350 mag mpg engine running rough 1000-2800 RPM

[jkilling]

I have been having off and on problems with my 350 mag mpi engine (s/n 0M621379) running rough in the 1000-2800 rpm range. It does not seem to be low on power, but has some vibration and does not run as smooth as it should. After 2800 rpm it either goes away or is not noticeable. Usually when I get this problem I change the distributor cap and rotor and 50% of the time it will help, but some times it does not make any difference (now is one of those times). I was going to take it into the shop to get looked at, but they are booked until August. Below is a list of what I was thinking to change address next, but I’m looking for any help or guidance from someone more experienced than me.

Items recently done:
1. Changed distributor rotor and cap
2. Set engine to TDC cyl 1 and verified rotor is pointing to #8
3. Changed spark plugs, ran better at first but started doing the same thing after ran engine for 30 min
4. ran 2 cans of sea foam in gas (about 10-15 gal)

Thought for next step

1. test coil resistance (does anyone have the primary and secondary resistance values?)
2. Change entire distributor (Already purchased a new one because I noticed some radial play maybe 1/8”)
3. Change crank position sensor (a mercruiser rep told me I could try adding or removing a shim from the sensor)
4. Change knock sensor

Any help would be greatly appreciated. This has become a very frustrating problem and I would love to get it resolved.

 

[Faztbullet]

Are the caps dirty when you chane them?? If so check the screen in bottom of distributer as if clogged the ozone will build up and dirty up the inside.. Also it sound like you need injectors pulled and cleaned...

 

[jkilling]

Distributor caps show corrosion on the terminals, but don’t look dirty. Is it possible to test injectors without removal? Where do you get injectors cleaned at?