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Discussion Starter #1
Dear Members, I am a newbie to this forum and really need some guidance on an maf issue I am having.

- I will give some background on my vehicle and the issue at hand. Any and all help is greatly appreciated.

1971 Ford Bronco
Engine 1991 Mustang 5.0 with:
edelbrock performer heads
Cobra replica intake with 65mm throttle body
Comp cams XE264hr cam with 1.7 roller rockers
Air intake is an 2006 mustang airbox that receives air at the grill with a wix air filter.

So I ordered a75mm bullet maf with 30 point calibration for the 19 lb/hr injectors and the truck ran terrible poor idle, lots of black smoke and would almost die under moderate and hard acceleration attempts.

I put the stock Ford sensor in a 73mm maf and it idles fine and drives well. Not to say it can't do better.

My 5.0 guy felt I needed larger injectors due to my engine combo so after calling the maf company and stating the truck was running so poorly that it may be due to the need for larger injectors I sent it back to be re-calibrated for the 24 lb/hr injectors.

-I get the 24 lb/hr injectors installed, receive my air box and recalibrated maf back and the truck runs even worse now. I am not happy at all at this point.

-Again I put in the "other" maf and stock Ford sensor and it runs/idles great.

-So the maf company had me run some voltage tests that they feel seem out of range.

-At idle the stock Ford sensor and 73mm maf had a voltage of 1.2v.
-The 75mm bullet maf was 1.8v at idle

-approx 2000rpm the stock Ford was 1.9 v and the 75mm bullet was 2.5v (and ran terrible)

-My TPS is at .89v at idle.

-The custom maf guys feel that I have the problem (i.e fuel delivery/poor grounds) which I disagree.

-Fuel system is 72gph low pressure pump to a 1 1/2 qt accumulator and them to an airtex e2000 high pressure pump.

-Ground system is overdone and I can confirm 12.3 v at the maf via the A/B wires and the maf ground wire to battery "+".

-Fuel pressure is a 39 psi

-vacuum is 20 with a rock solid needle (with the stock Ford sensor).

-Could my engine be pulling in more air than normal and thus giving the maf sensor a reading that may have been intended for a higher rpm?

-Please advise this is so frustrating and I apologize for it being so long winded but am trying to get all pertinent info included.

Thank you,
Don Vieira

2002 F150 XLT
11,023 Posts
Try it with the MAF unplugged to see what happens.
Then check this. (From a test manual.)

Mass Air Flow Sensor Testing
Ford’s MAF has a voltage output that increases
with engine air flow. The mass air flow sensor has
0 volts output with key-on-engine-off and 0.50 to
0.80 volts at idle. The specifications will give the
specific voltage at idle. The output must increase
with engine RPM. A test drive is a good diagnostic
test for MAF sensors.
Snap wide open throttle test:
MAF sensors that become contaminated with
deposits don’t respond quickly to changes in air
flow. An easy test is to do a quick wide open throt-
tle acceleration test. The signal voltage must go
over 3.7 volts. Check sensors that don’t respond
MAF Sensor Test Drive:
A test drive is the best method of testing the MAF
sensor. The MAF signal should follow smoothly
with changes in engine speed. Watch for sudden
changes when engine speed is relatively steady.
The MAF output must be a smooth even increase as
engine speed increases.
MAF Values For a Typical Test Drive
KOEO 0.0 V
Idle 0.70 V
30 MPH 1.0-1.3 V
55 MPH 1.6-2.2 V
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