GT40 RPM Dropping

R

rossl

Cadet
Joined
Jul 15, 2007
Messages
6
Hi All,

I have a PCM GT40 351 in a 1996 Nautique Super Sport V Drive, when running at any rpm it suddely looses power and rpm's for a few seconds (we slow down) and them goes back to the exact rpm and speed we where going before (speed's up).

Its also almost the same rpm ratio as well eg. 1800 -> 1200, 2800 -> 2200, 3200 -> 2500rpm etc. It can happen every couple of minutes, then not occur for an hour. Any idea's?

Cheers
Ross
 
Reel Poor

Reel Poor

Vice Admiral
Joined
Jan 29, 2005
Messages
5,522
Re: GT40 RPM Dropping

It sounds like it may be dropping a cylinder. When was the last time it had a complete tune up, plugs, cap, wires, rotor, fuel filter(s), timing checked?
 
R

rossl

Cadet
Joined
Jul 15, 2007
Messages
6
Re: GT40 RPM Dropping

There does seem to be more smoke from the exhaust when it happens, could it be un-burnt fuel?

cheers
rossl
 
Haut Medoc

Haut Medoc

Supreme Mariner
Joined
Jun 29, 2004
Messages
10,645
Re: GT40 RPM Dropping


It could.....
Like RP says, when was a full tune up last done?.....
I would pay close attention to the plug wire & see if there is any chafing.....
Does it have any effect on the other gauges?......:confused:​
 
R

rossl

Cadet
Joined
Jul 15, 2007
Messages
6
Re: GT40 RPM Dropping

No other gauges effected, only tach, i've ordered cap, rotor, leads, plugs to see if that makes a difference, is there a coil on a gt40 (i can't see one as its a bit tight in the vdrive)

cheers
rossl
 
R

rossl

Cadet
Joined
Jul 15, 2007
Messages
6
Re: GT40 RPM Dropping

Have now changed plugs, wires, cap and rotor and its still the same, testing it at idle the rpm will go from 600->750rpm and sometimes stall going into gear, somebody else told me it may be running too rich? What do you think?

cheers
rossl
 
Bondo

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,525
Re: GT40 RPM Dropping

somebody else told me it may be running too rich?
Click to expand...

You Just changed the Sparkplugs,...........
What did they Tell you,..??..??.......
What Color were they,..??......
 
R

rossl

Cadet
Joined
Jul 15, 2007
Messages
6
Re: GT40 RPM Dropping

Plugs look ok light brown color, but our boat runs on LPG Gas (autogas), so harder to tell.

rossl
 
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