Need quick help with noisy MAF

[pontisteve]

The car is on the dyno, and I'm having a heck of a time with MAF signal noise. In the full throttle range, MAF Hz is jumping around in the 500 to 1000 range!!

Its a 5.3 swap into an older car. I've already ran great grounds from batt to frame to engine, engine to firewall, and PCM case to firewall at that same spot where I put the engine ground strap. I ohm'd the wiring and the MAF gets a good solid ground with no resistance, and a steady 12v.

The problem seems to be the signal wire. Why doesn't GM shield the signal wire anyway? I've spent tons of time on the wiring/grounds, and am convinced that's not it, although the signal wire does run thru the harness with every other wire, and the harness runs right below the entire injector/coil rail.

The noise is always there, but definitely gets much worse with rising RPM. Any suggestions? The MAF Hz looks like dang O2 sweeps, it's so noisy.

[Montecarlodrag]

I have never had noise from MAF signal.
You can replace the wiring from MAF to PCM with new wire and make it braided.

Did you try another MAF?

[redhardsupra]

clean your airfilter. i'm not kidding.

[pontisteve]

I already did clean the k&n and ran a new Maf Signal wire. Unfortunately, it didn't help. I just checked voltage at the meter, And it appears to be a steady 14. 08 - 14.12 at wot. The meter is smooth down low, but when you get into full throttle it becomes jumpy big time.

I'm going to stick a new chevy maf on it now and hope that helps!

[pontisteve]

Rats, still noisy! Tried straight tubing before maf, no help. Tried no filter. Tried maf right on throttle body. Its actually better like that! I think its real reversion, not signal/wiring.

[pontisteve]

I've come to the conclusion that this may be real reversion from the engine that I'm seeing. The motor seems to run fine though. And when the MAF is fitted right in front of the throttle body, it seems to be cleaner not worse... which really confuses me.

The intake path is like this: K&N, MAF, about 16" of 4" tubing that has a 45 degree (or less) bend right after the MAF, then a 90 degree bend into the throttle body. In other words, the intake tube is somewhat of a wide U shape with the cone filter and MAF on one end, and the throttle body on the other.

The motor is a stock 5.3 swapped into an older car. The wiring has been confirmed good in every way you can think of. The MAF has been replaced with a new GM unit. I have no reason to suspect the computer.

Can anyone think of any other reason why my MAF Hz is bouncing around 500 - 800 on the top end? I was able to dyno tune the car and get a good solid a/f ratio, but this still sucks. If it weren't for the MAF signal filtering in the computer, this thing would be awful.

[pontisteve]

Never did have luck figuring out why the MAF is so noisy on this stock 5.3 motor. Although I have run across other posts where people have had similar issues from time to time. Here's a screenshot to show just how noisy the yellow MAF HZ line and blue MAF lb/min lines are.

Also noteworthy, the dynamic air line seems to be a nice, smooth average of the MAF lb/min line. This is obviously a filtered airflow model.

[redhardsupra]

Would you mind posting some graphs from Excel, to be precise I'd like to see a scatter plot of MAFfreq vs MAFflow, and another one vs DynAirFlow.

[pontisteve]

Here's a picture of the scatter graph at all WOT positions on a dyno run from about 2 - 5000 RPM. Also attached is a log.

[pontisteve]

And here's the scatter log of grams per second of MAF.

[pontisteve]

And here's the Dyn Air scatter log. As you can see, the Dyn Air looks smoother. I'm assuming that's a filtered/smoothed version of the raw MAF Hz/MAF lb-min data.

[blown-vp]

check ignition coil ht leads break or corrosion.ive noticed that they dont use shielded cable in the australian commodore delco ecu wiring.they have components in the ecu for filtering signals.probably cheaper to do that than use shielded cable.

[pontisteve]

Hmmm... plug wires. Not a bad thought. Makes sense, would cause reversion, breaks down worse at higher RPM and throttle positions. It's a good theory, I'll check it out.

The car ran awfully smooth though, and seemed to rev up clean.

[tpcaz]

Yep, I'd suspect plug wires. If you are using low resistance performance wires, they may not be providing adequate RFI/EMI protection. Some wires actually warn against using them on cars with electronic engine controls.

[jimmyblue]

In the service manuals they recommend pulling the MAF
wires out of the harness as a diagnostic against EMI. It
could be that some noisemaker is beating against the
MAF frequency (injector driver and coil drive being the
most likely culprits I think).

I've seen raggedy MAF readings on extremely ported
pieces. MAF location will affect reversion seen, the
standing wave amplitude @ RPM varies with position
in the pipe (vs wavelength). Same deal as figuring
out where to put the balance tube in a dual exhaust,
there is likely to be a sweet spot and you may want
to try a few positions based on raggediness observation.

[pontisteve]

I cut the MAF signal wire at the MAF and at the computer, and crimped in a new wire, which I ran in front of the car while it was on the dyno. No change, so that rules out inductive noise in the harness. Although I'm wondering if spark plug/wire noise could still affect it.

The motor is a stock truck 5.3, except the LS1 intake and throttle body. Completely stock. So no cam reversion. The LS1 intake is apparently a direct bolt-on for the 5.3 heads, so I don't suspect any head/intake port reversion either.

I tried several MAF locations, several different variations of the tubing being used, and even some straight tubing on the inlet of the MAF that was about 6" long. I even tried sticking the MAF right on the front of the throttle body. There was some variation, depending on MAF location, but none of it was a cure.

The other odd thing is that as RPM increases, the MAF gets noisier, not quieter.