Ok, so you read the good in my Engine Bling post; now here's the bad. The today, I started getting the dreaded Restricted Performance message. Now, understand, I just upgraded the supercharger (larger lower s/c pulley, bored out intake/exhaust ports, larger intercooler radiator, new K&N Air Filter) but all was fine yesterday. Today, coming back from the bank I get the Restricted Performance message and what I initially described as a growl but listening to it tonight think it sounds more like a knocking. Went to AutoZone and got the codes read:

Bank 1 & 2 too Lean

P0171 & P0174

My thoughts, after talking to motorcar man, are a possible dirty MAF sensor (not sure about the knocking here) or a possible vacuum leak (again, not sure about the knocking). Now, here's the real strange part. I can rev the engine when in park and no knocking. However, when I put it in gear I get the knocking above about 1000 rpm and 15 mph. I am ready and willing to sacrifice a small animal or virgin (your choice) if you can help me identify the cause.

Mark

 

The sudden lean condition is most likely an intake vacuum leak from the supercharger R&R. All these parts were in play and one maybe did not go back air tight. Another possibility is the increase in volumetric compression from the ported supercharger has overwhelmed the engine management software for fuel compensation and the fuel can't match the air being driven into the system, you may need a programmable chip to fix it. It is not programmed for a big change to the supercharger. I'm no engineer so I can't run calculations but the theory is there. The rest of the possibilities such as bad O2 sensor and such are less likely since the supercharger change precipitated the issue.

 

I agree with a potential vacuum leak. As for overwhelming the ecm, it was not that big of a change and has been done before without a performance chip. Thanks for the advice. I'm taking it in tomorrow so we'll see.

Mark

 

Knocking as in it sounds like spark knock? Or is it something different sounding?

One quick thing to check is the vacuum line that comes off of the supercharger outlet (V8 part). I had this cme off once and it is not only a vacuum leak at idle but is also the manifold pressure reference for the fuel pressure so can cause lean conditions under load.

If you have a scan tool and can watch the short term fuel trims, you can try fogging MAF or carb cleaner around parts and watch for changes. If the STFT suddenly drops when something is sprayed, you've found a leak.

 

Had the exact same issue (minus the knocking) after putting on my new intake. Issue was it leaked and once I found and corrected the leaks and cleared the codes the problem went away.

 

A shop by my hoise identified a vacuum leak from one of the new supercharger gaskets. No time to get it fixed as I had to leave on a business trip to Chicago. Will post again in a couple weeks when I get it resolved.

Mark

 

At least you know what it is, that's some consolation.

If it's one of the joints on top, either the V8 piece or the intercoolers, then it should be minimally invasive to fix too.

 

There is actually a TSB on charge cooler air leaks. Make sure the revised parts are fitted.