Well that didnt fix the miss. Im gonna replace the plugwires this weekend. I replaced the coil yesterday and it was corroded bad. What would make my right o2 sensor only read 350-400mv all the time even after installing a new one? Also my map sensor drops a bit when it stumbles from 10.8 to about 10.2.

 

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I took a look under the hood while it was dark and I've got two plug wires arcing pretty bad. Number 3 and especially number 7 plugwire which is the cylinder that had the exhaust leak. Definately gotta changes the wires.

 

The MAP reading is basically the "inverse" of what a vacuum gauge would show. Misfires cause vacuum to fluctuate, so MAP will fluctuate in the same way.

Do you have a harness extension on the right side O2? If so, maybe it's shorted or open. A complete loss of connection will produce a constant voltage reading of about 450mV.

 

I do have a extension on the right o2. I'll check it out. Maybe it is touching a primary. It was hard finding a way to route the wires on that side.

 

The right o2 extension was touching the header and melted a bit. I replaced it. Still the same problem. The o2 reads mostly 375ish-450 mv. If a cylinder was misfiring on that side and not burning the a/f mix wouldn't this show up as a high mv reading? Possibly a bad wire further up the harness maybe?

I replaced the plug wires on the drivers side. The miss seems to be gone. Might still be missing slightly on the passenger side. I'll replace those wires later today maybe.

Timing is still being pulled. At part throttle it is being pulled as much as 8 deg. At full throttle it's seems to be a constant 5 deg.

Took it for a drive this morning. First time I've drove it much since the header install. I am VERY happy with the headers. Sounds awesome! Even with the timing issue I am happy the way the car is turning out so far.

 

If a cylinder misfires, it dumps the raw fuel and air into the exhaust. The O2 sensor can only "see" O2 (air), so it reads "lean" = low millivolts.

 

Ok I changed all the wires on the passenger side. Wrapped them in heat shields and heat reflective tape. Still no change. I still can't figure out why the left o2 sensor readings are out of whack.

Fred you said a complete loss of connection will produce a constant voltage reading of about 450mV. So if there was no connection wouldn't that throw a code? I might try and unhook the sensor and see what happens to the readings.

 

Unplugged the o2 and the reading stays the same. So I thinks it's safe to assume I have a wiring problem. So I'm operating in open loop constantly? Is it possible this and my knock retard problem are related?

 

You should get a code for an open circuit (DTC 13, DTC 63) if the voltage stays between 350 - 550mV for 60 seconds, the TPP is greater than 5%, the coolant is above 70*C and it is at least 2 minutes since the engine was started. When you get these codes, the PCM will not go into closed loop.

 

I seen the voltage drop to 347mv and lower with the o2 sensor unpluged. Would it be ok to cut off the plug and replace it with one from a extension? How would I check the harness?

 

Checked continuity through the o2 sensor harness and it looked ok. I'm running outta ideas.

I still can't find where the knock is coming from either. I can here a slight ticking in cylinder 7, the one that had the exhaust leak. It's so faint I can really only here it with a stethoscope. I might try to adjust the rockers this week to see if that cures it.

 

Good Luck!

 

I think I finally may have found the knock problem (hopefully). Today I heard a knock that sounds like it's coming from below the intake manifold. My first guess is a stuck lifter. It's is definately not firing on all cylinders also. At idle it is vibrating really bad. It sounds like I have a bass cd in lol.

I am thinking real seriously about doing a top end rebuild.

 

Well I am still fighting this problem. So far I have replaced both o2s, motor mounts, new plugs, wires, opti, and pcm. All except the pcm were in need of replacement.

I talked to a mechanic yesterday and he said it could be out of time. More than likely after 125k miles the timing chain has stretched. Could this be a possability? It backfires through the intake and is hard to start sometimes.

I still need to fill it up with race fuel to check to see if it's false knock.

Thoughts?