'99 Mariner optimax 135 rpm studder

[blakes52]

Serial # 0G805271
1999 Mariner 135 optimax

Today when at about 3700rpm i noticed that the motor was a little shakey and the rpm was bouncing between 3700 to 3900 rpm. i didnt get any alarms at first, only after i got back to the dock did my check engine light turn on. What is weird though is that if i throttle higher than 4000rpm it goes away and i have no problem meeting my high end rpm (5500) and normal top speed. Also there maybe a little bit of something happening at idle/slower speeds but not nearly as bad as at the 3700-3900rpm range. Any thoughts, i am thinking it is a plugs/coils, fuel, or injectors issue but am not sure.

[SilverFox579]

How old are the plugs (hours or years)? How about maintenance history for this engine? Great FAQ topic at top of forum - Recommended Annual Maintenance or Winterization for Optimax Engines

If you suspect any fuel delivery issue at all (and most certainly if never done) - FUEL LINES AND PERFORMANCE PROBLEMS

[EuropeanAM]

Good idea to check the basics... just a hunch here but it would be wise to have TPI voltage sweep test done (and check for faults/counters indicating a problem in this area).

[blakes52]

thanks @silverfox579. I just bough the boat in december but i dont know exactly how old the plugs are... im going to check a few things on the boat the order a set of plugs because i will replace them sometime soon/if i cant fix the issue

[blakes52]

thank you @europeanAM is that a test that i myself can run or something i would have to have done at a mechanic?

[EuropeanAM]

Best done on the Computer Diagnostic System (which should be able to accomplish both).

Voltage sweep test "can" be done with a voltmeter (still best done as described above).

[leonreno]

It can be done by you but you will need to order the service manual for your motor from Mercury, which will be the best investment you can make for your motor. European Marine can get one for you, check his signature to order parts.

[leonreno]

Listen to Don, may best be done on diagnostics software , completely missed you had an Optimax. Didn’t realize Mariner had an Optimax. Also, any PDF of the service manual is a copyright infringement as they only sell them as hard copy books.

[EuropeanAM]

thanks @leonreno i just found a pdf online... already found some good info in it

Since Mercury sell electronic copies of their Service manuals (print ONLY), that is a Bootleg Copy (Copyright infringement). See Forum Announcements for more details.

[blakes52]

im still going to order a paper one as the pdf is not ideal. i tested today and all the cylinders are firing at idle.. im looking into investing in a scanner tool as it is hard for me to take the boat to a shop, any advice? right now im just looking for a used scanner based on what is in the manua.l

[EuropeanAM]

Used is like looking for a needle in a haystack. Check out Diacom Software (by Rinda Technologies).

[blakes52]

thanks, funny you say that because i was reading through old post about techmate pro and diacom software. my question is with the diacom software you are buying the current version of the software, but with the scanner you can update it for what seems to be free (they have a link on their site that directly downloads the firmware file). For me that makes the techmate pro more appealing as i will eventually be upgrading this motor and that will allow me to use this unit on newer models. PLus it seems the only difference between diacom and techmate pro is that the diacom allows saving of data which can then be printed (but both can provide the same information and data). thank you for all the help

[EuropeanAM]

You would need to talk with them regarding any updates, etc.

I had the equivalent of the Techmate many years ago... never was very fond of it. Can only see so much info at a time on that tiny screen.

[blakes52]

I was finally able to scan my motor today, with techmate pro. I am getting a fault on Injector number 3, would i be able to clean the injector (could that be causing the error) or am i better off just replacing it completely (im thinking this is the best option). i believe i have to remove the fuel rail in order to remove the injector, is this correct? thank you for all the help.

[leonreno]

You can send the injectors to Don for cleaning and calibration check, you may decide to have them cleaned and checked first after seeing the replacement cost.

[blakes52]

After running further checks with the scanner it is the Direct Injector (air) that is causing the error. the Direct injector test runs each injector, one at a time, and there was an audible difference between the faulting one and the others, plus the fault code would trigger after testing that injector. thanks for the advice... the price is up there for sure.

[SilverFox579]

I'd send the entire fuel system to Don for cleaning and calibration.

[EuropeanAM]

You may want to verify that it's actually the injector, and not a wiring or connector problem.

PCM can only ascertain open or short circuit faults (the actual fault name indicates WHICH the fault is).

[blakes52]

ok thanks will do

[blakes52]

All the injectors (fuel and direct) were serviced locally (cleaned, inspected, and flow tested). I had a slight leak on 2 of the direct injectors and 2 fuel that were replaced. After the cleaning all the injectors were not leaking and fully functional on the flow test. Just reinstalled them all back in the boat and replaced in-line fuel water separators (in boat and motor) and replaced the spark plugs. With the plugs i went with the ones (heavy duty) in the service manual as the plugs in the motor were different than recommended. At first everything was going good, injectors were all tested one by one and they were clicking...after all were tested the boat had no active faults. When we went for a drive the motor seemed good but after driving a couple minutes and getting to wot i was at only 4900rpm (not 5500 that i am proped at) and the light turned on again (after scanning it was injector number 3 again). When i got back to the dock i swapped the signal wire to the injector to another (number 5 injector) to test the signal and there were not any faults. I am lost for things to do and loosing $ between scanner,plugs and injector service :(