stock 5.3 2 issues, random MAF spike on accell and random misfire on all cylinders

[Crashgnx]

Just as it says, Stock 5.3 with a P01 ECU. getting random misfires on all cylinders. (annoying but no knock) and when im driving or just gagging the gas at idle I get sputtering randomly that coincides with the MAF hz going from 2500hz-4000hz up to 10k+ hz in a direct spike when it shouldnt be. MAF is a new Delphi 10043 unit. attached is a log of it just stabbing it at idle and even gradually going to redline.

Is this an issue with the tune or just a bad MAF sensor? also would it cause random misfires to be detected throughout the RPM range idle-6200?

Thanks

Well apparently my logs didn't upload, I'll add them when I get to them this evening.

[matty b]

Is this a swap? IF it is, I'd bet you have wiring issues.

[Crashgnx]

Swap, Yes, Wiring issues, No. MAF works great other than random spikes, I built the harness and I am very confident it is not a wiring issue. Posting the log and tune here, I believe you will agree. I am banking on a bad MAF and ordered another one to swap it with and verify but I want to cover my bases with the tune.

5-1-2016 change timing map to stock L33 5.3.hpt
MAJOR MAF issues.hpl

[matty b]

Random spikes are a big red flag for wiring issues. Wanna rule it out? Wiggle test the harness along the length where the MAF harness runs back to the computer. Dont wanna call you foolish, but automatically discounting a possible cause is just that. Sensors dont typically spike, they just read wrong all the time when they are broken.

The most likely spot is right at the MAF connector, especially if this is a modified stock harness that has already seen a lot of miles. The wiring cracks in the insulation at the terminal strain relief. I've only (sarcasm) seen this 7-8X on swaps using original harnesses and have seen it many more times on stock vehicles. The EGR uses a similar connector and they exhibit the same failures.

[Crashgnx]

I thought of that, brand new MAF connector and pigtail (mine was already clipped). I even kinda tapped on the sensor to see if there was a change anywhere and nothing makes it do anything abnormal.

When it does occur, MAP stays normal, MAF signal spikes up, not down oddly.

[jimmyblue]

There's wiring issues and there's wiring issues. GM shop manual
calls out EMI as a possible MAF accuracy problem. Bundling it
with any active switching signals (the MAF output, that is)
can couple noise that then perturbs the sensed frequency.
To test, de-bundle the MAF output wire from wherever it is
now. Might also look, however, for drops in the 12V feed or
ground jumps (though this may be outside most peoples'
tool sets, and inconvenient for on-pavement problems).
At any rate MAF frequency is showing crazy numbers and
there's not too many ways to get the frequency bent so
abruptly, besides interference.


Question why you show a constant 8.7 degrees cranking
advance when you're obviously not cranking. Your spark
is crazy too in places where you're steady-TPS cruising.
It appears that Dynamic Airflow is jumping unreasonably
and also see "IAT advance" flickering, which may enter
the Dynamic Airflow number and drive spark advance.
IAT should be slow moving, but its jumping may point to
a connector intermittent or something.

Some crazy stuff going on at idle too, with 55 degrees
base and -35 degrees idle advance. Might be time to
step back to some factory-ish tables or at least use the
compare tool to see just how far off things have
wandered across all the tune-trying.

[Crashgnx]

Good point on the EMI interference. If the second MAF I ordered does not fix the issue, I'll go ahead and re-run the MAF, Crank, and Cam Sensors in EMI shielded wire. Currently I have the wires bundled going down the passenger side of the intake kinda next to the fuel rail. Injectors or Coils could be causing it but I would figure it would be a jittery signal if it was EMI interference and not huge spikes like it is.

As for the timing tables, I basically copied over the tables from a L33 tune that somewhat fit my build and I would tune from there but I have not had enough drive time or a wideband hooked up yet. I just wired up the wideband last night and it reads on the gauge but havent coupled it to HPTuners yet. I did notice that my timing was higher than I really expected it to be but havent seen any knock yet. I didnt notice the -35 idle advance but ill go back and look to see what is going on.

Thanks for the input.

[matty b]

There's wiring issues and there's wiring issues. GM shop manual
calls out EMI as a possible MAF accuracy problem. Bundling it
with any active switching signals (the MAF output, that is)
can couple noise that then perturbs the sensed frequency.
To test, de-bundle the MAF output wire from wherever it is
now. Might also look, however, for drops in the 12V feed or
ground jumps (though this may be outside most peoples'
tool sets, and inconvenient for on-pavement problems).
At any rate MAF frequency is showing crazy numbers and
there's not too many ways to get the frequency bent so
abruptly, besides interference.


Question why you show a constant 8.7 degrees cranking
advance when you're obviously not cranking. Your spark
is crazy too in places where you're steady-TPS cruising.
It appears that Dynamic Airflow is jumping unreasonably
and also see "IAT advance" flickering, which may enter
the Dynamic Airflow number and drive spark advance.
IAT should be slow moving, but its jumping may point to
a connector intermittent or something.

Some crazy stuff going on at idle too, with 55 degrees
base and -35 degrees idle advance. Might be time to
step back to some factory-ish tables or at least use the
compare tool to see just how far off things have
wandered across all the tune-trying.

I suppose we can do a wait and see with his new MAF, but you saw what I did, IAT and MAF moving around erratically. Guess what two sensors are tied to the same spot? IAT and MAF. I hope a new sensor fixes this, but a new sensor is already in it which really makes me think there's a wiring issue beyond even EMI. I've seen EMI do this on Ford crank sensors, but those are variable reluctance and not hall effect like GM uses. That makes a big difference as a VR sensor uses EMI in a controlled form to create the signal where hall effect has a reference voltage and ground to work against. MAF is the same way and has never really been an issue with LS motors. Thats not to say that GM hasn't had issues, they did with Cadillacs quite a while back and the fix was to re route the MAF wiring seperate from the harness.

[Crashgnx]

I'm not seing the IAT being erratic anywhere in the log, especially where the MAF is spiking, it went down 2deg due to me hitting the throttle and pulling in cooler air. I unrouted the MAF cable and ran it better than 10 inches from any coil or injector and still had the MAF spike randomly. Also I see where you were getting the -35deg idle advance, its only on long decel back to idle from 5k+ RPM and its trying to let the motor slow and catch the idle. I should get the other MAF in at latest Monday and verify if that is the issue or not. Figuring with my luck its just a bad MAF. I agree the 8 Deg of cranking advance throughout the log is kinda odd.

[Crashgnx]

After going over a few logs last night and getting my wideband dialed into HPTuners, I dont see the cranking advance being applied while running so its just referencing where it would be at .vs ECT only while cranking. I'll probably just remove it from the logged parameters.

Odd thing I did notice, I was copying more tables over from a stock 5.3 L33 in the timing IAT advance section and in the process I decided to reduce my Max timing advance from 60deg to 50deg. applied the changes and found that the car would barely start and idle, wanted to die or idle much slower than normal. I adjusted all the tables back minus the Max timing advance, applied changes and the idle was still crap. Adjusted the Max timing back to 60deg, applied, and start/idle was back to normal. I'll apply the tables again tonight and see what happens. I'm sure there is a reason for that to happen but I cant imagine what it might be other than it uses that Max timing advance as a scale to base other features on instead of using it as a highest advance cap as you would expect it to. Anyway, just thought it was odd.

[Crashgnx]

Initial tests with the second MAF seems to have fixed the issue, I'll post again if I find it did not.

[larboc1]

I'd bet MAF. I helped diagnose a stock 5.3 that would have a horrible bang occasionally at highway speeds from the 4l60 trying to either downshift or be in two gears at once. Nobody could figure it out. Logged data with the vcm scanner and saw random spikes in the MAF signal when it did it. Changed out MAF and tossed the K&N filter for a paper element and the problem disappeared.