Spark plug leads. Resistance testing.

[justy_123]

Hey all.

I have a 2004 XPdi. Great machine. Been playing up inconsistently over the last few months. (Bogging out without warning but would run perfect most of the time). Changing the plugs over as I type, however, thought I would just do a quick resistance test on my spark plug leads as the plugs that I am about to change are only 10 hrs old.

So the results of my test on the leads are Mag side 4220 ohms PTO side 6110 ohms. Manual states replace the lead if Mag side over 5700 ohms and PTO side 4300.

So... my results are pretty much opposite than what they should be. The mag side is the cylinder at the front of engine closest to the mag / flywheel isn't it? Am I missing something? Or is my pto lead shot?

Or has my manual got the figures back to front. I would of thought the longer pto lead would have more resistance than the shorter mag lead. I'm confused!

As a final note. The manual says to "always replace the leads with genuine ones otherwise fuel injection system operation will be impaired". How is this so? Leads $80 each

 

[Dr Honda]

It's really not that critical. When you check the wires with a meter... you a really looking for burnt, or broken wires. With the numbers you are getting... I'd say they are OK.

No... you don't have to buy OEM wires. Any good quality resistor/RF suppression wire will be fine.

Your bogging is probably more likely from:

1) A fuel pump that is startling to give up

2) A leak in the air system.

 

[justy_123]

Thanks Dr Honda.
Leads look ok from the outside. No obvious signs of damage. Have put new ngk iridiums in. See how they go. The old plugs I took out were black and covered with dry soot.

Have checked available fuel pump pressure to be well over the specified 105 psi. Fuel regulator when installing lanyard regulates fuel pressure at 27 psi which is also right on specifications. Engine running fuel pressure is somewhere between 100 and 105 psi. Hard to tell exactly because my fuel pressure gauge was fluctuating a lot.

No air leaks are evident. Used soapy water on all the air lines while engine was running. Only thing to test next is probably the available pressure from the air compressor. The ski filled with water a couple of years ago. May have bent air compressor con rod maybe. Hope not.

Looking in the back of the ski tonight I did notice black soot around the exhaust pipe to muffler rubber joiner. I was able to tighten up the 2 worm drive clamps a little. So this could be my problem too. A little exhaust leak in the hull. As I think of it it, the ski really only starts playing up during the later parts of the day. Signs of exhaust leak.

See how the ski goes this weekend. Will report back.

 

[Dr Honda]

I know you just spent extra $$$ on the Iridium plugs... but Rotax engines dont' like them You are better off using conventional NGK's.

As far as the soot on the exhaust, and plugs... it's still a 2-stroke, so it will make soot.

The only way to get a true fuel pressure, is to leave the gauge on it, and go for a ride. When it bogs... then look at the gauge.

Did you check the pressure on the air system?

 

[SabrToothSqrl]

Does it bog down after you land it hard off a jump or wave?
My 98 GTX and 99 GSX both did that... luckily I now know what was causing it for me.

A bad seal between the exhaust manifold and the pipe. Your 04 should be a rubber gasket in there, but I'd check it anyway.

What was happening for me was, rough water / jumps / etc would send water leaking out from between the manifold and pipe. Then with the 951's intake right below it, it would suck water into the engine. I didn't know what was happening at the time several years ago, but it was slowly destroying the engine (turns out, they don't run well ON water).

In addition to the Doc's recommendations about the fuel system, I'd most likely pull the pipe and just redo all of it. It's a bit of an 'art' but on a XP it's not that bad...

Remove all of it, clean everything up very, very well, then with the right parts, (new rubber gasket due to age) and the gold RTV stuff (not sure what you guys call it), thread lock, and the torque specs... get it back on and know it's right.

Also, on the XP, you have a lot of areas for other exhaust leaks. There's a 4' long pipe under your right foot (when your on it) that carries the exhaust. Each end has a rubber coupler and 2 exhaust clamps. check all of them and check the ones near the VTS.

If your blowing exhaust into the hull, it will kill the HP...

I also 2nd that the BR8ES is a fine, sturdy, reliable, cheap plug. use that.

 

[justy_123]

Great info guys. Have checked the exhaust system and only found evidence of exhaust leak around where that 4 inch pipe connects to the muffler. Surging intermittent even on calm water. SAbrtooth that is interesting about your water leak into the engine. Bet you were happy to eventually find that one!

I am surprised that the rotax engine doesn't like the ngk irridiums. Far superior plug. Can't do any harm? See how it runs with them if no good will go back to the standard ngk's.

Haven't had a chance to check the air pressure as of yet dr. Trying to figure out the best way to hook up the tester to it. Doing a test run on the ski saturday and will prob have the fuel pressure tester hooked up then.Taking the ski out to the river for a week over xmas and new years so running out of time to fix anything major. Will have to wait until I return.

I remember earlier this year I had similar surging problems with this ski. Even posted a thread. http://www.seadooforum.com/showthread.php?47403-XP-DI-bogging-down-sometimesCleaned the tank out, new plugs and changed both fuel filters. Surging went away until now. 10 hrs later. Strange. Filters surely couldn't be shot after 10 hours hey?

I may have to put a close on this thread and post on the above thread that I started in september this year.
Thanks guys

 

[Minnetonka4me]

They def do NOT like any water in the system. I would also figure out if that exhaust is indeed leaking. That would be the first place to start.