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Engine hesitation & Code 172

capena

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April 17, 2004
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Tempe, AZ
Year, Model & Trim Level
'94 Limited
I have two problems and don't know if related. First The engine hesitates often. Sometimes it will hesitate when I'm pulling out into traffic. On the hwy the rpms will start steadily decline until I punch the gas. This lasts for a while down cycle repeats itself. Replaced the fuel filter, but no change. I also get the check eng lite. Ran the diagnostic and got code 172 - lack of heated O2 switches indicates lean bank 1 and 536 - Brake on/off circuit failure. Also my fuel quantity gauge reads 0 all the time. Suspect bad fuel sending unit. Could I also have a bad fuel pump?
 
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MrShorty

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I know one of the symptoms of a bad O2 sensor on my BII was engine hesitation except at WOT. 1st thing I would do is identify which test the codes come from (KOEO hard fault, KOER, or continuous memory). A KOER 536 is quite common, and usually operator error during the KOER test. The computer expects to see you press the brake just after engine i.d.
Then go to the pinpoint tests for a code 172. 1st, inspect the wiring to the O2 sensor.
Check the fuel pressure. Check for exhaust leaks.
 
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putter

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it wont tell you in the diagnostic flow chart. But if you check in the tech updates you need to check your mass air flow sensor. I have replaced many faulty MAF sensors for the same problem.
 
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MrShorty

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Putter:
Out of curiosity, how did you isolate the fault to the MAF sensor in those cases where the MAF was the problem? Did the MAF throw it's own code?
 
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putter

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no the MAF sensor will not throw its own code, though i am not sure why the do not i personally think it is a design flaw in the diagnostic sytstem. Sometimes if the hesitation is real bad tou can unplug the maf and drive the vehicle. this will cause the vehicle to use a standard value for the maf and that will get rid of the most of the hesitation. then if that helps replace the sensor and clear the codes. Also some ford use the MAF to tell barometeric pressure abd when the MAF goes bad your barometeric pressure reading will be off, but you need to have a scanner to check that.
 
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Glacier991

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Thanks MrShorty for posing that Q, I've been pondering this same question as a result of some other threads. Interesting. Thanks putter!
 
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capena

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Code 172

I guess I'm going to be busy this weekend tinkering under the hood. I'll try disconnecting the MAF sensor first since thats the easiest. Will let you know how that goes. Lots of good advice ideas.
Great forum. Thanks.
 
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putter

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me to bought some add ons for the front end that should be here tommorow. let me know what happens with yours
 
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capena

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MAF Sensor

Well finally got around to replacing the MAF sensor on my '94. Worked like a charm. Fixed the hesitation and the check engine light.

Putter you are a genious. Thanks.
 
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USS RIGHTEOUS

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Had the same problem with mine. No MAF code, just lean O2 sensors and poor drivability. Unhooked MAF and made a big difference. Thanks for the helpful post.
 
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