Please help diagnose

[wt4z28]

Here's the background:
--95 z28 129,000miles
--rough idle, stumble, surging etc...
--initial scan showed left block learn about 10 lower than right, with both below 128 ( about 110/120)
--swapped injectors, problem didn't move to other side
--replaced EGR valve
--just replaced spark plugs and wires.......here's the new dilemma. I was dumb enough to purchase cheap autolite wires, replaced driver's side, took car to shop to replace passenger side, wires didn't fit passenger side, shop installed NAPA wires on passenger side ONLY,

--now, my left block learn reads 108 at idle ( injector 3.5ms), and the right block learn is way up to 150 (injector 4.7ms).....O2's look normal ( actually the right never dipped below stays primarily above 150mv now, previously they looked completely normal).......very rough idle and acceleration..........could the difference in wires make this dramatic of a change ? Or could it be the EGR gasket leaking? I am going to install the NAPA wires on the driver's side tomorrow......Anyone have any ideas -- Joe, Injuneer ????

Thanks for any ideas, Bill

[wolfdogs]

what about your opti spark?

[wt4z28]

Opti

Opti was replaced about 3 years ago, but I guess that's always a possibility again, the problem just seemed to magnify itself while doing the plugs/wires. There are no codes being set. This fiasco just set me back $300.00........

[Injuneer]

Do you have any sort of scan data..... a more detailed log that I can look at? It would help to have the BLM's for as many of the 16 main operating Cells as possible. And your comments about the O2 levels is puzzling.... in closed loop they should be switching around approx 9 times per second, covering the full range of 0xx - 9xx milliVolts. You can't just look at the O2's in a single record in closed loop... they are meaningless.

If your O2 sensor is sort of locked at/near 150mV it may be deceased. Did you try swapping the O2 sensors side-to-side to see if the problem follows the sensors.

High BLM's on one side generally relate to misfires and exhuast leaks, low BLM's sometimes relate to leaking injectors. Swapping the injectors side to side seems to rule out a leaky injector problem.

Having mismatched wires on one side of the engine should not show up as a problem at idle and low/moderate driving... the voltage demands on the plugs/wires is so low that just about any wires could handle it. A huge mismatch in total resistance, using the wrong wires on one side, or the wrong terminals may be a contributing factor though.

And provide the basic info.... what years it it, tranny, any significant mods? Even a poorly installed throttle body air foil can produce split BLM's.

[wt4z28]

It is a 95 z28, A4, the only mod being a K&N CAI.


I have an EZ scan 3000 and the O2 readings do fluctuate quickly, but I guess I just noticed that tonight the right reading never went as low as the left (50mv-850mv left) ( mostly 150mv-850 right)-previously they both fluctuated about the same range. I watched the cell readings while increasing rpm at idle and by holding the brake and the BL was consistently 30-40 lower than the right ( 108-128 left) ( 140-151 right) I know this covers only a few cells but that's all I have now. As for the wires, the left are now 7.5mm autolite and the right are NAPA 7mm with autolite AP106 plugs.........I'm too much of a wannabe amateur mechanic for this stuff