Merc 2003 5.0 to 5.7 conversion causes backfiring

[usemdw]

I have a 2003 5.0 Merc that had a cracked block. After $5K and a new long block converted the motor to a 5.7L. I took it to the lake and at 3000 RPM it backfired and had no power. The shop says it may be timing or maybe needs a new ECM which is $1300. Can the old ECM be re-flashed? Any ideas?

 

[Don S]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

What was the serial number of your original engine?

 

[usemdw]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

What was the serial number of your original engine?

Not sure. the old block is laying on the ground at the shop.

 

[Tail_Gunner]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

Yes you need a reflash as Don posted...post your serial number or the serial number on the ecm..It could be a $1000 post. ID bet your timing is off also

 

[Don S]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

Not sure. the old block is laying on the ground at the shop.

You might want to get that SN (and tag) off the old block and keep it. You will need it for all the engine accessories as well.

 

[usemdw]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

You might want to get that SN (and tag) off the old block and keep it. You will need it for all the engine accessories as well.

Thanks, I'll see what I can come up with.

 

[usemdw]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

The boat people told me it was just timing, then when they had a real mechanic look at it, the timing was fine. Now they think it is either jets or the EC unit.

 

[Bondo]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

The boat people told me it was just timing, then when they had a real mechanic look at it, the timing was fine. Now they think it is either jets or the EC unit.

Ayuh,.... Welcome Aboard,... What's the induction system on it,..??

Carbs have Jets, 'n Efis don't....

Efis have an ecm, 'n carbed motors Don't,...

So just WHAT are We workin' on...???....

 

[usemdw]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

Ayuh,.... Welcome Aboard,... What's the induction system on it,..??

Carbs have Jets, 'n Efis don't....

Efis have an ecm, 'n carbed motors Don't,...

So just WHAT are We workin' on...???....

It is carbureted. It has a 2 barrel.

 

[Bondo]

Re: Merc 2003 5.0 to 5.7 conversion causes backfiring

I have a 2003 5.0 Merc that had a cracked block. After $5K and a new long block converted the motor to a 5.7L. I took it to the lake and at 3000 RPM it backfired and had no power. The shop says it may be timing or maybe needs a new ECM which is $1300. Can the old ECM be re-flashed? Any ideas?

It is carbureted. It has a 2 barrel.

Ayuh,.... Ok then,...
You have a fuel delivery issue, that's probably the carb, but could be anything from the tank to the carb, or the fuel itself....

You Don't have an Ecm.... It's probably a T-Bolt V ignition, which is very tunable...

Either rebuild that carb, 'n Hope,...
Or,...
Diagnose the fuel system up to the carb, 'n Try it...
Better yet, spring for a new intake, 'n drop on an Edlebrock Performer carb...
It's a carbon copy of the 4bbl. Merc is currently usin'....