Local Perf shop saying... Help...Thoughts?

jster91 said:

Cel is throwing lean code in bank 1. Backfires once in a while. Hesitates at low speed and part throttle. I replaced both o2 sensors. Code comes back. Is 10.5 to 1 dangerously rich? Doesn't make sense, lean code and rich tune. Bottom line, can't get the lean code to stay away.

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Have you considered an exhaust leak as a possible cause of how a bank could have a LEAN code and yet be chronicly RICH?

Remember the O2 sensors react to the presense of oxygen in the exhaust. Unmetered air in the exhaust is going to make the O2 sensor think the AF is LEAN. The PCM resonds by adding fuel.

I am not a tuning expert. I don't know about what it really takes to make BIG HP. I do have a fair understanding of how the stock Ford ODB2 adaptive fuel strategy works. Having said that, an AF ratio of 10.5 seems awful fat to me.

So what if a very fat tune plus a chronicly rich O2 (exhaust leak) is causing a dangerous condition? Something to think about.

Backfire is another symptom of excessive fuel in the exhaust.

I almost wonder if the fact that you have long-tubes is causing the O2 sensors to run cool (even though they have heaters). LTs have thin-wall tubes and place the O2 sensor down in the airstream in the collectors. Perhaps there's simply not enough heat down there for them to function properly.

BTW, with a blower I don't think you can run "dangerously rich."

+1 on the LT and not enough heat in the O2's.

Since we are playing "what if" games. What if the O2's are not getting hot enough. This is causing the PCM to go "open loop". Under open loop operation the injector pulse width is table driven. I am sure the WOT tables are very rich.

Another "what if". Consider that narrow band O2 sensors are very inaccurate outside of their design limits. Their accuracy "sweet spot" is very narrow. The technical name for this a non-linear function. If you have ever seen a graph of the curve it is quite interesting.

Bottom line, narrow band O2 sensors are inaccurate outside of their design limits. This is where a wide band O2 sensor would be far better.

A quart every 2 weeks? So how many miles per quart of oil? This is critical information so calculate it carefully. A quart every 1000 miles is quite a bit, but could be considered normal, especially on a stroker engine where the ring pack isn't ideal. If you are talking about a quart every 300 miles, then you would certainly see a lot of smoke if you were burning the oil. Since you don't see a lot of smoke, then you might want to look for leaks. But that all depends on how many miles per quart of oil.

Miles/quart is key as bhuff sez. Sounds like you may be into a leakdown test at the very least.

It could be that the builder/previous owner didn't break the motor in properly and the rings never seated properly. Or it wasn't built right (e.g. ring gaps too large or too small (broken rings), sloppy piston fit or valve guides etc...) A puff on start may indicate valve seals or guides.

How is the PCV system connected? If there's excessive crankcase pressure due to blow-by, you may be forcing oil into the top end via the PCV.

A leak down can give an indication of how well the rings seal, thus how much blow by you could get. I'd be curious how the PCV is connected as well. It vents into the unpressurized area, before the supercharger, right? Also, does it leak oil at all? I would think a quart every 500 miles would make quite a smoke screen if you were burning all of it. A little bit of oil goes a long ways. Maybe have someone follow you to see if you leave a trail of blue smoke always, it smokes only at idle, or if it only smokes when you step on it.

To give you some comparison of smoking, my 97 uses a quart in ~2500 miles. I do occasionally catch it smoking at idle, and only a small puff and for a short time (14 year old valve seals). If you were really burning a quart every 500 miles, I would think it would be quite a scene.

Is the air/fuel 10.5 at all times , or just at WOT ? It should be near 14.7 at idle and cruise , 10.5 is too rich for WOT as well , it should be close to 11.5 , I would say the oil issue is either rings or valve seals , either way I would advice tearing it down to inspect everything if you dont know whats in it .

Running rich should not hurt an engine initially but over time it can hurt the engine...something about cylinder washout and compression lost due to increased space from the piston ring. How long has this rich condition been there? Also, maybe it's running soo rich that you are actually losing oil from the excessive fuel...you might indeed have an exhaust leak upstream of the O2 sensor (as mentioned earlier) which may be triggering the lean code. Check to see what the other bank is doing as far as the fuel trim is concerned. Listen for leaks and carefully check for them while the car is running (try not to burn yourself). Also, don't rule out a faulty O2 sensor, a bad connection, or even a criss-cross of the sensors in which case one bank will run rich while the other runs lean.