chrisut

I have a 2007 tow sports 5.7 black scorpion. I bought it with the engine block cracked and put a 383 in it. Motor is in and running.
only mods were the cam (xm270hr) and the displacement.
Do I need to tune it, or will the computer make it run well enough? If I need to tune what's the best way to do that?

AllDodge

Don't see a motor serial number so I'll guess it has a 555 ECM. Merc tunes all motors fat and it may be ok but would need to get AFR readings to determine if a retune is needed. With out AFR readings or lots of plug analysis, then it needs to be retuned

chrisut

The motor is from 07 so I'm pretty sure it's the 555.
I'm pretty sure it has 02 sensors and cats.
I hadn't thought of checking afr. What are mechanics on doing that? Imagine that I want to be able to have the O2 sensors working properly so I guess I'd have to drill another hole?

chrisut

Accidental double post, sorry.

AllDodge

I'm looking up on BAM's site and last 350 MAG MPI had 555 but did not have CATs. CAT's came to Merc town in about 2010

If your motor does have CAT's then it has at least a PCM09

While reflashing a 555 is hard and not many can "actually" do it, no one can do a PCM09 that I've heard of

To measure AFR it requires as you say O2 probes installed in the exhaust and see what's going on with AFR meters

New ECM is $2300

AmiableDave

Whipple can do both.....

Trash

I would get current real time wide band readings and see what your existing AFRs are doing. If within limits run it. If not then get it tuned as mentioned above.

AllDodge

They say they can, but talk is cheap

AmiableDave

I called Whipple a couple of years ago and they told me they could reprogram PCM 0905. But I would have to run 91 octane and I didn't go through with it.
NOW YOU'RE SAYING THEY LIE TO ME? Do you work there? I'm curious to know how you know their talk is cheap.

AllDodge

Nothing of the kind, you believe them I don't. Prime example, would have to run 91 octane easiest way to do nothing when reprogram is required, say use higher octane fuel so if it runs lean there will be less chance of damage. A Merc 383 only needs 87

Another thing is Only whipple can do it, if it was do-able others would also

You may be correct and they are the only ones that can do it, I just don't believe it