Is this an electrical or fuel problem?

[tommy1976]

Hi everyone....

I'm looking for some guidance if this sounds more like a fuel problem or electrical problem. Basically I have a Challenger 1800 with twin 787's. I purchased it used 3 years ago with 1 engine not working. I brought it to a dealership who said its an MPEM problem so I had them install a new MPEM, re-time the engines, link it to my DSS key and now both engines work. The problem is I only have a 90 day part warranty on the MPEM so I want to make 100% sure this MPEM is not the cause of the problem I'm experiencing as it was an awfully expensive part to replace.

When I have the boat out on the water it runs great - no issues at all. After about 1 hour of run time the right engine rolls back to about 5000 RPM. Left continues to run without any issues at all. If it let it idle for a bit then i can get the engine up to 7500 RPM again but only for a few seconds before it rolls back to 5000 RPM. If I let the boat sit overnight the next day everything works great again for the first hour on the lake.

I've pulled the carbs and the internal filters were dirty (but not clogged). The rest of the carb (jets, etc.) were all very clean without issues. I've rebuilt everything and its still doing it (although the boat does seem like it has more power). I've also swapped the high voltage boxes on the engines and its still doing it. I'm considering swapping the carbs and rectifier tonight too but to be honest I feel like I'm just guessing in the dark here.

Any advise would be GREATLY appreciated here - specifically - any advise on
i. what i should test next
ii. what can i test to help me confirm if this is a fuel or electrical problem
iii. any tests I can do on the water when the issue happens to further narrow it down

Many thanks as always for everyones contributions

 

[timmafod]

I'm having the same issue but on both engines now ('98 challenger 1800). I had this issue on only one engine last season (a 'newer' SBT replacement engine from previous owner), and rarely. But this past weekend (first time this year with more than just me and the wife on board) both engines did what you describe...operate fine for about 30 min, then wouldn't rev past 5000. If the boat had time to cool like it did when we stopped for lunch & a swim, it'd be fine for a little while, then same issue. Royal PITA cause that's not enough to get my boat on plane with the amount of people I had in there. I tried playing with the RAVE valves (went from red screw level with black cap to all the way in) and that helped a little, and also if I flicked the choke cables quickly they'd bog a little then rev to 7000 and stay there until I touch the throttle, then it'd bog and come down back to 5000, hinting at a lean fueling issue for me. I rebuilt all carbs and also replaced both fuel pumps with new OEM parts over the winter (fuel pumps were basically destroyed even though they "worked"). Replaced the fuel pump pulse line with some generic silicone rubber hose...perhaps this hose is too squishy and isn't sending a clean signal (and therefore less fuel pressure/flow) so reinstalling the original cruddy pulse lines is on my list of things to try tomorrow night when I go out with my dad to try to fix this thing. He's an old school carb guy who is much better at reading spark plugs than I am.

I also removed both water regulators last night as these supposedly can cause this same issue when searching on the various forums. 5000rpm limit seems to be a common issue that can be caused by a few things. Anyway both water regulators seem to be in outwardly good condition (haven't disassembled yet) and seem to operate as designed. I was hoping they'd be cracked so life would be easy. I also plan on removing all RAVEs tonight and cleaning them again, I didn't do that over the winter this time around. I doubt that's the problem as all RAVEs feel nice and loose when I just wiggle and operate them with my hand when installed. I also had even/good compression across all cylinders when I checked at the beginning of last winter.

I'll let you know if I find anything, and I'll be watching this thread for any updates.

 

[tommy1976]

... and also if I flicked the choke cables quickly they'd bog a little then rev to 7000 and stay there until I touch the throttle, then it'd bog and come down back to 5000, hinting at a lean fueling issue for me...

Thanks for sharing. Chocking it when they hit the limit is a great idea as that will give some hits as to if its an issue with the fuel supply...I will definately try this.

Regarding water regulators I didn't consider this but now that you've mentioned it I looked it up in the manual and it mentions that it can be linked to such performance problems. Its an easy enough part to swap so I will add that to my list of things to try.

Thanks again

 

[Dr Honda]

If the water regulator is clogged... that's not good. You can melt the exhaust couplers.

When was the last time the RAVE valves were serviced? If they are sticking... the engines will hang in the mid 5000 RPM range. (and as they get hot... the will be more likely to stick)

Speaking of sticky RAVE's... what oil are you using?

 

[tommy1976]

If the water regulator is clogged... that's not good. You can melt the exhaust couplers.

When was the last time the RAVE valves were serviced? If they are sticking... the engines will hang in the mid 5000 RPM range. (and as they get hot... the will be more likely to stick)

Speaking of sticky RAVE's... what oil are you using?

Thansk for the input. Regarding the RAVEs - do they stick in the closed or open position - or is it possible that they cause surging. For example - if I'm at 7000 RPM and all of a sudden drop to 5000 - and then do nothing - it might spike up to 7000 again for a second. Could RAVEs cause this or would they more likely to just stick open or closed?

 

[timmafod]

When I removed both of my water regulators I blew into the hose that goes to the pipe. After blowing the water thru the hose it was very little restriction to my forceful blow. uhh.....that doesn't sound right.

I run XPS synthetic. Oil cable adjusted per factory manual. Throttles opening fully. All fuel lines replaced years ago with new E10 compatible marine hoses and they still looked good on the inside when I glanced at them when removing the carbs last winter for rebuild. Internal carb fuel filters were clear, external filters are clear. I run regular 87 octane.

My boat will run fine at WOT initially at the beginning of the day, then slowly rpms will drop to about 6700ish, then it'll come off the pipe and drop to ~5100. This takes about 20-30 min for me. At that point no throttle change from about half to full does anything more than 5100. Again, quickly "blipping" the choke cable will bog the engine down (obviously) then it'll rev up. one engine is a little more lively...one will rev to 7000+ the other only to 6700 or so at this point in the process. I have to be about 7/8 throttle for this to work; blipping choke at full throttle won't do it. And then they will stay there until I even gently touch the throttle levers, either more or less. Frustrating.

I've cleaned the Raves before but never the cylinder port hole slider area.

If you run no rave valve at all, and just a plate covering the holes in the engine, what would that theoretically do to the RPM? I assume that if the raves stick in the down position it could cause the 5000rpm hold issue. If no rave was in there, or if I can manually lock them in the open position for testing purposes/to rule them out, would that be a good check to see if its the rave valves sticking closed? I can quickly fab up a cover plate tonight and try it, I have a few rave gaskets lying around and some stainless plate. Alternatively, I have no problem taking the caps off and operating them manually while my dad works the throttles. I have earplugs

EDIT: I did try removing the caps/springs when this issue started for me this past Sunday, thinking the raves would open up and stay there (I'm not sure if this actually occured if they were sticking shut). This made no change to my issue. I then reinstalled the caps/springs and screwed the red cap screw things all the way in, and that helped somewhat. I did not try the choke blip with the rave caps/springs out or the red cap screw at it's initial setting of even with the top of the black rave cap.

I put brand new spark plugs in for sunday as well. Maybe I should try the old crudded up plugs from last year

 

[tommy1976]

My boat will run fine at WOT initially at the beginning of the day, then slowly rpms will drop to about 6700ish, then it'll come off the pipe and drop to ~5100. This takes about 20-30 min for me. At that point no throttle change from about half to full does anything more than 5100. Again, quickly "blipping" the choke cable will bog the engine down (obviously) then it'll rev up. one engine is a little more lively...one will rev to 7000+ the other only to 6700 or so at this point in the process. I have to be about 7/8 throttle for this to work; blipping choke at full throttle won't do it. And then they will stay there until I even gently touch the throttle levers, either more or less. Frustrating.

Just to clarify in your boat - When you say RPMs drop to 5100 this is a sudden drop or a slow degregation? On mine its instant - we can be going at 45MPH and all of a sudden the engine rolls back to 5000ish and boat slows down immediately.

Also - on your boat you mention BOTH engines are doing this. Are they doing this at the approximately the same time or does one take longer than misbehave than the other?

I havn't tested on mine yet if the choke will produce any feedback but to me if choking it produces a surge in RPM this makes me strongly suspect a fuel delivery problem. There is an initial starving of fuel, and when you choke it for a second it bogs down which will reduce fuel flow rate giving the supply an opportunity to catch up which will keep enough fuel in the supply for a short period of to allow the RPMs to rev up.

 

[timmafod]

Just to clarify in your boat - When you say RPMs drop to 5100 this is a sudden drop or a slow degregation? On mine its instant - we can be going at 45MPH and all of a sudden the engine rolls back to 5000ish and boat slows down immediately.

Also - on your boat you mention BOTH engines are doing this. Are they doing this at the approximately the same time or does one take longer than misbehave than the other?

I havn't tested on mine yet if the choke will produce any feedback but to me if choking it produces a surge in RPM this makes me strongly suspect a fuel delivery problem. There is an initial starving of fuel, and when you choke it for a second it bogs down which will reduce fuel flow rate giving the supply an opportunity to catch up which will keep enough fuel in the supply for a short period of to allow the RPMs to rev up.

It's a slow degradation from 7100 to 6700 or so over the course of 20-30 min, then it drops suddenly to ~5100. I say it 'comes off the pipe' like a typical 2stroke would. When that happens, the boat slows down considerably, and depending on how many lunatic women are on board, will come off plane. Hysteria ensues as "all those big boats are going to hit us".

As of Sunday, both engines are doing it. Previously, only the port engine would do it, and rarely. I though it was possibly seaweed or something (even though that would logically cause cavitation and an increase in rpm), cause I would jsut shut the boat down, pull the weed grate lever, start it up, and it'd be fine for a while. I did notice in the morning the starboard engine started to drop RPMs first. About 5-10 min later, the port engine did it, but we were just pulling up to our hang out spot so I didn't try anything to fix it at that time. Same for the ride home after a few hour break for lunch and stuff. On the ride home I let the wife drive because the previous 2 times we took the boat out this year (without any issue) she was driving the entire time. When the boat started to act up I went back and unscrewed the gas cap to see if it was possibly the gas tank vent not venting, forming a vacuum in the tank and therefore restricting the fuel flow to the engine. That didn't help.

 

[tommy1976]

It's a slow degradation from 7100 to 6700 or so over the course of 20-30 min, then it drops suddenly to ~5100. I say it 'comes off the pipe' like a typical 2stroke would. When that happens, the boat slows down considerably, and depending on how many lunatic women are on board, will come off plane. Hysteria ensues as "all those big boats are going to hit us".

When its running at 5k - does it sound normal (as when if you are trying to run it at 5k?) or does it make any noise like its hitting the rev limiter or starving for fuel?

Mine makes a very muffled noise - definately not a normal behavour. I'll see if I can upload a vid clip of it next time I'm out.

 

[timmafod]

Mine doesn't seem to change it's tune when it's stuck at ~5000 regardless of throttle position, but it may have been too loud in the boat to notice. I had people talking and lots of gear/tubes/towels on top of the compartment above the engine.

I too will attempt to remember my video camera when I hopefully go out tomorrow night to try to find a fix.

 

[nightrod]

I'm having the same exact crap going on with my 97 speedster and it's driving me crazy! One weird thing though on mine when I can't get the rpms up if I hit a wake and the jets come out of the water it will suddenly jump back up tp 7000 rpms and take off again.

 

[timmafod]

Last night I added a large length of fuel line to each engine so I can install a fuel pressure gauge while out on the water.

I noticed that the fuel lines in my boat are routed differently than what the shop manual states on page 06-02-4. My lines go from the tank pickup, to the fuel filters, to the fuel pumps, then to the carbs. The shop manual shows it going from the tank, to the fuel pumps, to the filters, to the carbs (filters under pressure). Perhaps these filters are causing a flow restriction, and the fuel pumps can't suck enough thru at WOT? Fuel pressure gauge should show this if so. I can also reroute the lines if necessary tonight, I brought along a bunch of extra fuel line.

 

[tommy1976]

Last night I added a large length of fuel line to each engine so I can install a fuel pressure gauge while out on the water.

I noticed that the fuel lines in my boat are routed differently than what the shop manual states on page 06-02-4. My lines go from the tank pickup, to the fuel filters, to the fuel pumps, then to the carbs. The shop manual shows it going from the tank, to the fuel pumps, to the filters, to the carbs (filters under pressure). Perhaps these filters are causing a flow restriction, and the fuel pumps can't suck enough thru at WOT? Fuel pressure gauge should show this if so. I can also reroute the lines if necessary tonight, I brought along a bunch of extra fuel line.

That's a great idea...let me know if you find anything useful Are you putting the gauge between the pump and carbs? My boat (1998 challenger 1800) has identical configuration pickup -> filter -> pump -> carb and then recirculating back into the tank. I've also looked at several other challenger 1800's - exact same configuration so I think the manual isn't quite right.

My fuel filters outside the boat are fine but there is also a filter INSIDE the baffle pickup at the very bottom. Since your engines are both having this issue at the same time it might be worthwhile to clean that out as it will affect both engines.

 

[timmafod]

Fuel pressure gauge will be placed right before the carbs. I'll do one side then the other.

My dad mentioned there might be a sock filter on the pick up inside the tank a while back but didn't see anything in the manual....i just looked and read further. Page 06-02-8 says, "#7, baffle pickup filter. Inspect no.7 of baffle pick up. clean or replace as necessary."


Darn, if so that could definitely be part of it. I've checked the external filters as well as the internal carb filters over the winter and they were all clear. Hopefully I can do this easily & quickly during lunch so I don't waste daylight time tonight.

 

[tommy1976]

Fuel pressure gauge will be placed right before the carbs. I'll do one side then the other.

My dad mentioned there might be a sock filter on the pick up inside the tank a while back but didn't see anything in the manual....i just looked and read further. Page 06-02-8 says, "#7, baffle pickup filter. Inspect no.7 of baffle pick up. clean or replace as necessary."


Darn, if so that could definitely be part of it. I've checked the external filters as well as the internal carb filters over the winter and they were all clear. Hopefully I can do this easily & quickly during lunch so I don't waste daylight time tonight.

Is in the Parts manual (attached). Page 56 - Part #8

 

[timmafod]

I just checked it; it was clear. I should have ate lunch before working on that...my sandwich smells like gas.

 

[parrothd]

Did you check the fuel pumps(you have to replace the entire pump, there's no rebuild kit, not cheap) and replace the fuel filters? Also, did you rebuild the accelerator pumps when you rebuilt the carbs?

 

[timmafod]

Did you check the fuel pumps(you have to replace the entire pump, there's no rebuild kit, not cheap) and replace the fuel filters? Also, did you rebuild the accelerator pumps when you rebuilt the carbs?

For me, I haven't replaced any fuel filters, just cleaned the one's that are there. Both of my fuel pumps are brand new OEM parts installed over the winter. I did not rebuild the accelerator pumps because they all squirt when I push on the linkage.

 

[timmafod]

OK so all evidence so far points to a lean mixture at 75% and higher throttle. My high speed mixture screws have been out all the way, which is only like 20degrees if that, because of the limiters seadoo placed on them. I plan on removing the little limiter tangs and enriching the screws. The Mikuni manual says maximum richness comes at 3 full turns out so I should have a lot of room to play.

Of course the fuel transfer hose from one carb to the other completely covers the forward/mag carb's high speed screw. Nothing can be simple.

Max fuel pressure at ~7000rpm was 6psi. This is on brand new oem fuel pumps. Not sure if this is low, normal, or high. At idle fuel pressure is 1-1.5psi.

 

[parrothd]

The high speeds screws are to be set at 0 turns out.
if you're trying to adjust a stock boat out(richer) you have an fuel issue and you need to fix that issue before you burn the engine up, opening the high speed is not the fix.

Did you check the gas tank vent line? When it acts up, unscrew the gas cap..

 

[timmafod]

The high speeds screws are to be set at 0 turns out.
if you're trying to adjust a stock boat out(richer) you have an fuel issue and you need to fix that issue before you burn the engine up, opening the high speed is not the fix.

Typically I'd agree since that's in the shop manual and seadoo knows more about these than I do, and why I haven't tried this yet. However, opening the high speed adjuster may be the fix if it's the high speed circuit that's lean. Why is it lean when the other circuits give a nice plug reading? Not sure, but it is. Screwing just one of the high speed adjusters (PTO carb, the one you can reach easily) in all the way (0 turns out, OEM recommended setting) just that 20 or so degrees rotation made it noticeably worse. Also, at WOT, there isn't much room to depress the accel pump plunger as the linkage closes it mostly, but even that little bit of "squirt" you can do would make the rpm's blip higher. It would have been nice if I had a way to easily manually squirt or pour more fuel in there but we didn't.

It want's more fuel at ~75% throttle and above, screwing out the high speed screw will give it more fuel in that range. I'm not going to go to 3 turns out and see what it does. I'll inch it up but more than the 20 or so degrees that seadoo limits you to using.

Did you check the gas tank vent line? When it acts up, unscrew the gas cap..

...When the boat started to act up I went back and unscrewed the gas cap to see if it was possibly the gas tank vent not venting, forming a vacuum in the tank and therefore restricting the fuel flow to the engine. That didn't help.

Don't get me wrong, I do appreciate any input!

 

[Luisecoco]

Hi everyone I have seadoo gtx di 2002 I have some problem with my fuel pulpit won't start but if I spray the starting fluid it will start I thingits my fuel pump but when you first put the key you can hear the pump running maybe don't have enough presure or maybe the injector are dirty a don't want the pump becouse I'm it's $750 if someone knows what other pump can I use instead the oem one let me know thanks for your time