Bee01

Alright. I had the pump side fuel hose replaced a while back. Shortly after, the car refused to start. Took it to mechanic he says no fuel pulse could be ecu or crank sensor. Car randomly starts and he gives it back to me confused. Car drives fine for a few days then no start or when it does it misfires at idle. I check spark, replace plugs, compression test, and do a head gasket test. All seem to be fine. Take it to new mechanic -says he cleaned and adjusted electrical connections and the car runs great for another few days and then no start. I replaced the crank sensor-- no start. Then I do the fuel pump ecu bypass and it starts and runs but has a misfire and smoke coming from both sides near exhaust manifold. I unplug maf sensor and plug it back in and it runs great even after reconnecting fuel pump ecu. A few days later it won't start and I do the bypass and now regardless if maf is plugged in or not it misfires. My thoughts are the following:
1. bad ecu
2. Clogged or broken fuel injector
3. Maf sensor failure/harness short
4. Exhaust/intake/vaccum leak
5. Gremlin somewhere.
Does anyone have any insight on this? I would appreciate the help this has been such a pain the last few months. Also lmk if I should post this to a specific thread in the forum

RXRodger

iTrader: (2)

If the ecu has not been rebuilt it would be my next thing to investigate since it is a known issue. The symptoms sound like it could be a place to start.

Tallyhoe

Check your ignitors, there is 2 of them. You may need an inspection mirror for bank 1 if you don't want to remove it, cuz the whole bracket gotta come out. If you're misfiring you're cooking your cats and if you live in an inspection state you will for sure fail smog on your next inspection. The ECU may be the issue, but at the same time it may not be. I had similar issues, and kept stalling long after I had the ECU rebuilt. What year is your SC4?