1998 Mariner Optimax 135

JD4WDJD4WD Posts: 8 Greenhorn
Hello everyone,

I wanted to post in regards to some engine trouble that my Dad is having and see if anyone has encountered a similar issue.

My Dad has two 1998 Mariner 135 Optimax motors powering an older Wellcraft hull. The port engine has started to act up where it will stutter once it warms up running above 3000rpm. No issues at all with idle and no issues below 3000rpm whatsoever. We did a test run a few days ago and it ran pefect for over an hour right at 3000rpm. As soon as he throttled up, it started sputtering. Here is a quick video I took while we were testing it:

We have replaced the both TPS sensors (front and back) and the issue still remains. Also, just to be sure that the new parts were not DOA from the factory, we moved the working sensors from the good motor over and the problem still remains.

Plugs are new, injectors have been serviced, and he only runs non-ethanol fuel. We think it might still be fuel related, possibly the low pressure fuel pump? What do you all think?

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