Overboost Bypass

[Saabin]

Hey everybody, my names Matt. I have an 89 900 Turbo with the LH2.4. This website, has DIY overboost bypass instructions;

Bypass the overboost switch on LH 2.4 cars

"This is done at the LH ECU.

You'll have to remove the carpet trim pieces by the door in the passenger footwell to peel the carpet back and gain access to the LH ECU. It is bolted to the sheetmetal on the righthand side of the passenger footwell.

Locate the system and fuel pump relays by the LH box, you'll see two brown&white wires each with a single-pin connector on the end. Disconnect them and connect them to each other and you'll have bypassed the overboost."

-But this confused me a little bit, do I take the big plug out of the ECU and pull the 2 brown/white wires out of the plug, and then connect them at the end? Or do I cut the wires and then splice them? I really dont want to mess it up so if someone could help me please!

[Hans]

He's talking about the relays, not the ECU; the relays are close to the ECU, just above it.

BUT...I don't think it would work. You would have to confirm, but my understanding is that, for overboost conditions, LH2.4 not only de-energizes the fuel pump relay but also shuts down the injectors.

If you want to avoid fuel cut-off on a modified LH2.4-equipped Saab, go to Saabnet's Performance board and search "zener diode" or "orange wire" (with quotes), and read about two strategies to prevent the air mass meter signal from reaching 5 volts, the overboost trigger point for LH2.4.

For information on a modified ECU, see http://forum.ecuproject.com/ which has a sub-forum on LH2.4, though, at the moment, I can't see it there...

If you happen to be hitting the cut-off with stock injectors/fuel regulator, you should anticipate engine damage.

[hutch]

What other mods do you have for the car? There are certainly things that should be done before cranking up the boost and getting rid of the fuel cut. If you have the standard 3" exhaust, better intercooler, 3bar FPR, etc... then it may be time to invest in a reprogramed ECU chip. Snipping wires and putting in resistors worked alright a decade ago but these days I'd suggest trying to do it the right way. Check out these guys, members on this site too, I'm pretty sure they do chips for 2.4 cars.
http://www.epartsland.com/pages/contact

Or if you want a DIY route check out ecuproject as mentioned before and learn how to do it yourself.