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Author Topic: MAF Codes 26/56/66 Troubleshooting  (Read 14145 times)
Joel5.0
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« on: March 09, 2011, 08:53:18 am »

MAF Codes 26/56/66 Troubleshooting

Codes Definitions:
26 - Mass Air Flow Sensor was greater than 0.7 volts with engine off (O), MAF sensor was not between 0.2 and 1.5 volts with engine running (R).
56 - Mass Air Flow/Vane Air Flow Sensor Circuit Above Maximum Voltage (O,CM,R)
66 - MAF input voltage went below minimum test voltage of .40vdc during engine operation (CM,R) or during KOEO (O).

Mass Air Flow (MAF) Sensor




Tools Required: (in addition to the generic tools)
  • Digital VOM or DMM
  • Wiring diagrams for your year Mustang
  • Vacuum diagram for your year Mustang

Testing Procedure:
1. For codes 26 and 66 perform the tests indicated in the following diagram.


2. If OK, check wire integrity to the ECM connector pins using the correct wiring diagram you'll find in this section of my5oh.com. Resistance reading should be less/equal to 5 ohms...NOK?...trace and correct open wire condition.

3. If results are OK, you might have an intermittent MAF sensor, connection, radiator fan wash turbulence affecting MAF readings, a boost bypass valve creating air flow ripple or an intermittent ECM.

4. For code 56, clear codes, disconnect MAF sensor, start and idle engine for 1-minute, rerun KOEO self-test and check for code 56 to show up....it doesn't?...replace MAF....it does?....goto 5.

5. Disconnect MAF sensor and ECM, Ign Off, measure resistance between MAF SIG and VPWR pins at the MAF harness connector...resistance over 10,000 ohms?......YES?....Bad ECM.....NO?...MAF SIG and VPWR wires are shorted, trace and repair.

Hope this helps someone....



Logged

ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
Joel5.0
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« Reply #1 on: March 15, 2011, 05:48:23 pm »

Date:
  • Tuesday, 3/15/11

Patient:
  • 1989 Mustang LX 5.0L Notch with Powerdyne SC, 24 lbs. Injectors, MAF housing manipulated calibration, F-303 cam, stock E7 heads, LT headers, Typhoon intake, 5-Spd.




Symptoms:
  • Backfiring through intake engine cold, lack of power engine cold or after a long engine shutdown, a little idle control issue.

Hack Fix Found:
  • Fuel pressure was set too high (65 psi+) trying to overcompensate the poor fuel trim control issue and the lean condition. This was causing the fuel pump to be overworked and a fuel pump siren sound over time (sign of FP overworking).

Codes:
  • The only codes present were 41/91 KOER, no MAF, BP or ECT reated failures logged.

Findings:
  • Going by a logical (or gut) instinct, I decided to monitor the MAF output signal engine off and engine running.
  • Noticed MAF stayed at .9-1.0 vdc engine running with no variation whatsoever when engine was revved. MAFSIG should increase when engine revs are raised....... it didn't.
  • As soon as time passed engine running, the MAFSIG would begin to increase. This is the sign of a problem with the hot wire element not heating as required.

  • Verified VPWR and GROUND circuits at MAF connector = OK
  • Verified MAFSIG using a KGU (Known Good Unit) unit I always keep on hand. With IGN ON MAFSIG varied as soon as air flow was streamed through the hot wire element.
  • Proceeded to install the KGU in the MAF housing and calibrated FP to 45 psi engine off (it netted 39 psi engine idling).
  • Started engine, did a Base Idle Reset, verified engine would rev fine w/out any backfires from the intake and waited for engine temp to reach 160°F to run a KOER = OK.
  • EUREKA!.... codes 41/91 were replaced by codes 44/94 (the equivalent to a system pass since smog pump is not installed.)  YESSSSSS

Conclusions:
  • MAF failures are not exclusively identified by EEC codes.
  • MAF failures are NOT PAS/FAIL exclusive type of failures.
  • YOU DEFINITELY NEED to monitor sensor signals real-time, specially when a symptom is present, in order to ID what the typical pinpoint tests cannot identify.

After all was set, calibrated and done correctly..... here it is idling the way it should for that hacked/fubar'ed setup it is.  

<a href="http://sbftech.com/vids/mcmp_0.8.swf?fpFileURL=http://sbftech.com/efi/EEC_TS/89_SC_Idle.FLV&amp;fpPreviewImageURL=http://sbftech.com/vids/SBF_log1.JPG&amp;colorScheme=ff0000&amp;cpBackgroundColor=ffff00&amp;cpHidePanel=mouseout&amp;cpHideDelay=.5&amp;fpButtonSize=63x63" target="_blank">http://sbftech.com/vids/mcmp_0.8.swf?fpFileURL=http://sbftech.com/efi/EEC_TS/89_SC_Idle.FLV&amp;fpPreviewImageURL=http://sbftech.com/vids/SBF_log1.JPG&amp;colorScheme=ff0000&amp;cpBackgroundColor=ffff00&amp;cpHidePanel=mouseout&amp;cpHideDelay=.5&amp;fpButtonSize=63x63</a>




« Last Edit: March 15, 2011, 08:28:53 pm by Joel5.0 » Logged

ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
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