Please help :Engine swap 1998 s70t5

[Ilovemyt5]

Hello I'm a new member, this is my first post.
I have a 1998 s70 t5m. I swapped the B5234T3 (blue tune) with a B5234T6 long block from a v70r awd.( Original engine had low compression)
It runs but i can't get the same performance as my old engine had. Anyone have experience with this swap? Do I need to retune? Can I swap ecus? When I reset the ecu it works great until the first key cycle. (The applied learned fuel trim?) It then over boosts (up to 20 psi) and and falls on its face. ( I kept the original maf, oxygen sensor, ecu, turbo, boost controller and fuel pump) Thanks for reading:)

[WhatAmIDoing]

Since we are both in the same boat regarding post engine swap troubleshooting, start with the basics. Check for vacuum and intake leaks. double check and reseat electrical connectors. Ensure vacuum lines are connected to where they are suppose to be connected, etc.

I'm not super familiar with the B5234T6, but based on my limited research the long blocks are the same and it should perform identical to your old motor. Did you test compression on the new motor?

[Ilovemyt5]

Thanks for the reply.
Yes I did a compression test before installation.
I went over all the vac lines and wires many times. Smoke test etc. No codes. I'm convinced it's the fuel trim. I just discovered that the fuel delivery systems are different between the s70 and the v70r 3.8 bar vs 4.0 and a "return less system" on the v70r?
What swap did you do?

[Chuck W]

What did you do for your fuel system? Did you swap over all of the parts from the old engine?

You need to keep whatever system was on the old engine.

[WhatAmIDoing]

Thanks for the reply.
Yes I did a compression test before installation.
I went over all the vac lines and wires many times. Smoke test etc. No codes. I'm convinced it's the fuel trim. I just discovered that the fuel delivery systems are different between the s70 and the v70r 3.8 bar vs 4.0 and a "return less system" on the v70r?
What swap did you do?

If you reused your old fuel rail and injectors (it sounds like you reused everything from the T5), then fuel delivery shouldn't be an issue unless you fuel pump is failing or you damaged the pressure regulator (it's hiding down under the firewall on the passenger side). I accidentally broke one of the barbs on my regulator spaghetti and had to fix it.

Did you test your fuel injectors? You can do this yourself unscientifically but it will make a large flammable mess. Did you check for fuel leaks?

Fuel trims are controlled by the ECU primarily through data from the O2 sensor and MAF (and probably some other stuff). If either sensor is reading erratically it will cause issues. Generally fuel trim issues are the result of vacuum or intake leaks.

I converted a low miles B5234T engine to a B5234T3 to replace the bad engine in my 98 S70 T5M. Currently tracing a large vacuum leak resulting in wacky fuel trims.

[Ilovemyt5]

Nice project. IM sure your aware but, Ive found a bad leak is the large pcv line (1inch ish) that connects to the intake hose by the turbo, its hard plastic and was cracked under the distributor on both my t5s. (Sucking in un metered air) Also the small white hard plastic vac lines often wear through.

I did not reuse the injectors or rail. And I just discovered the part numbers are different between the white bosch injectors. I thought all the white t5 were the same.

[Chuck W]

The vac leak will cause problems.

The white and blues are close enough to not really be the issue. Flow rates are the same, but they do have a different spray pattern and resistance.

However, do you still have a functioning return line? I know on the '98's the FPR isn't located on the fuel rail, so you *should* just have a feed to the engine from the old set-up, and return vs return-less shouldn't be an issue in that case.