Maf reading for 04 gt

Jul 9, 2018
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#1
So I've been having problems with my car idling. First I cleaned the maf. It idled better afterwards. Before it wouldn't even idle without giving it gas. It would just start up and die. I drive it for a few days and it's running fine and idling good but I get random missfire codes. So I try changing spark plugs because there 3 years old. Cleared the keep alive memory. Start it and it doesn't want to idle again. So I clean the maf again. Clear the KAM. Start it. It idles fine. Then i start getting too rich codes both banks. So I try cleaning the maf again. Now it's getting stuck rich codes. If I unplug the maf sensor it runs fine though and I dont get any code except for the maf and iat sensor. Today i started data logging with livewire. With maf unplugged fuel pressure was at 40 psi. O2 sensor were at like .46. This is at idle. Today I data logged with the maf plugged in. I had to keep tapping on the gas just to keep if from stalling. Fuel pressure was at 50psi at the rail. 02 sensors were reading .94. The maf says it's at like 2500 grams per second. Which seems way too high but I cant find anywhere on what it should be at. If anyone knows what it should read or think they have an idea on what my problem is it would be greatly appreciated. I'm thinking the maf needs replaced. Just dont want to start replacing good parts. Thanks.
 
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wmburns

SN Certified Technician
Aug 14, 2009
4,471
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Houston Texas
#2
I cant find anywhere on what it should be at. If anyone knows what it should read.
My Ford service manual says:

PID Hot Idle 2500 RPM Units
MAF 4.7-6 16-19 G/S

So I would agree that 2500 grams/second at idle is waaaaaaaaaaay too much.
 
Jul 9, 2018
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Illinois
#3
Would that increase the fuel pressure and cause my random missfire/ too rich/ stuck rich condition?
 
Jul 9, 2018
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Illinois
#5
It's actually idling on it's own now. The fuel pressure is normal but the maf still seems high. Am I reading that right then? 858 grams per second?
 
Jul 9, 2018
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Illinois
#6
I'm starting to think that's the wrong parameters. Should I be looking at airflow rate from mass air flow sensor?
 

wmburns

SN Certified Technician
Aug 14, 2009
4,471
263
154
Houston Texas
#8
Slooooooow down.

IF the MAF is way over stating the air entering the motor doesn't it make sense that the motor would be running chronic rich? The fuel injector pulse width (and direct measure of the amount of fuel) is computed from the values supplied by the MAF.

I gave you the information on what are "typical" MAF values at idle (4.7-6 G/S) and 2500 RPM's (16-19 G/S). The numbers are approximate.

MAF counts are not the same unit of measure as flow. Counts are a digital unit that is usually expressed as a ratio to what ever the maximum.

There are some DTC codes that the PCM will increase fuel pressure in response to.

Throwing out numbers without all of the conditions behind the numbers isn't very useful. For example 40 G/S at 2500 RPM's with the motor pulling a heavy load might seem reasonable. 40 G/S at 2500 RPM's with no load is about twice what it should be. Problem? Maybe.
 
Jul 9, 2018
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Illinois
#13
The maf is around 5 grams per second at idle and 18 at 2500 rpm. The bank 1 o2 sensor is at .00 sometimes -.02. Bank 2 is at .02. Shrt term fuel trim is at .75 both banks. I dont understand how it goes to the complete opposite.
 
Jul 9, 2018
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Illinois
#14
I converted it back to the stock tune. Runs good idles great. It idles around 750. If my maf was messed up when I had it dyno tuned then would my tune not be right? I loaded my email tune I got from sve. It idled okay but it was kind of rich. Then I loaded my dyno tune and it was stuck lean. I did LTs mid pipe catback egr delete under drive pullies and gears. After I installed everything it didnt want to idle. So I had it dyno tuned. They said it was maxed out on fuel and they had to pull a bunch out. So maybe it was dumping so much fuel because the maf was over calculating the air coming in? So now the tune is lean? Sorry. I've never messed with tuning. New to all this.
 

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