speedracer69

I have this 96 corvette that we replaced the dist. with a new msd --installed new msd wires--replaced the plugs. car ran really strong and great for about 2 weeks. now it has missfires set in the codes and when a scanner is hooked up to it 1-3-5-7 have missfires--number 7 is the worst. The plugs are very sooted on the left side. i check the compression and wires all ok. i tried another maf sensor and replaced #7 injector. no help. I removed the sensor 1 bank 1 o2 sensor and it had as much soot on it as the plugs. But we replaced it anyway. something interesting is when you unplug the maf sensor the missfire goes away. and the only plugs missfireing are on the left side. I am baffeled. only other codes set in the computer was for the o2 sensor and it was because of the really rich running. most of the time when you first start it cold it won't miss for a little bit and then #7 starts missing first. any help would be appreciated.

speedracer69

Help!!

Injuneer

What was the exact code for the O2 sensor?

A misfire sort of snowballs into a general rich condition. It causes the O2 sensor to indicate "lean" when it isn't, and the PCM adds fuel to the entire bank, making the cylinders run rich. A single bad wire, loose wire, cracked plug porcelain, loose plug, etc will cause problems. How did you verify that the wires were "ok"?

On the other hand, a faulty O2 sensor can cause the same problems.

speedracer69

OTC Genisys with a lap scope-- to check the wires
The plugs were pulled and cleaned.. then switched.
same problem is still there :-(

speedracer69

So now get this.

The problem is only there when the MAF is plug in. We tried ones that work and still the same problem. We looked at all of the wires from the MAF to the harenss and no problems..
could it be the computer?

Injuneer

Any chance you have a high voltage wire next to the MAF sensor signal wire? An ignition wire could be inducing a frequency on the MAF signal wire, and since the MAF output is a frequency based signal, it could be messing with the MAF signal, causing it to indicate more air than is actually flowing.

With your scanner, what is the MAF output signal frequency at idle? What is the corresponding idle RPM? What does the scanner show the MAF AFGS reading to be? What do the long term fuel corrections look like in Cell 16, right and left bank? What do the long terms look like in the other Cells?

MichiganSkip

Just for giglges, could you try loading a stock file from a known good source? I've seen one time where the file was corrupted and it did some really wierd stuff. Worth a try and it won't cost you anything

speedracer69

ended up being a broken valve spring and bad injecter