Not likely. Its not impossible (you can verify by logging the MAP value while the issue occurs to see if it does anything really odd), but they're not nearly as common of a failure point as a MAF.

Anything else peculiar on the scan tool? O2 values, timing, etc when it happens?

The cylinder 6 misfire may get you on a good starting track - perhaps its completely losing spark on that cylinder and dumping the fuel charge straight to exhaust causing an afterfire (which also dumps a chunk of raw O2 which can further screw up fueling as the O2 sensor thinks its a lean condition).


Any other hints from when it ran fine until it started having this issue? Was it sudden or did it gradually get worse?

 

I don't know.
Perhaps it could be something simple like a PVC valve sticking open... I've heard it can cause lean running and missing.

 

Both o2 sensors had a sort of square wave pattern bouncing between .2 to 1 volt approximately. I remember being a bit worried about timing for some reason, I'll have to log the timing again. I replaced the fuel pressure regulator today and the car runs about the same. Gonna go for a drive and log commanded A/F vs actual A/F to see if there's some major differences.


Edit: it was very sudden failure, the car ran perfectly untill it stuttered at a light, a little ways down the road I floored it to pass, while dropping from 4th to 2nd the exhaust was a bunch of pops, once second gear engaged fully the car behaved perfectly normal. The next day it started stuttering at every light I stopped at and hesitating very badly if I use more than 5% throttle to take off from a light.

 

Commanded vs actual A/F yeilded no results. Another symptom I should note is that the car will idle between 600-700 rpm in neutral, but in drive idle can be anywhere between 500-800 with lots of shaking.

 

Is it picking up any misfires on any specific cylinders? Might help point you to a stuck injector or specific ignition issue.

Keep in mind (since you mentioned hard acceleration) that the factory O2 sensor won't have a useful reading at heavy throttle/ PE enrichment. Stock type narrowband sensors only have very limited operation around 14.7:1 before making out, so they're useless when the engine goes to PE mode and 13:1 AFR or less.

 

I did have a code pop for cylinder 6 misfire I pulled the plug and it had a bit of a green tint to the electrode, and the gap checked out at .55 on one of those coin gappers.

Some more log data:



Throttle position in green, timing advance in red.
I stopped at a light and it's showing that the throttle opened a little. It's only half a percent but maybe the throttle position sensor is bad? This image also shows 40 degrees timing with just 5 percent throttle?? I did do a full throttle pull at 35-40 mph:





Okay that pull was shorter than I thought, and also doesn't show show as much as I thought, besides the erratic timing while the throttle was closed.




Here's a rescaled view of the half percent little blips of the throttle, I promise I never touched the throttle lol.

 

here's a graph of idle (green line) this range is a bit smaller than I've noticed in the past but shows how absolutely erratic it is.
The issue was much worse this morning while the motor was cold, I also desperately need gas lol. I figure if I fill up and the problem gets significantly better then the fuel pump is going bad. I attempted to replace the fuel filter as well but the nut on the front is completely rusted through, it's like trying to wrench on a soggy donut. Maybe I'll cut and reflare the line if I can find a new nut.

 

Okay, one last post, I filled the tank last night and the car is behaving better, almost as well as the day the issue first popped up. I can pull away from lights with more throttle without experiencing nearly as much hesitation/missing. How likely is it that I need a new fuel pump?

 

I am at a loss, I have replaced the fuel pressure reg, and fuel pump, removed and inspected/ fine tuned the spark plug gap, swapped the 6/3 coil for the 5/2 (both 6 and 3 were misfiring, after swapping the coil 5 and 1 are misfiring now (??????)), physically inspected the injectors/ rail for fuel leaks, noticed the car was adding up to 4 degrees of knock retard so I filled with 91 yesterday and the problem has just been randomly getting better and worse. Recently #5 has started to have some misfires during cruising/light acceleration, most of the time she only misses while sitting at a light, I've been putting the car in neutral at lights and this helps to some degree, but doesn't solve the problem. I am also still getting the popping sound from the exhaust during downshifts, with no misses logged during that time. There are only two things I can think might be wrong: either the ignitor (the thing the coils bolt to) is going bad, or the rocker arm bolts have come loose on the rear bank, if that were the case though I'm pretty sure I'd notice the valve noise. Does anyone else have any ideas? the ignitor is to expensive to be replacing as part of troubleshooting...

Thanks in advance for any help you can provide.

 

I am not up to speed on this thread. Looking at your recent comments, you move coils and now the misfire seems to have changed to cylinders on different coils instead of the same coil OR same spot on the ICM? If this is the case, I might start looking at the ICM. You can remove it and some parts stores can bench test it (keep in mind, that bench test is not 100%, but if it fails the test, I would believe in the failure). They can start having issues and it is possible the coil swap you did messed with something on it. Just a theory.