Hello all,

I've been struggling for a few weeks trying to figure out the issue with my 1997 Camaro SS LT1 with 94k miles, T56 transmission. When my MAF is connected, I get misfire codes. When it is not connected, the misfires go away (and a P0100 code appears...naturally since it is disconnected). Also interesting is the fact that when I clear the code, the code reappears after about 30 seconds (cold or hot engine), and it shows misfire on cylinder 6. If I turn off key, and recheck the codes, the scanner goes from P0306 to P0300 (random misfire). I'm using a ScanTool MX for OBDII scanner.

Before figuring out that disconnecting the MAF would cause the misfire code to not appear again:

- I removed the injector rail and verified all injectors are working properly and free of debris
- I have verified that all injectors are firing with NOID lights and stethoscope
- Fuel filter is new, fuel pump is new, fuel pressure regulator is new...averaging 43 lbs of fuel pressure at rail
- New Optispark from Summit, NGK plugs, and new wires installed (yes, I have verified several times that the plug wires are correct and plugs are seated)
- Averaging 150 lbs. of compression across cylinders
- Battery is new, cranks right up
- Getting a steady 18 in Hg vacuum pressure at brake booster

Getting same results after those changes/checks.

After figuring out disconnecting the MAF would cause the codes to disappear:

- I purchased and installed a new MAF
- Checked voltage at connector, getting +12v, ground, and +5v
- Checked the lb/min rate of MAF with scanner diagnostics. They are:
@ 810 RPM (idle) >> 1.18 lb/min
@ 1471 RPM >> 2.03 lb/min
@ 2170 RPM >> 3.08 lb/min
@ 3247 RPM >> 4.64 lb/min

So, I am at a bit of a loss as to what is causing this misfire when MAF is connected.

Thoughts on where to check next?

 

with maf disconnected the motor remains running in open loop

since your scan shows 0306 concentrate on that cyl.

you could swap injectors between 6 & 8 and see if the problem migrates to # 8. If so its the injector

same with a plug wire to rule it in/out

same with spark plug

if problem remains...opti is suspect. maybe cap is corrupt on #6

any non ac delco opti is suspect right out of the box. Unfortunately no ac delco optis with Mitsubishi optical sensors are available other than used ones

 

I would perform a smoke test, it’s possible you have a vacuum leak.

 

I was initially going to say you should clean the MAF thinking maybe it was throwing your fueling off but after reading your whole post what I want to know is: does the car run okay? Can you actually feel the misfire or is it just throwing the code? I'm wondering if you have some weird electrical or PCM gremlin.