Hi guys,

I was impressed at the expertise shown in some of the posts here at bbc. Though mine is a saltwater fishing boat, I hoped you might help to provide some suggestions to help debug my ailing motor.

The problem is that the motor doesn't get up to the same RPM that it used to achieve.

The low max rpm was observed immediately after I received the boat back from two back-to-back rounds of repairs by my authorized Johnson dealer. First, the boat refused to start and they fixed that by replacing ignition module. I got it back and ran for just a few minutes before the engine started to "load up", smoke and run very rough. I took it back and they replaced Lift pump, Ignition module, ECU and plugs. I had never had any problems with the motor before this. After the second repair the engine ran smooth and nice but never hits top speed.

I know that I was getting 5400 rpm and 29mph (GPS) at WOT immediately before the above repairs because I had just gone through re-propping. There were no changes to boat weight or balance. Now I get 4200 rpm and about 22mph. In both of these cases the boat weight, balance and prop were the same, done in the same location and an average of upwind/downwind.

I've checked for kinked fuel hoses and clogged fuel tank vent. All looks ok. I also squeezed the primer bulb while running WOT and it didn't make any difference to rpms.

I also syphoned all the old fuel out of fuel tank and filled it up with fresh gas.

I also checked the throttle cable - It seems to be opening up the throttle plates all the way open.

I was having a little trouble with the Ficht Diagnostic Software (version 1.42) so I was unable to retrieve Service Codes.

Other than the max rpm problem, the motor runs pretty good. Very smooth and quiet with no rough spots at any speed.

Unfortunately, it's been a year since I got the boat back from the shop so I don't expect they'll be too receptive to my complaint. Since they already have all the repair money allotted to my boat for the next couple of years, I'm trying to debug part of this myself (with your kind help).

I'm having trouble finding the model number and serial number stamped on the motor: I think those parts were cut off when the motor was mounted on the OMC Sea Drive Bracket. Here's the best information I could find.

The ECU information screen on the diagnostic program reads as follows:
Engine Model J150FSXEC
Engine Serial 0
ECU Serial 9740
Software Version 3030000
Software PCN 10768
Engine Hours 661

The ECU bears a sticker that reads as follows:
P/N 778612
S/N 3270401500
Remanufactured

The flywheel cover bears a sticker that reads as follows:
Engine equipped with upgrade kit P/N 15000512 (this number difficult to read)
use only OMC spark plug P/N 5000322 or equivalent

If you know where on the engine I can get s/n and model # I'll gladly look it up.

many thanks -- thornfish