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My Solstice says "hi everyone." Moving on.

I've had some really rough starting over the past month or so. I hadn't had time to really look at it until a few days ago, when I noticed the downstream O2 sensor harness had been cut, I'm assuming by some kind of road debris, though I'm not sure how.

Yesterday I replaced the sensor and harness connector (which had melted while hanging freely next to the turbo / exhaust manifold), and, lo and behold, my CEL disappeared and the car starts much more smoothly, though not perfect.

The other (possibly-related) problem is that, under WOT, the car hesitates to the point where it feels like a fuel cut. It's intermittent, but frequent.

While I was changing the sensor, I noticed that the gasket between the turbo and the exhaust manifold had blown. There's about a 2mm space between the turbo flange and the manifold on one corner, and a piece of the gasket is sticking out.

I've ordered a new gasket, planning to install it this weekend.

The Question

Can a large exhaust leak cause this sort of hesitation? It hesitates, surges, sounds really bad and I have to lift, then gradually accelerate to get it to stop. Not fun, a bit dangerous the first time it happened.

Cheers.

Update

It may be worth nothing that this just started a few days ago, before I changed the O2 sensor. I believe the car was running rich before that (makes sense as the ECU couldn't read anything from the downstream sensor), may have messed up the plugs. Too many things to check! Out comes the service manual, diagnostic section. :/

Update the 2nd

Unplugging the battery for half an hour re: @Paulster2's suggestion appears (so far) to have addressed the rough starting issue, but the weird hesitation at WOT is still happening. I haven't tried the tape yet. I did, however, notice that my AFR gauge is reading about 10.0-10.2 when it's happening, which is typical with this tune (though it seems a little excessive to me). That leaves air and spark. I'll check the plugs as they seem to be the most likely culprit.

  • Hey David ... did you set the ECU back to stock settings after replacing the O2 sensor and harness? – Pᴀᴜʟsᴛᴇʀ2 Aug 23 '16 at 20:41
  • @Pᴀᴜʟsᴛᴇʀ2 Hi, Paul! No, I didn't Is that important? Is disconnecting the battery sufficient, or should I re-flash it? (Reflashing is oddly cathartic.) – 3Dave Aug 23 '16 at 20:42
  • Don't reflash it ... just pull the power and leave it set for a good 30 minutes. This will pull all of the long term fuel trims out and cause it to start all over again. It may help what's going on, but really it's the best place to start. Let the computer get back to it's base tune and then it'll figure things out for itself from there. – Pᴀᴜʟsᴛᴇʀ2 Aug 23 '16 at 20:44
  • @Pᴀᴜʟsᴛᴇʀ2 Will do. Thanks for your help, as always. – 3Dave Aug 23 '16 at 20:51
  • You did realize what I meant by "stock" ... I'm sure your Solstice has been tuned for the turbo. Just setting it back to the "stock" fuel map of the new tune ... not to the factory tune, lol. I don't want you to blow up your Solstice, especially after all that work getting a good engine into it! – Pᴀᴜʟsᴛᴇʀ2 Aug 23 '16 at 21:14
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So, that's not what is generally meant by a "boost leak" – a boost leak is on the compressor side of the turbocharger, compressed air that should be going into the engine is leaking out before it gets there. What you have is an exhaust leak before the turbo charger.

That said, I don't think your exhaust leak would cause the behavior you're describing (but it should still be fixed promptly). The reason I think this is because I would expect the leak to possibly limit the boost pressure that can be obtained, but not to cause it to fluctuate. Depending on the volume of the leak it might not have any impact at all – especially at WOT. I think you could confirm (or deny) this with a quick and dirty test with some tape. It wouldn't even have to be heat resistant tape, I think you'd be able to tell before the tape burned off. Just wrap the joint tightly with several layers of tape and take it for a drive. That would either rule out the leak as the cause of the problem or prove me wrong.

  • Thanks, terminology corrected. My thinking was that the leak isn't as bad at low pressure, but really "opens up" at WOT. I'll slap some HVAC tape on there and see what happens. I may hook up my HP Tuners and do some logging, though not sure if I'm experienced enough to interpret the data. – 3Dave Aug 23 '16 at 19:32
  • At worst you'd have some data that makes no sense to you that you can post another question about :-) – dlu Aug 23 '16 at 19:34
  • Excellent point. :) Thanks! Any other ideas if the tape doesn't (temporarily) solve the problem? – 3Dave Aug 23 '16 at 19:53

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