View Full Version : "old" TBI stuff on a Vortec engine?

06-08-2008, 01:06 PM
well . . I had a broken valve seat . . which ate one of my cylinders in my '96 Indmar 275HP TBI . . I took it apart and noticed that it had a few other problems as well (looked like it overheated quite a few times . . the second head had a crack . . and so on) I decided to get a new longblock . . and I got a good deal on a brand new '03 Indmar with Vortec heads (for a 310hp TBI ) . . (the seller told me that this would work perfect . .)

Now I have changed everything from the old one to the new engine (replaced the whole throttle body as well . . different story though) other than the coil having no place to be fixed (I have this solved as well . . ) . . I had no problems at all . . everything fits like perfect

but now I have the feeling that it runs a bit rough (at least rougher than the old one did . .). . . could it be that the "old" ECU doesn't match with the "new" cam? . . . or does anybody has a idea whet could be the problem?

06-08-2008, 02:05 PM
If you send an e-mail to MC or Indmar, provide the motor and ECM serial number, so they can let you know of any incompatibilities. As I recall, they started using the Vortec heads in '97 but at that time, the ECM was still MEFI II. I don't know the specific timing curve or fuel mapping but I don't think they were too different. Once you find out if your ECM is compatible and if you find a full-service MC/Indmar dealer, MC or Indmar can e-mail the correct software/firmware to the dealer so it can be downloaded to the ECM. It takes about 5 minutes.

As far as roughness, the first things I would look at are:

Plug wires not being exactly right (it happens)
Bad plug wire
Old cap/rotor
Bad spark plug

If you have a timing light, verify the base timing (the ECM needs to be in 'Service Mode' for this and can't be done without that step. If you look at the timing mark without the ECM being in Service Mode, the mark should jump above and below the 10 degree mark. If it doesn't, the ignition control (IC) module isn't working, for some reason.