225 efi lost top end rpms

[Ryno 615]

Serial # 0G871286
I've recently lost rpm's on my 99 3 liter efi and cannot figure out why. It will turn 4800-4900 and that is it.I know there are a few old threads on here with the same issue, but never any answers as to what the fixes are. Im running the same setup and nothing has changed in the last 4 years that i've owned it. Compression is the same as the day I bought it (90-92psi) in each cylinder, tested with two different testers. I started out with changing all filters, ordered a set of TDR reeds from Don, verified spark on each cylinder with an inline tester at an idle. My stator ohms are 1050-1150, verified it is reaching full throttle with the pedal(throttle body is completely open), rebuilt the VST, replaced the pump, replaced the spark plugs, ql77cc gapped to .035, and had the injectors flowed and tested. Added the two redundant grounds for the ecu, and I did rev it one time while on the water at idle, it stopped at 5000.So far, nothing has made a difference. I feel as if I have exhausted all of my resources and done everything that I can test. And now, my latest predicament. I've called 3 different shops looking to have my TPS checked out. 2 of the shops say they will not work on anything older than a 2000 model, one of those would not look at it with "low compression". The latest shop believed he still has the equipment somewhere on an old laptop, that may or may not work anymore, but wasn't sure if he had any mechanics that would even know how to do it, as most are fresh out of school. Don or Joe, any ideas?

[JOE54]

fresh is sure right and if you put it in front of one with out cowling or ser number they couldn't tell the difference from 99 or 2000 , prop size and brand ???? has it ever reached 5800 ????? sleeves borescoped ???? air temp sensor tested ???? tuner inspection.....

[Ryno 615]

I’m running a 24p Trophy Plus that’s not been worked, in excellent shape. Yes, I have not had this rpm issue until a few weeks ago, before I had done any work to the motor. When I lost rpm’s, is when I decided to start diagnosing this issue. I also replaced the fuel line from the tank, to the motor around a year and a half ago. I cut a small section of the fuel line out and it had no signs of ethanol eating away from the inner lining. Sleeves and air temp sensor has not been inspected yet. From what I can see with the lower unit removed, the tuner isn’t clogged. I know there are several holes that cannot be seen from there, yet my holeshot isn’t sluggish. I will look at the sleeves, and figure out how to test the air temp sensor. Thanks Joe.

[JOE54]

service manual is your friend

[EuropeanAM]

Air temp sensor would be my first priority. And check the map sensor reference hose and port to make sure it's not plugged/restricted (or perhaps even connected to the wrong hose/fitting).

[NoSloProcraft]

If you don't want to trow any more parts at it pick up a Diacom 94111 kit. It allows you to plug unto the 1995-2001 ECU's and view real-time data. I was able to diagnose an intermittent air temp sensor with it on my 2001. Use it to adjust the TPS each season as well.
https://www.rinda.com/rindashop/shop...acom-94111-kit

You may have a failing ECU as well. I was running the 250XB-fuel 300PM-IGN ECU's, one of which was intermittently failing. Finally swapped back the originals and all is good.
Seems like it would drop 4-500 RPM WOT and randomly cut back in. Went through 6 CDM's, stater, Injector service, new reeds (found a bad one), rebuilt VST, added ECU grounds etc.

Last but not least, you sure about the 90 psi compression test? My 2001 tests stock at 120PSI, and 130PSI with the cut heads. I know the earlier models were lower but I didn't think below 100 psi?

[EuropeanAM]

90-110 psi w/max variance of 15 psi.

[Ryno 615]

I went ahead and purchased a new IAT sensor, as it was cheap enough to just try. I made it to the lake today, and same issue. But, I did let it warm up for a long time today, and the motor stalled at an idle in neutral. Would not start back, and found the bulb to have gotten soft. Pumped it up, and would run fine, minus only reaching 5000~ rpm. So, I may have something new to dig into, or could be unrelated at this point. I will locate a fuel gauge to test fuel pressure. Any other suggestions short of attempting to locate someone to diagnose this motor?

[JOE54]

still would inspect sleeves for rotation , also inspect screen at regulator for clogging causeing high psi in fuel system, what is TPS voltage at WOT ????

[NoSloProcraft]

Your fuel tank wouldn't happen to have an anti siphon valve would it? I've heard of these going bad causing a restriction. These look like a NPT to barbed fitting, but contain an internal ball and spring.

[Ryno 615]

So, some updates. I took my boat to a shop that supposedly had the diagnostic tool, a week later they told me they did not have the right equipment. I decided to back probe my TPS sensor just now. I tested each wire individually and found that it is getting the 5v. When I back probed it with my meter, I have 3.5V on the signal wire at idle, and it gradually decreases to 0.7V at full throttle. I've read online where some people tested it this way and it reads backwards as well. Is it possible to properly diagnose a TPS sensor this way, without the test harness? I'm having an EXTREMELY difficult time finding anyone around that can look at it. From what I can find online, I should be seeing 3.8V~ WOT, and 0.90V at rest.

[JOE54]

sent you a guys number

[Ryno 615]

Thought I'd post an update on the issue. Still haven't had anyone to look at the diagnostics, Joe sent me a guys number, unfortunately it is 4~hrs one way, not exactly wanting to make that trip if I can help it. Now, I have figured out I'm able to get WOT occasionally. I have to go WOT before I even touch the trim, and slowly bump it, only way it will reach 5600-5800. If I am just cruising along, and decide to open it up, it will not pass 4800 rpm, so its shut down and try from a stop. Also, the times that I reach full throttle(5800rpm), it will not stay there for long. I can be on slick calm, straight runs, and the rpm's will gradually drop from WOT to the 4800 rpm range, while never backing off the throttle. It has this noticeable feel when it will actually open up, around that 5000 rpm range. Even my coangler can feel when it will open up and decide to run. I'm stumped. Seems like nothing is wrong, but at the same time, something definitely isn't right.

[Bob G.]

Did you see post #6?

[Jig A Low]

Hey, I JUST went through this exact same issue last week ---after tons of trouble shooting and parts replacement what I found was the very fine screen in the fuel pressure regulator was about 80% plugged up with trash. pulled it out and cleaned it now it runs as good as it ever has. may not be your issue but it's free and only takes about 15 minutes to do. if you find any trash in there I'd bet that is the issue.

[Ryno 615]

Appreciate the ideas fellas. Yes I did see post #6, locating an ecu to try has been a chore as well, but have not given up hope on that yet. I have removed and sprayed out the FPR in the past, when I rebuilt the VST. But I can take a closer look at it again.

[Bob G.]

I was referring to the Diacom kit in post #6.

[JOE54]

fuel psi when problem occurs ???? please , im afraid if you continue to run this engine much more you will find a much worse problem (findng a new engine )

[lpugh]

So, some updates. I took my boat to a shop that supposedly had the diagnostic tool, a week later they told me they did not have the right equipment. I decided to back probe my TPS sensor just now. I tested each wire individually and found that it is getting the 5v. When I back probed it with my meter, I have 3.5V on the signal wire at idle, and it gradually decreases to 0.7V at full throttle. I've read online where some people tested it this way and it reads backwards as well. Is it possible to properly diagnose a TPS sensor this way, without the test harness? I'm having an EXTREMELY difficult time finding anyone around that can look at it. From what I can find online, I should be seeing 3.8V~ WOT, and 0.90V at rest.

A dvom is not suitable for testing a TPS sensor, need a DSO or Lab scope for accurate testing, graphing will work but still not near as accurate as the previous. I have seen a lot of tps sensors thru the years that dvom would indicate were good when in fact they were junk. Scan tool sweep test is another good way however my confidence is with the DSO (digital storage scope)

[EuropeanAM]

If you don't have access to a DSO (or Diagnostic System)- another option that's better than a DVOM would be an ANALOG voltmeter (ie: Needle-display device). Not too hard to see the twitches and jumps of the needle.