MIL light intermitent. Not sure if its vacuum/boost leak or tuning problem

[moparmadd]

Ok so about 3 or 4 weeks ago I just got done rebuilding my 1991 Talon TSI AWD. Now for some background before the problem. The bottom end now has eagle H-beams and 9:1 wiseco pistons. The block was decked but only to clean a few scratces off. The head was also milled all 3 sides but again, just enough to clean any imperfections. I upgraded the injectors to Precision Turbo 550's. Of course the exhaust manifold was cracked so I upgraded tp a UPC Tubular manifold. Replaced the O2 sensor since it was getting .9 of a volt and the wiring was somewhat melted from before. Also installed polyeurethane motor mounts. Right now the new motor has 1000+ miles on it

Now for the problem... Under high RPM boosting or cruising above 75 mph the engine will kick the the MIL and have a "31 : knock sensor" code. It goes away if you let off the gas and slow down. If i cruise at 70, it won't kick the code. I dont have a manual for a 91 so Im not sure if thats just saying its a bad knock sensor or its tripping the sensor. The EGR is still installed as I was afraid with the higher compression might raise the combustion chamber temp too much. I heard something about "phantom knock"? I have no clue what it was about, I merely heard it in passing and thought it might relate. Now I am also contemplating if it is boost leak since that would raise the metered air count but the engine would only still see the 10 psi getting to it. It is feeling a bit boged down by a rich mixture and the O2 sensor is saying the same thing. It is staying at .9v instead of making a steady Sin wave from approx. .2v to .7v. Or maybe I just need to tune it with the new injectors?

I am looking for some input on what else I should check and diagnose this weekend when I teturn to my shop in Cincinnati.

 

[GVR4592]

If you installed 550's with no way to control them your engine is running very rich. You should take them out or get something to control them. You should also get a datlogger if you plan on doing any kind of modifications.

 

[moparmadd]

But I have had many many reputable people tell me without a doubt in their mind that 550's shouldnt need any tuning, just once you go 650 and over. any one else have an opinion?

 

[timloomis]

Pull out your plugs,that will tell you what the guy just posted.Ill bet theyre black as hell from being too rich.You HAVE to have something to tune bigger injectors with,no way around it.Thats why your o2 voltage is so high,.9 volt is maximum rich.You have a logger?If you do,your fuel trims are probably way too low.You need a logger too before you tune anything.

 

[GVR4592]

But I have had many many reputable people tell me without a doubt in their mind that 550's shouldnt need any tuning, just once you go 650 and over. any one else have an opinion?

Those people have no idea what they are talking about. Ask them what the ecu does to control larger injectors when it's in open loop. Ask them how much fuel the ecu can pull while in closed loop using oxygen sensor feedback. I'm betting they won't have any idea what you're talking about. You need something to control the injectors.

 

[moparmadd]

Actually it turns out all of my ideas were wrong. It was a leak in the exhaust manifold causing it. Before I thought the leak was coming from the area after the O2 sensor but I put a little PB Blaster in a vacuum line to produce a little smoke to see where it was coming from and it was right at the collector of my new UPC tubular exhaust manifold, thus throwing the O2 sensor way off (It was absolute hell trying to get the manifold warranteed). The 550's run just fine now with no knock sensor code and good O2 sensor readings. Also before fixing the problem, I did check the spark plugs and they looked just fine.