2001 GTX RFI "limp mode" limited to 4400 rpm

[Jpnovak]

Hi Everyone. New to the forum and hoping you can help me go to the next step of troubleshooting. I had a 97 Speedster boat years ago. Carbs are easy. The RFI is causing me problems.

2001 Seadoo GTX RFI - 2 stroke
History: Bought used with new engine but not running right.
Issue: RPM limits to 4400 rpm when warm (5-10min into run). Will run at 6840rpm with WOT as long as you stay there. Once you slow down the rpm limit starts.
No diagnostic codes in CAN-DOO. No indicated codes in dash panel diagnostic (beeps and LEDs), No MAINT indicator.

I have read through all the posts in this link.
{forum title /threads/gtx-rfi-2000-wont-get-over-4000-rpm.64074/
[edit - can't post a link yet as new user]


Usual first step is "change the rectifier". Yeah, I have read almost all the threads and here is what I have done thus far. I am usually very good about using search functions and learning from those who have crossed this path before me. Many similar threads do not post a solution if they found one.

Existing troubleshooting:
new 4tec rectifier. Probably money well spent even though this did not change running condition.
Stator wires all measure in spec
Stator output voltage correct
Ski puts out 13.8V to battery while running above about 3K rpm. Goes up slightly at WOT under load on the water. I ran a jumper wire to meter taped to console while driving it.
battery has been load tested good and has a maintenance charger as well as disconnect
Fuel pressure correct.
Fuel screens on pump have been cleaned
new plugs
Plug wires trimmed back at leads
Front and rear fuse panels cleaned
1A and 20A fuses intact
TPS has been replaced (had dead spot in it)
TPS properly zeroed out in CAN-DOO.
Tried spare MPEM and had same issues.
Swapped Bosch ECU within MPEM and had same issues.
CHT sensor measures in spec
Rave valves cleaned and move freely


I am pretty confident this is not a mechanical issue. The ski runs great and will maintain WOT at max revs for as long as you don't slow down. It takes approximately 10-15 min (temperature dependent) before the issue starts up. I have read CanDoo codes before and after and there are none.

The limp mode supposedly will occur for low voltage to ECU. The only thing I have not done is measure voltage at ECU. I think this is Connector 3-P7 (red/purple) wire.

Do the two power wires and ground wires to Connector 3 have crimp issues or other high resistance contacts that would cause a low voltage scenario?

Any other suggestions?


Thanks

Jamie
newbie in Austin, TX

 

[etemplet]

You could have a bad rev limiter on the computer. I had this issue with an RFI but it sounded like the rev limiter cut out but the RPM was at 4130 for me. If I could coax the engine past 4250 it would accelerate to 6900. Once it dropped below 4200rpm the same issue. I'd suggest swapping the computer if you have access to another one.

I won't even get into what I think about the Can Don't or Can Won't. Good Luck.

 

[Jpnovak]

Thanks. It is definitely a rev limit of some type. I will guess firmware controlled.

Any information out there on what triggers it? I guess I need to figure out what input signal drives this.

 

[etemplet]

What I mean by rev limiter is "what controls the 7200rpm engine cut" for rpm protection. That is internal in the computer. If your RPM is being limited because of a condition or input from a sensor then it is not the rev limiter. Good Luck !

 

[Jpnovak]

Yes, understood.

I assume the ECU is telling the engine don't go over 4400 rpm. Supposedly a low voltage condition is one trigger (maybe their are others) but I just don't see a low voltage condition at the battery.

If there is another hardware protection in the system I can check.

I think my next step is to disassemble the harness connector to the ECU, install some measurement leads to the pins and monitor input voltage to the MPEM while running. Then I can repeat the same on the input voltage to the ECU inside the MPEM. I think most Bosch ECUs have the same pinout.

 

[etemplet]

Cool idea. Do you know someone with a RFI computer you can swap?? I working on a GSX right now... we tested everything and found a few issues but still runs like crap. LOL I have lots of spare parts and we did those swaps too. I'm thinking we have a wiring harness issue.

Check your rubber exhaust hose for being soft. They come apart. Probably isn't your issue but worth a look anyway. Post up on your tests... I'll be interested. Good Luck !!

 

[Jpnovak]

I do not have access to another computer.

I have called a number of shops in the area and no one will work on an early 2-stroke RFI ski. Probably because they burn too many shop hours troubleshooting like I am. Ha!

Exhaust hose is probably not the issue. That would have some variability in the final rpm where it chokes down. This one is definitely controlled by some electronic limitation.

I appreciate the responses.

I will be carefully checking the harness for any issues. I might buy pins and just run new power leads to the ECU. That would be easier than replacing the entire harness.

I will update after I have a chance to do more testing.

 

[etemplet]

Cool.... check that hose... they come apart.

 

[Jpnovak]

Are you referring to the coupler hose after the tuned pipe? This is #3 in the FSM on page 04-08-3.

Or #22? 24?

Lots of Helmholtz chambers in this exhaust system according to the pictures.

 

[Jpnovak]

I just wanted to post a follow up to this issue.

Turns out there was a bad CLT sensor. It would measure in spec all the way through warmup and then go open at full hot. This would shut down the ECU into limp mode. I built a pigtail to monitor resistance of the sensor while riding the ski. I thought it just went off scale and then noticed it was open.

New sensor and sent my son out to test for an hour. Said it never ran better.

 

[etemplet]

What are you calling a CLT? I thought I knew all of them sensors by first name. LOL Glad you got it figured out. That is the difficulty with the RFI and DI.

 

[Jpnovak]

coolant sensor, cylinder head sensor, engine temp sensor.

Sorry, I used to lots of other fuel injection systems where these terms are often used interchangeably.

The one on the top by the spark plugs.

 

[etemplet]

Good Catch !

 

[Jpnovak]

Well, Its spring and we have been using the craft. Ski was running well for many trips and just started doing the same limp mode. No errors on the dash. No codes in Candoo. Really frustrated I can't figure out what stops working when the engine gets to warm operating temp.

 

[etemplet]

Can Doo.... I call it the can DON'T. Good for making keys that's about it. Good old fashion troubleshooting works much better. What RPM are you having the problem? Can you unload the impeller by going over a wave or a wake. If you're at 4200rpm you may have a revlimter issue in the computer.

Find someone with a ski like yours and swap the computer.

 

[Jpnovak]

Yes. Old fashioned troubleshooting.

The limit is always between 4200 and 4400. Sometimes it will pin at either of these RPMs. Yes, the engine can unload and spin up. The engine will maintain WOT rpm as long as you don't slow down. It just won't accelerate after slowing below 4k rpm.

I suspect there is an ignition problem and why I was focused on the rev limit possibilities. It is possible that the coil is aging and getting hot. I don't have any experience with these engines.

What rpm will a single cylinder support if one channel on the coil is dropping out?

I think something is getting hot and failing. I just can't find it. I have not yet measured out the coil when hot. It test fine when cold. Same with ignition wires. Plugs are new and look about right for a 2 stroke after a hard run.

BTW, I bought a spare MPEM with ECU. I have swapped ECU and swapped MPEM and still have the same issue. I do not think this is specifically the ECU telling the engine to rev limit. Probably why I do not see any codes telling me so.

Happy to entertain any suggestions.

 

[etemplet]

If you have a spare Electronic Module Change it out and give another one a try. That is exactly what one of my RFIs was doing. It only did it after it warmed up a few minutes. I could hold the throttle at a specific point and play with it for a few minutes and sometimes the ski would take off and run 6900 rpm. Once you dropped below 4200... it would not accelerate again. That is exactly what mine was doing so give that a shot definitely.

 

[Jpnovak]

I will swap again for the test. Might have to pull the potting compound and reflow some of the solder joints.

Funny that my neighbor has the same year but is GTI and not GTX. It has carbs. That one is so easy to work on compared to RFI. Otherwise, everything is very new on our lake. I can't find anyone local that will work on 2-stroke RFI engine...

 

[etemplet]

I prefer the RFI over the carb. Much easier to work on as long as the electronics are working. Way better ski in my opinion. Easier for the ladies to start and ride.

 

[mikidymac]

I would check your RAVE valves. The fact that you can get it over the hump and it will rev fine until you let off and get below that RPM sure sounds like a RAVE valve issue. Maybe the solenoid isn't working.

 

[Jpnovak]

The RAVE valve "forks" are spotless and move very easily when hot.

I have not checked the solenoid...

There is some kind of air pump too. Right?!

Any good threads on diagnosing this system?

 

[Jpnovak]

Digging through the manual to understand more about how the RAVE system works. I have a list of things to check now. Will report back this weekend after some measurements and test.

Debating to get another RAVE solenoid to compare. I am going to guess that these are not able to disassemble and clean. I can certainly apply external voltage and see if it will actuate.

 

[etemplet]

When I swapped the computer the RFI in question ran great but I checked all that before I put it together. Rave system is pretty simple. Pressure comes from the engine through a check valve to the rave solenoid. At specific RPM the computer opens the rave solenoid. Air pressure than opens the rave valves. Disconnect the pressure line from the rave solenoid, should be able to suck air through but not blow back. Apply voltage to the rave solenoid it should click. Remove the rave caps, get a small hose connect to the rave solenoid. Blow in the hose, apply voltage and the raves should move. If forget the voltage to the rave solenoid.... maybe 5 volts. I've used 12. LOL good Luck.

 

[Jpnovak]

Perfect. Thank you. This is unbelievably helpful.

Now.. The $10 question.... You stated "At specific RPM the computer opens the rave solenoid."

What is this rpm? Does it vary with load or other condition? I would like to know so that I can verify the ECU operation.

I would also like to check the valves (Check valve and RAVE solenoid valve) when up. Since this issue happens at full operational temp.

 

[etemplet]

Does it sound like the engine is on the limiter, just at a lower RPM? Is it bogging?
If you have a rave issue it's usually around 4800-ish RPM you'll have issues.

Actually I've wondered if the raves on an RFI will open without power. I may check this. I'm just finishing up on a RFI rebuild.