96 Challenger rev limiting

[hrl48]

I have a 96 Challenger runs and idles great but has low power on the water. I have had the wear ring replaced. A friend looked at it a said it was rev limiting to 4500 RPM's and replacing the MPEM would fix it. (For this boat about $900) Is his assessement correct? Is so can these be repaired?

Also looking at a post from SEADOOSNIPE below it seems it could be in the tach or info center...ideas???

"One of the things I read about was the grey wire that is used for the communication of the tach. If it's pinched or grounded, it will let your pwc run for about 30 seconds before the mpem shuts it down. Also, if the wire is good, there a possiblity that the tach or info center is bad. This would require further testing.
There is also a special feature in the mpem to control the engine if there is low voltage. For example, if the volts DC drops to 8.9, the rpm is limited to 4480, if the voltage drops to 7 for 30 seconds, the mpem will shut the motor down.
Here's a couple questions for you. When you start, do you hear anything other than the 3 beeps? Please try again and be sure your hearing three and not 4 or 6. Does the info display signal any faults or errors? Also, if you can, with only seconds to spare, you'll have to be ready. Get a multi tester ready and as soon as you start, check the VDC (volts direct current) to your battery. You should have about 11.8 to 12.4 vdc before starting and somewhere in the 13.5 to 14 vdc while running."

 

[seadoosnipe]

Welcome to the forum!

When you say "low power", you are saying the engine has a smooth run to it, all the way to 4500 rpm, then goes no further?
Have you cleaned or checked your RAVE's lately? This sounds more to me like a RAVE stuck open that a limiter problem. Let me know what you think!:cheers:

 

[robin savell lloyd]

I would think that one way to find out if it is mpem is to start it out of the water. put it in gear and quickly run rpms up and then back down. dont let it rev high for more than a couple of secounds. if rpms are higher look other places like Seadoosnipe said rave valves. good luck. Robin :cheers:

 

[hrl48]

It does appear to limit revs to about 4500rpm out of the water. Would this eliminate the rave valves...This boat has been sitting for 3 years and I'm sure they have not been cleaned in forever?

 

[robin savell lloyd]

I guess you know it is supose to limit rpms low in neutral but high in gear. are you sure it is in gear? and if it is in gear are the rpms higher than in neutral?

 

[seadoosnipe]

Neutral limit switch...

The neutral limit switch is set for 3000, so, if your making 4500 out of 7000, I would check to see if the raves are sticking. If they are, they will limit the engines ability to build compression.

 

[robin savell lloyd]

I was thinking that a no load engine would see higher rpms even with a problem than one that is in the water. If you are seeing 4500 rpms out of the water and 4500 rpms in the water the only thing I can say, if it is rave valves they sure do a accurate job of controling rpms. just a thought may not be correct. good luck Robin :cheers:

 

[seadoosnipe]

....good point

That's a good point Robin.....but now, makes me wonder if his rpm gage is off. Because in that year model, the mpem only limits 3000 for the lower end and 7000 (or maybe 7200) on the upper end. There is no limiter in between.
The idea of the RAVEs do apply to the idea that he's only getting 4500 on the water.....didn't notice or remember he states the same problem on land.
So, if the gage is off, then something like the neutarl switch may be sticking.

 

[robin savell lloyd]

I agree Louis on rpms. I was wandering about tach. I also thought they were normally correct or broken. I am thinking the same as you rave valves or some other problem carbs, ect. I was only trying to rule out mpem. I have a question for you Louis. On pwc's I have read of the regulator rectifire causeing rpm problems does this apply to boats as well as I can not find any where some one talks about it on boats. I would think it would apply to boats as well but I am not sure. Robin :agree:

 

[seadoosnipe]

Rectifier/regulator....?

I think the MPEM can be ruled out. I think the problem is somewhere in, like you said, the carbs or the RAVE. I don't think his problem is electrical.
What you've probably read on the rectifier is that, under circumstances, if the battery is dead or going bad, the regulator/rectifier can't keep up with the electrical demands of both, running the electrical system of the ski and charge a battery (that's not holding a charge). This will mostly apply to newer models using the ECM and the EMS systems. The 4-TEC for instance, has a big electrical demand on the power system to operate the ski properly. If that power demand falls short, the ski will either go into limp mode or just shut down. The 951 RFI and DI motors have a high demand also.
So in a way, your right. The rectifier/regulator can play a significant role in how the ski runs or if it's going to allow it to run at all.

 

[robin savell lloyd]

It seems that I have read that when it is bad it interfers with electrical system. maybe sending ac curent instead of dc not sure though. but if you disconect it a mag it is supose to run normal untill batery dies. I can be wrong but it is something like that. ps this hapens on old skis probly before and after the year of 1996

 

[seadoosnipe]

Never heard that....

I've never heard that before Robin, but I'd think if the regulator stopped regulating at 14vdc or the rectifier stopped converting the AC power to DC and sent an AC charge to the electrical system, you'd blow every fuse on the ski...............that's opinion, not research.....
Louis

 

[Gunsrunner]

my 2 bob,
you state that the boat has been sittiing for years and if the old fuel was left in there it would be very stale by now, drain and replace. You can tell if the revs are being limited by the mpem by the missing of the engine on the rev limiter, if you can not hear the engine missing it is not being rev limited. I would be doing the carbies first as they are cheapest to put a kit in, Then i would also check raves as Louis said.