305 to 350 Swap 96 K1500

[Jesse_Wenting]

Sorry to waken an old thread but I actually just swapped a seized 350 for a 305 (both 98) and wasn't sure about the ECU. My truck has dual cats and a total of 4 O2 sensors, but the donor vehicle I got the 305 from has a single cat and a total of 3 O2 sensors.

I have both ECUs but wasn't sure which one I should use. Future plans to put in a 350 down the line so please don't chew me up for "downgrading" to a 305 temporarily lol

 

[98 Nitro]

305 Vortecs are decent, not the boat anchors the Tbi 305s are. Just run the 350 computer should run ok maybe a little rich.

 

[PlayingWithTBI]

The 350 PCM will be looking for the 4th cat and throw a code. If you have the original PCM that came with the 305, use it. Then saw back when you get your 350.

 

[Jesse_Wenting]

If you have the original PCM that came with the 305, use it

So I've been running the 305 with it's PCM and up until a few weeks ago everything felt fine and dandy. Out of nowhere though I went from getting an average of 16MPG down to like 8. Nothing's changed other than the weather, but I did realize that the 305's ECM is also programmed for 3.73 gears while my truck (which it's still running in) has 3.42s

Any ideas what's going on? I also seems to be burning more oil than usual, but there's no visible leaks serious enough to explain the rate of loss I'm experiencing.

 

[PlayingWithTBI]

Nothing's changed other than the weather, but I did realize that the 305's ECM is also programmed for 3.73 gears while my truck (which it's still running in) has 3.42s

Well, your odometer thinks you're covering less miles than you actually are. But I think that's due to your DRAC or VSSB. Depending on what year, your ECM/PCM doesn't drive the odometer.

Any ideas what's going on? I also seems to be burning more oil than usual, but there's no visible leaks serious enough to explain the rate of loss I'm experiencing.

1st thing I'd do is a compression and leak down test.

edit: Also, put a scanner on it and look for any abnormalities.

 

[Schurkey]

Oil burning has poisoned the O2 sensor? Maybe plugged the catalyst?

As said...connect scan tool, verify all sensors and outputs. Look for misfire.

Compression and leakdown testing won't hurt.

I'd verify fuel pressure, too.

 

[Jimbo2312]

I am a awakening an old thread here, just want to clearly verify what components need to be changed in this swap. I know I need a new ECM, but will the spider injectors for sure work for the 350?

 

[L31MaxExpress]

I am a awakening an old thread here, just want to clearly verify what components need to be changed in this swap. I know I need a new ECM, but will the spider injectors for sure work for the 350?

They are the same part number, 305 or 350. As long as yours on the 305 are working correctly, they will work correctly on the 350. The whole intake manifold and air induction setup is also identical. Biggest difference is the PCM programming and the oxygen sensor and catalyst configuration. The 305 has 4 02 sensors, but 3 are in front of a single cat and one after. 350 has dual cats with an oxygen sensor in front and behind each cat.

 

[Schurkey]

will the spider injectors for sure work for the 350?

Do some research. What I'm seeing on Amazon is that the same part number spider assembly is listed for 5.0L and 5.7L.

 

[L31MaxExpress]

Do some research. What I'm seeing on Amazon is that the same part number spider assembly is listed for 5.0L and 5.7L.

Same part number and same injector data programmed into a 4.3L, 305 and 350 PCM for a given injector type. The poppets have one set of data. The MFI upgrade another set of data.