2.5 -> 2.0, Now P0170

[Numbchux]

01 Forester. Originally a 2.5, replaced with a JDM SOHC 2.0. Install went smoothly (reused many of the 2.5 parts, as per usual), engine runs great, car drives very nicely.

Throws a P0170 (fuel mixture rich). Live data reads LTFT -20% or so, which makes sense as I've reduced engine capacity by 20%. I've seen dozens of posts about doing this swap. The dealership I worked at did it many times. I don't recall hearing about a code like this.

However, quick google search does turn up a few mentions. I see some using smaller injectors, I might try the ones from the 2.0.

 

Any experiences/insight/recommendations?

[idosubaru]

Can you test the O2 sensor?

Are there differences or is it worth trying the 2.0 injectors instead of 2.5? 

Why was the engine replaced and how sure are you that it didn’t have this code before the swap?

[Numbchux]

I'll check live data again to see what I can read of that sensor. I don't remember if it's an AF or O2 sensor. Either way it is a new Bosch one.

The 2.0 injectors appear to be physically interchangeable (although I haven't disassembled them). This engine was clearly much newer, and had many differences above the block. So no guarantee that the injectors will be 20% smaller.... But, when I get some time, I think I will try to swap them.

 

This car had no engine when I got it. The engine that was in it was pulled to use in a nicer car, so all my components are cobbled from my collection or new. That said, I was very careful to check part numbers on things, and used all new gaskets, plugs, wires, timing components, and more. I have no running issues, and no other codes.

 

If the battery has been disconnected, it usually stalls on the first startup attempt. But once it learns itself for a trip or 2, it starts perfectly.

Edited September 7, 2021 by Numbchux
thought of a symptom

[Numbchux]

On 9/7/2021 at 11:59 AM, Numbchux said:

But, when I get some time, I think I will try to swap them.

 

It happened, I got some time for a project!

They're both top feed injectors, but the 2.5 one is different, using a different O-ring and a retaining clip to the rail, and with an extra section on the end for the Air Injection system.

2021-10-18_10-01-19 by Numbchux, on Flickr

 

I put it back together as it was, but it leaks, so it'll have to come apart, again. I've seen people talking about using WRX top feed injectors when turbocharging an EJ251, but they generally block off the air injection system. I'd rather leave things as stock as possible.....but might have to experiment.

 

I think it's either modify until the 2.0 injectors work. Adjustable pressure regulator to drop the fuel pressure. Or have a trouble code.

[1 Lucky Texan]

if it's just the code, you might be able to flash the ecu and kill it off. depends on the definitions available I guess.