DT150 running great until I hit the trim

[Summer88]

My 1988 DT150SS was finally running great. I cleaned and rebuilt the carbs, that helped a little. Then I put in a new throttle position sensor and that did the trick. The motor was running perfect. That lasted for two days, and on day three, at about 3/4 throttle and going fast, I trimed the motor up like I always do on my bass boat. The second I hit the button my rpms fell dramatically. It became harder and harder to get on a plane over the next two days and now it wont do that. Any ideas? Another note is that my tachometer is also being very erratic, but I'm not sure if that's a related problem or not. Thanks for your time. I really appreciate anybody willing to help with any advice.

Neal

[boats.net]

Look for bad ground wire connections on engine.

[Summer88]

Thanks for your reply. That was my fist thought as well. I looked for grounds and only found one that went to the exterior of the case. It was sparkling clean. I've had this engine for a four years and it's really clean inside the cowling. The battery ground was good as well. Are there some other grounds I should be looking for on the engine? That would sure make a lot of sense if it were a ground.

[keakar]

the trim relays are switches that have positive and negative power that get reversed for the trim to work.

since all this started with them, its possible one or both the trim relays could be shorted causing a power drain on the electrical system. disconnect the power wires from the trim relays and just hook them to the starter relay and see how it runs.

if its not the relays then I think you have a short in the wiring harness, the tach being erratic is symptomatic of fluctuating voltages like bad wiring

[Summer88]

I haven't been able to track down any wiring problems. I researched the forum and found a post from 2009 that had the exact same problem. The tech he talked to told him to bypass the tachometer control unit/module by connecting the yellow leads to themselves instead of going through the unit. He never posted again so I don't know if it worked. I'd like to try that, but I don't want to damage my engine. Do you know if that could cause any damage? It would sure solve all my symptoms if that were the problem.

[keakar]

no I wouldn't go sticking any wires together to bypass anything based on old unclear information like that.

it sounds like that guy had a bad tach control unit and he was told how to bypass it but that doesn't mean your wiring is the same.

try asking a mechanic about it and see if he agrees that's the correct way to bypass the control but unless its super expensive why not just replace the tach control unit and see if that solves the problem? lets face it if you bypass it and it works you would replace it anyway right?

you certainly don't want to blow out your rectifier or wiring harness by crossing the wrong wires