Rebuilt 951 DI Running Rough - Electrical?

[WaarrEagle]

My long saga continues with my 2000 GTX DI. Had SES rebuild my motor after it blew. Got it back together and it was running pretty well. Put about 5 hours on it, multiple heat cycles, increased RPM's each time. But it had a mild, intermittent misfire. Interestingly, this misfire has been around for YEARS, well before the engine failed. It is most noticeable when the motor is under heavy load such as when coming onto plane. I suspected fuel pressure but put a gauge inline and it looks great. Solid 27 with key and 107 when running. The gauge does bounce around A LOT at lower RPM's but stabilizes at higher RPM's.

Today I finally got comfortable running WOT and wanted to see what it would run to test overall performance. I very briefly went WOT and saw 6860. Immediately after that the motor started running very rough, and even died at idle a couple times. I changed the spark plugs and it was no better. Pics of the plugs used during break in:


Air and fuel injectors were cleaned by FuelInjectorMan as part of the rebuild. No maint light. I just rented a compression gauge from O'Reilly and got 120/118 on a warm motor. Both numbers held solid after I stopped cranking. I know this is a tad low but I suspect the rental gauge may be off.

Given the misfire has a long history I am starting to suspect something electrical. No obvious issues inside the electrical box, but I may focus on the coils. Spark plug boots look and feel firm. Any other thoughts or suggestions? I am determined to get this thing running again!

 

[WaarrEagle]

I finally broke down and bought a CanDooPro. I also bought 2 used ignition coils for the DI. Part of me suspects a bad coil. If neither of those work, I am going to troubleshoot the air compressor. I am seeing a TON of vibration in fuel pressure at low RPM's. Given it stabilizes at higher RPM's and is solid with just a key insert, I wonder if the air compressor is problematic. Regardless, I'll post an update when I get to it!

 

[WaarrEagle]

Update: CanDooPro arrived. I have isolated the issue to the PTO cylinder. When I use the CanDoo to shut down the Mag cylinder, the engine immediately stops... not even a stutter. I have swapped every electrical component and get the same behavior.... the coil, spark plug, spark plug wire. Next step is to take the fuel injection rail apart and check for blockages in the air and fuel injectors. Both were cleaned/calibrated recently so surprised they would be the problem but not sure where else to go from here. Any suggestions?

 

[nhmort]

I’m having the same issue with mine.

Except I can’t go past 5500rpm, if I try it stumbles and bogs down.

I’ve been trying to figure this out for over a year. Hooked up a the Candoo as well. But, good old Seadoo didn’t have any sensors on the fuel system.

I’m thinking it’s the fuel rail, either the fuel regulator or air regulator.

I’m about ready to sell this thing for parts.

 

[WaarrEagle]

I’m having the same issue with mine.

Except I can’t go past 5500rpm, if I try it stumbles and bogs down.

I’ve been trying to figure this out for over a year. Hooked up a the Candoo as well. But, good old Seadoo didn’t have any sensors on the fuel system.

I’m thinking it’s the fuel rail, either the fuel regulator or air regulator.

I’m about ready to sell this thing for parts.

Yep, just worked on mine for a bit and I am now suspect of the air pressure being slightly low or the fuel/air regulator. I can easily test fuel pressure but am having trouble figuring out how to test just air pressure. I may take the fuel rail apart next to see if there is any obvious issue in there. Swapping the air and fuel injectors from side to side on mine made no change to its inability to run on the PTO cylinder.

 

[nhmort]

I’ve tried the same parts swapping as you. With no fix.

I don’t understand that if we get 27psi from the pump with the key and 107psi while running at all rpms, why does it bog down.

One would think that if the fuel/air pressure is 107psi it should work fine per the trouble shooting flow chart in the manual.

My cylinder doesn’t quit though, it just bogs down past about 5500rpm.

etemplet or any other DI owners out there have any ideas?

 

[WaarrEagle]

Took apart the whole fuel rail and no major issues, some moisture in the air regulator. My fuel pressure is solid 27 with the key but a bit low when cranking/running. I am suspecting the air compressor more and more so i took the top off. Found white slime just like this guy: Gtx di air pump pressure test

Ordered a new gasket since that is the only one I reused during the recent rebuild. Anyone know if that white slime is normal or a sign of water entry?