Generating p0171 and p0174 on a 4.9l. Idles perfectly cold fast, hot 650, smooth. No misses, no spark knock, no backfires. Checked fuel pressure, 45 psi full vacuum, 55 psi no vacuum. Replaced MAF : ( no change. If my Mother of 81 years old would drive it, there would be no complaints, and she is very picky, just not heavy footed. It was running PERFECTLY one minute the next the check eng light on, and didn't notice a problem until the next big up hill, no power. HELP
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1996 Ford F-150
Question: Run and starts perfectly, but no power at full throttle.
Answer #1milesauto from Miles Auto Service Inc., March 18, 2013, 14:17Master
Both codes are for a lean condition. You could have a lack of fuel volume due to weak fuel pump, restricted fuel filter, dirty mass air flow sensor, or vac. leaks. Just to name a few possibilities.
Replybentheredonethat, March 18, 2013, 15:09Rookie
Name some more possibilities. If you can give me one that fixes it that I have not checked I will pay! I know it is a lean condition. I stated the fuel pressure reading on the original post. I changed the fuel filter and ran a volume check. I replace the MAF after I had already cleaned it. There are NO vacuum leaks. The only thing I can come up with is a faulty PCM ?? But it is controlling everything else perfectly. Cold start and warm up,,,,????? maybe timing,,,,???? it just occurred to me that maybe it's not getting full advance ? I know it is going out as far as 11 degrees, saw it on the reader, but did not check to see 40 degrees at high continued RPM...... what's you thoughts ?
I am going to drive it and watch the timing on the pid's.
Replymilesauto, March 18, 2013, 17:55Master
You say you are willing to pay for the fix....heck we all can start guessing and may never fix it with a bushell basket full of parts....pehaps you would be money better spent taking to a good tech for a diagnosis.
Answer #2pushrod March 18, 2013, 15:43Master
Hook up fuel pressure gauge run it under the hood so you can see what pressure is at WOT. while driving. Checked for exhaust restricton? Any cat. rattle, tap with rubber hammer?
Pcm failure is very rare on this vehicle but possible.
Replybentheredonethat, March 18, 2013, 16:03Rookie
I thought some more about the timing issue,, would not produce a lean condition : (
The fuel pressure/volume is good.
No airy / hissing sounds from the exhaust at high rpms.
I really would love to have the PCM checked but don't know anyone "reputable" to check it. I guess I am going to have to find a willing owner of a 1996 4.9l, autotrans, f-150 to let me try his PCM. God I hate to just change part : ( I wish I hadn't bought the $90 MAF. And the scary thing about it is I really don't know I bought a good one, I have had bad new parts before : (
Replypushrod, March 18, 2013, 16:16Master
Is the maf new or reman? Ditto on bad parts! Any tps glitches? I dont think a lean condition is actually the problem as much as a result.
Replybentheredonethat, March 18, 2013, 16:19Rookie
reman,, With a big smiley "QA" sticker on it.
As for the TPS: I can power brake it to WOT and hold,, not a hiccup, smooth all the way through.
Replypushrod, March 18, 2013, 16:21Master
Swap maf back out with the parts store!