PCM Pro-Boss GT-40 MP EFI - rpm Failures

Hello,

I own a 1995 Ski Nautique with a PCM Pro-Boss GT40 EFI engine and this summer I started having some problems with inconsistent RPM at all speeds.





While I'm driving I hear very slight and short (but constant) RPM breakdowns. It seems that the engine is having very fast hiccups. I barely feel any speed changes and the indicator on the RPM gauge varies only slightly but you can clearly hear that the engine is running inconsistently. Furthermore, I only have this problem while driving. If I disengage the shift mechanism I don't feel the problem when I advance the throtle.

I replaced the HP and LP three years ago and I had my gas filters changed last month.

Do you have any idea where I should start looking with my mechanic? Do you think there maybe be shortages of fuel delivery to the engine? Could it be a problem with the injectors?

Thanks in advance!

Gt40 is multiport, no protec. It was still labeled pro boss.

Fuel rail pressure first. When's the last time you tuned up any of the ignition system?

TRBenj wrote: Gt40 is multiport, no protec. It was still labeled pro boss.

Good to know... no wonder I am confused... did they label all the gt-40 motors "proboss" ?   Is the TBI a 1994 only deal?    

Sorry for the thread jack

Hollywood wrote: All PCM HO 351s are "pro boss"

Exactly. Carb, TBI and MPEFI... so long as it was HO, it was a Pro Boss.

Yep early GT40 with the sort after tubular inlet manifold and no FCC (Fuel Control Cell).

Like the guys said start with fuel pressure readings. And general tune up items plugs leads and dissy cap.

A code reader may help if one of your sensors is playing up. At $25 this Ford Code Reader is worth having even for a one time use.

gun-driver wrote: If he hasn't tuned it up in the 3 years he owned it and we don't know when the PO last tuned it up, sounds like it could be an electrical miss. This is all a guess not knowing how many hours a year he puts on the boat. I do like that fire bottle set up

Could you please explain the meaning of "tuned it up"? I'm from Portugal and sometimes I have some difficulties understanding some words/expressions.

There are wear items on the ignition side that should be replaced. I'm a "if it ain't broke don't fix it" guy myself but now would be a good time for a cap rotor and plugs.

No, your boat is EFI, no carb. It could be something as simple as a faulty plug or plug wire.   As suggested I would start by replacing plugs/wires/cap/rotor first and see what that gets you. It's easy, relatively inexpensive, and you can do it yourself. Just make sure you don't cross your plug wires into the distributor in the wrong configuration.

bhectus wrote: No, your boat is EFI, no carb. It could be something as simple as a faulty plug or plug wire.   As suggested I would start by replacing plugs/wires/cap/rotor first and see what that gets you. It's easy, relatively inexpensive, and you can do it yourself. Just make sure you don't cross your plug wires into the distributor in the wrong configuration.

So, together with "fuel pressure readings, starting with the rail pressure" your post practically sums what all the guys are recommending:

- Fuel pressure readings
- Replacement of some of the ignition system components, namely: spark plugs/plugs wires/cap/rotor

Do you think you could give me a hand finding the right tune up kit? I get very confused trying to understand the service manuals for the engines...

One more thing, are these changes suitable to be performed with the boat on the water? Or should I wait 'till winter to do it off the water?


Btw, the boat has now around 750hrs. I add around 40hrs each year.

bhectus wrote: Where in Portugal are you? My mom lived there when she was a teenager and my parents actually just returned from there 2 weeks ago. They go every few years. I've visited many places in Portugal myself, I love it there! I really liked Cascais and of course the Algarve with all the topless ladies. :)

Thank you very much for the support with the part numbers!

Small world hey? I'm from Porto (in the North). I know Algarve very well and I know what you are saying about the ladies :D I've been in Cascais and Lisbon a couple of times as well. And now I'll tell you something funny, you know Carl deAndrade from White Lake Marine? He was born in Portugal :) in the Açores island!!!

So I'll order the parts you mentioned and see how it works.

Thanks a lot. If you ever show up in Portugal I'll be more than glad to offer you a pull in my Nautique :)

Congrats on the fix

I added this fix to the GT-40 thread and spreadsheet:
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=25584&PN=1&title=poor-mans-gt40-diagnosis