1G Running lean after boost leak fix

[91lzer]

So the other day I fixed a large boost leak from the throttle body and my car started running very lean. My A/F gauge reads 18.0 and off the charts at WOT and 16.5- 17.0 at idle. I couldn’t figure out what was making it run lean and so I loosened the TB to make a boost leak so I could see if that was the problem. And with a boost leak the car runs perfect. I think the previous owner tuned the car with a boost leak. Any suggestions on what it could be or how I can fix it?

 

[91lzer]

Do you have wideband gauge that you're basing this off of? Is there a fuel pressure regulator (afpr) on the car? It's possible previous owner just used afpr to "make it run right". DSMers weren't that sophisticated back in the day.

Hey man, thanks for the input. yeah, I have a wideband gauge that I'm using, but no AFPR.

 

[91lzer]

Well, I turned off my boost controller and went for a drive. My wastegate crack pressure is 8lbs, don't know if that's factory. But turning the boost down did nothing for me, car still runs like shite. Tomorrow I will take a look at the ECU.

 

[Spleen8urLSX]

I couldn’t help but to notice your turbo to manifold gasket looks like it might be separated. With that, an exhaust leak as such before the wideband o2 sensor would not only make the gauge read very lean, but that would also mean it’s leaking exhaust before the narrowband o2 sensor which would throw the o2 feedback off and throw the fuel trims out of wack in closed loop making it run poorly.

If that gasket itself is not the culprit I’m still suspecting an exhaust leak of sorts somewhere throwing things off. Any exhaust leak before the wideband o2 sensor can throw the reading off so far that it’s meaningless so you wouldn’t know if it’s actually running mean based on that reading.

Also looks as if your manifold is cracking at the collector, that would create an exhaust leak and cause the same kinds of problems.

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[91lzer]

I couldn’t help but to notice your turbo to manifold gasket looks like it might be separated. With that, an exhaust leak as such before the wideband o2 sensor would not only make the gauge read very lean, but that would also mean it’s leaking exhaust before the narrowband o2 sensor which would throw the o2 feedback off and throw the fuel trims out of wack in closed loop making it run poorly.

If that gasket itself is not the culprit I’m still suspecting an exhaust leak of sorts somewhere throwing things off. Any exhaust leak before the wideband o2 sensor can throw the reading off so far that it’s meaningless so you wouldn’t know if it’s actually running mean based on that reading.

Also looks as if your manifold is cracking at the collector, that would create an exhaust leak and cause the same kinds of problems.

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Well, I did an exhaust leak test and I’m leaking from every gasket including the one in the pic

 

[Spleen8urLSX]

Well, I did an exhaust leak test and I’m leaking from every gasket including the one in the pic

There’s your problem! Along with the potential crack in the manifold. Those Chinese tubular manifolds are prone to cracking as it is and bad for the flanges to be warped right out of the box, on a stock flange turbo there’s far better options for similar or less money invested that will not only be more durable but perform better. A stock 2g exhaust manifold properly ported would be much more reliable, inexpensive, flow and perform better, and give the option of utilizing a heat shield. The cheapo t3 flange manifolds are good for running larger framed turbos on a budget with a little milling of the flanges if the user knows the risks, but for stock td05 flange stuff there’s such better options for the money the cheap tubular ones are pointless.

As far as the exhaust leaks go, I’d bet the flanges are warped which leaked from the get go or caused the gaskets to burn out, plus that looks like a cheap composite turbo to manifold gasket. Get a hold of a manifold with good true surfaces (if you pick up something used a machine shop can mill the flanges pretty cheap if they’re out of flat) and a good felpro composite or multi layer steel exhaust manifold gasket and a steel turbo to manifold gasket and o2 housing gasket (machine shop can true up the o2 housing as well), tighten everything in sequence with good hardware and nickel antiseize, and you should be free of leaks and your issues should be corrected.