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Mercury 2004 135 optimax running rough...

O

outerbanks

New member
Have one engine that is running very rough. (Not running on all cylinders)

Has a hard time starting. Will only idle for about 1 min. Idles rough. If I run the engine in nutral at about 1200 rpms it will stay online, but again very rough. I took it out and the engine will only reach about 3500 rpms in gear. Replaced all the plugs and noticed that the plugs on the port side of the motor were not firing. pulled the injectors and tested them as well with a meter and all seems fine. Pressure tested Air and Fuel rail all is perfect. Pulled the tracker valve again all is fine. Checked the shift / throttle control along with position censor and again all is fine.

I pulled one of the plugs left it connected and grounded it to a external (off motor) ground and it was firing. Once back in the engine... it was not firing.

Ran through all of the coils with meter and resistance matches whats stated on the manual.

I am at a stand still... the engine is not throwing any codes.


Anyone deal with anything like this?

Thanks,
Steve
 
Have you checked the compression of this engine? Results?
Also check the ground straps around the coil plate and also around the head that is not firing.
 
Did you check the 20 amp fuses? Did you pull the new plugs to see if they are wet from fuel? I connect a timing light to the plug wires at the plug end to see if the plugs are getting spark.
 
Have not done the timing light. Have checked fuses but not relays.

The plugs are wet. I am sure they are not firing while in the engine...i have ran the engine few times checking things and each time I pull the plugs (New Plugs) they look clean as new. I checked the right side of the engine and they are normal dark (used) plugs. Like i said before when i pulled one and left it connected used external ground they were firing.

.........

I would love to get it on a computer... My roommate is a O/B mechanic but his shop is not a Merc dealer so he does not have the computer.
Going from some people he knows and a few others around here. I have placed about 6 calls in the last three weeks. And can not get a mobile mechanic out to my house. If you know any one please let me know... We have done almost everything the manual can tell us.

Thanks!

Steve
 
Had a Merc guy come out with the computer.

They results were three bad air injectors.

Any idea why this would happen....and why three?
 
First he ran many tests with the laptop.

Second he had a devise that he plugged into each injector which manually tested each one. He did this with each one including the good engine to show me the difference between the good one and a bad one.
 
Update...

Replaced all three direct injectors... She sounded a little better. Still not running perfect...

Checked compression and all was perfect. Just as a final go round we swapped the fuel injectors from the good engine to the bad engine and she ran like new. Not sure why the computer said fuel injectors were fine, but thats what fixed it.

We will see what happens when I get her back out on the water.
 
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