We're trying to finish up a 2003 Silverado SS here in the shop with a 414 in it. We had it on the dyno last week, and the MAF was reading all over the place. The tuner could hold the truck at 45 mph on the dyno, and it would read 420 g/s on the MAF. We would make a pull with the AFR at 12.8, shut the truck down, restart and make another pull and the AFR would lean out anywheres from 15 to 19, and the MAF would now be reading 350 g/s at 45 MPH and the same RPM. There AFR readings are changing even though we have not touched the tune. Everytime we flash a new tune, we will get one or two ok pulls, and then they will start going extremely lean again.

We have tried switching MAFs, trying MAF Cleaner, and have also switched out the PCM. When loggin the truck, the MAF is not a smooth curve, it curve would be very jagged and look similar to an O2 that is switching on/off, just not as severe.

The truck has also started throwing a MAF Performance code which we cannot figure out. Sometimes it will set as soon as we start it up, other times during the run. Now that I have back at the shop though, we cannot get it to set off again, but we are letting it idle as we try and figure it out.

The tuner also said that the STFTs are active/adjusting during open loop when they should not be. When we swapped PCMs, the first pull with the new PCM the STFTs were not active during open loop, but as soon as we turned the truck off and back on, the STFTs were active again in open loop.

I'm about to switch the engine harness to another one that we have here in the shop to see if that somehow affects it as the harness currently on the truck is a used harness that we bought for this project. It was a stock '03 Silverado SS harness and as far as I could tell, nothing was wrong with it. We have checked out grounds on the harness that is currently on the truck also, and everything seems to be in check.

Does anyone have any ideas on what we can check as we are completely stumped and need to get this truck running ASAP.

 

you might want to post the tune and the log file.

 

Check the connector at the maf. Look real close at the female pins. They have a tendency to spread open. When they do you get intermittent contact, and problems just like you're having.

 

What is the fix for this? Take the pins out and close the gap and reinsert?


I was just about to go check the resistance on all the maf wires also per the GM Service Manual for the P0101 code.

 

I would suggest trying to relocate the MAF further
out in the inlet tract, from the TB. With a big cam,
big lung motor you can get a lot of crazy reversion
effects that make the MAF output jitter like mad
or just drive it to read high by "oversampling" the
air (sees some of it twice).

MAF harness can pick up EMI from other nearby
wiring (like ignition and injector current pulses).
The Helm manual says you should try breaking
the MAF wires out of the bundle if all else fails
troubleshooting-wise.

A weak +12V feed will require the MAF to put
out more pulses of said 12V to the sense elements,
to get the same feedback-power. This makes the
MAF output IGN-voltage sensitive. Might check
that you do not have an alternator going into
brush-skip or some other line sag problem, maybe
intermittent.

 

The MAF is about 3 inches from the Air Filter. I can move it back those three inches, but that will be all that I'm getting as the filter is up against the fender already.

I have HIDs on the truck, that do come on during the dyno. The tuner said there would be no chance of interference from these though. Most of the MAF harness is already separate from the main harness, but I can see if I can pull the last little bit out and make sure it is not routed next to anything such as ignition etc.

Any easy way to test if the 12V feed is good? The alternator is a fairly new 145 Amp unit.

 

Attached is the hptuners bin, and three log files. The log files show how the MAF is reading anywhers from 2.9 to 3.25 lb/min on the MAF at 2000 rpms on different startups.

This is after taking the MAF Connector apart, and pressing the pins down so they make better contact. I also cleaned them to make sure there was no corrosion/dirt etc.

The truck is still throwing P0101 MAF Sensor performance and also P0106 for the MAP.

 

Log the intake air temp. Make sure it about the air temp of outside air temp. If it reads to high then the ECM thinks the air has less O2.

 

Scanning the truck, and holding idle at 2000 rpm, it would read from 3.0 lb/min to 3.25 lb/min but when I go to scan a stock Escalade with a 6.0L, and do the same test, it reads 4.0 to 4.1 lb/min on the maf. Shouldn't the 414 in the truck be reading more through the MAF at the same RPM? My tuner told me I should expect about 20 g/s with the truck at 2000 RPM, and I believe 3.0lb/min is right around 22 g/s.

 

I'll go back and check the IAT, but I don't remember it being off. Still doesn't solve the problem of the MAF and MAP SES Codes.

 

Attached is a log of a WOT run locked in 3rd gear to prevent wheel spin. I only made it to about 45 before I had to let off.

Do the MAF readings look ok to everyone? The MAF bounces around quite a bit and the tuner told me that should not be happening.

 

I have seen MAF bounce a lot, especially down
low. I am not sure if it's internally unstable at
low flows (its heater control loop) or if there is
just a lot of "airflow ripple" in the pipe. Anecdotally
I think the instability looked worst on the unit I
had most aggressively ported. The Dynamic
Airflow in contrast is very smooth, yet nearly as
responsive to air-steps.

One solution might be to move the MAF cutover
RPM higher, if you can observe that the MAF
output becomes acceptably stable above XXXX
RPM (which it should at some point). Stick with
the dynamic airflow as far out as you can (making
it a more-speed-density tune in effect, but MAF
up where you would be with an unlocked converter
at full throttle).

So speaking of this, do you see an injector-pulse-
width jitter that corresponds to MAF or is it smooth
like Dynamic Airflow? Just because the MAF is freaking,
doesn't necessarily matter if it's being ignored.

 

Just bin it, you know it makes sense