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Good morning gentleman an ladies. Ive been playing with a 171 and 174 on my 97 crown vic. I really dont like to guess on parts, more of a prove it guy. I've been taking educated guesses (kinda like gov worker) and have changed fuel pump and reg because pressures were borderline. I drove around for a week with fuel pressure gauge and scanner hooked up. During that time i never saw pressure drop below minimun nor and unusual activity in comp system. Next day, after removing equipment, mil came on and car acted up again. Re-checked while happening and saw no clues except fuel trims around 25+. Ive tested the maf sensor every way i know and all tests pass. Replaced maf and problem is gone. As stated earlier, i dont like guessing and would like to know is there some secret test that can be done to prove this symptom in the future without just changing part. It would really be even worse if maf was guessed and a defective one was installed, now assuming maf guess was wrong, spend countless hours with more useless diag. Bottom line here is, if there is no conclusive evidence during a 171,174 diag, then i guess a guess is the only way, i guess. Have an awesome day everyone.

The only thing I can think of is having a oscilloscope hooked up at time of failure. We also introduce heat from a heat gun while taping on it to help make it act up.

I learned a while ago on these the maf is the first thing I go for. At first I would try cleaning them but after a few failures I stsrted replacing them. If you look real close you'll see debris on the reader in the flow chamber.

Often the Baro reading will be skewed, causing a lean condition. Best way is to do a volumetric efficiency test. If you're an iAtn member there's plenty of info about VE there.

It sounds like sometimes errors can be seen for sure and other times it can't. I bought a lifetime wrrty one so that in the future i'll just change it first. I do wish that there was a definitve way to component test, thanks Ford. The reed was very clean, all tests said it was ok, even the baro reading, however, the maf fixed the issue. thank you for the responses.

Fuel trims should have been on the plus side if it was setting 171/174 codes. To test the MAF I do a WOT acceleration to redline then take engine size in liters (4.6) multiply times engine RPM in thousands ( 4856 rpm = 4.8 ) then multiply that result by eight and you should be with in ten percent of the indicated MAF in grams per second. At idle you will typically see about one gram per liter of engine size.

!!!This ONLY works on non turbo/supercharged cars/trucks!!!

i need to pay attention to my typing, fueltrims were around 25+ . going to edit now

Did yah check for vacuum leaks??

Rich wrote:Did yah check for vacuum leaks??

One of the first things was to smoke the vac system, and it was sealed up tighter than a bulls a** at fly time.

Basic lean code testing first wants to identify if the problem is sealing or control. Very simple to distinguish between the two. If your trims are off more at idle than at higher rpm, then it's likely a vacuum leak. If the trims are off the same at idle as higher rpm, then no need to check for vac leaks, it's something else.

Friggin Fords. For a while they threw me for a loop, especially the MAF issues. The earlier computer control systems allowed for a wider range before throwing codes. I would look at all the running specifications and they would vary between sensors but just be within the allowable or should I say acceptable range but the vehicle had drivability issues. I had air charge sensors and MAF sensors that I knew were good that fit most applications to try after I scanned the system. Some of the biggest diagnostic issues started with some other shop had tried to or should I say succeeded in adjusting the curb idle to try to resolve a rough idle issue. If I saved all the maf's I replaced that were within specs to solve problems I know without a doubt it would have filled a 55 gallon trash can. If I remember correctly there was a run of bad remans from Ford as well. Does anyone besides me remember when Ford coated the inside of their intakes with a plastic sealer and even though there were warning labels all over it some shops used carb cleaner on them and really messed things up along with the pressure cable clips for transmission cable that were heated enough from exhaust manifold temp it would become brittle break and if the car was driven around town for 10 or 15 miles the % of the transmission trashing was over 80. I'll end with the clutch pedal height on the F series that Ford was voiding warranties on because techs were extending the rod to the master from pedal to give better height. All sorts of hype on that until Ford came out with their own version, then it was OK. Enough bashing from me.