extra speakers, additional bilge pump and going to do a bit of rewiring. Mrs says I cant take it to the house until the campervan is finished though.
going to borescope it, but compression is healthy. Its a pain to get the engines out as the hatch is small and awkward to lean over, and access is tight for aligning them with the drives, so they will only be coming out if necessary.
the boat has never been named, but as I am fitting a vhf radio I think I should give it a name.
I am thinking either Daethehing, Didyeaye, HWFG or Andiamo. Any one of those stand out in particular?
the boat has never been named, but as I am fitting a vhf radio I think I should give it a name.
I am thinking either Daethehing, Didyeaye, HWFG or Andiamo. Any one of those stand out in particular?
hidetheelephants said:
Very pretty; my limited experience is that they're not much use for finding fish and the moving display will tell you what you've just run aground on if going at more than walking pace. 
Useful for accurate speedo, compass, and waypoint navigation, And my friend is going to teach me some scuba diving, he reckons the clearview is good for locating wrecks. Seat refurb kit arrived and the quality looks awesome.
my van broke down today though and getting that dealt with will likely slow down progress this weekend.
the 2010 and 2004 vivaros in my fleet are 100x more reliable than my 2019 MAN. Waste of f
king money and unimpressive service. 
Well 2021 was a washout, didnt get time to even take the cover off the boat was so busy with work and diy. Got stuck into it this weekend though. Flushed the tank, replaced the fuel lines, got it running off the carbs the way they were but the throttle and choke spindles are seized so popped them off for a rebuild, flooring ripped out and hull cleaned up, once the old graphics are off going to polish it, get the new upholstery in and new graphics.
Reverse cable is broken and replacement is $294 so f
k that going to have to fabricate something to get a £35 one to fit. Battery still had enough oomph to start it after 2 years sat isolated so at least thats a good bit, yuasa are always impressive. 
Not counting my time, only materials apart from the vhf and sonar i reckon I will have saved around 4k over buying a working one in similar condition to how this will finish up, but I will know that all the important things have been looked at, motors are good borescoped and compression tested, all the coolant oil and fuel hoses are changed, jet pumps overhauled, control cables overhauled, carbs rebuilt, fresh upholstery, people dont sell boats with all those plus points cheap, people sell boats either when they are fked or they suspect they will fk up soon.
If i bought a running one for one of these for 4 to 6k i would end up having to do the same jobs after a season or 2, but the maths are skewed as i bought mine at a price based on the previous owner being told by multiple boat mechanics it was unrepairable or they didnt want to look at it.
If i was paying someone to do the work then it would be cheaper initally to buy a runner, but a runner in my price range would need work after not long at all, they all do, then I would be paying someone to do the work anyway so any advantage would be lost, plus i would just get fobbed off by the same mechanics the previous owner was fobbed off by.
I really cant understand why so few people get their hands dirty working on their own stuff now, it makes me despair for how far backwards we are going. My girls enjoy playing with tools, and my oldest is really good at it so thats quality time together, and I'm sure its a positive experience for them getting to go out on something they had a hand in building.
My oldest really enjoyed going out on the jetski, as she done most of the rebuild on the engine with me just telling her what to do and lending a hand on the brute force bits.
ked or they suspect they will fk up soon.If i bought a running one for one of these for 4 to 6k i would end up having to do the same jobs after a season or 2, but the maths are skewed as i bought mine at a price based on the previous owner being told by multiple boat mechanics it was unrepairable or they didnt want to look at it.
If i was paying someone to do the work then it would be cheaper initally to buy a runner, but a runner in my price range would need work after not long at all, they all do, then I would be paying someone to do the work anyway so any advantage would be lost, plus i would just get fobbed off by the same mechanics the previous owner was fobbed off by.
I really cant understand why so few people get their hands dirty working on their own stuff now, it makes me despair for how far backwards we are going. My girls enjoy playing with tools, and my oldest is really good at it so thats quality time together, and I'm sure its a positive experience for them getting to go out on something they had a hand in building.
My oldest really enjoyed going out on the jetski, as she done most of the rebuild on the engine with me just telling her what to do and lending a hand on the brute force bits.
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